Astron. Astrophys. 359, 337-346 (2000)

Observations of the supernova remnant W28 at TeV energies

G.P. Rowell ¹, T. Naito ⁶, S.A. Dazeley ², P.G. Edwards ³, S. Gunji ⁴, T. Hara ⁶, J. Holder ¹, A. Kawachi ¹, T. Kifune ¹, Y. Matsubara ⁸, Y. Mizumoto ⁹, M. Mori ¹, H. Muraishi ¹⁰, Y. Muraki ⁸, K. Nishijima ⁷, S. Ogio ⁵, J.R. Patterson ², M.D. Roberts ¹, T. Sako ⁸, K. Sakurazawa ⁵, R. Susukita ¹¹, T. Tamura ¹², T. Tanimori ⁵, G.J. Thornton ², S. Yanagita ¹⁰, T. Yoshida ¹⁰ and T. Yoshikoshi <sup>1

1</sup> Institute for Cosmic Ray Research, University of Tokyo, Tokyo 188-8502, Japan
² Department of Physics and Math. Physics, University of Adelaide, Adelaide 5005, Australia
³ Institute of Space and Astronautical Science, Kanagawa 229-8510, Japan
⁴ Department of Physics, Yamagata University, Yamagata 990-8560, Japan
⁵ Department of Physics, Tokyo Institute of Technology, Tokyo 152-8551, Japan
⁶ Faculty of Management Information, Yamanashi Gakuin University, Yamanashi 400-8575, Japan
⁷ Department of Physics, Tokai University, Kanagawa 259-1292, Japan
⁸ Solar-Terrestrial Environment Lab., Nagoya University, Aichi 464-8601, Japan
⁹ National Astronomical Observatory of Japan, Tokyo 181-8588, Japan
¹⁰ Faculty of Science, Ibaraki University, Ibaraki 310-8512, Japan
¹¹ Institute of Physical and Chemical Research, Saitama 351-0198, Japan
¹² Faculty of Engineering, Kanagawa University, Kanagawa 221-8686, Japan

Received 19 October 1999 / Accepted 26 April 2000

Abstract

The atmospheric erenkov imaging technique has been used to search for point-like and diffuse TeV gamma-ray emission from the southern supernova remnant, W28, and surrounding region. The search, made with the CANGAROO 3.8 m telescope, encompasses a number of interesting features, the supernova remnant itself, the EGRET source 3EG J1800-2338, the pulsar PSR J1801-23, strong 1720 MHz OH masers and molecular clouds on the north and east boundaries of the remnant. An analysis tailored to extended and off-axis point sources was used, and no evidence for TeV gamma-ray emission from any of the features described above was found in data taken over the 1994 and 1995 seasons. Our upper limit ( TeV) for a diffuse source of radius 0.25^o encompassing both molecular clouds was calculated at 6.64 cm^-2 s^-1 (from 1994 data), and interpreted within the framework of a model predicting TeV gamma-rays from shocked-accelerated hadrons. Our upper limit suggests the need for some cutoff in the parent spectrum of accelerated hadrons and/or slightly steeper parent spectra than that used here (-2.1). As to the nature of 3EG J1800-2338, it possibly does not result entirely from decay, a conclusion also consistent with its location in relation to W28.

Key words: ISM: supernova remnants ISM: individual objects: W28 gamma rays: observations

Present address: Max Planck Institut für Kernphysik, 69029 Heidelberg, Germany

Correspondence to: Gavin.Rowell@mpi-hd.mpg.de

SIMBAD Objects

Contents

• 1. Introduction
• 2. The CANGAROO 3.8m telescope
• 3. Extended source analysis
• 4. Results
• 5. Gamma ray production in SNR
• 6. Conclusion
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: June 30, 2000
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