Title: Observation of the starburts galaxy NGC 253


Proposal ID: 0120275
Subject category: Extragalactic Object
Principal investigator: Bhattacharya
Institute: University of California, Riverside


Abstract

NGC 253 and M82 are nearby starburst galaxies with inferred high supernova rates. The nuclear X-ray emission of these objects is complex; it might arise from unresolved supernovae, SN-heated ISM, SNRs, other point sources such as X-ray binaries or hidden AGN. At higher energies, in observations carried out in 1991, the CGRO/OSSE instrument detected gamma rays in the (50-265) keV range at a level which seems to be an order of magnitude higher than the extrapolated values from X-ray data. The OSSE detection may be explained by Compton effects occuring in the disk and halo of NGC 253, or alternatively by a supernova explosion! The high density of the relativistic electrons responsible for the Compton component possibly arises due to high supernova rate within the NGC 253 core. The flux upper limits obtained by OSSE for M82 fall below the extrapolated X-ray power law. In this proposal, we ask for an 200 ksec of INTEGRAL observations of NGC 253 and a 200 ksec observation of M82. This is to ascertain the existence ofa power law continuum extending above 50 keV for these galaxies. The existence of a such a non-thermal component will provide insight into the role of cosmic rays and supernovae in starbursts. We also want to look for variability in the hard X-ray flux which could indicate a contribution from the LINER active nucleus. The data will also be searched for line emission from a serendipitous supernova occuring within these galaxies.