Galactic sources: comments to the Table 1

0053+604
( Cas, 3A 0053+604, BD+59 144, HD 5394, LS I +60^o133, 2S 0053+604, 1H 0053+604, 4U 0054+60)
Cassiopeiae is one of the best known Be stars; it was the first emission-line star discovered by Angelo Secchi in 1866, and it has spectral classification of B0 IVe. Its visual magnitude varies between about 3.0 and 1.6, although usually it stays around 2.5. This object is one of the ROSAT bright sources and also was detected by IRAS. Cas has long been known to be very variable in optics and it is also a moderately strong X-ray source with a luminosity of the order of 10³³ erg s^-1 (Mason, White & Sanford (1976); White et al. (1982)). Such a luminosity would not be surprising for X-ray emission from an early type star of spectral type O or B - some active early type stars have a similar luminosity (Corcoran, Waldron, MacFarlane et al. (1994); Koyama, Maeda, Tsuru et al. 1994)). However, the hardness of the X-ray emission of Cas is extraordinarily high in comparison with usual X-ray emission from early type stars. If we fit the spectrum with a thermal model the resultant temperature is roughly 10 keV or more (Horaguchi, Kogure, Hirata et al. 1994); Murakami et al (1986)). It is not common for early type stars, and resembles more spectra of X-ray pulsars and accreting white dwarf binaries. There are currently two competing interpretations of the nature of the observed X-ray emission: one is the accretion of the wind from Cas onto a white dwarf companion and the other is that X-rays originate due to some physical processes in the outer atmosphere of Cas itself. Arguments for and against these two hypotheses are best summarized in studies by Kubo et al. (1998) and Robinson & Smith (2000).

0115+634
(V635 Cas, 1H 0115+635, 4U 0115+63, 3U 0115+63, 2E 0115.1+6328, H 0115+634, 4U 0115+634)
This source is one of the best studied Be/X-ray systems. This transient was first reported in the Uhuru satellite survey (Giacconi, Murray, Gursky et al. (1972); Forman, Jones, Cominsky et al. (1978)), though a search in the Vela 5B data base revealed that the source had already been observed by this satellite since 1969 (Whitlock, Roussel-Dupre & Priedhorsky (1989)). X-ray outbursts have been observed from 4U 0115+63 by Uhuru (Forman, Tananbaum & Jones (1976)), HEAO-1 (Wheaton, Doty, Primini et al. (1979); Rose, Marshall, Holt et al. (1979)), Ginga (Tamura, Tsunemi, Kitamoto et al. (1992)), CGRO/Batse (Bildsten, Chakrabarty, Chiu et al. (1997)), RXTE (Wilson, Harmon & Finger (1999); Heindl & Coburn (1999); Coburn, Rotschild & Heindl (2000)) and reoccured with intervals from one to several years. Precise positional determinations by the SAS 3, Ariel V and HEAO-1 satellites (Cominsky, Clark, Li et al. (1978); Johnston, Bradt, Doxsey et al. (1978)) were used to identify this system with a heavily reddened Be star with a visual magnitude V = 15.5 (Johns, Koski, Canizares & McClintock (1978); Hutchings & Crampton D (1981)).  Rappaport, Clark, Cominsky et al. (1978) used SAS 3 timing observations to derive the orbital parameters of this binary system. Due to the fast rotation of the neutron star centrifugal inhibition of accretion prevents the onset of X-ray emission unless the ram pressure of accreted material reaches a relatively high value. Reig, Larionov, Negueruela et al. (2006) have performed optical/IR photometric observations and optical spectroscopic observations of 4U 0115+63 over ten years. They have have focused on the Halpha line variability and the long-term changes of the photometric magnitudes and colours and investigated these changes in correlation with the X-ray activity of the source. The optical and infrared emission is characterised by cyclic changes with a period of ~ 5 years. X-ray outbursts in 4U 0115+63 come in pairs, i.e., two in every cycle (Reig, Larionov, Negueruela et al. (2006)). However, sometimes the second outburst is missing. Their results can be explained within the framework of the decretion disc model. The neutron star acts as the perturbing body, truncating and distorting the disc. The first outburst would occur before the disc is strongly perturbed. The second outburst leads to the dispersal of the disc and marks the end of the perturbed phase. Magnetic field of the neutron star is 1.3 × 10¹² G (Makishima, Mihara, Nagase & Tanaka (1999)). Pulse fraction was obtained in a model-dependent way in the range 20-50 keV (see Harmon et al. (2004) for details and references). HEAO 1 observation of the pulsar 4U 0115+634, during an outburst reported possible presence of QPOs at 62 mHz (Soong & Swank (1989)). Apart from the 62 mHz QPO, another low frequency QPO at 2 mHz were detected in RXTE observations of the pulsar during 1999 March-April outburst (Heindl, Coburn,Gruber et al. (1999)). These QPOs were explained as due to the obscuration of the neutron star by hot matter in the accretion disk. The blobs of hot matter in the inner accretion disk are understood to be because of the in-homogeneities caused by the interactions of the neutron star magnetosphere and the accretion disk. Dugair, Jaisawal, Naik & Jaaffrey (2013) reported the detection of a ∼41 mHz QPO in the transient pulsar 4U 0115+634. These ∼41 mHz QPOs were found to be variable in 27-46 mHz frequency range.

J01363+6610
(IGR J01363+6610)
IGR J01363+6610 was discovered by INTEGRAL in 2004. The average flux over 2.3 hours of observations was 17 mCrab in the 17-45 keV band. Reig, Negueruela, Papamastorakis et al. (2005) concluded that the optical counterpart to IGR J01363+6610 is a B1V star, that is probably identical with the catalogued emission line star [KW97] 6-30 (Kohoutek & Wehmeyer (1999)).  The presence of Balmer emission lines and the lack of radio emission suggests that IGR J01363+6610 is a Be/X-ray binary. The detection of the variable hard X-ray source XMMU J013549.5+661243 at the location of a Be star provides confirmation that IGR J01363+6610 is a Be/X-ray binary (Tomsick, Heinke, Halpern et al. (2011)).

J0146.9+6121
(V831 Cas, 2S 0142+61, RX J0146.9+6121, LS I +61^o235)
RX J0146.9+6121 is an accreting neutron star with a 25 min spin period, the longest known period of any X-ray pulsar in a Be-star system. This fact was realized (Mereghetti, Stella & De Nile (1993)) only after the re-discovery of this source in the ROSAT All Sky Survey and its identification with the 11th magnitude Be star LS I +61^o235 (Motch, Belloni, Buckley et al. (1991)). Indeed the 25 min periodicity had already been discovered with EXOSAT (White, Mason, Giommi et al. (1987)), but it was attributed to a nearby source 4U 0142+614. The optical star is probably a member of the open cluster NGC 663 at a distance of about 2.5 kpc (Tapia, Costero, Echevarra & Roth (1991)). For this distance, the 1-20 keV luminosity during the EXOSAT detection in 1984 was ~10³⁶ erg s^-1 (Mereghetti, Stella & de Nile (1993)). All the observations of RX J0146.9+6121 carried out after its re-discovery yielded lower luminosities, of the order of a few 10³⁴ erg s^-1, until an observation with the Rossi XTE satellite showed that in July 1997 the flux started to rise again (Haberl, Angelini & Motch (1998)), though not up to the level of the first EXOSAT observation. The V band light curve of LS I +61^o235 shows three strong periodicities at 0.34 d, 0.67 d and 0.10 d (Sarty, Kiss, Huziak et al. (2008)). In interpretation by Sarty, Kiss, Huziak et al. (2008), the 0.34 d period may be from pulsation in the radial fundamental mode, the 0.68 d period is the Be star spin period and the 0.10 d period is a higher order p-mode pulsation. From archival RXTE ASM data Sarty, Kiss, Huziak et al. (2008) found ¨super¨ X-ray outbursts roughly every 450 d. If these super outbursts are caused by the alignment of the compact star with the one-armed decretion disk enhancement, then the orbital period is approximately 330d (Sarty, Kiss, Huziak et al. (2008)). This orbital period agrees with the value expected from the Corbet spin-orbit relation (Corbet (1986)).

