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T. Kifune

Publications and source records attributed to T. Kifune.

At least 19 recordsLinked to original sources
arXiv2012

Searches for very high energy gamma rays from blazars with CANGAROO-III telescope in 2005-2009

We have searched for very high energy (VHE) gamma rays from four blazars using the CANGAROO-III imaging atmospheric Cherenkov telescope. We report the results of the observations of H 2356-309, PKS 2155-304, PKS 0537-441, and 3C 279, performed from 2005 to 2009, applying a new analysis to suppress the effects of the position dependence of Cherenkov images in the field of view. No significant VHE gamma ray emission was detected from any of the four blazars. The GeV gamma-ray spectra of these objects were obtained by analyzing Fermi/LAT archival data. Non-simultaneous wide range (radio to VHE gamma-ray bands) spectral energy distributions (SEDs) including CANGAROO-III upper limits, GeV gamma-ray spectra, and archival data are discussed using a one-zone synchrotron self-Compton (SSC) model in combination with a external Compton (EC) radiation. The HBLs (H 2356-309 and PKS 2155-304) can be explained by a simple SSC model, and PKS 0537-441 and 3C 279 are well modeled by a combination of SSC and EC model. We find a consistency with the blazar sequence in terms of strength of magnetic field and component size.

astro-ph.HE↗
arXiv2011

CANGAROO-III observation of TeV gamma rays from the unidentified gamma-ray source HESS J1614-518

We report the detection, with the CANGAROO-III imaging atmospheric Cherenkov telescope array, of a very high energy gamma-ray signal from the unidentified gamma-ray source HESS J1614-518, which was discovered in the H.E.S.S. Galactic plane survey. Diffuse gamma-ray emission was detected above 760 GeV at the 8.9 sigma level during an effective exposure of 54 hr from 2008 May to August. The spectrum can be represented by a power-law: 8.2+-2.2_{stat}+-2.5_{sys}x10^{-12}x (E/1TeV)^{-Gamma} cm^{-2} s^{-1} TeV^{-1} with a photon index Gamma of 2.4+-0.3_{stat}+-0.2_{sys}, which is compatible with that of the H.E.S.S. observations. By combining our result with multi-wavelength data, we discuss the possible counterparts for HESS J1614-518 and consider radiation mechanisms based on hadronic and leptonic processes for a supernova remnant, stellar winds from massive stars, and a pulsar wind nebula. Although a leptonic origin from a pulsar wind nebula driven by an unknown pulsar remains possible, hadronic-origin emission from an unknown supernova remnant is preferred.

astro-ph.HE↗
arXiv2009

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 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.

astro-ph.HE↗
arXiv2009

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.

astro-ph.HE↗
arXiv2009

CANGAROO-III Observation of TeV Gamma Rays from the vicinity of PSR B1 706-44

Observation by the CANGAROO-III stereoscopic system of the Imaging Cherenkov Telescope has detected extended emission of TeV gamma rays in the vicinity of the pulsar PSR B1706$-$44. The strength of the signal observed as gamma-ray-like events varies when we apply different ways of emulating background events. The reason for such uncertainties is argued in relevance to gamma-rays embedded in the "off-source data", that is, unknown sources and diffuse emission in the Galactic plane, namely, the existence of a complex structure of TeV gamma-ray emission around PSR B1706$-$44.

astro-ph.HE↗
arXiv2002

Observation of gamma-rays greater than 10 TeV from Markarian 421

We have observed Markarian 421 in January and March 2001 with the CANGAROO-II imaging Cherenkov telescope during an extraordinarily high state at TeV energies. From 14 hours observations at very large zenith angles, $\sim70^\circ$, a signal of 298 $\pm$ 52 gamma-ray--like events (5.7 $σ$) was detected at $E>10$ TeV, where a higher sensitivity is achieved than those of usual observations near the zenith, owing to a greatly increased collecting area. Under the assumption of an intrinsic power-law spectrum, we derived a differential energy spectrum $dN/dE = (3.3 \pm 0.9_{stat.} \pm 0.3_{syst.})\times10^{-13} (E/10 {Te V})^{-(4.0 ^{+0.9}_{-0.6}_{stat.} \pm 0.3_{syst.})}$ ph./cm$^2$/sec/TeV, which is steeper than those previously measured around 1 TeV, and supports the evidence for a cutoff in the spectrum of Markarian 421. However, the 4 $σ$ excess at energies greater than 20 TeV in our data favors a cutoff energy of $\sim$8 TeV, at the upper end of the range previously reported from measurements at TeV energies.

astro-ph↗
arXiv2001

The CANGAROO-III Project: Status report

We report on the status of the construction of an array of four 10 m atmospheric Cherenkov telescopes for gamma-ray astronomy, near Woomera, in South Australia -- the CANGAROO-III project. The first telescope of this array is the upgraded version of the CANGAROO-II 7 m telescope and has been in operation since March 2000. The second telescope, an improved version of the first, is being constructed for installation in late 2001. Stereoscopic observation of sub TeV gamma-rays with the two 10 m telescopes will begin in 2002 and the full array will be operational in 2004.

