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 sub-TeV 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 sub-TeV gamma-rays using the 10m CANGAROO-II telescope in August and September, 2001, and July and September, 2002. The total observation times are 85.2 hours for ON source, and 80.8 hours for OFF source data. No significant excess of sub-TeV gamma rays has been found at 3 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 microgauss for the center of the brightest X-ray emission region and 6.3 microgauss 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.

Because accretion and merger shocks in clusters of galaxies may accelerate particles to high energies, clusters are candidate sites for the origin of ultra-high-energy (UHE) cosmic rays. A prediction was presented for gamma-ray emission from a cluster of galaxies at a detectable level with the current generation of imaging atmospheric Cherenkov telescopes. The gamma-ray emission was produced via inverse Compton upscattering of cosmic microwave background photons by electron–positron pairs generated by collisions of UHE cosmic rays in the cluster. We observed two clusters of galaxies, Abell 3667 and Abell 4038, searching for very high energy gamma-ray emission with the CANGAROO-III atmospheric Cherenkov telescope system in 2006. The analysis showed no significant excess around these clusters, yielding upper limits on the gamma-ray emission. From a comparison of the upper limit for the northwest radio relic region of Abell 3667 with a model prediction, we derive a lower limit for the magnetic field of the region of ∼0.1 μG. This shows the potential of gamma-ray observations in studies of the cluster environment. We also discuss the flux upper limit from cluster center regions using a model of gamma-ray emission from neutral pions produced in hadronic collisions of cosmic-ray protons with the intracluster medium. The derived upper limit of the cosmic-ray energy density within this framework is an order of magnitude higher than that of our Galaxy.

We have detected gamma-ray emission at the 6σ level at energies greater than 500GeV from the supernova remnant RX J0852.0−4622 (G266.2−1.2) using the Department of Physics, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan; katagiri@cr.scphys.kyoto-u.ac.jp,enomoto@icrr.u-tokyo.ac.jp Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan RSAA, Australian National Univ., ACT 2611, Australia Dept. of Physics, Univ. of Adelaide, SA 5005, Australia Department of Physics, Yamagata University, Yamagata, Yamagata 990-8560, Japan Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Kanagawa 229-8510, Japan Faculty of Management Information, Yamanashi Gakuin University, Kofu, Yamanashi 400-8575, Japan Department of Physics, Tokai University, Hiratsuka, Kanagawa 259-1292, Japan Department of Physics, Konan University, Kobe, Hyogo 658-8501, Japan Ibaraki Prefectural University of Health Sciences, Ami, Ibaraki 300-0394, Japan Faculty of Engineering, Shinshu University, Nagano, Nagano 480-8553, Japan Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya, Aichi 464-8602, Japan National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588, Japan School of Allied Health Sciences, Kitasato University, Sagamihara, Kanagawa 228-8555, Japan Faculty of Science, Ibaraki University, Mito, Ibaraki 310-8512, Japan

We have used the CANGAROO-III imaging atmospheric Cerenkov telescopes to observe the high-frequency-peaked BL Lacertae (HBL) object PKS 2155–304 between 2006 July 28 (MJD 53,944) and August 2, triggered by the H.E.S.S. report that the source was in a high state of TeV gamma-ray emission. A signal was detected at the 4.8 σ level in an effective live time of 25.1 hr during the outburst period. The flux of very high energy gamma rays from the CANGAROO-III observations shows variability on the timescale of less than a few hours. The averaged integral flux above 660 GeV is (1.6 ± 0.3stat± 0.5syst) × 10−11 cm−2 s−1, which corresponds to ~45% of the flux observed from the Crab Nebula. Follow-up observations between August 17 (MJD 53,964) and 25 indicate that the source activity had decreased.

We present the detection of nearby BL Lacertae object PKS 2155-304 with the CANGAROOIII imaging atmospheric Cherenkov telescope system. This observation was triggered by the H.E.S.S. report in July 2006 that the outburst at TeV gamma-ray energy range occured on this object. Observations have been performed between 2006 July 28 and August 2. A signal from PKS 2155-304 was detected at 5.7 σ level. The time averaged integral flux above 590 GeV and the differential energy spectrum are obtained

More than forty gamma-ray sources have been detected by atmospheric Cherenkov telescopes at TeV energies. Although there are many theoretical predictions on the possible gamma-ray ux es from these gigantic objects assuming various emission mechanisms, no cluster of galaxies have been proven to be a TeV gamma-ray emitter until now. We have observed a couple of clusters of galaxies in the southern sky with the CANGAROO-III atmospheric Cherenkov telescope system in 2005-2006, and preliminary results on the analysis to search for gamma-ray signature are reported.

We have observed the blazar PKS 2155-304 between 2006 July 28 to August 2 and between August 17 to 25 with the CANGAROO-III imaging atmospheric Cherenkov telescope in South Australia, which was triggered by the alert from the H.E.S.S. that the strong outburst of TeV gamma-ray emission was detected. The flux variation of very high energy gamma-rays was studied. The highest activity during our observations was seen early night in July 28 up to 180 % Crab flux level. The source activity had decreased in August.

