Observations of the supernova remnant W28 at TeV energies

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2000

Authors

Rowell, G.
Naito, T.
Dazeley, S.
Edwards, P.
Gunji, S.
Hara, T.
Holder, J.
Kawachi, A.
Kifune, T.
Matsubara, Y.

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Astronomy and Astrophysics (A & A), 2000; 359(1):337-346

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G.P. Rowell, T. Naito, S.A. Dazeley, P.G. Edwards, S. Gunji, T. Hara, J. Holder, A. Kawachi, T. Kifune, Y. Matsubara, Y. Mizumoto, M. Mori, H. Muraishi, Y. Muraki, K. Nishijima, S. Ogio, J.R. Patterson, M.D. Roberts, T. Sako, K. Sakurazawa, R. Susukita, T. Tamura, T. Tanimori, G.J. Thornton, S. Yanagita, T. Yoshida and T. Yoshikoshi. For the CANGAROO collaboration

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Abstract

The atmospheric Cerenkov 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 3.8m 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 (E>1.5 TeV) for a diffuse source of radius 0.25deg encompassing both molecular clouds was calculated at 6.64e-12 photons 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 pi-zero decay, a conclusion also consistent with its location in relation to W28.

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© European Southern Observatory (ESO) 2000 Submitted to Cornell University’s online archive www.arXiv.org in 2000 by Gavin Rowell. Post-print sourced from www.arxiv.org.

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