Sources in the LMC: comments to the Table 2

J0501.6-7034
(RX J0501.6-7034, 2E 0501.8-7038, 1E 0501.8-7036, HV 2289, CAL 9)
This Einstein and ROSAT variable source was identified with a Be star by Schmidtke, Cowley, Frattare et al. (1994). Later Schmidtke, Cowley, Hauschildt et al. (1996) identified this star with HV 2289, a known variable with a large amplitude of variability.

J0502.9-6626
(RX J0502.9-6626, CAL E)
The X-ray source RX J0502.9-6626 was originally detected by the Einstein observatory (Cowley, Crampton, Hutchings et al. (1984)) at a flux of ~3 x 10³⁶ erg s^-1. The source was detected three times with the ROSAT PSPC at luminosities ~10³⁵ - 10³⁶ erg s^-1 and once with the HRI during a bright outburst at 4 x 10³⁷ erg s^-1 (Schmidtke, Cowley, McGrath & Anderson (1995)). During the outburst, pulsations at 4.0635 s were detected. The identification of this source with the Be star [W63b] 564 = EQ 050246.6-663032.4 (Wooley (1963)) was confirmed by Schmidtke, Cowley, Frattare et al. (1994).

J0516.0-6916
(RX J0516.0-6916)
The identification of this source with a Be-star is unclear. In several observations the source did not display any characteristics of Be behaviour, however, Schmidtke, Cowley, Crane et al. (1999) classify it as a Be-star.

J052016.0-692505
(XMMU J052016.0-692505)
This super-soft X-ray source was discovered with XMM-Newton (Kahabka, Haberl, Payne & Filipovic (2006)). The likely optical counterpart of XMMU J052016.0−692505 is the LMC variable star LMCV2135 (Kahabka, Haberl, Payne & Filipovic (2006)). The infrared and optical colors and magnitudes of this star are consistent with a hot star of likely spectral type B. The long-term MACHO light curve shows variability with a timescale of ~500 and ~1000 days (Kahabka, Haberl, Payne & Filipovic (2006)). The optical spectra show strong Hα and H emission lines which indicate a B0–3e star. The radial velocities of the Hα and H emission lines show a variation from ~400-450 km s⁻¹ to ~5-20 km s⁻¹ which is consistent with the systemic velocity of the LMC and an intrinsic variation most likely due to the rotation of the Be disk. Kahabka, Haberl, Payne & Filipovic (2006) discuss XMMU J052016.0−692505 as a Be/white dwarf binary system in the LMC. The super-soft X-ray spectrum of the source could be due to a stable nuclear burning white dwarf.

J0520.5-6932
(RX J0520.5-6932)
This X-ray source has been observed at a low X-ray luminosity (5 x 10³⁴ erg s^-1) in early 90-s by ROSAT (Schmidtke, Cowley, Frattare et al. (1994)). The light curve of the optical counterpart exhibits significant modulation with a period of 24.5 d, which is interpreted as the orbital period (Coe, Negueruela, Buckley et al. 2001)). A spectral type O9V was proposed for the optical counterpart. In a recent paper Edge, Coe, Galache & Hill (2004) present new optical and IR data and archive BATSE data on the outburst.

J0529.8-6556
(RX J0529.8-6556, RX J0529.7-6556)
The transient X-ray source RX J0529.8-6556 was detected during one single outburst as a 69.5-s X-ray pulsar by Haberl, Dennerl, Pietsch & Reinsch 1997), who identified it with a relatively bright blue star showing weak Hα emission.

J0530.1-6551
(RX J0530.1-6551, XMMU J053011.2-655122)
This X-ray source was detected in ROSAT data (Haberl & Pietsch (1999)). Haberl, Dennerl & Pietsch (2003) proposed this source as a new candidate HMXB based on its hard X-ray spectrum and the presence of a likely optical counterpart. For this X-ray source during the XMM-Newton observations probable pulsations were found with a period of 271.97(5) s (Haberl, Dennerl & Pietsch (2003)). Detection of a possible pulse period for XMMU J053011.2-655122 leaves little doubt about the HMXB and most likely Be/X-ray binary nature of this source (Haberl, Dennerl & Pietsch (2003)).

053109-6609.2
(EXO 053109-6609.2, RX J0531.2-6609, RX J0531.2-6607, EXO 0531.1-6609)
This source was discovered by EXOSAT during deep observations of the LMC X-4 region in 1983 (Pakull, Brunner, Pietsch et al. (1985)). It was detected again in 1985 by the SL2 XRT experiment. The lack of detection in EXOSAT observations made between these dates demonstrates the transient nature of the source. The companion is optically identified with a Be star (Haberl, Dennerl & Pietsch (1995)). Burderi, di Salvo, Robba et al. (1998) reported a timing analysis of the Be transient X-ray binary EXO 053109-6609.2 in outburst observed with BeppoSAX. The pulsed fraction is nearly constant in the whole energy range. The source shows pulsations from 0.1 up to 60 keV. In the MECS (Medium Energy Concentrator Spectrometer) pulse profile in the 1.8-10.5 keV band the pulsed fraction is 0.54±0.05. In the LECS (Low Energy Concentrator Spectrometer) pulse profile (the 0.1-1.8 keV band), the main pulse is still evident, while the interpulse is more broadened, and pulsed fraction is 0.78±0.28. The PDS (Phoswich Detection System) pulse profile (15-60 keV energy band) still shows a double-peaked structure (pulsed fraction is 0.64±0.16) in phase with the previous ones. Although the statistics is poor, the pulsed fraction does not seem to decrease with energy (Burderi, di Salvo, Robba, et al. (1998)).