J01583+6713
(IGR J01583+6713)
This hard X-ray transient has been discovered by the IBIS/ISGRI imager on board INTEGRAL in 2005 (Steiner, Eckert, Mowlavi et al. (2005)).  Kennea, Racusin, Burrows et al. (2005) proposed an optical/IR candidate for this X-ray transient based on its positional coincidence with a Swift XRT source detection. Halpern & Tyagi (2005) obtained a low-resolution optical spectrum of this candidate. It reveals strong Hα and weak H emission lines. Kaur, Paul, Kumar & Sagar (2008) carried out a multiwavelength study on the transient source IGR J01583+6713, identified the spectral type of the companion star to be B2 IVe, and suggested a distance of ∼ 4 kpc. From the Swift observations, they also reported a possible pulse period of ∼ 469 s, but the evidence of pulsation was only marginal (Kaur, Paul, Kumar & Sagar (2008)), requiring additional confirmation. Wang (2010) studied the temporal profiles and spectral properties of IGR J01583+6713 around its outburst on 2005. During the outburst, the mean X-ray luminosity reached around 4 × 10³⁵ erg s^-1 in the energy range of 20 – 100 keV. In addition, the electron resonant cyclotron absorption lines were detected at ∼ 35 keV and possible at ∼ 67 keV, implying that a magnetic neutron star of B ∼ 4 × 10¹² G is located in IGR J01583+6713.

0236+610
(V615 Cas, 2E 0236.6+6101, LS I +61^o303, 1E 0236.6+6100, RX J0240.4+6112)
LS I +61^o303 is a radio emitting X-ray binary which exhibits radio outbursts every 26.5 d. The radio outburst peak and the outburst phase are known to vary over a time scale of $\sim$ 4 yr (Gregory, Xu, Backhouse & Reid (1989); Gregory (1999)). LS I +61^o303 consists of a massive B0Ve star and a compact object orbiting the primary every 26.5 d. According to radial velocity measurements of the absorption lines of the primary (Casares, Ribas, Paredes et al. (2005), Aragona, McSwain, Grundstrom et al. (2009)), the orbit is elliptical (e = 0.537±0.034), with periastron passage determined to occur around phase φ = 0.275. The compact object interacts with the Be circumstellar disk thereby sampling a wide range of physical parameters and producing remarkable, periodic flaring events each orbital cycle. Hutchings & Crampton (1981) confirmed the radio period 26.5 d by analysis of three-year observation of radial velocity. The 4 yr modulation has been discovered on the basis of continued radio monitoring.

0331+530
(BQ Cam, EXO 0331+530, V 0332+53)
V 0332+53 was discovered in 1973 by the Vela 5B satellite during a type II, i.e., a giant outburst (Terrell & Priedhorsky (1984)). EXOSAT observed three outbursts from V0332+53 between 1983 November and 1984 January. Two properties of the system were discovered: the 4.4 s spin period and a sudden decrease of luminosity at the end of ~1 month long recurrent outbursts. The latter was interpreted as an onset of the centrifugal barrier (Stella, White, Davelaar et al. (1985); Stella, White & Rosner (1986)). An upper limit of ~5 × 10³³ erg s^-1 to the source quiescent emission (1-15 keV) was derived on that occasion with the EXOSAT Medium Energy Detector. Doppler shifts in pulse arrivals indicate that the pulsar is in orbit around a Be star with a period of 34.3 days and eccentricity 0.3 (Stella, White, Davelaar et al. (1985)). Observations during a subsequent outburst with Ginga led to the discovery of a cyclotron line feature corresponding to 3 × 10¹² G magnetic field (Makishima, Kawai, Koyama et al. (1984)). BeppoSAX and Chandra observations allowed to study this transient at the faintest flux levels thus far (Campana, Stella, Israel et al. (2002)). Campana, Stella, Israel et al. (2002) concluded that the quiescent emission of this X-ray transient likely originates from accretion onto the magnetospheric boundary of the neutron star in the propeller regime and/or from deep crustal heating resulting from pycnonuclear reactions during the outbursts. Recently, the source was observed by Integral Kreykenbohm, Mowlavi, Produit et al. (2005). The authors confirm the existence of cyclotron lines: the fundamental line at 24.9±0.1 keV, the first harmonic at 50.5±0.1 keV as well as the second harmonic at 71.7±0.8 keV. Reig, Martinez-Nunez & Reglero (2005)  have investigated the evolution of the X-ray colours of this high-mass X-ray pulsar through the decay of a type II outburst. The aperiodic variability consists of band-limited noise and two QPOs at 0.05 Hz and 0.22 Hz.

0352+309
(X Per, HD 24534, 3A 0352+309, 2E 0352.2+3054, H 0352+309, 4U 0352+30, 4U 0352+309, 1H 0352+308, 2A 0352+309, H 0353+30, HD 24534, 3U 0352+30)
The X-ray source 4U 0352+309 is a persistent low luminosity pulsar in a binary system with the Be star X Persei (X Per). Its 837 s pulsation period was discovered with the UHURU satellite (White, Mason, Sanford & Murdin (1976); White, Mason & Sanford (1977)), and is still one of the longest periods of any known accreting pulsar (Bildsten, Chakrabarty, Chiu et al. (1997), and references therein). X Per is a bright and highly variable star with a visual magnitude that ranges from ~6.1 to ~6.8 (Mook, Boley, Foltz & Westpfahl (1974); Roche, Larionov, Tarasov et al. (1997)). The spectral class has been estimated to be O9.5 III to B0 V (Slettebak (1982); Fabregat, Reglero, Coe et al. (1992); Lyubimkov, Rostopchin, Roche & Tarasov (1997)). Based on spectroscopic parallax, distance estimates range from 700±300 pc up to 1.3±0.4 kpc (Fabregat, Reglero, Coe et al. (1992); Lyubimkov, Rostopchin, Roche & Tarasov 1997); Roche, Larionov, Tarasov et al. (1997); Telting, Waters, Roche et al. (1998)). The X-ray luminosity varies on long timescales (years) from ~3 × 10³⁵ erg s^-1 to ~5 × 10³⁴ erg s^-1 (for the assumed distance 1.3 kpc (Roche, Coe, Fabregat et al. (1993))). Delgado-Marti, Levine, Pfahl & Rappaport (2001) have determined a complete orbital ephemeris of the system using data from the Rossi X-ray Timing Explorer (RXTE). Coburn, Heindl, Gruber et al. (2001) have discovered a cyclotron resonant scattering feature at 29 keV in the X-ray spectrum of 4U 0352+309 using observation taken with the RXTE. The cyclotron resonant scattering feature energy implies a magnetic field strength at the polar cap of 3.3 × 10¹² G.

J0440.9+4431
(RX J0440.9+4431, VES 826, LS V +44 17)
RX J0440.9+4431/BSD 24-491 was confirmed as an accreting Be/X-ray system following the discovery of X-ray pulsations, with barycentric pulse period of 202.5±0.5 s from RXTE observations (Reig & Roche (1999)).

0535+262
(V725 Tau, HD 245770, 1A 0535+26, 1H 0536+263, 3A 0535+262, BD+26 883, 4U 0538+26, 1A 0535+262, H 0535+262)
The transient A 0535+26 is one of the best studied Be/X-ray binaries. This source was discovered in 1975 by Ariel 5 (Rosenberg, Eyles, Skinner & Willmore (1975)) and showed a 104 s periodicity indicating the presence of a highly magnetized neutron star. The optical counterpart was later identified with the Be star HDE 245770 (Li, Clark, Jernigan & Rappaport (1979)) allowing the classification of the source as a Be/X-ray binary. The pulsed fraction is 20% at 30-40 keV and increases significantly with energy, reaching 100% at 100 keV (Frontera, dal Fiume, Morelli & Spada (1985)). Magnetic field of the neutron star is 4.3 × 10¹² G (Makishima, Mihara, Nagase & Tanaka (1999)).

