SRG/eROSITA-triggered XMM-Newton observations of three Be/X-ray binaries in the LMC: Discovery of X-ray pulsations

Abstract

Using data from eROSITA, the soft X-ray instrument aboard Spectrum-Roentgen-Gamma (SRG), we report the discovery of two new hard transients, eRASSU J050810.4-660653 and eRASSt J044811.1-691318, in the Large Magellanic Cloud. We also report the detection of the Be/X-ray binary RX J0501.6-7034 in a bright state. We initiated follow-up observations to investigate the nature of the new transients and to search for X-ray pulsations coming from RX J0501.6-7034. We analysed the X-ray spectra and light curves from our XMM-Newton observations, obtained optical spectra using the South African Large Telescope to look for Balmer emission lines and utilised the archival data from the Optical Gravitational Lensing Experiment (OGLE) for the long-term monitoring of the optical counterparts. We find X-ray pulsations for eRASSU J050810.4-660653, RX J0501.6-7034, and eRASSt J044811.1-691318 of 40.6 s, 17.3 s, and 784 s, respectively. The Halpha emission lines with equivalent widths of -10.4 A (eRASSU J050810.4-660653) and -43.9 A (eRASSt J044811.1-691318) were measured, characteristic for a circumstellar disc around Be stars. The OGLE I- and V-band light curves of all three systems exhibit strong variability. A regular pattern of deep dips in the light curves of RX J0501.6-7034 suggests an orbital period of ~451 days. We identify the two new hard eROSITA transients eRASSU J050810.4-660653 and eRASSt J044811.1-691318 and the known Be/X-ray binary RX J0501.6-7034 as Be/X-ray binary pulsars.

Accepted for publication in Astronomy & Astrophysics

References in corpus (13)

• The Gaia mission
• The eROSITA X-ray telescope on SRG
• The eROSITA Final Equatorial Depth Survey (eFEDS): The X-ray catalog
• The ART-XC telescope on board the SRG observatory
• XMM-Newton observations of the Small Magellanic Cloud: Be/X-ray binary pulsars active between October 2006 and June 2007
• On the Spin Period Distribution in Be/X-ray Binaries
• Three new high-mass X-ray binaries in the Large Magellanic Cloud
• eROSITA calibration and performance verification phase: High-mass X-ray binaries in the Magellanic Clouds
• RX J0529.8-6556: a BeXRB pulsar with an evolving optical period and out of phase X-ray outbursts
• Fast flaring observed from XMMU J053108.3-690923 by eROSITA: a supergiant fast X-ray transient in the Large Magellanic Cloud
• Optical and X-ray study of the peculiar high mass X-ray binary XMMU J010331.7-730144
• Broadband study and the discovery of pulsations from the Be/X-ray binary eRASSU J052914.9-662446 in the Large Magellanic Cloud
• First characterization of a new High Mass X-ray Binary in LMC eRASSU J050810.4$-$660653 with SRG/ART-XC, NuSTAR and Swift

Cited by in corpus (2)

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