A1 Refereed original research article in a scientific journal
INTEGRAL constraints on the Galactic hard X-ray background from the Milky Way anticenter
Authors: Krivonos R, Tsygankov S, Revnivtsev M, Sazonov S, Churazov E, Sunyaev R
Publication year: 2012
Journal: Astronomy and Astrophysics
Journal name in source: Astronomy and Astrophysics
Article number: A92
Volume: 537
First page : 7
Number of pages: 7
ISSN: 0004-6361
DOI: https://doi.org/10.1051/0004-6361/201118053
Abstract
We present results of a study of the Galactic ridge X-ray emission (GRXE) in hard X-rays with the IBIS telescope onboard INTEGRAL in the region near the Galactic anticenter (GA) at l = 155°. We assumed a conservative 2σ upper limit on the flux from the GA in the 25-60 keV energy band of 1.25 × 10 erg s cm (12.8 mCrab) per IBIS field of view, or 6.6 × 10 erg s cm (0.7 mCrab) per degree longitude in the 135° < l < 175° region. This upper limit exceeds the expected GRXE intensity in the GA direction by an order of magnitude, given the near-infrared (NIR) surface brightness of the Milky Way in this region and the standard hard X-ray-to-NIR intensity ratio for the GRXE, assuming stellar origin. Based on the CGRO/EGRET surface brightness of the Galaxy above 100 MeV as a tracer of the cosmic-ray (CR) induced gamma-ray background, the expected GRXE flux in GA exceeds the measured 2σ upper limit by a factor of 4. Therefore, the non-detection of hard X-ray emission from the GA does not contradict the stellar nature of the GRXE, but is inconsistent with CR origin. © 2012 ESO.
We present results of a study of the Galactic ridge X-ray emission (GRXE) in hard X-rays with the IBIS telescope onboard INTEGRAL in the region near the Galactic anticenter (GA) at l = 155°. We assumed a conservative 2σ upper limit on the flux from the GA in the 25-60 keV energy band of 1.25 × 10 erg s cm (12.8 mCrab) per IBIS field of view, or 6.6 × 10 erg s cm (0.7 mCrab) per degree longitude in the 135° < l < 175° region. This upper limit exceeds the expected GRXE intensity in the GA direction by an order of magnitude, given the near-infrared (NIR) surface brightness of the Milky Way in this region and the standard hard X-ray-to-NIR intensity ratio for the GRXE, assuming stellar origin. Based on the CGRO/EGRET surface brightness of the Galaxy above 100 MeV as a tracer of the cosmic-ray (CR) induced gamma-ray background, the expected GRXE flux in GA exceeds the measured 2σ upper limit by a factor of 4. Therefore, the non-detection of hard X-ray emission from the GA does not contradict the stellar nature of the GRXE, but is inconsistent with CR origin. © 2012 ESO.
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