NuSTAR HARD X-RAY SURVEY OF THE GALACTIC CENTER REGION. II. X-RAY POINT SOURCES

Abstract

We present the first survey results of hard X-ray point sources in the Galactic Center (GC) region by NuSTAR. We have discovered 70 hard (3-79 keV) X-ray point sources in a 0.6 deg 2 region around SgrA * with a total exposure of 1.7 Ms, and 7 sources in the SgrB2 field with 300 ks. We identify clear Chandra counterparts for 58 NuSTAR sources and assign candidate counterparts for the remaining 19. The NuSTAR survey reaches X-ray luminosities of ∼4× and ∼8×10 32 erg s -1 at the GC (8 kpc) in the 3-10 and 10-40 keV bands, respectively. The source list includes three persistent luminous X-ray binaries (XBs) and the likely run-away pulsar called the Cannonball. New source-detection significance maps reveal a cluster of hard (>10 keV) X-ray sources near the SgrA diffuse complex with no clear soft X-ray counterparts. The severe extinction observed in the Chandra spectra indicates that all the NuSTAR sources are in the central bulge or are of extragalactic origin. Spectral analysis of relatively bright NuSTAR sources suggests that magnetic cataclysmic variables constitute a large fraction (>40%-60%). Both spectral analysis and logN-logS distributions of the NuSTAR sources indicate that the X-ray spectra of the NuSTAR sources should have kT>20 keV on average for a single temperature thermal plasma model or an average photon index of Γ=1.5-2 for a power-law model. These findings suggest that the GC X-ray source population may contain a larger fraction of XBs with high plasma temperatures than the field population.

Exploring molecular complexity with ALMA (EMoCA): Simulations of branched carbon-chain chemistry in Sgr B2(N)

“…Also, the large post-collapse visual extinction used in the models (as indeed confirmed by the observational H 2 column density of around 5 × 10 24 cm −2 ) is likely to lead to some further attenuation of the CR field. Other sources of ionization affecting the chemistry in the hot core are unlikely; for example, there is no evidence for an embedded X-ray source in Sgr B2(N) (Hong et al 2016). While an embedded UCHII region does exist within Sgr B2(N2) (De Pree et al 2015), with an angular size of ∼0.12", the gas probed by our EMoCA observations has a scale size of 1"; a rudimentary calculation would indicate an intervening visual extinction on the order of at least several thousand magnitudes, far beyond any value at which the UV field associated with the UCHII region might conceivably affect the chemistry traced by our EMoCA observations.…”

The NuSTAR Serendipitous Survey: The 40-month Catalog and the Properties of the Distant High-energy X-Ray Source Population

“…We exclude from the survey NuSTAR fields with bright science targets, identified as fields with > 10 6 counts within 120 of the on-axis position. We also exclude the dedicated extragalactic (COSMOS, ECDFS, EGS, GOODS-N, UDS) and Galactic survey fields (the Galactic center survey; Mori et al 2015;Hong et al 2016; and the Norma Arm survey; Fornasini et al, in prep. ).…”

Observational artifacts of Nuclear Spectroscopic Telescope Array: ghost rays and stray light

“…10, they were identified as originating from the binary 1A 1743-294 in an outburst during the observations. 12 …”

“…Fig. 10 During a Galactic Plane survey, 12 the streak appeared at two different locations, and, by generating the sky mosaic and tracing back the streaks, it was discovered that they came from 1A 1742-294, an x-ray binary that was in outburst.…”