We searched for TeV gamma-rays from the remnant of SN 1987A around 5400 days after the supernova. The observations were carried out in 2001, from November 16 to December 11, using the CANGAROO-II Imaging Atmospheric Cherenkov Telescope. In total, 708 minutes of ONand 1019 minutes of OFF-source data were obtained under good conditions. The detection threshold was estimated to be 1 TeV, due to the mean zenith angle of 39◦. The upper limits for the gamma-ray flux were obtained and compared with the previous observations and theoretical models. The observations indicate that the gamma-ray luminosity is lower than 1× 10 erg s at ∼ 10 TeV. Subject headings: supernovae: individual (SN 1987A)— gamma rays: observations Institute for Cosmic Ray Research, University of Tokyo, Chiba 277-8582, Japan Department of Physics, Kyoto University, Kyoto 6068502, Japan MSSSO, Australian National University, ACT 2611, Australia Department of Physics and Math. Physics, University of Adelaide, SA 5005, Australia Institute of Space and Astronautical Science, Kanagawa 229-8510, Japan Department of Physics, Yamagata University, Yamagata 990-8560, Japan Faculty of Management Information, Yamanashi Gakuin University, Yamanashi 400-8575, Japan Department of Physics, Tokai University, Kanagawa 259-1292, Japan Department of Physics, Konan University, Hyogo 6588501, Japan Faculty of Science, Ibaraki University, Ibaraki 3108512, Japan Faculty of Engineering, Shinshu University, Nagano 380-8553, Japan Department of Physics, Tokyo Institute of Technology,

We have observed the giant radio galaxy Centaurus A and the globular cluster omega Centauri in the TeV energy region using the CANGAROO III stereoscopic system. The system has been in operation since 2004 with an array of four Imaging Atmospheric Cerenkov Telescopes ( IACT) with similar to 100m spacings. The observations were carried out in 2004 March and April. In total, approximately 10 hr of data were obtained for each target. No statistically significant gamma-ray signal has been found above 420 GeV over a wide angular region (a 1 degrees radius from the pointing center), and we derive flux upper limits using the wholefield of view. Implications for the total energy of cosmic rays and the density of the cold dark matter are considered.

More than forty gamma-ray sources have been detected by atmospheric Cherenkov telescopes at TeV energies. Although there are many theoretical predictions on the possible gamma-ray ux es from these gigantic objects assuming various emission mechanisms, no cluster of galaxies have been proven to be a TeV gamma-ray emitter until now. We have observed a couple of clusters of galaxies in the southern sky with the CANGAROO-III atmospheric Cherenkov telescope system in 2005-2006, and preliminary results on the analysis to search for gamma-ray signature are reported.

Sub-TeV gamma-ray emission from the northwest rim of the supernova remnant RX J0852.0-4622 was detected with the CANGAROO II telescope and recently confirmed by the HESS group. In addition, the HESS data revealed a very wide (up to 2° in diameter), shell-like profile of the gamma-ray emission. We carried out CANGAROO III observations in 2005 January and February with three telescopes and show here the results of threefold coincidence data. We confirm the HESS results about the morphology and the energy spectrum and find that the energy spectrum in the NW rim is consistent with that of the whole remnant.

We made stereoscopic observations of the Vela pulsar region with two of the 10 m diameter CANGAROO-III imaging atmospheric Cerenkov telescopes in 2004 January and February in a search for sub-TeV gamma rays from the pulsar and surrounding regions. We describe the observations, provide a detailed account of the calibration methods, and introduce the improved and bias-free analysis techniques employed for CANGAROO-III data. No evidence of gamma-ray emission is found from either the pulsar position or the previously reported position offset by 0.degrees 13, and the resulting upper limits are a factor of 5 less than the previously reported flux from observations with the CANGAROO-I 3.8 m telescope. Following the recent report by the H. E. S. S. group of TeV gamma-ray emission from the pulsar wind nebula, which is similar to 0.degrees 5 south of the pulsar position, we examined this region and found supporting evidence for emission extended over similar to 0.degrees 6.

CANGAROO-III is a stereoscopic observation system with four telescopes, which started full operation in March 2004. We have observed the Crab nebula in 2003 at zenith angles > 55 degrees because our telescopes are located in the southern hemisphere. The observations were made with an independent trigger mode using two telescopes. In the case of larger distances between showers and telescopes, events have a lower accuracy on the determination of intersection points, which degrades the theta-squared distributions. We are, therefore, trying to improve analysis methods. We report the current results of these observations and the performance of our system compared with Monte Carlo simulations.

CANGAROO-III consists of four telescopes installed in Woomera, South Australia to observe celestial gamma-ray sources by detecting Cherenkov light from air showers. Stereo observations have been performed since March 2004 with an improved angular resolution and a lower energy threshold.In this paper, we present some preliminary results of optical measurements by cooled CCD cameras.