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arXiv2001

Search for gamma-rays above 10 TeV from Markarian 421 in a high state with the CANGAROO-II telescope

A preliminary result from Markarian 421 observations in the energy region above 10 TeV with the CANGAROO-II 10 m telescope is presented. In January 2001, the HEGRA group reported that Markarian 421 had become very active, with flux levels up to 4 times that of the Crab Nebula. As a result, we observed Mkn 421 during six nights from January 24th to February 1st, and four nights from March 1st to 4th. Observations were carried out using the very large zenith angle technique ($\sim$70 degree) and the energy threshold is estimated from Monte Carlo simulations to be around 10 TeV. We have detected gamma-ray emission in this energy range.

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arXiv2000

The optical reflector system for the CANGAROO-II imaging atmospheric Cherenkov telescope

A new imaging atmospheric Cherenkov telescope (CANGAROO-II) with a light-weight reflector has been constructed. Light, robust, and durable mirror facets of containing CFRP (Carbon Fiber Reinforced Plastic) laminates were developed for the telescope. The attitude of each facet can be adjusted by stepping motors. In this paper, we describe the design, manufacturing, alignment procedure, and the performance of the CANGAROO-II optical reflector system.

astro-ph↗
arXiv2000

Observations of the supernova remnant W28 at TeV energies

The atmospheric Cerenkov imaging technique has been used to search for point-like and diffuse TeV gamma-ray emission from the southern supernova remnant, W28, and surrounding region. The search, made with the CANGAROO 3.8m telescope, encompasses a number of interesting features, the supernova remnant itself, the EGRET source 3EG J1800-2338, the pulsar PSR J1801-23, strong 1720 MHz OH masers and molecular clouds on the north and east boundaries of the remnant. An analysis tailored to extended and off-axis point sources was used, and no evidence for TeV gamma-ray emission from any of the features described above was found in data taken over the 1994 and 1995 seasons. Our upper limit (E>1.5 TeV) for a diffuse source of radius 0.25deg encompassing both molecular clouds was calculated at 6.64e-12 photons cm^-2 s^-1 (from 1994 data), and interpreted within the framework of a model predicting TeV gamma-rays from shocked-accelerated hadrons. Our upper limit suggests the need for some cutoff in the parent spectrum of accelerated hadrons and/or slightly steeper parent spectra than that used here (-2.1). As to the nature of 3EG J1800-2338, it possibly does not result entirely from pi-zero decay, a conclusion also consistent with its location in relation to W28.

astro-ph↗
arXiv2000

Very High-Energy Gamma-Ray Observations of PSR B1509-58 with the CANGAROO 3.8m Telescope

The gamma-ray pulsar PSR B1509-58 and its surrounding nebulae have been observed with the CANGAROO 3.8m imaging atmospheric Cherenkov telescope. The observations were performed from 1996 to 1998 in Woomera, South Australia, under different instrumental conditions with estimated threshold energies of 4.5 TeV (1996), 1.9 TeV (1997) and 2.5 TeV (1998) at zenith angles of ~30 deg. Although no strong evidence of the gamma-ray emission was found, the lowest energy threshold data of 1997 showed a marginal excess of gamma-ray--like events at the 4.1 sigma significance level. The corresponding gamma-ray flux is calculated to be (2.9 +/- 0.7) * 10^{-12}cm^{-2}s^{-1} above 1.9 TeV. The observations of 1996 and 1998 yielded only upper limits (99.5% confidence level) of 1.9 * 10^{-12}cm^{-2}s^{-1} above 4.5 TeV and 2.0 * 10^{-12}cm^{-2}s^{-1} above 2.5 TeV, respectively. Assuming that the 1997 excess is due to Very High-Energy (VHE) gamma-ray emission from the pulsar nebula, our result, when combined with the X-ray observations, leads to a value of the magnetic field strength ~5 micro G. This is consistent with the equipartition value previously estimated in the X-ray nebula surrounding the pulsar. No significant periodicity at the 150ms pulsar period has been found in any of the three years' data. The flux upper limits set from our observations are one order of magnitude below previously reported detections of pulsed TeV emission.