0556+286
(4U 0548+29, 1H 0556+286)
The X-ray source was detected by HEAO1. Probably earlier it was observed by UHURU 4U 0548+29 (Wood, Meekins, Yentis et al. (1984)). No detection was made after that. A Be-star is known in this direction. HD 249179 was proposed as possible optical counterpart of this X-ray source. It is late type Be star. This argues against this source being Be+neutron star binariy since all well established Be+NS systems have spectral types earlier than B3. Torrejon & Orr (2001) consider this system as almost certainly not neutron star accreting Be/X-ray binary and that it is not X-ray binary at all.

J06074+2205
(IGR J06074+2205)
This transient X-ray source has been discovered with both JEM-X telescopes on board INTEGRAL (Chenevez, Budtz-Jorgensen, Lund et al. (2004)). Halpern & Tyagi (2005) found a Be star that is a probable optical counterpart of this transient X-ray source and has an H-alpha emission line and diffuse interstellar absorption bands. These typical spectral features of a Be/X-ray binary.

J0635+0533
(SAX J0635+0533)
Discovered by BeppoSAX (Kaaret, Piraino, Halpern & Eracleous (1999)). Ziolkowski (2002) gives the spectral classification of the optical counterpart as B0.5 IIIe. X-ray luminosity is (9 - 35) × 10³³ erg s^-1 (2-10 keV) for d = 2.5 - 5 kpc (Kaaret, Piraino, Halpern & Eracleous (1999)). Bolometric luminosity (0.1-40 keV) was estimated to be 1.2 × 10³⁵ erg s^-1 for d = 5kpc (Cusumano, Maccarone, Nicastro et al. (2000)). Pulse fraction was obtained by BeppoSAX (2-10 keV). The source can be identified with the gamma-ray source 2EG J0635+0521. Low luminosity together with very fast rotation propose that the neutron star has a low magnetic field (see discussion in Cusumano, Maccarone, Nicastro et al. (2000).

0656-072
(MXB 0656-072, MXB 0656-07, XTE J0658-073)
This source was first classified as a transient source by Clark, Schmidt & Angel (1975) when detected at 80 mCrab in 1975 by SAS-3. Subsequently Ariel V observed the source at 50 and 70 mCrab in 1976 (Kaluzienski (1976)). During a large, extended outburst in 2003, which lasted over 2 months and reached an X-ray luminosity of 200 mCrab, it was identified as a pulsating X-ray binary with a pulse period of 160.7 s (Morgan, Remillard & Swank (2003)) and with an optical counterpart of spectral type O9.7 Ve (Pakull, Motch & Negueruela (2003)). Orbital parameters of the system remain undetermined. The pulsar shows a spin-up of 0.45 s over the duration of the outburst (McBride, Wilms, Coe et al. (2006)). From optical data, the source distance is estimated to be 3.9 ± 0.1 kpc. The source spectrum shows a cyclotron resonance scattering feature at 32.8 keV, corresponding to a magnetic field strength of 3.67 × 10¹² G (McBride, Wilms, Coe et al. (2006)). The pulse profiles show the pulsed fraction increasing steadily from 26% in the 2–5 keV band up to 40% in the 30–60 keV band (McBride, Wilms, Coe et al. (2006)).

0726-260
(4U 0728-25, 3A 0726-260, V441 Pup, 1H 0726-259, LS 437)
Detected by many experiments (UHURU, HEAO1, Ariel 5, ROSAT, RXTE). Pulse fraction was estimated as (I_max - I_min)/(I_max+I_min) from the graph in paper by Corbet & Peele (1997) (RXTE 2-20 keV). The spectral and photometrical analysis of this source led Negueruela, Reig, Buckley et al. (1996) to conclude that the primary is an O8-9Ve star.

0739-529
(1H 0739-529)
Detected by HEAO1 (Wood, Meekins, Yentis et al. (1984)).

0749-600
(1H 0749-600)
Detected by HEAO1 (Wood, Meekins, Yentis et al. (1984)). Situated in the open cluster NGC 2516 (Liu, van Paradijs & van den Heuvel (2000)). HD 65663 was proposed as possible optical counterpart of this X-ray source. It is late type Be star. This argues against this source being Be+neutron star binariy since all well established Be+NS systems have spectral types earlier than B3. Torrejon & Orr (2001) consider this system as almost certainly not neutron star accreting Be/X-ray binary and that it is not X-ray binary at all.

J0812.4-3114
(RX J0812.4-3114, V572 Pup, LS 992)
RX J0812.4-3114 was discovered by Motch, Haberl, Dennerl et al. (1997) during a search for high-mass X-ray binaries by cross-correlating SIMBAD OB star catalogs with low Galactic latitude sources from the ROSAT all-sky survey. Thus, this X-ray source has an identified optical counterpart, the Be star LS 992, and so it was suspected that this source belongs to the Be/X-ray binaries. Reig, Negueruela, Buckley et al. (2001) classify it as B0.2 IVe. The X-ray light curve of LS 992/RX J0812.4-3114 is characterized by 31.88 second pulsations, while the X-ray spectrum is best represented by an absorbed power-law component with a exponentially cut-off (Reig & Roche (1999)). In December 1997 the source made a transition from a quiescent state to a flaring state (Corbet & Peele (2000)), in which regular flares separated by 80 day intervals were detected with the All-Sky Monitor (ASM) on-board the Rossi X-ray Timing Explorer. Corbet & Peele (2000) attributed the origin of these flares to the periastron passage of the neutron star, hence this periodicity was naturally associated with the orbital period. Corbet & Peele (2000) have found strong evidence for the presence of a ~80 day period in the ASM light curve of RX J0812.4-3114. By comparison with other Be star X-ray binaries, the time of maximum flux is likely to coincide with periastron passage of a neutron star. The orbital period of ~80 days combined with the ~32 second pulse period is consistent with the correlation between orbital and pulse period that is found for the majority of Be/neutron star binaries (Corbet (1986)).

0834-430
(GS 0834-430)
The hard X-ray transient GS 0834-430 was discovered by the WATCH experiment on board GRANAT in 1990 at a flux level of about 1 Crab in the 5-15 keV energy band (see Wilson, Harmon, Scott et al. (1997)). The source was later observed by GINGA (Makino (1990a); Makino (1990b)) and ROSAT as a part of the All Sky Survey (Hasinger, Pietsch & Belloni (1990)). The pulsations at a period of 12.3 s were observed during the GINGA, ROSAT and ART-P observations (Makino (1990c); Aoki, Dotani, Ebisawa et al. (1992); Hasinger, Pietsch & Belloni (1990); Grebenev & Sunyaev (1991)). GS 0834-43 was also monitored by BATSE between April 1991 and July 1998. In particular, seven outbursts were observed from April 1991 till June 1993 with a peak and intra-outburst flux of about 300 mCrab and <10 mCrab, respectively (Wilson, Finger, Harmon & Scott (1997)). The recurrence time of 105-115 days was interpreted as the orbital period of the system. However, no further outbursts have been observed since July 1993 either by CGRO/BATSE or by the the All Sky Monitor on board RXTE. All these findings suggest that GS 0834-43 is a new Be-star/X-ray binary system with an eccentric orbit (Wilson, Finger, Harmon & Scott (1997)). Based on both photometric and spectroscopic findings Israel, Covino, Campana et al. (2000) concluded that optical counterpart of this X-ray pulsar is most likely a B0-2 V-IIIe star at a distance of 3-5 kpc. Pulse fraction was obtained by BATSE (20-50 keV).

