Search for VHE gamma rays from SS433/W50 with the CANGAROO-II telescope

Sei Hayashi*, F. Kajino, T. Naito, A. Asahara, G. V. Bicknell, R. W. Clay, Y. Doi, P. G. Edwards, R. Enomoto, S. Gunji, S. Hara, T. Hara, T. Hattori, C. Itoh, S. Kabuki, H. Katagiri, A. Kawachi, T. Kifune, L. T. Ksenofontov, H. KuboT. Kurihara, R. Kurosaka, J. Kushida, Y. Matsubara, Y. Miyashita, Y. Mizumoto, M. Mori, H. Mori, H. Muraishi, Y. Muraki, T. Nakase, D. Nishida, K. Nishijima, M. Ohishi, K. Okumura, J. R. Patterson, R. J. Protheroe, N. Sakamoto, K. Sakurazawa, D. L. Swaby, T. Tanimori, H. Tanimura, G. Thornton, F. Tokanai, K. Tsuchiya, T. Uchida, S. Watanabe, T. Yamaoka, S. Yanagita, T. Yoshida, T. Yoshikoshi

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    12 Citations (Scopus)


    SS433, located at the center of the supernova remnant W50, is a close proximity binary system consisting of a compact star and a normal star. Jets of material are directed outwards from the vicinity of the compact star symmetrically to the east and west. Non-thermal hard X-ray emission is detected from lobes lying on both sides. Shock accelerated electrons are expected to generate VHE gamma rays through the inverse-Compton process in the lobes. Observations of the western X-ray lobe region of SS433/W50 system have been performed to detect VHE gamma rays using the 10 m CANGAROO-II telescope in August and September, 2001, and July and September, 2002. The total observation times are 85.2 h for ON source, and 80.8 h for OFF source data. No significant excess of VHE gamma rays has been found at three regions of the western X-ray lobe of SS433/W50 system. We have derived 99% confidence level upper limits to the fluxes of gamma rays and have set constraints on the strengths of the magnetic fields assuming the synchrotron/inverse-Compton model for the wide energy range of photon spectrum from radio to TeV. The derived lower limits are 4.3 μG for the center of the brightest X-ray emission region and 6.3 μG for the far end from SS433 in the western X-ray lobe. In addition, we suggest that the spot-like X-ray emission may provide a major contribution to the hardest X-ray spectrum in the lobe.

    Original languageEnglish
    Pages (from-to)112-119
    Number of pages8
    JournalAstroparticle Physics
    Issue number2
    Publication statusPublished - Sept 2009


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