J053115.4-705350
(XMMU J053115.4-705350)
This source is considered likely HMXB candidate (Shtykovskiy & Gilfanov (2005)). Luminocity was calculated using the archival data of the
XMM-Newton observatory (2-10 keV) (Shtykovskiy & Gilfanov (2005)).

J0532.4-6535
(RX J0532.4-6535)
This source was observed by the ROSAT PSPC (Haberl & Pietsch (1999)). The hardness ratios of this source suggest an X-ray binary or background AGN. The fact that it is one of three sources from the catalogue of Reid, Glass & Catchpole (1988) which are X-ray emitters, with one of them the known Be/X-ray transient A0538-66, favour an HMXB nature of RX J0532.4-6535. For a Be/X-ray binary in the LMC the X-ray luminosity is between 3 and 7 x 10³⁴ erg s^-1 (0.1-2.4 keV) (Haberl & Pietsch (1999)). The relatively low variability suggests a system like X Per or RX J0146.9-6121 detected during the persistent quiescent state.

J0531.5-6518
(RX J0531.5-6518)
This source was detected with the ROSAT PSPC in June 1990 (Haberl & Pietsch (1999)). The source is probably variable, since other pointings failed to detect it. The optical counterpart is probably a Be star coming back from an extended disk-less phase (Negueruela & Coe (2002)).

J0535.0-6700
(RX J0535.0-6700)
This source was observed by the ROSAT PSPC at a luminosity ~3 x 10³⁵ erg s^-1 (Haberl & Pietsch (1999)). Its positional coincidence with an optically variable star in the LMC (RGC28 in paper by Reid, Glass & Catchpole (1988)) is very good. RGC28 is an early-type Be star and likely it is the optical counterpart to RX J0535.0-6700 (Negueruela & Coe (2002)). The star displays periodic variability in its I-band lightcurve at 241 d, which Reid, Glass & Catchpole (1988) originally believed to be the period of a Mira variable. Haberl & Pietsch (1999) suggested that this variability can be related to the orbital period.

0535-668
(RX J0535.6-6651, 1A 0538-66, 1A 0535-66)
This source was discovered by the Ariel 5 satellite in June 1977, during outburst in which the flux peaked at ~9 x 10³⁸ erg s^-1 (White & Carpenter (1978)). When active, 1A 0535-66 displays very bright short X-ray outbursts separated by 16.6 days, which is believed to be the orbital period. The optical counterpart experiences drastic changes in the spectrum, with the appearance of strong P-Cygni-like emission lines, and brightening by more than 2 mag in the V band (Charles, Booth, Densham et al. (1983)). The Be star has a V magnitude of ~14.8 during the X-ray quiescent periods. The magnitude reaches a peak of 12.5 mag during the X-ray outbursts. Detection of a 69-ms pulsation in the X-ray signal has been reported only once (Skinner, Bedford, Elsner et al. (1982)). Further X-ray observations of outbursts were made by Skinner, Shulman, Share et al. (1980) using the HEAO 1 satellite. The X-ray outbursts were found to last up to at least 14 days or to be as short as a few hours. 1A 0535-66 in its largest outbursts (Skinner, Shulman, Share et al. (1980)) has luminosity around 10³⁹ erg s^-1. ROSAT (Mavromatakis & Haberl (1993)) and ASCA observations (Corbet, Smale, Charles & Southwell (1995)) have revealed low-level outbursts with luminosities of 4 x 10³⁷ erg s^-1 and 2 x 10³⁷ erg s^-1 in the two ROSAT observations and ~5.5 x 10³⁶ erg s^-1 in the ASCA observation. Due to the low count rate and sampling frequency it was not possible to determine whether the 69 ms pulsations were present in the data. The ratio of L_max to L_min in soft X-rays is >1000. Alcock, Allsman, Alves et al. (2001) reported the discovery of 421 day periodicity.

J054134.7-682550
(XMMU J054134.7-682550)
This source is considered likely HMXB candidate (Shtykovskiy & Gilfanov (2005)). The pulse period is 61.601 ± 0.017 seconds, with a pulsed semi-amplitude of about 40% (Markwardt, Swank & Corbet (2007)). There are no obvious signs of orbital Doppler modulation. Assuming this source is a Be star system having a giant, "Type II" outburst, the estimated orbital period is about 80 days (within a factor of ~2) based on a fit to the P_spin vs. P_orb for other similar systems (Markwardt, Swank & Corbet (2007)). For a distance of 52 kpc, the mean 2-40 keV luminosity is 2.0 x 38 erg s^-1 (Markwardt, Swank & Corbet (2007)).

0544-665
(H 0544-665, H 0544-66)
This source was discovered with the HEAO-1 scanning modulation collimator by Johnston, Bradt & Doxsey (1979). The brightest object within the X-ray error circle was found to be a variable B0-1 V star (van der Klis, Tuohy, Elso et al. (1983)) but no emission lines have been observed in its spectrum to identify it as a Be star. van der Klis, Tuohy, Elso et al. (1983) published photometry which showed a negative correlation between optical magnitudes and color indices, typical of Be stars whose variability is due to variations in the circumstellar disc. Stevens, Coe & Buckley (1999) suggested that the object may be a Be star in the state of low activity.

J0544.1-7100
(RX J0544.1-7100, AX J0544.1-7100, AX J0548-704, 1WGA J0544.1-7100, 1SAX J0544.1-7100)
This source is a transient X-ray pulsar (P = 96 s) with hard X-ray spectrum observed by BeppoSAX (Cusumano, Israel, Mannucci et al. (1998)) and by ROSAT in the LMC (Haberl & Pietsch (1999)). The observations of the optical counterpart were presented by Coe, Negueruela, Buckley et al. (2001), who found it to display large variability in the I-band lightcurve and Hα in emission. An approximate spectral type of B0 Ve was proposed.