J1008-57
(GRO J1008-57 )
Discovered by BATSE in 1993. Pulse fraction $\sim$ 60% was obtained by ROSAT (0.1-2.4 keV) (Harmon, Wilson, Fishman et al. (2004)). High-energy data (BATSE: 20-70 keV) gives nearly the same value about 67% (Harmon, Wilson, Fishman et al. (2004)). Orbital period is uncertain. An estimate of 247.5 days comes from the best fit of BATSE data (Negueruela & Okazaki 2001)). Other (earlier) estimates were about 135 days (Liu, van Paradijs & van den Heuvel (2000)). The counterpart is shown to be an OB star with a strong infrared excess and Balmer emission lines, suggesting a Be-type primary (Coe, Roche, Everall et al. (1994)).

1036-565
(3A 1036-565, 1A 1034-56)
Probably the same object as J1037.5-5647.

J1037.5-5647
(LS 1698, RX J1037.5-5647)
Discovered by ROSAT in 1997. Probably the same source as 4U1036-56/3A1036-565. The source was observed in quiescence (Reig & Roche (1999)). L_min = 1.1 × 10³⁴ erg s^-1. Pulse fraction was obtained by RXTE (3-20 keV).

1118-615
(1A 1118-615, 1A 1118-616, WRAY 15-793, 2E 1118.7-6138)
The hard X-ray transient A 1118-615 was discovered serendipitously in 1974 by the Ariel-5 satellite (Eyles, Skinner, Wilmore & Rosenberg (1975)) during an observation of Cen X-3 (4U 1119-603). The same series of observations revealed pulsations with a period of  405.3±0.6 s (Ives, Sanford & Bell-Burnell (1975)). However, in the initial announcement of the discovery of the pulsations, they were wrongly attributed to an orbital period, suggesting that A 1118-615 consisted of two compact objects (Ives, Sanford & Bell-Burnell (1975)). This hard X-ray transient underwent a major outburst only twice: in 1974, when it was discovered by Ariel-5 satellite, and from December 1991 to February 1992 (Bildsten, Chakrabarty, Chiu et al. (1997)). The source was observed by Motch, Janot-Pacheco, Pakull & Mouchet (1988) using the Einstein and EXOSAT observatories in 1979 and 1985 respectively. On both occasions a weak signal was detected confirming that low-level accretion was occurring. The correct optical counterpart was identified as the Be star He 3-640/Wray 793 by Chevalier & Ilovaisky (1975). The primary has been classified as O9.5IV-Ve (Janot-Pacheco, Ilovaisky & Chevalier (1981)), with strong Balmer emission lines indicating the presence of an extended envelope. According to Villada, Giovannelli, & Polcaro (1992), the exact classification is complicated by many faint absorption and emission lines (mostly of Fe II), but the overall spectrum is found to be similar to that of the optical counterparts to other known Be/X-ray sources. The source was observed by Coe & Payne (1985) at UV wavelengths using the IUE satellite. They confirmed the identification of the counterpart and reported prominent UV lines characteristic of a Be star. Despite the large observational efforts made during last years and mainly after the 1991-1992 outburst, the Hen3-640/1A 118-615 system is still poorly understood. The orbital period of the system is unknown. Corbet's pulse period/orbital period diagram (Corbet 1986)) gives an orbital period estimate of ~350 days.

J11305-6256
(IGR J11305-6256)
This weak transient source IGR J11305−6256 was detected by IBIS/ISGRI in May 2004 (Produit, Ballet & Mowlavi (2004)). The only conspicuous catalogued object within the INTEGRAL error box of IGR J11305−6256 is the emission-line star HD 100199, which has V = 8.23 and B − V = +0.01 (Fernie (1983)). This is classified as a blue giant of spectral type B0 IIIe (Garrison, Hiltner & Schild (1977)). Its identification as an early-type emission-line star suggests HD 100199 as a strong candidate for IGR J11305−6256, by analogy with other High-Mass X–ray Binaries (HMXBs).

J11435-6109
(IGR J11435-6109)
Reported as a hard X-ray transient by Grebenev, Ubertini, Chenevez et al. (2004). Evidence of the possible presence of 166 s pulsations was reported by Swank & Markwardt (2004) which was confirmed by BeppoSAX Wide Field Camera observations by in ’t Zand & Heise (2004). In ’t Zand & Heise (2004) also reported a possible 52.5 day outburst recurrence period from detections in 1996-1997 and 2001-2002, but non-detection during the intervening period. This outburst period was confirmed by Corbet & Remillard (2005) from RXTE/ASM observations. An initial suggestion that IGR J11435−6109 corresponds to 1RXS J114358.1−610736 is apparently excluded by optical observations of the optical counterpart of 1RXS J114358.1−61073 by Torrejon & Negueruela (2004) who instead propose a Be star counterpart which is 1.2 arc minutes away from 2E 1141.6−6050. The pulse profile is broad with a 2-6 keV pulsed fraction of roughly 50% (In ’t Zand & Heise (2004)). A deeper search of the error circle using the method described in Negueruela & Schurch (2007) detected a fainter candidate emission-line object, namely 2MASS J11440030-6107364 = USNO-B1.0 0288-0337502, which has been confirmed as the correct counterpart by a Chandra localisation (Tomsick, Chaty, Rodriguez et al. (2007)).

1145-619
(V801 Cen, 2S 1145-61, 2S 1145-619, 2S 1145-62, LS 2502, 3U 1145-61, 4U 1145-62, 4U 1145-619, 4U 1145-61, 3A 1145-619, 2E 1145.5-6155, H 1147-62, H 1145-619)
Initially observed by UHURU (together with 1145.1-9141). Two sources were distinguished by Einstein observatory (HEAO2). In the paper by Liu, van Paradijs & van den Heuvel (2000) the optical counterpart was classified as B1 Vne. Pulse fraction was obtained by BATSE (20-50 keV).

1249-637
(1H 1249-637, 2E 1239.8-6246, BZ Cru, HD 110432) - Cas-like object
Detected by HEAO1 (Wood, Meekins, Yentis et al. (1984)). HD 110432 (B0.5 IIIe star) has been proposed as a possible optical counterpart of this X-ray source (Codina, de Freitas Pacheco, Lopes & Gilra (1984)). The unabsorbed X-ray luminosity of this source during the pointed observation was 3.4 × 10³² erg s⁻¹ (2-10 keV), assuming a distance of 301 pc (ESA (1997)) or 7 × 10³² erg s⁻¹ (2-10 keV) assuming a distance of 430 pc (Codina, de Freitas Pacheco, Lopes & Gilra (1984)). Torrejon & Orr (2001) confirmed 1H 1249−637 as low luminosity Be/X-ray binary. The spectrum can be well fitted by thermal emission of a hot, optically thin, plasma (Torrejon & Orr (2001)). Such an emission is more consistent with system harbouring white dwarf instead of neutron star as the compact object. Torrejon & Orr (2001) have found an X-ray pulse period of ~1.42 × 10⁴ s which would make this object the best Be+WD candidate found to date. Even if this pulse period is not confirmed, the spectrum is not the typical for a neutron star binaries (Torrejon & Orr (2001)). It is much closer to the spectra of cataclysmic binaries. Torrejon & Orr (2002) consider this X-ray source as very similar to Cas in nearly all respects.

1253-761
(1H 1253-761)
Detected by HEAO1 (Wood, Meekins, Yentis et al. (1984)). Probably a white dwarf accretor.

1255-567
(1H 1255-567, µ² Cru)
Detected by HEAO1 (Wood, Meekins, Yentis et al. (1984)).

1258-613
(GX 304-1, 4U 1258-61, V850 Cen, H 1258-613, 2S 1258-613, 3A 1258-613 )
Discovered by UHURU. In Ziolkowski (2002) classified as B0.7Ve.

