NuSTAR observations of black hole binary candidates in the Galactic Center and its environs
Abstract
The recent discovery of a diffuse, hard X-ray emission in the central 10 pc (Perez et al. 2015) interpreted as magnetic cataclysmic variables (Hailey et al. 2017) leaves open the question of whether a sub-dominant population of sources could exist much closer to the supermassive black hole (SMBH), which NuSTAR could not resolve. Here we report the recent NuSTAR observations of two new transient hard X-ray sources within ~ 1 pc of the Galactic Center, which were discovered by Swift. These sources have no known counterparts at other energies. The spectral properties of these sources rule out NS-HMXBs. Continuous monitoring of the Galactic Center by Swift, combined with the known short (<~ 5 year) recurrence time of neutron star LMXBs, strongly suggest that these new transients are black hole binary candidates (BHC). We will present 3-79 keV NuSTAR spectra of these sources that further support a black hole binary interpretation. These new BHCs, combined with at least one other previously discovered BHC near the Galactic Center, hint at a potential substantive black hole population in the vicinity of the SMBH, and we present an estimate of their numbers, given knowledge of the black hole binary giant outburst recurrence times. We also report recent results from the NuSTAR Galactic Legacy Survey of a larger region, ~ 0.7 square degrees, focusing on the search for more BHCs.
- Publication:
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AAS/High Energy Astrophysics Division #16
- Pub Date:
- August 2017
- Bibcode:
- 2017HEAD...1610912H