2003/01/31 by M. P. Muno, F. K. Baganoff, M. W. Bautz +7 · 9 citations
Physics and Astronomy · #Active galactic nucleus #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Astrophysics and Cosmic Phenomena #Flux (metallurgy) #Galactic Center #Galaxy #Luminosity #Photon #Point source #Spectral line #Stars #astro-ph
paper · pdf · doi:10.1086/374639
published as Astrophys.J.589:225-241,2003 · Published in ApJ. 22 pages, including 15 figures. Minor changes to match published version
openalex publication_date 2003/05/20 · arxiv created 2003/07/09 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We present a catalog of 2357 point sources detected during 590 ks of Chandra observations of the 17' × 17' field around Sgr A*. This field encompasses a physical area of 40 × 40 pc at a distance of 8 kpc. The completeness limit of the sample at the Galactic center is 10 31 ergs s -1 (2.0-8.0 keV), while the detection limit is an order of magnitude lower. The 281 sources detected below 1.5 keV are mainly in the foreground of the Galactic center, while comparisons to the Chandra deep fields at high Galactic latitudes suggest that only about 100 of the observed sources are background AGNs. The surface density of absorbed sources (not detected below 1.5 keV) falls off as 1/θ away from Sgr A*, in agreement with the distribution of stars in infrared surveys. This demonstrates the X-ray sources trace the general stellar population at the Galactic center. Point sources brighter than our completeness limit produce 10% of the flux previously attributed to diffuse emission. The log N - log S distribution of the Galactic center sources is extremely steep (power-law slope α = 1.7). If this distribution extends down to a flux of 10 -17 ergs cm -2 s -1 (10 29 ergs s -1 at 8 kpc, 2.0-8.0 keV) with the same slope, then point sources would account for all of the previously reported diffuse emission. However, there are numerous diffuse, filamentary structures in the field that also contribute to the total flux, so the 2.0-8.0 keV luminosity distribution must flatten between 10 29 and 10 31 ergs s -1 . Many types of stellar systems should be present in the field at the luminosities to which we are sensitive. However, the spectra of more than half of the Galactic center sources are very hard and can be described by a power law ( E -Γ ) with photon index Γ < 1. Such hard spectra have been seen previously only from magnetically accreting white dwarfs (polars and intermediate polars) and wind-accreting neutron stars (pulsars), suggesting that there are large numbers of these systems in our field.