J130159.6-635806
(1RXP J130159.6-635806, 2RXP J130159.6-635806)
This source was observed at different epochs with ASCA, BeppoSAX, XMM-Newton and INTEGRAL. The source shows coherent X-ray pulsations at a period ~700 s (Chernyakova, Lutovinov, Rodriguez & Revnivtsev (2006)). A broad band (1-60 keV) spectral analysis of 2RXP J130159.6-635806 based on almost simultaneous XMM-Newton and INTEGRAL data demonstrates that the source has a spectrum typical of an accretion powered X-ray pulsar (Chernyakova, Lutovinov, Rodriguez & Revnivtsev (2006)). The long term behaviour of the source, its spectral and timing properties, tend to indicate a high mass X-ray binary with Be companion. Chernyakova, Lutovinov, Rodriguez & Revnivtsev (2006) report on the identification of the likely infrared counterpart to 2RXP J130159.6-635806. They have calculated the 2−10 keV pulse fraction in all the XMM-Newton observations. It is interesting to note that the pulse fraction is not constant and varies with time from ~10–25% to ~60% during the outburst.

J1324-6200
(SAX J1324-6200)
The X-ray pulsar SAX J1324–6200 was serendipitously discovered in 1997 during an observation of the bright X-ray burster 4U 1323–619 (Angelini, Church, Parmar et al. (1998)). Its X-ray spectrum, a highly absorbed power law with photon index ~1, and its pulsations period of 171 s are typical of accreting pulsars in binary systems. However, due to the lack of an accurate position, an optical identification has not been obtained to date. Meregetti, Romano & Sidoli (2008) showed that this source most likely belongs to the class of low-luminosity, persistent Be/neutron star binaries.

J1346.5-6255
(1WGA J1346.5-6255, HD 119682) - Cas-like object
The X-ray source 1WGA J1346.5−6255 is a ROSAT X-ray source found within the radio lobes of the supernova remnant G309.2−00.6. This source also appears to coincide with the bright and early-type star HD 119682, which is in the middle of the galactic open cluster NGC 5281. The radio morphology of the remnant, consisting of two brightened and distorted arcs of emission on opposite sides of the 1WGA J1346.5−6255 source and of a jet-like feature and break in the shell, led to the suggestion that 1WGA J1346.5−6255/G309.2−00.6 is a young analog of the microquasar SS 433 powering the W50 nebula.  Safi-Harb, Ribo, Butt et al. (2006) studied this source at X-ray and optical wavelengths (new Chandra observations of 1WGA J1346.5−6255, archival XMM-Newton observations of G309.2−00.6, and optical spectroscopic observations of HD 119682) in order to search for X-ray jets from 1WGA J1346.5−6255. They studied its association with the SNR, and tested for whether HD 119682 represents its optical counterpart. They did not find evidence for jets from 1WGA J1346.5−6255 and ruled out its association with G309.2−00.6, and they confirmed that HD 119682 is its optical counterpart. Safi-Harb, Ribo, Butt et al. (2006) derived a distance of 1.2±0.3 kpc, which is consistent with the distance estimate to NGC 5281 (1.3±0.3 kpc), and much smaller than the distance derived to the SNR G309.2−00.6. They discuss the nature of the source, unveil that HD 119682 is a Be star and suggest it is a new member of the recently proposed group of -Cas analogs. They have detected the X-ray periodicity of ∼1500 s that could be the rotational period of an accreting neutron star or white dwarf in this binary.

1417-624
(2S 1417-624, 2S 1417-62, 4U 1416-62, 2E 1417.4-6228, 3A 1417-624, H 1417-624)
The X-ray source 2S 1417-62 was detected by SAS-3 in 1978 (Apparao, Naranan, Kelley et al. (1980)). Analysis of the SAS 3 observations showed an evidence of ~57 mHz pulsations (Kelley, Apparao, Doxsey et al. (1981)). Einstein and optical observations identified a Be star companion at a distance of 1.4-11.1 kpc (Grindlay, Petro & McClintock (1984)). From the timing analysis of BATSE observations orbital parameters were determined and a correlation was found between spin-up rate and pulsed flux (Finger, Wilson & Chakrabarty (1996)). Orbital period and eccentricity of the source were found to be 42.12 days and 0.446 respectively.

J1452.8-5949
(1SAX J1452.8-5949)
1SAX J1452.8-5949 was discovered during a BeppoSAX galactic plane survey in 1999 (Oosterbroek, Orlandini, Parmar et al. (1999)). Coherent pulsations were detected with a barycentric period of a 437.4±1.4 s. The X-ray properties and lack of an obvious optical counterpart are consistent with a Be star companion at a distance of between approximately 6 and 12 kpc. Pulse fraction is high. It was determined in the BeppoSAX band 1.8-10 keV. Be/X-ray systems display a correlation between their spin and orbital periods (Corbet (1986)) which in this case implies an orbital period of >200 days for 1SAX J1452.8-5949.

J1543-568
(XTE J1543-568)
The transient X-ray source XTE J1543-568 was discovered by RXTE in 2000 (in't Zand, Corbet & Marshall (2001)). A subsequent pointed PCA observation revealed a pulsar with a period of 27.12±0.02 s. Later the pulsar was found in earlier data from BATSE on board the Compton Gamma-Ray Observatory. The orbital period is  75.56±0.25 d. The mass function and position in the pulse period versus orbital period diagram are consistent with XTE J1543-568 being a Be/X-ray binary. The eccentricity is less than 0.03, so it is among the lowest for twelve Be/X-ray binaries whose orbits have now been well measured. This confirms the suspicion that small kick velocities of neutron stars in HMXBs are more common for these systems than it is generally expected for neutron stars (in't Zand, Corbet & Marshall (2001); Podsiadlowski, Langer, Poelarends et al. (2004)). There is only a lower limit for its distance. Optical component is unknown, so in't Zand, Corbet & Marshall (2001) were able only to put limits V=21 for 10 kpc and V=23 for 26 kpc. The spectral class determination given by Ziolkowski (2002) is, probably, a misprint (see also Okazaki & Negueruela (2001)). Pulse fraction (RXTE) slightly depends on energy (from 2 to 20 keV).

J15539-6142
(IGR J15539-6142)
The X-ray source IGR J15539-6142 was discovered with INTEGRAL in the Circinus region in an ultra-deep mosaic image (20-60 keV) targeted at radio pulsar PSR B1509-58 (Keek, Kuiper & Hermsen (2006)). Masetti, Bassani, Bazzano et al. (2006) proposed HD 141689 (classified as B2/B3ne by Henize (1976)) as a possible optical counterpart of this hard X-ray source.

1553-542
(2S 1553-542, 2S 1553-54, H 1553-542)
The X-ray source 2S 1553-542 was discovered during observations with SAS 3 in 1975 (Kelley, Rappaport & Ayasli (1983)). Pulse fraction was determined by SAS-3 (2-11 keV).

1555-552
(1H 1555-552, LS 3417, RX J155422.2-551945, 2E 1550.3-5510, 1E 1550.4-5510)
Detected by HEAO1 (Wood, Meekins, Yentis et al. (1984)). The Be star HD 141926 has been proposed as a possible optical counterpart of this X-ray source. Torrejon & Orr (2001) have observed it in the 1.8–10 keV energy range, using BeppoSAX. Their study has allowed them to confirm, for the first time, its nature as a Be/X-ray emitting system, as was suspected from early observations with the HEAO-1 experiment. Torrejon & Orr (2001) confirmed 1H 1555-552 as low luminosity Be/X-ray binary. The spectrum can be well fitted by thermal emission of a hot, optically thin, plasma (Torrejon & Orr (2001)).

J16207-5129
(IGR J16207-5129)
This hard X–ray source was detected for the first time with INTEGRAL (Bird, Barlow, Bassani et al. (2004)), with a flux of 3.8±0.3 mCrab in the 20 – 40 keV band; only an upper limit of <4 mCrab was instead obtained in the 40 – 100 keV band. An emission-line star, HD 146803, is the only remarkable catalogued object present inside the INTEGRAL error box. This star shows Hα in emission (MacConnell (1981)) and is more likely a late-type B star of luminosity class III (Masetti, Pretorius, Palazzi et al. (2005)). The spectral characteristics of this star strongly suggest it to be the optical counterpart of the hard X–ray source detected by INTEGRAL. From the observed magnitudes of B = 10.41 and V = 10.45 Masetti, Pretorius, Palazzi et al. (2005) obtained a distance of d ~ 1.9 kpc, and a color excess of E (B − V ) = 0.07 along the HD 146803 line of sight. This places HD 146803 in the Sagittarius arm of the Galaxy. On the assumption that this star is the optical counterpart of IGR J16207−5129, the above distance estimate implies a 20 – 40 keV band luminosity of ~1.3 × 10³⁴ erg s⁻¹ (Masetti, Pretorius, Palazzi et al. (2005)).

