Spatial distribution of black hole binaries within ~ 1 pc of the Galactic Center revealed by NuSTAR and Chandra X-ray observations
Abstract
We report NuSTAR observations of two new X-ray transients detected by the Neil Gehrels Swift Observatory in the Galactic Center (GC). Broadband 3-79 keV NuSTAR spectra of both transients exhibit various components including thermal disk blackbody, X-ray reflection with relativistically broadened Fe emission lines, and a power-law like continuum well described by thermal Comptonization models. A milli-Hz QPO feature was detected from one of the transients. These spectral and timing characteristics, as well as the deduced physical parameters, are consistent with those of black hole (BH) transients. In addition, the BH binary scenario is further supported by the lack of detection of prior X-ray outbursts by Swift and other X-ray telescopes that frequently monitored the GC in the last decade, whereas neutron star LMXBs have short (<~ 10 year) outburst recurrence time. The two new BH transients, combined with the 12 quiescent BH-LMXBs discovered by Chandra (Hailey et al. 2018) and another BH transient detected with radio jet (Muno et al. 2005), allow us to investigate their spatial distribution in the central 1 pc region. Our results have strong implications for binary formations in galactic nuclei and test the predictions from recent theoretical models.
- Publication:
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American Astronomical Society Meeting Abstracts #233
- Pub Date:
- January 2019
- Bibcode:
- 2019AAS...23326704M