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 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,

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.

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

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.

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.

In 2004, we searched for very high energy (VHE) gamma-ray emission from the Galactic Plane using the CANGAROO-III stereoscopic observation system. Two different longitude regions (ℓ = −19°.5 and ℓ = +13°.0) on the Galactic Plane were observed during July and August 2004. We analyzed events that triggered three telescopes aiming to measure the diffuse emission component. No significant signal associated with the Galactic Plane was found from either of the regions. Assuming that the gamma-ray spectrum is described by a single power-law for energies ranging between a few GeV and TeV, lower limits of the power-law spectral indices were found to be 2.2 for both of the regions with a 99.9% confidence level. This result is consistent with the other VHE measurements and constrains a hypothesis in which a very hard (∼2.0) cosmic ray electron spectrum was introduced to explain the EGRET GeV anomaly.

We have observed the giant radio galaxy Centaurus A (Cen A) in the TeV energy region using the CANGAROO-III stereoscopic system. The system has been in operation since 2004 and is an array of four Imaging Atmospheric Cherenkov Telescopes (IACT) with about a 100 m spacing. The observations were carried out between March and April 2004. In total 20-hour data were obtained. No statistically significant gamma-ray signal has been found above 530 GeV and we obtain an integral flux upper limit of 3.2 X 10(-12) cm(-2) sec(-1) (2-sigma, level). This upper limit is less than 7% of the gamma-ray flux from the Crab nebula. Although some groups reported detections of Cen A in the past, we give upper limits more than one-order of magnitude lower for this object.

1 Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan 2 Faculty of Management Information, Yamanashi Gakuin University, Kofu, Yamanashi 400-8575, Japan 3 Department of Physics and Mathematical Physics, University of Adelaide, SA 5005, Australia 4 Institute of Space and Astronautical Science, Sagamihara, Kanagawa 229-8510, Japan 5 Department of Physics, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan 6 Research School of Astronomy and Astrophysics, Australian National University, ACT 2611, Australia 7 Department of Physics, Yamagata University, Yamagata, Yamagata 990-8560, Japan 8 Department of Physics, Tokai University, Hiratsuka, Kanagawa 259-1292, Japan 9 Department of Physics, Konan University, Kobe, Hyogo 658-8501, Japan 10 Faculty of Science, Ibaraki University, Mito, Ibaraki 310-8512, Japan 11 Faculty of Engineering, Shinshu University, Nagano, Nagano 480-8553, Japan 12 Department of Physics, Tokyo Institute of Technology, Meguro, Tokyo 152-8551, Japan 13 Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya, Aichi 464-8602, Japan 14 National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588, Japan 15 Ibaraki Prefectural University of Health Sciences, Ami, Ibaraki 300-0394, Japan 16 Department of Physics, Osaka City University, Osaka, Osaka 558-8585, Japan

We have detected sub-TeV gamma-ray emission from the direction of the Galactic center (GC) using the CANGAROO-II Imaging Atmospheric Cerenkov Telescope. We detected a statistically significant excess at energies greater than 250 GeV. The flux was 1 order of magnitude lower than that of the Crab Nebula at 1 TeV with a soft spectrum proportional to E-4.6±0.5. The signal centroid is consistent with the GC direction, and the observed profile is consistent with a pointlike source. Our data suggest that the GeV source 3EG J1746-2851 is identical to this TeV source, and we study the combined spectra to determine the possible origin of the gamma-ray emission. We also obtain an upper limit on the cold dark matter density in the Galactic halo.

The CANGAROO-III project, a system of four 10 m telecopes dedicated for gamma-ray astrophysics, has started in 1999 and is expected to complete in 2004 in Woomera, South Australia. We report the construction work during the first year, which includes the completion of the first 10 m telescope built as a 7 m telescope in 1999, and the work in progess to increase the performance by constructing three more similar telescopes based on the experience gained during the construction of the first telescope.

A Cherenkov imaging camera for the CANGAROO-III experiment has been developed for observations of gamma-ray-induced air showers at energies from 1011 to 1014eV. The camera consists of 427pixels, arranged in a hexagonal shape at 0.17° intervals, each of which is a 34-in. diameter photomultiplier module with a Winston-cone-shaped light guide. The camera was designed to have a large dynamic range of signal linearity, a wider field of view, and an improvement in photon-collection efficiency compared with the CANGAROO-II camera. The camera, and a number of the calibration experiments made to test its performance, are described in detail in this paper.

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,

The supernova remnant RCW86 (G315.4-2.3) has been observed with the CANGAROO-II 10 m telescope from Woomera, South Australia. ASCA detected non-thermal X-ray emission from the south-west shell of RCW86, which is brighter than that from SN1006. The multiwavelength spectrum of RCW86 derived from radio and X-ray data indicates that the emission is due to the synchrotron radia- tion, and it is argued that high energy electrons emitting the detected synchrotron radiation are expected to be accelerated up to 20 TeV. Therefore, the radiation due to inverse Compton scattering with the photons of the 2.7 K cosmic microwave background is also expected to be detectable with the CANGAROO-II telescope if the magnetic field is as weak as that of SN1006. We observed RCW86 in 2001 and 2002 for a total observation time of 79 hours for ON-source data. The detec- tion energy threshold was estimated from Monte Carlo simulations to be around 1 TeV.