J1626.6-5156
(SWIFT J1626.6-5156)
This transient pulsar was detected for the first time by Swift-BAT (Palmer, Barthelmy, Cummings et al. (2005)). Strong pulsations are detected at the ~15.37s period from observations, with a peak-to-peak pulsed amplitude of about 50% (RXTE PCA), weakly dependent on energy (Belloni, Homan, Campana et al. (2006)). During the flares, the pulsed fraction increases to ~80% (RXTE PCA); after the flare, the pulsed fraction went below its pre-flare value (Belloni, Homan, Campana et al. (2006)). Observational features strongly suggest that the counterpart to this source is a Be star and hence SWIFT J1626.6-5156 is an unusual Be/X-ray binary (Negueruela & Marco (2006)).

J170006-4157
(AX J170006-4157, AX J1700-419, AX J1700.1-4157)
This source was discovered and observed three times between 1994 and 1997 by ASCA (Torii, Sugizaki, Kohmura et al. (1999)). Significant pulsations with P = 714.5±0.3 s were discovered from the third observation. The X-ray spectrum is described by a flat power-law function with a photon index of 0.7. Although the spectrum could also be fitted by thermal models, the obtained temperature was unphysically high. The hard spectrum suggests that the source is a neutron star binary pulsar similar to X Persei (4U 0352+309), but the possibility that it is a white dwarf binary cannot be completely excluded. Not marked as a Be-candidate in Liu, van Paradijs & van den Heuvel (2000). Pulse fraction in the range 0.7-10 keV was determined from the graph in paper by Torii, Sugizaki, Kohmura et al. (1999).

J1700.2-4220
(AX J1700.2-4220)
An INTEGRAL source is coincident with this faint ASCA source. Masetti, Morelli, Palazzi et al. (2006) chose a known emission-line star HD 153295 in the INTEGRAL error box as the putative counterpart. A better position for AX J1700.2-4220 is necessary before the association with HD 153295 (Negueruela & Schurch (2006)).

J1739.4-2942
(RX J1739.4-2942)
Discovered by ROSAT (Motch, Guillout, Haberl et al. (1998)). Probably identical with GRS 1736-297.

J1744.7-2713
(RX J1744.7-2713, HD 161103, V3892 Sgr, LS 4356) - Cas-like object
Discovered by ROSAT (Motch, Haberl, Dennerl et al. (1997)). The luminosity was estimated for the energy range 0.1-2.4 keV. The pulse fraction was taken from paper by Harmon, Wilson, Fishman et al. (2004). It has been obtained by BATSE in the range 20-40 keV.

J1749.1-2733
(AX J1749.1-2733)
Discovered during surveys by ASCA in 1993–1999 (Sakano, Koyama, Murakami et al. (2002)). AX J1749.1−2733 is a high-mass X-ray binary pulsar with an orbital period of 185.5 ± 1.1 days and a spin period of ~66 s, typical of a Be/X-ray binary (Zurita Heras & Chaty (2008)). The outbursts lasts ~ 12 d. A spin down of P = 0.08 ± 0.02 s yr⁻¹ is also observed, likely due to propeller effect. The only optical candidate counterpart within the X-ray error box has magnitudes of R = 21.9 ± 0.1, I = 20.92 ± 0.09, J = 17.42 ± 0.03, H = 16.71 ± 0.02 and Ks = 15.75 ± 0.07, which points towards a Be star located far away (> 8.5 kpc) and highly absorbed (N_H ~1.7 × 10²² cm⁻² )(Zurita Heras & Chaty (2008)). The 22–50 keV luminosity is 0.4 − 0.9 × 10³⁶ erg s⁻¹ during the long outburts with a peak of 3 × 10³⁶ erg s⁻¹ during the bright flare occurred at MJD 52891 (Zurita Heras & Chaty (2008)). The pulse fractions reach I_max=22 ± 6 and I_min=29 ± 11% (Zurita Heras & Chaty (2008)). All the X-ray properties observed in AX J1749.1−2733 lead Zurita Heras & Chaty (2008) to classify this object as an X-ray binary, most probably a high-mass X-ray binary with a Be companion star and whose compact object is a neutron star. The only optical candidate counterpart located inside the best X-ray error box is compatible with a B star located far in the galaxy and suffering large extinction (Zurita Heras & Chaty (2008)). AX J1749.1−2733 seems to be an obscured Be/X-ray binary located far away in the Galaxy.

J1749.2-2725
(AX J1749.2-2725)
Discovered by ASCA (Torii, Kinugasa, Katayama et al. (1998)). Not marked as a Be-candidate in paper by Liu, van Paradijs & van den Heuvel (2000).

J1750-27
(GRO J1750-27, AX J1749.1-2639)
GRO J1750-27 is the third of the transient accretion-powered pulsars discovered using BATSE. A single outburst from GRO J1750-27 was observed with BATSE (see Scott, Finger, Wilson et al. (1997)). Pulsations with a 4.45 s period were discovered on 1995 July 29 from the Galactic center region as part of the BATSE all-sky pulsar monitoring program (Bildsten, Chakrabarty, Chiu et al. (1997)). An orbit with a period of 29.8 days was found by Scott, Finger, Wilson et al. (1997). Large spin-up rate, spin period and orbital period together suggest that accretion is occurring from a disk and that the outburst is a "giant" one typical for a Be/X-ray transient system.

J180816.8-191940
(1XMM J180816.8-191940) - Cas-like object
 ...

J1820.5-1434
(AX J1820.5-1434)
This X-ray source was discovered in 1997 by ASCA (Kinugasa, Torii, Hashimoto et al. (1998)). Pulsations with a period $\sim$ 152 s were detected in the 2-10 keV flux of the source with a pulsed fraction of $\sim$ 50%. The pulse fraction is not energy dependent. Both timing and spectral properties of AX J1820.5-1434 are typical for an accretion-driven X-ray pulsar. Israel, Covino & Polcaro (2000) proposed O9.5-B0Ve star as an optical counterpart of the pulsar.

J183327.7-103523
(1XMM J183327.7-103523, SS 397) - Cas-like object
 ...

J183328.7-102409
(1XMM J183328.7-102409, USNO 0750-13549725) - Cas-like object
 ...

J18410-0535
(IGR J18410-0535, AX J1841.0-0536?)
The source, IGR J18410-0535, was discovered with INTEGRAL during Galactic Plane Deep Exposure, as it was undergoing a ~70 mCrab flare in the 20-60 keV energy range, and 20 mCrab in the 60-200 keV range (Rodriguez, Garau, Grebenev et al. (2004)). Halpern & Gotthelf (2004) noted that the INTEGRAL source IGR J18410-0535 is possibly an outburst of the transient 4.74 s X-ray pulsar AX J1841.0-0536, which in turn was identified using Chandra with a Be star counterpart (Halpern, Gotthelf, Helfand et al. (2004)).

1843+00
(GS 1843+00)
The transient X-ray source GS 1843+00 was discovered during the Galactic plane scan near the Scutum region by X-ray detectors on board the Ginga satellite (Turner, Thomas, Patchett et al. (1989)). Coherent pulsations with a period of about 29.5 s were observed with a very small peak-to-peak amplitude of only 4 per cent of the average flux. Pulse fraction was obtained by BATSE (20-50 keV). Luminosity estimates are the following: 1) 2 x 10³⁶ erg s^-1 (20-200 keV, 10 kpc) (Manchanda (1999)); 2) 3 x 10³⁷ erg s^-1 (0.3-100 keV, 10 kpc) (Piraino, Santangelo, Segreto et al. (2000)).

