Discovery of a Luminous, Variable, Off-Center Source in the Nucleus of M82 with the Chandra.pdf

a r X i v : a s t r o - p h / 0 0 0 9 2 5 0 v 2 1 6 O c t 2 0 0 0 Discovery of a Luminous, Variable, Off-Center Source in the Nucleus of M82 with the Chandra HRC H. Matsumoto1, T. G. Tsuru2, K. Koyama2,3, H. Awaki4, C. R. Canizares1, N. Kawai5, S. Matsushita6, A. Prestwich7, M. Ward8, A. L. Zezas7, and R. Kawabe9 Received ; accepted Accepted by ApJL 1Center for Space Research, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139-4307, USA; e-mail(HM) matumoto@ 2Department of Physics, Faculty of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan 3CREST: Japan Science and Technology Corporation (JST), 4-1-8 Honmachi, Kawaguchi, Saitama 332-0012, Japan 4Faculty of Science, Ehime University, 2-5 Bunkyo-cho, Matsuyama 790-8577, Japan 5RIKEN (The Institute of Physical and Chemical Research), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan 6Submillimeter Array, Harvard-Smithsonian Center for Astrophysics, 60 Keawe St. Suite 204, Hilo, HI 96720, USA 7Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA 8X-ray Astronomy Group, Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK 9Nobeyama Radio Observatory, Minamimaki, Minamisaku, Nagano 384-1305, Japan – 2 – ABSTRACT We present results from observations of the most famous starburst galaxy M82 with the High-Resolution Camera onboard the Chandra X-Ray Observatory. We found nine sources in the central 1′ × 1′ region, but no source was detected at the galactic center. Comparing the observations on 1999 October 28 and on 2000 January 20, we found four of the nine sources showed significant time variability. In particular, CXOM82 J095550.2+694047, which is 9′′ away from the galactic center, showed extremely large time variability. We conclude that this source is the origin of the hard X-ray time variability of M82 detected with ASCA. Assuming a spectral shape obtained by the ASCA observation, its luminosity in the 0.5 – 10 ke