# 28th Texas Symposium on Relativistic Astrophysics

13-18 December 2015
International Conference Centre Geneva
Europe/Zurich timezone

## NuSTAR Discovery of Galactic Center Hard X-ray Emission

17 Dec 2015, 15:03
21m
Level -1, Room 17 (International Conference Centre Geneva)

### Level -1, Room 17

#### International Conference Centre Geneva

17 Rue de Varembé, 1211 Geneva

Kerstin Perez

### Description

The Galactic Center region contains one of the highest concentration of X-ray sources in the Milky Way. Recently NuSTAR, with its sub-arcminute spatial resolution, has discovered an unresolved hard (20-40 keV) X-ray emission within the central 10 pc. This emission is consistent with either stellar origins, such as large populations of intermediate polars, low-mass X-ray binaries, or millisecond pulsars, or diffuse origins, such as cosmic-ray outows from the supermassive black hole Sagittarius A*. However, each of these explanations implies source properties peculiar to this central region. In particular, the implied average white dwarf mass for the intermediate polar population is $>0.8 M_\odot$. The relation of this population to the much lighter $\sim0.5 M_\odot$ population implied by previous Chandra and XMM-Newton measurements of the surrounding $\sim50$ pc, or to the $\sim0.5$-$0.8M_\odot$ populations implied by previous Galactic bulge and ridge, nearby field, or SDSS survey measurements, is unclear. We present in this contribution details of the central hard X-ray discovery, as well as follow-up work on a possible intermediate polar interpretation. Using the broad-band (3-79 keV) energy resolution of NuSTAR and observations of the intermediate polars TV Columbae and IGR J17303-2601, we argue that both the broad-band NuSTAR measurement of the central 10 pc and the low-energy measurements of the surrounding $\sim50$ pc could be attributed to a single population of intermediate polars with mean white dwarf mass $\sim0.85 M_\odot$.
Collaboration The NuSTAR Collaboration