A Rapidly Varying Red Supergiant X-Ray Binary in the Galactic Center

Abstract

We analyzed multiwavelength observations of the previously identified Galactic center X-ray binary CXO 174528.79-290942.8 (XID 6592) and determine that the near-infrared counterpart is a red supergiant based on its spectrum and luminosity. Scutum X-1 is the only previously known X-ray binary with a red supergiant donor star and closely resembles XID 6592 in terms of X-ray luminosity (L X), absolute magnitude, and IR variability (L IR,var), supporting the conclusion that XID 6592 contains a red supergiant donor star. The XID 6592 infrared counterpart shows variability of ∼0.5 mag in the Wide-field Infrared Survey Explorer-1 band (3.4 μm) on timescales of a few hours. Other infrared data sets also show large-amplitude variability from this source at earlier epochs but do not show significant variability in recent data. We do not expect red supergiants to vary by ∼50% in luminosity over these short timescales, indicating that the variability should be powered by the compact object. However, the X-ray luminosity of this system is typically ∼1000× less than the variable luminosity in the infrared and falls below the Chandra detection limit. While X-ray reprocessing can produce large-amplitude fast infrared variability, it typically requires >> L X L IR,var to do so, indicating that another process must be at work. We suggest that this system may be a supergiant fast X-ray transient (SFXT), and that a large (∼10 38 ergs s −1), fast (10 2-4 s) X-ray flare could explain the rapid IR variability and lack of a long-lasting X-ray outburst detection. SFXTs are normally associated with blue supergiant companions, so if confirmed, XID 6592 would be the first red supergiant SFXT, as well as the second X-ray red supergiant binary.

Accretion of a clumped wind from a red supergiant donor onto a magnetar is suggested by the analysis of the XMM-Newton and NuSTAR observations of the X-ray binary 3A 1954+319

“…The X-ray binary 3A 1954+319 was recently reclassified from being a SyXB into a SgXB thanks to the discovery that the donor star in this system is an M-type supergiant. SgXB with RSG donors are rare: so far only two other RSG X-ray binaries are known in our Galaxy (Scutum X-1 and CXO 174528.79-290942.8; see Kaplan et al 2007;Gottlieb et al 2020). A handful of RSG X-ray binaries identified in nearby galaxies are ultraluminous X-ray sources (ULX) (NGC 300 ULX-1, RX J004722.4- 252051 in NGC 253, ULX J022721+333500 in NGC 925, and ULX J120922+295559 in NGC 4136, Heida et al 2015Heida et al , 2016Heida et al , 2019.…”

SRGA J181414.6-225604: A New Galactic Symbiotic X-Ray Binary Outburst Triggered by an Intense Mass-loss Episode of a Heavily Obscured Mira Variable

“…The classification of the donor star as a very-late-type pulsating AGB star offers a novel addition to the growing population of Galactic SyXRBs. The majority of previously known SyXRBs (Table 1 in Yungelson et al 2019) contain early M-type donors consistent with red giants, in addition to some sources where the donor has been suggested to be an RSG (Gottlieb et al 2020;Hinkle et al 2020). The brightest known source, GX 1+4, also has an M6-III red-giant donor that is nearly overflowing its Roche lobe and the luminous X-ray emission (Chakrabarty & Roche 1997).…”

Star Formation in Self-gravitating Disks in Active Galactic Nuclei. III. Efficient Production of Iron and Infrared Spectral Energy Distributions

“…Considering the discovery of stellar disks composed of ∼200 young massive stars in the GC (e.g., Bartko et al 2010;von Fellenberg et al 2022), there must remain some sMBHs after the SN explosion of massive stars in the AGN accretion disks. Indeed, there is growing evidence for such a population of black holes (with a number of ∼2 × 10 4 ; e.g., Hailey et al 2018;Gottlieb et al 2020). Exploring the geometric and dynamic relation of those black holes (evolved from massive stars) with the young stars will advance the understanding of physics in the central regions.…”