CANGAROO-III Search for Gamma Rays from SN 1987A and the Surrounding Field

Optical images of SN 1987A show a triple ring structure. The inner (dust) ring has recently increased in brightness and in the number of hot spots suggesting that the supernova shock wave has collided with the dense pre-existing circumstellar medium, a scenario supported by radio and X-ray observations. Such a shocked environment is widely expected to result in the acceleration of charged particles, and the accompanying emission of very high energy gamma-rays. Here, we report the results of observations made in 2004 and 2006 which yield upper limits on the TeV gamma-ray flux, which are compared with a theoretical prediction. In addition, we set upper limits on the TeV flux for four high energy objects which are located within the same field of view of the observation: the super-bubble 30 Dor C, the Crab-like pulsar PSR B0540$-$69, the X-ray binary LMC X-1, and the supernova remnant N157B.Comment: 5 pages, 5 figures, Accepted for publication in Ap

Observation of Very High Energy Gamma Rays from HESS J1804-216 with CANGAROO-III Telescopes

We observed the unidentified TeV gamma-ray source HESS J1804-216 with the CANGAROO-III atmospheric Cerenkov telescopes from May to July in 2006. We detected very high energy gamma rays above 600 GeV at the 10 sigma level in an effective exposure of 76 hr. We obtained a differential flux of (5.0+/-1.5_{stat}+/-1.6_{sys})\times 10^{-12}(E/1 TeV)^{-\alpha} cm^{-2}s^{-1}TeV^{-1} with a photon index \alpha of 2.69 +/- 0.30_{stat} +/- 0.34_{sys}, which is consistent with that of the H.E.S.S. observation in 2004. We also confirm the extended morphology of the source. By combining our result with multi-wavelength observations, we discuss the possible counterparts of HESS J1804-216 and the radiation mechanism based on leptonic and hadronic processes for a supernova remnant and a pulsar wind nebula.Comment: 11 pages, 12 figures, Accepted in Ap

Observation of an extended VHE gamma-ray emission from MSH 15-52 with CANGAROO-III

We have observed the supernova remnant MSH 15-52 (G320.4-1.2), which contains the gamma-ray pulsar PSR B1509-58, using the CANGAROO-III imaging atmospheric Cherenkov telescope array from April to June in 2006. We detected gamma rays above 810 GeV at the 7 sigma level during a total effective exposure of 48.4 hours. We obtained a differential gamma-ray flux at 2.35 TeV of (7.9+/-1.5_{stat}+/-1.7_{sys}) \times 10^{-13} cm^{-2}s^{-1}TeV^{-1} with a photon index of 2.21+/-0.39_{stat}+/-0.40_{sys}, which is compatible with that of the H.E.S.S. observation in 2004. The morphology shows extended emission compared to our Point Spread Function. We consider the plausible origin of the high energy emission based on a multi-wavelength spectral analysis and energetics arguments.Comment: 9 pages, 9 figures, Accepted in Ap

CANGAROO-III search for TeV Gamma-rays from two clusters of galaxies

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 (CMB) 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 north-west 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 micro G. 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 intra-cluster medium (ICM). The derived upper limit of the cosmic-ray energy density within this framework is an order of magnitude higher than that of our Galaxy.Comment: 7 pages, 6 figures, Accepted in Ap

CANGAROO-III Search for Gamma Rays from Centaurus A and the ω\omega Centauri Region

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 withan array of four Imaging Atmospheric Cherenkov Telescopes (IACT) with $\sim$100-m spacings. The observations were carried out in March and April 2004. In total, approximately 10 hours data were obtained for each target.No statistically significant gamma-ray signal has been found above 420 GeV over a wide angular region (a one-degree radius from thepointing center) and we derive flux upper limits using all of the field of view.Implications for the total energy of cosmic rays and the density of the cold dark matter are considered.Comment: 7 pages, 6 figures, to appear in ApJ, emulateapj.cl

CANGAROO-III Observations of the supernova remnant RX J0852.0−-4622

Sub-TeV gamma-ray emission from the North-West rim of the supernova remnant RX J0852.0$-$4622 was detected with the CANGAROO-II telescope and recently confirmed by the H.E.S.S. group. In addition, the H.E.S.S. data revealed a very wide (up to two degrees in diameter), shell-like profile of the gamma-ray emission. We have carried out CANGAROO-III observations in January and February 2005 with three telescopes and show here the results of three-fold coincidence data. We confirm the H.E.S.S. results about the morphology and the energy spectrum, and find the energy spectrum in the NW-rim is consistent with that of the whole remnant.Comment: 9 pages, 13 figures, to appear in Ap

CANGAROO-III Search for Gamma Rays from Kepler's Supernova Remnant

Kepler's supernova, discovered in October 1604, produced a remnant that has been well studied observationally in the radio, infrared, optical, and X-ray bands, and theoretically. Some models have predicted a TeV gamma-ray flux that is detectable with current Imaging Cherenkov Atmospheric Telescopes. We report on observations carried out in 2005 April with the CANGAROO-III telescope. No statistically significant excess was observed, and limitations on the allowed parameter range in the model are discussed.Comment: 6 pages 6 figures, to appear in ApJ, August 20, 2008, v683n

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Abstract: 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 fluxes from these gigantic objects assuming various emission mechanisms, no cluster of galaxies have been proven t

Cangaroo-III observations of the 2006 outburst of PKS 2155-304

Copyright © 2008. The American Astronomical Society. All rights reserved. Printed in U.S.A.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. © 2008. The American Astronomical Society. All rights reserved.Y. Sakamoto, K. Nishijima, T. Mizukami, E. Yamazaki, J. Kushida, R. Enomoto, M. Ohishi, G. V. Bicknell, R. W. Clay, P. G. Edwards, S. Gunji, S. Hara, T. Hattori, S. Hayashi, Y. Higashi, Y. Hirai, K. Inoue, C. Itoh, S. Kabuki, F. Kajino, H. Katagiri, A. Kawachi, T. Kifune, R. Kiuchi, H. Kubo, R. Mizuniwa, M. Mori, H. Muraishi, T. Naito, T. Nakamori, S. Nakano, D. Nishida, A. Seki, V. Stamatescu, T. Suzuki, D. L. Swaby, T. Tanimori, G. Thornton, F. Tokanai, K. Tsuchiya, S. Watanabe, Y. Yamada, S. Yanagita, T. Yoshida, T. Yoshikoshi, and Y. Yukaw