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Fe K emission in the ultraluminous infrared galaxy Arp220

K. Iwasawa·D. B. Sanders·A. S. Evans·N. Trentham·G. Miniutti·H. W. W. Spoon
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Abstract

Prominent Fe K line emission is detected at around 6.7 keV in the XMM-Newton spectrum of the ultraluminous infrared galaxy Arp220. The continuum emission in the 2.5-10 keV band is flat and a few other spectral features are suggested. The large EW of the Fe K line poses a problem with interpreting the hard X-ray emission as integrated X-ray binary emission. A thermal emission spectrum with a temperature of kT~7 keV modified by some absorption, which would be expected from an internally shocked hot bubble in a starburst region, can describe the spectrum. An ensemble of radio supernovae in a dense environment, as suggested from VLBI imaging, could be another possibility, if frequent occurence of such powerful supernovae is sustained. However, the apparent lack of X-ray binary emission does not match the high supernova rate required by both interpretations. Highly photoionized, low-density gas illuminated by a hidden Compton-thick AGN is a possible alternative, which can be tested by presence/absence of radiative recombination continua in better quality data expected from a forthcoming observation.

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K. Iwasawa, D. B. Sanders, A. S. Evans, N. Trentham, G. Miniutti, H. W. W. Spoon. 2004-11-19. Fe K emission in the ultraluminous infrared galaxy Arp220. https://doi.org/10.1111/j.1365-2966.2005.08644.x

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