1845-024
(2S 1845-024, GS 1843-02, 4U 1850-03, 1A 1845-02, 1H 1845-024, 3A 1845-024, GRO J1849-03)
The pulsar GS 1843-02 was discovered by Ginga in 1988 (Makino (1988)) during a galactic plane scan conducted as part of a search for transient pulsars (see Finger, Bildsten, Chakrabarty et al. (1999)). The same source is known as GRO J1849-03. X-ray outbursts occur regularly every 242 days. Finger, Bildsten, Chakrabarty et al. (1999) presented a pulse timing analysis that shows that the 2S 1845-024 outbursts occur near the periastron passage. The orbit is highly eccentric (e = 0.88±0.01) with a period of  242.18±0.01 days. The orbit and transient outburst pattern strongly suggest that the pulsar is in a binary system with a Be star. From the measured spin-up rates and inferred luminosities Finger, Bildsten, Chakrabarty et al. (1999) concluded that an accretion disc is present during outbursts.

J18483-0311
(IGR J18483-0311)
The transient X-ray source IGR J18483−0311 was discovered with the IBIS instrument (Ubertini, Lebrun, Di Cocco et al. (2003)) on board the INTEGRAL satellite during observations of the Galactic Center field. The average X-ray flux was ∼10 mCrab and ∼5 mCrab in the energy bands 15–40 keV and 40–100 keV respectively. A possible X-ray outburst was observed on 26 April, when the X-ray flux increased up to ∼40 mCrab (15–40 keV). Sguera, Hill, Bird et al. (2007) reported on 5 newly discovered outbursts from IGR J18483−0311 detected by INTEGRAL. For two of them it was possible to constrain a duration of the order of a few days. The strongest outburst reached a peak flux of ∼120 mCrab (20–100 keV). Timing analysis of INTEGRAL data allowed Sguera, Hill, Bird et al. (2007) to identify periodicities of 18.52 days and 21.0526 seconds which are likely the orbital period of the system and the spin period of the X-ray pulsar respectively. Swift XRT observations of IGR J18483−0311 provided a very accurate source position which strongly indicates a highly reddened star in the USNO–B1.0 and 2MASS catalogues as its possible optical/NIR counterpart. The X-ray spectral shape, the periods of 18.52 days and 21.0526 s, the high intrinsic absorption, the location in the direction of the Scutum spiral arm and the highly reddened optical object as possible counterpart, all favour the hypothesis that IGR J18483−0311 is a HMXB with a neutron star as compact companion. The system is most likely a Be X-ray binary, but a Supergiant Fast X-ray Transient nature can not be entirely excluded.

J1858+034
(XTE J1858+034)
The hard X-ray transient XTE J1858+034 was discovered with the RXTE All Sky Monitor in 1998 (Remillard, Levine, Takeshima et al. (1998)). The spectrum was found to be hard similar to spectra of X-ray pulsars. Observations were made immediately after this with the Proportional Counter Array (PCA) of the RXTE and regular pulsations with a period of  221.0±0.5 s were discovered (Takeshima, Corbet, Marshall et al. (1998)). The pulse profile is found to be nearly sinusoidal with a pulse fraction of ~25%. From the transient nature of this source and pulsations they suggested that this is a Be/X-ray binary. The position of the X-ray source was refined by scanning the sky around the source with the PCA (Marshall, Lochner, Santangelo et al. (1998)). From the RXTE target of opportunity (TOO) public archival data of the observations of XTE J1858+034, made in 1998, Paul & Rao (1998) have discovered the presence of low frequency QPOs. Pulse fraction was obtained by RXTE (2-10 keV). WeU. Mukherjee, Bapna, Raichur et al. (2006) have obtained a clear energy dependence of the RMS variation in the QPOs, increasing from about 3% at 3 keV to 6% at 25 keV. The X-ray pulse profile is a single peaked sinusoidal, with pulse fraction increasing from 20% at 3 keV to 45% at 30 keV (Mukherjee, Bapna, Raichur et al. (2006)).

J1859+083
(XTE J1859+083)
The X-ray source XTE J1859+083 was discovered by Marshall et al. (1999) in observations made with the Rossi X-ray Timing Explorer (RXTE) Proportional Counter Array (PCA) in 1999. Marshall et al. (1999) found pulsations at a period of 9.801 ± 0.002 s. The transient nature of XTE J1859+083 and its pulsations suggest that it might be a member of the Be/neutron star binary class of objects. A 60.65 day period would be consistent with the orbital period expected for a Be star system containing a 9.8 s X-ray pulsar based on the correlation between orbital and pulse periods for this type of system (Corbet, in´t Zand, Levine & Marshall (2009)).

1901+03
(4U 1901+03)
4U 1901+03 was detected in outburst by Uhuru and Vela 5B in 1970–1971 (Forman, Tananbaum & Jones (1976); Priedhorsky & Terrell
(1984)). Galloway, Wang & Morgan (2005) described observations of the 2003 outburst of this source with the Rossi X-ray Timing Explorer. Proportional Counter Array (PCA) observations over the 5-month duration of the 2003 outburst revealed a 2.763 s pulsar in a 22.58 d orbit. Galloway, Wang & Morgan (2005) suggested that the surface magnetic field strength of the neutron star is below ~ 5 × 10¹¹ G. The neutron star in 4U 1901+03 probably accretes from the wind of a main-sequence O-B star, like most other high-mass binary X-ray pulsars. The almost circular orbit (e = 0.036) confirms the system’s membership in a class of wide, low-eccentricity systems in which the neutron stars may have received much smaller kicks as a result of their natal supernova explosions (Galloway, Wang & Morgan (2005)). Pulse fraction was obtained with the Rossi X-ray Timing Explorer. The fractional pulse amplitude varied over the outburst, and was generally between 4 and 22% (Galloway, Wang & Morgan (2005)).

1936+541
(1H 1936+541)
Detected by HEAO1 (Wood, Meekins, Yentis et al. (1984)). DM +53 2262 (Be star) is a proposed optical counterpart of this X-ray source. It has never been observed by imaging X-ray telescopes since its detection during the HEAO-1 survey. Observations by Torrejon & Orr (2001) with BeppoSAX also showed negative results. This lack of detection does not exclude its nature as a Be/X-ray binary because it could be in a quiescent state usually found in many Be/X-ray systems (Torrejon & Orr (2001)).

J1946+274
(XTE J1946+274, GRO J1944+26, 3A 1942+274, SAX J1945.6+2721)
Pulse fraction obtained by Indian X-ray Astronomy Experiment - IXAE (2-18 keV). Coburn, Heindl, Rothschild et al. (2002) present a data on cyclotron feature in the spectrum of XTE J1946+274 which corresponds to the field ~3.9 × 10¹² G. Wilson, Finger, Coe & Negueruela (2003) propose a distance 9.5±2.9 kpc basing on a correlation between measured spin-up rate and flux.

J1948+32
(GRO J1948+32, GRO J2014+34, KS 1947+300)
This transient X-ray source was discovered in 1989 during the observations of the Cyg X-1 region by the TTM telescope aboard the Kvant module of the Mir space station (Borozdin, Gilfanov, Sunyaev et al. (1990)). The flux recorded from it was 70±10 mCrab in the energy range 2-27 keV. In 1994 the BATSE monitor discovered the X-ray pulsar GRO J1948+32 with a period of 18.7 s in the same region (Chakrabarty, Koh, Bildsten et al. (1995)). Galloway, Morgan & Levine (2004)] presented results which can indicate a glitch in that system. Based on the behavior of the pulsation period during the outburst of 2000-2001, they determined the parameters of the binary: the orbital period P_orb =  40.415±0.010 d and the eccentricity e =  0.033±0.013. The optical counterpart is a B0 Ve star. Tsygankov & Lutovinov (2005) estimated the magnetic field strength of the pulsar ~2.5 x 10¹³ G, and the distance to the binary d = 9.5±1.1 kpc. The pulse fraction depends on the source's intensity, the orbital phase and the energy range (Tsygankov & Lutovinov (2005)).

