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T. Naito

Publications and source records attributed to T. Naito.

At least 55 records · Page 3Linked to original sources
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.

astro-ph↗
arXiv2001

Impedance Analysis of Bunch Length Measurements at the ATF Damping Ring

We present energy spread and bunch length measurements at the Accelerator Test Facility (ATF) at KEK, as functions of current, for different ring rf voltages, and with the beam both on and off the coupling resonance. We fit the on-coupling bunch shapes to those of an impedance model consisting of a resistor and an inductor connected in series. We find that the fits are reasonably good, but that the resulting impedance is unexpectedly large.

physics.acc-ph↗
arXiv2001

Multi-bunch generation by thermionic gun

KEK-ATF is studying the low-emittance multi-bunch electron beam for the future linear collider. In ATF, thermionic gun is used to generate 20 bunches electron beam with the bunch spacing of 2.8 ns. Due to a distortion of the gun emission and the beam loading effect in the bunching system, the intensity for each bunch is not uniform by up to 40 % at the end of the injector. We have developed a system to correct the gun emission by precisely controlling the cathode voltage with a function generator. For the beam loading effect, we have introduced RF amplitude modulation on Sub Harmonic Buncher, SHB. By these technique, bunch intensity uniformity was improved and beam transmission for later bunches was recovered from 67% to 91%, but intensity for first five bunches is still lower than others.

physics.acc-ph↗
arXiv2000

Intrabeam Scattering Analysis of ATF Beam Data Taken in April 2000

In April 2000 the single bunch energy spread, bunch length, horizontal emittance, and vertical emittance were measured as functions of current in KEK's ATF damping ring. In this report the measurement results are analyzed in light of intrabeam scattering theory. The measurements are found to be relatively consistent with theory, although the measured effects appear to be stronger than theory. In addition, the factor of 3 growth in vertical emittance at a current of 3 mA does not seem to be supported.

physics.acc-ph↗
arXiv2000

Bunch Length Measurements at the ATF Damping Ring in April 2000

This report presents bunch length and energy spread measurements performed in April 2000 at the ATF Damping Ring, at KEK. Measurements were performed with the beam on and then off the linear (difference) coupling resonance. Due to strong intra-beam scattering in the ATF ring, the results depended strongly on the coupling.

physics.acc-ph↗
arXiv2000

Development of rf reference line for the linear collider

The rf distribution system for the linear collider requires stable x-band(11.424GHz) rf phase signal over 25km length. In order to realize the distribution system, a fiber optic link using a phase stabilized optical fiber was tested. The phase stabilized optical fiber has been employed at LEP, KEKB, etc.. This paper describes the hardware system and result of the preliminary test of the feed back system for stabilization of the phase change.

hep-ex↗
arXiv2000

Energy stabilization of 1.5 GeV S-Band linac

KEK-ATF is studying low emittance, multi-bunch electron beam for the future linear collider. The energy instability of the 1.5 GeV linac has been a problem making the beam injection to the damping ring unstable. Because the unstable beam generates also large amount of the radiation, the beam current is limited by the KEK radiation safety policy much lower than what we expect. Stabilizing the S-band linac is therefore important not only to improve the beam quality, but also to clear the radiation safety limit to start the multi-bunch operation. We have made various modifications to solve the problem on the electron gun, modulator, klystron etc. For the modulator, we have developed a feed-forward controlled De-Q module. This module compensates the voltage jitter by controlling the deQ timing with a feed-forward circuit because the amount of the excessive charge up is strongly correlated to the charge up slope that can be measured prior to the deQ timing. The energy stability was examined and was improved by a factor of 3, from 0.6% to 0.2% of itself. Modification for the feed-forward circuit to get more stability was made. The test for the new circuit is in progress. For the long term instability, phase-lock system for klystron RF is being installed. In the test operation, it showed a good performance and compensate the phase drift less than 1 deg.

physics.acc-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.

astro-ph↗
arXiv1999

Search for TeV Gamma Rays from the SNR RXJ1713.7-3946

The shell type SNR RXJ1713.7-3946 is a new SNR discovered by the ROSAT all sky survey. Recently, strong non-thermal X-ray emission from the northwest part of the remnant was detected by the ASCA satellite. This synchrotron X-ray emission strongly suggests the existence of electrons with energies up to hundreds of TeV in the remnant. This SNR is, therefore, a good candidate TeV gamma ray source, due to the Inverse Compton scattering of the Cosmic Microwave Background Radiation by the shock accelerated ultra-relativistic electrons, as seen in SN1006. In this paper, we report a preliminary result of TeV gamma-ray observations of the SNR RXJ1713.7-3946 by the CANGAROO 3.8m telescope at Woomera, South Australia.

astro-ph↗
arXiv1999

Construction of New 7m Imaging Air Čerenkov Telescope of CANGAROO

CANGAROO group has constructed the new large imaging Air \v Cerenkov telescope to exploit hundred GeV region gamma-ray astronomy in March 1999 at Woomera, South Australia. It has a 7m parabolic mirror consisting of 60 small plastic spherical mirrors, and a fine imaging camera with 512 PMTs covering the field of view of 3 degree. Observation will start from July 1999.

astro-ph↗