Astrophysics > High Energy Astrophysical Phenomena
[Submitted on 16 Aug 2021 (v1), last revised 19 Oct 2021 (this version, v2)]
Title:The X-ray binary population in the Galactic Center revealed through multi-decade observations
View PDFAbstract:We present an investigation of the quiescent and transient X-ray binaries (XRBs) of the Galactic Center (GC). We extended our Chandra analysis of the non-thermal X-ray sources, located in the central parsec, from Hailey et al. (2018), using an additional 4.6 Msec of ACIS-S data obtained in 2012-2018. The individual Chandra spectra of the 12 sources fit to an absorbed power-law model with a mean photon index $\Gamma$~2 and show no Fe emission lines. Long-term variability was detected from nine of them, confirming that a majority are quiescent XRBs. Frequent X-ray monitoring of the GC revealed that the 12 non-thermal X-ray sources, as well as four X-ray transients have shown at most a single outburst over the last two decades. They are distinct from the six known neutron star LMXBs in the GC, which have all undergone multiple outbursts with <~ 5 year recurrence time on average. Based on the outburst history data of the broader population of X-ray transients, we conclude that the 16 sources represent a population of ~240-630 tightly-bound BH-LMXBs with ~4-12 hour orbital periods, consistent with the stellar/binary dynamics modelling in the vicinity of Sgr A*. The distribution of the 16 BH-LMXB candidates is disk-like (at 87% CL) and aligned with the nuclear star cluster. Our results have implications for XRB formation and the rate of gravitational wave events in other galactic nuclei.
Submission history
From: Kaya Mori [view email][v1] Mon, 16 Aug 2021 18:53:09 UTC (2,179 KB)
[v2] Tue, 19 Oct 2021 12:21:14 UTC (2,180 KB)
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