2030+375
(EXO 2030+375, V2246 Cyg)
EXO 2030+375 was discovered in 1985 May with EXOSAT satellite during a large outburst phase (Parmar, White, Stella et al. (1989)). This outburst was first detected at a 1-20 keV energy band and its luminosity is close to the Eddington limit (assuming 5 kpc distance to the source) for a neutron star (Parmar, Stella, Ferri & White (1985)). The X-ray emission of the transient pulsar EXO 2030+375 is modulated by $\sim$ 42 s pulsations and periodic $\sim$ 46 days Type I outbursts, that are produced at each periastron passage of the neutron star, i.e. when the pulsar interacts with the disk of the Be star. Wilson, Fabregat & Coburn 2005) presented results of observations of transition to global spin-up in this source somewhen between between June 2002 and September 2003. The source is not marked as a Be-candidate in Liu, van Paradijs & van den Heuvel (2000). Pulse fraction was obtained by BATSE in the range 30-70 keV (see Harmon, Wilson, Fishman et al. (2004)). See a detailed description in paper by Wilson, Finger, Coe et al. (2002).

J2030.5+4751
(RX J2030.5+4751, SAO 49725) - Cas-like object
Discovered by ROSAT (see Motch, Haberl, Dennerl et al. (1997)). This object is marked as a likely Be/X-ray candidate in Liu, van Paradijs & van den Heuvel (2000), but not in many other papers. The pointing data show that the X-ray source is relatively hard. The L_x/L_bol ratio is close to 3 x 10^-6. This is rather strong evidence in favor of an accreting compact object around SAO 49725 (Motch, Haberl, Dennerl et al. (1997)).

J2058+42
(GRO J2058+42, CXOU J205847.5+414637?)
GRO J2058+42 is a transient 198 s X-ray pulsar. It was discovered by BATSE during a "giant" outburst in 1995 (see Wilson, Finger, Harmon et al. (1998)). The pulse period decreased from 198 to 196 s during the 46 day outburst. BATSE observed five weak outbursts from GRO J2058+42 that were spaced by about 110 days. The RXTE All-Sky Monitor detected eight weak outbursts with approximately equal durations and intensities. GRO J2058+42 is most likely a Be/X-ray binary that appears to produce outbursts at periastron and apastron. The optical counterpart to GRO J2058+42 has been identified with a V=14.9 O9.5-B0IV-Ve star located at a distance of ~ 9 ± 1 kpc (Reig, Negueruela, Papamastorakis et al. (2005)). After a period of high X-ray activity (1995-2002) GRO J2058+42 entered a quiescent phase in mid 2002 that continues up to the present. The Chandra observations of February 2004 failed to detect pulsations and estimated the unabsorbed 2–10 keV flux to be (3 − 9) × 10³³ erg s⁻¹(Reig, Negueruela, Papamastorakis et al. (2005)). No X-ray source was present in the error circle in archival ROSAT observations (Wilson, Finger, Harmon et al. (1998)). Wilson, Weisskopf, Finger et al. (2005) have suggested that GRO J2058+42 and CXOU J205847.5+414637 are the same source. Pulse fraction was obtained by BATSE in the range 20-70 keV (see Harmon, Wilson, Fishman et al. (2004) for details).

J2103.5+4545
(SAX J2103.5+4545)
SAX J2103.5+4545 is a transient HMXB pulsar with a ~358 s pulse period discovered with the WFC on-board BeppoSAX during an outburst in 1997 (Hulleman, in 't Zand & Heise (1998)). Its orbital period of 12.68 days and eccentricity of 0.4 ± 0.2 have been found with the RXTE during the 1999 outburst (Baykal, Stark & Swank (2000)). The likely optical counterpart, a Be star with a magnitude V=14.2, has been recently discovered (Reig & Mavromatakis (2003)). During the outburst in 1999 Baykal, Stark & Swank (2002) for the first time observed with RXTE a transition from the spin-up phase to the spin-down regime, while the X-ray flux was declining. Inam, Baykal, Swank & Stark (2004) observed a soft spectral component (blackbody with a temperature of 1.9 keV) and a transient 22.7 s QPO during a XMM-Newton observation performed in 2003. They estimated the magnetic field of the neutron star to be ~ 7 × 10¹² G. INTEGRAL observations provided the first broad-band spectrum and showed significant emission up to 150 keV (Blay, Reig, Martínez-Nunez et al. (2004)). The pulsed fraction increases with energy from ~ 45% at 5-40 keV to ~ 80% at 40-80 keV (Falanga, di Salvo, Burderi et al. (2005)).

2138+568
(GS 2138-56, Cep X-4, V490 Cep, 1H 2138+579, 4U 2135+57, 3A 2129+571)
The X-ray source Cep X-4 was discovered with a transient high level X-ray flux in 1972 by OSO-7 (Ulmer, Baity, Wheaton et al. (1973)). The source was not detected again till 1998 when a new outburst was detected by GINGA. During these observations coherent 66 s pulsations were discovered revealing an X-ray pulsar with a complex X-ray spectrum including a possible 30 keV cyclotron absorption feature (Koyama, Kawada, Tawara et al. (1991); Mihara, Makishima, Kamijo et al. (1991)). Cep X-4 has been associated with a Be star that lies within the ROSAT error box. A cyclotron line was detected by Mihara, Makishima, Kamijo et al. (1991), it corresponds to the magnetic field B = 2.3 x 10¹² (1+z) G. Pulse fraction strongly depends on energy and is highly variable with time from nearly 0 up to >80% (see Wilson, Finger & Scott 1999)). The RXTE pulse fraction is decreasing with intensity.

2214+589
(1H 2214+589)
Detected by HEAO1 (Wood, Meekins, Yentis et al. (1984)). This object is mentioned in Liu, van Paradijs & van den Heuvel (2000) as a Be-candidate. However, it is not mentioned in many lists of Be/X-ray systems (for example in Ziolkowski (2002)). Not much is known about this source.

J2239.3+6116
(3A 2237+608, SAX J2239.3+6116, SAX J2239.2+6116, 3U 2233+59, 4U 2238+60)
Discovered by BeppoSAX (see in't Zand, Swank, Corbet & Markwardt (2001)). SAX J2239.3+6116 is an X-ray transient which often recurs with a periodicity of 262 d (in't Zand, Halpern, Eracleous et al. (2000)). Because of the Be-star nature of the likely optical counterpart the periodicity may be identified with the orbital period of the binary. Pulse fraction was determined from the graph in in't Zand, Swank, Corbet & Markwardt (2001) as (I_max - I_min)/(I_max+I_min). It corresponds to the energy range ~1-10 keV. L_max corresponds to the distance 4.4 kpc and the highest flux 10^-9 erg cm^-2 s^-1 in the energy range 2-28 keV (in't Zand, Swank, Corbet & Markwardt (2001)).

MWC 656
(HD 215227)
This X-ray source is the first binary system at a distance of 2.6 ± 0.6 kpc composed of a Be star and a black hole (Casares, Negueruela, Ribo et al. (2014)). MWC 656 is a Be star located within the error box of the point-like γ–ray source AGL J2241+4454 (Lucarelli, Verrecchia, Striani et al. (2010)). Casares, Negueruela, Ribo et al. (2014) obtained orbital elements for MWC 656 and updated the spectral classification of the Be star to B1.5–B2 III, which implies a Be mass in the range 10–16 M⊙ and a BH companion of 3.8–6.9 M⊙. The total X-ray luminosity is L_x = (3.7±1.7)×10³¹ erg s^-1 in the 0.3–5.5 keV band. This luminosity represents (6.7 ± 4.4) × 10−8 L_Edd for the estimated range of BH companion masses (Munar-Adrover, Paredes, Ribó et al. (2014)).