A hard X-ray constraint on the presence of an AGN in the ultraluminous infrared galaxy Arp 220
Abstract
We present X-ray results on the ultraluminous infrared galaxy Arp 220 obtained with BeppoSAX. X-ray emission up to 10keV is detected. No significant signal is detected with the PDS detector in the higher energy band. The 2-10keV emission has a flat spectrum (Γ~1.7), similar to M82, and a luminosity of ~1×1041ergs-1. A population of X-ray binaries may be a major source of this X-ray emission. The upper limit of an iron K line equivalent width at 6.4keV is ~=600eV. This observation imposes the tightest constraint so far on an active nucleus if present in Arp 220. We find that a column density of X-ray absorption must exceed 1025cm-2 for an obscured active nucleus to be significant in the energetics, and the covering factor of the absorption should be almost unity. The underluminous soft X-ray starburst emission may need a good explanation, if the bolometric luminosity is primarily powered by a starburst.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- September 2001
- DOI:
- 10.1046/j.1365-8711.2001.04478.x
- arXiv:
- arXiv:astro-ph/0103417
- Bibcode:
- 2001MNRAS.326..894I
- Keywords:
-
- GALAXIES: ACTIVE;
- GALAXIES: INDIVIDUAL: ARP 220;
- GALAXIES: STARBURST;
- X-RAYS: GALAXIES;
- Astrophysics
- E-Print:
- 7 pages, MNRAS in press