Astronomy and Astrophysics, volume 537A, 92-92 (2012/1-1)
INTEGRAL constraints on the Galactic hard X-ray background from the Milky Way anticenter.
KRIVONOS R., TSYGANKOV S., REVNIVTSEV M., SAZONOV S., CHURAZOV E. and SUNYAEV R.
Abstract (from CDS):
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 25-60keV energy band of 1.25x10–10erg/s/cm2 (12.8mCrab) per IBIS field of view, or 6.6x10–12erg/s/cm2 (0.7mCrab) 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 100MeV 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.