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.