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Issue A&A
Volume 427, Number 3, December I 2004
Page(s) L21 - L24
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:200400089



A&A 427, L21-L24 (2004)
DOI: 10.1051/0004-6361:200400089

Letter

Hard X-ray emission clumps in the $\gamma$-Cygni supernova remnant: An INTEGRAL-ISGRI view

A. M. Bykov1, A. M. Krassilchtchikov1, Yu. A. Uvarov1, H. Bloemen2, R. A. Chevalier3, M. Yu. Gustov1, W. Hermsen2, F. Lebrun4, T. A. Lozinskaya5, G. Rauw6, T. V. Smirnova7, S. J. Sturner8, J.-P. Swings6, R. Terrier4 and I. N. Toptygin1

1  A. F. Ioffe Institute for Physics and Technology, 26 Polytechnicheskaia, 194021 St. Petersburg, Russia
    e-mail: byk@astro.ioffe.ru
2  SRON National Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
3  Department of Astronomy, University of Virginia, PO Box 3818, Charlottesville, VA 22903, USA
4  CEA - Saclay, DSM/DAPNIA/Service d'Astrophysique, 91191 Gif-sur-Yvette Cedex, France
5  Sternberg Astronomical Institute, Moscow State University, 13 Universitetskij, 119899 Moscow, Russia
6  Institut d'Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août 17, Bât. B5c, 4000 Liège, Belgium
7  Astro Space Center of the Lebedev Physics Institute, 84/32 Profsoyuznaia, 117810 Moscow, Russia
8  NASA Goddard Space Flight Center, Code 661, Greenbelt, MD 20771, USA

(Received 22 September 2004 / Accepted 9 October 2004)

Abstract
Spatially resolved images of the galactic supernova remnant G78.2+2.1 ( $\gamma$-Cygni) in hard X-ray energy bands from 25 keV to 120 keV are obtained with the IBIS-ISGRI imager aboard the International Gamma-Ray Astrophysics Laboratory INTEGRAL. The images are dominated by localized clumps of about ten arcmin in size. The flux of the most prominent North-Western (NW) clump is ( $1.7\pm0.4)\times10^{-11} \rm ~erg~cm^{-2}~s^{-1}$ in the 25-40 keV band. The observed X-ray fluxes are in agreement with extrapolations of soft X-ray imaging observations of $\gamma$-Cyg by ASCA GIS and spatially unresolved RXTE PCA data. The positions of the hard X-ray clumps correlate with bright patches of optical line emission, possibly indicating the presence of radiative shock waves in a shocked cloud. The observed spatial structure and spectra are consistent with model predictions of hard X-ray emission from nonthermal electrons accelerated by a radiative shock in a supernova interacting with an interstellar cloud, but the powerful stellar wind of the O9V star HD 193322 is a plausible candidate for the NW source as well.


Key words: gamma rays: observations -- X rays: ISM: supernova remnants -- individual: G78.2+2.1 ( $\gamma$-Cygni) -- radiation mechanisms: nonthermal -- cosmic rays

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