T. Nakamori, Y. Adachi, A. Asahara, G.V. Bicknell, R.W. Clay, Y. Doi, P.G. Edwards , R. Enomoto, S. Gunji, S. Hara, T. Hara, T. Hattori, Sei. Hayashi, Y. Higashi, R. Inoue, C. Itoh, S. Kabuki, F. Kajino, H. Katagiri, A. Kawachi, S. Kawasaki, T. Kifune, R. Kiuchi, K. Konno, L.T. Ksenofontov, H. Kubo, J. Kushida Y. Matsubara, Y. Mizumoto M. Mori, H. Muraishi Y. Muraki T. Naito D. Nishida, K. Nishijima, M. Ohishi, J.R. Patterson, R.J. Protheroe, Y. Sakamoto, M. Sato, S. Suzuki, T. Suzuki, D.L. Swaby, T. Tanimori, H. Tanimura, G. Thornton, K. Tsuchiya, S. Watanabe, T. Yamaoka, M. Yamazaki, S. Yanagita, T. Yoshida, T. Yoshikoshi, M. Yuasa, Y. Yukawa (a) Department of Physics, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan (b) Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 237-8582, Japan (c) Research School of Astronomy and Astrophysics, Australian National University, ACT 2611, Australia (d) Department of Physics and Mathematical Physics, University of Adelaide, SA 5005, Australia (e) Department of Physics, Yamagata University, Yamagata, Yamagata 990-8560, Japan (f) Institute of Space and Astronautical Science, Sagamihara, Kanagawa 229-8510, Japan (g) Faculty of Management Information, Yamanashi Gakuin University, Kofu, Yamanashi 400-8575, Japan (h) Department of Physics, Tokai University, Hiratsuka, Kanagawa 259-1292, Japan (k) Department of Physics, Konan University, Kobe, Hyogo 658-8501, Japan (l) Ibaraki Prefectural University of Health Sciences, Ami, Ibaraki 300-0394, Japan (m) Faculty of Engineering, Shinshu University, Nagano, Nagano 480-8553, Japan (n) Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya, Aichi 464-8602, Japan (o) National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588, Japan (p) School of Allied Health Sciences, Kitasato University, Sagamihara, Kanagawa 228-8555, Japan (q)Faculty of Science, Ibaraki University, Mito, Ibaraki 310-8512, Japan

CANGAROO-III is an array of four 10m-diameter imaging atmospheric Cherenkov telescopes to search for sub-TeV gamma-rays from celestial objects in collaboration with Japanese and Australian institutions, which is located in southern hemisphere (Woomera, South Australia). Three of four telescopes were made with the same design for stereo observation. We have started observations in stereo mode using those three telescopes since March 2004.We report the recent status of the analyses for stereo observations including several targets of which our previous data are inconsistent with the recent HESS results.

We have detected gamma-ray emission at the 6σ level at energies greater than 500GeV from the supernova remnant RX J0852.0−4622 (G266.2−1.2) using the Department of Physics, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan; katagiri@cr.scphys.kyoto-u.ac.jp,enomoto@icrr.u-tokyo.ac.jp Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan RSAA, Australian National Univ., ACT 2611, Australia Dept. of Physics, Univ. of Adelaide, SA 5005, Australia Department of Physics, Yamagata University, Yamagata, Yamagata 990-8560, Japan Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Kanagawa 229-8510, Japan Faculty of Management Information, Yamanashi Gakuin University, Kofu, Yamanashi 400-8575, Japan Department of Physics, Tokai University, Hiratsuka, Kanagawa 259-1292, Japan Department of Physics, Konan University, Kobe, Hyogo 658-8501, Japan Ibaraki Prefectural University of Health Sciences, Ami, Ibaraki 300-0394, Japan Faculty of Engineering, Shinshu University, Nagano, Nagano 480-8553, Japan Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya, Aichi 464-8602, Japan National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588, Japan School of Allied Health Sciences, Kitasato University, Sagamihara, Kanagawa 228-8555, Japan Faculty of Science, Ibaraki University, Mito, Ibaraki 310-8512, Japan

The imaging atmospheric Cherenkov telescope system of CANGAROO-III has-been in full operation with four 10 meter diameter telescopes since March 2004 near Woomera, South Australia. The system is used to study gamma-ray astrophysics at sub-TeV energies in the southern hemisphere. The performance of the stereoscopic system such as angular and energy resolutions for gamma rays has been investigated using Monte Carlo simulations, which are based on various calibration results, e.g., calibration of fight collection efficiency using muon ring images. We present the estimated performance of the CANGAROO-III system as well as the reliability of our simulation code, comparing simulation results with observed data.

We observed two high-energy-peaked BL Lacs (HBL), PKS 2155-304 (z = 0.116) and Mrk 421 (z = 0.031) in 2004, with the CANGAROO-III atmospheric Cherenkov telescope system located at Woomera in South Australia. Observations are carried out with each telescope independently and the stereo multiplicity requirement is performed off-line using GPS time stamps and event number (off-line stereo). Here we report the status of these observations and analyses.