astro-ph↗
arXiv2000

Evidence for TeV gamma-ray emission from the shell type SNR RXJ1713.7-3946

We report the results of TeV gamma-ray observations of the shell type SNR RXJ1713.7-3946 (G347.3-0.5). The discovery of strong non-thermal X-ray emission from the northwest part of the remnant strongly suggests the existence of electrons with energies up to 100 TeV in the remnant, making the SNR a good candidate TeV gamma-ray source. We observed RXJ1713.7-3946 from May to August 1998 with the CANGAROO 3.8m atmospheric imaging Cerenkov telescope and obtained evidence for TeV gamma-ray emission from the NW rim of the remnant with the significance of 5.6 sigma. The observed TeV gamma-ray flux from the NW rim region was estimated to be (5.3 +/- 0.9[statistical] +/- 1.6[systematic]) * 10^{-12} photons cm^{-2} s^{-1} at energies >= 1.8 +/- 0.9 TeV. The data indicate that the emitting region is much broader than the point spread function of our telescope. The extent of the emission is consistent with that of hard X-rays observed by ASCA. This TeV gamma-ray emission can be attributed to the Inverse Compton scattering of the Cosmic Microwave Background Radiation by shock accelerated ultra-relativistic electrons. Under this assumption, a rather low magnetic field of 11 micro gauss is deduced for the remnant from our observation.

astro-ph↗
arXiv1999

The SNR W28 at TeV Energies

The southern supernova remnant (SNR)W28 was observed in 1994 and 1995 by the CANGAROO 3.8m telescope in a search formulti-TeV gamma ray emission, using the Cerenkov imaging technique. We obtained upper limits for a variety of point-like and extended features within a +-1 degree-region and briefly discuss these results, together with that of EGRET within the framework of a shock acceleration model of the W28 SNR.

astro-ph↗
arXiv1999

Initial Performance of CANGAROO-II 7m telescope

CANGAROO group constructed an imaging air Cherenkov telescope (CANGAROO-II) in March 1999 atWoomera, South Australia to observe celestial gamma-rays in hundreds GeV region. It has a 7m parabolic mirror consisting of 60 small plastic spherical mirrors, and the prime focus is equipped with a multi-pixel camera of 512 PMTs covering the field of view of 3 degrees. We report initial performance of the telescope.

astro-ph↗
arXiv1999

The Cangaroo-III Project

The CANGAROO-III project,which consists of an array of four 10 m imaging Cherenkov telescopes,has just started being constructed in Woomera, South Australia,in a collaboration between Australia and Japan. The first stereoscopic observation of celestial high-energy gamma-rays in the 100 GeV region with two telescopes will start in 2002,and the four telescope array will be completed in 2004. The concept of the project and the expected performance are discussed.

astro-ph↗
arXiv1999

A Dark Cloud Associated an Unidentified EGRET Source

CO J=1-0 mapping observations of the dark nebula Lynds 227, which is possibly associated with the unidentified EGRET source 2EG J1811-2339, are presented. We detected a large amount of molecular gas along Lynds 227 with a total mass of (1-2)E4 Msun surrounding an X-ray synchrotron nebula, which was detected by the ASCA satellite within the error circle of 2EG J1811-2339. Molecular gas along Lynds 227 shows spatial anti-correlation with the X-ray synchrotron nebula, suggesting that the synchrotron nebula is interacting with the Lynds 227 cloud. We propose a $γ$-ray emission mechanism for 2EG J1811-2339: High energy electrons are injected from a rotation-powered pulsar and accelerated further in shock waves generated by the interaction with ambient matter. The high energy electrons move into the molecular cloud at the Lynds 227 and collide with dense interstellar matter to yield high energy $γ$-ray photons, mainly through relativistic bremsstrahlung.

astro-ph↗
arXiv1999

An Optical Reflector for the CANGAROO-II Telescope

We have been successful in developing light and durable mirrors made of CFRP (Carbon Fiber Reinforced Plastic) laminates for the reflector of the new CANGAROO-II 7 m telescope. The reflector has a parabolic shape (F/1.1) with a 30 m^2 effective area which consists of 60 small spherical mirrors of CFRP laminates. The orientation of each mirror can be remotely adjusted by stepping motors. After the first adjustment work, the reflector offers a point image of about $0.^\circ 14$ (FWHM) on the optic axis.

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