S. Gunji

Detection of Sub-TeV Gamma Rays from the Galactic Center Direction by CANGAROO-II

K. Tsuchiya, R. Enomoto, L. T. Ksenofontov, M. Mori, T. Naito, A. Asahara, G. V. Bicknell, R. W. Clay, Y. Doi, P. G. Edwards, S. Gunji, S. Hara, T. Hara, T. Hattori, Sei. Hayashi, C. Itoh, S. Kabuki, F. Kajino, H. Katagiri, A. Kawachi, T. Kifune, H. Kubo, T. Kurihara, R. Kurosaka, J. Kushida Y. Matsubara, Y. Miyashita, Y. Mizumoto, H. Moro, 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, T. Uchida, S. Watanabe, T. Yamaoka, S. Yanagita, T. Yoshida, and T. Yoshikoshi

A new type of proportional counter using a capillary plate

Abstract We have developed a new type of proportional counter with the capability of fine position resolution and high gas gain. It consists of a bundle of fine glass capillaries with electrodes on both the inlet and the outlet. The capillaries are 100 μm in diameter and 800 μm in length and gas multiplication was found to occur in each capillary with an applied voltage between the inlet and the outlet. The resulting proportional counter was found to operate up to a gain of 104 without the onset of breakdown and had an energy resolution of 26% for 5.9 keV X-rays at a gas gain of 7000. Its detection efficiency was identical to a conventional single wire device.

A Search for TeV Gamma-Ray Emission from the PSR B1259–63/SS 2883 Binary System with the CANGAROO-II 10 Meter Telescope

Observations of the PSR B1259-63/SS 2883 binary system using the CANGAROO-II Cerenkov telescope are reported. This nearby binary consists of a 48 ms radio pulsar in a highly eccentric orbit around a Be star and offers a unique laboratory to investigate the interactions between the outflows of the pulsar and Be star at various distances. It has been pointed out that the relativistic pulsar wind and the dense mass outflow of the Be star may result in the emission of gamma rays up to TeV energies. We have observed the binary in 2000 and 2001, ~47 and ~157 days after the 2000 October periastron. Upper limits at the 0.13-0.54 crab level are obtained. A new model calculation for high-energy gamma-ray emission from the Be star outflow is introduced, and the estimated gamma-ray flux, considering bremsstrahlung, inverse Compton scattering, and the decay of neutral pions produced in proton-proton interactions, is found to be comparable to the upper limits of these observations. Comparing our results with these model calculations, we constrain the mass-outflow parameters of the Be star.

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

We have observed the giant radio galaxy Centaurus A and the globular cluster ω 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 ~100 m 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° 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.

Development of an atmospheric Cherenkov imaging camera for the CANGAROO-III experiment

Abstract A Cherenkov imaging camera for the CANGAROO-III experiment has been developed for observations of gamma-ray-induced air showers at energies from 10 11 to 10 14 eV . The camera consists of 427 pixels , arranged in a hexagonal shape at 0.17° intervals, each of which is a 3 4 -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.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 10 eV. The camera consists of 427 pixels, arranged in a hexagonal shape at 0.17◦ intervals, each of which is a 3/4-inch 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.

Detection of diffuse TeV gamma-ray emission from the neaby starburst galaxy NGC 253

Department of Physics, Osaka City University, Osaka, Osaka 558-8585, JapanA&A 396, L1-L4(2002). A&A402, 443-455(2003)ABSTRACTContext.Aims. The CANGAROO-II telescope observed sub-TeV gamma-ray emission from the nearby starburst galaxy NGC 253. The emission regionwas extended with a radial size of 0.3-0.6 degree. On the contrary, H.E.S.S could not confirm this emission and gave upper l imits at the levelof the CANGAROO-II flux. In order to resolve this discrepancy, we analyzed new observational results for NGC 253 by CANGAROO-III andalso assessed the results by CANGAROO-II.Methods. Observation was made with three telescopes of the CANGAROO-III in October 2004. We analyzed three-fold coincidence data bythe robust Fisher Discriminant method to discriminate gamma ray events from hadron events.Results. The result by the CANGAROO-III was negative. The upper limit of gamma ray flux was 5.8% Crab at 0.58 TeV for po int-sourceassumption. In addition, the significance of the excess flux o f gamma-rays by the CANGAROO-II was lowered to less than 4 sigma afterassessing treatment of malfunction of photomultiplier tubes.Key words. gamma rays: observation – galaxies: starburst – galaxies: i ndividual: NGC 253 – galaxies: halos: cosmic rays

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

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 ha ve set constraints on the strengths of the magnetic fields ass uming the synchrotron/inverse-Compton model for the wide energy range of photon spectrum from radio to TeV. The derived lower limits are 4.3µG for the center of the brightest X-ray emission region and 6.3µG 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.

A Search for TeV Gamma Rays from SN 1987A in 2001

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 Cerenkov telescope. In total, 708 minutes of ON- and 1019 minutes of OFF-source data were obtained under good conditions. The detection threshold was estimated to be 1 TeV, owing 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 × 1037 ergs s-1 at ~10 TeV.