arXiv subjects

K. Nishijima

Publications and source records attributed to K. Nishijima.

At least 91 records · Page 5Linked 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

Supernova Relic Neutrino Search at Super-Kamiokande

A new Super-Kamiokande (SK) search for Supernova Relic Neutrinos (SRNs) was conducted using 2853 live days of data. Sensitivity is now greatly improved compared to the 2003 SK result, which placed a flux limit near many theoretical predictions. This more detailed analysis includes a variety of improvements such as increased efficiency, a lower energy threshold, and an expanded data set. New combined upper limits on SRN flux are between 2.8 and 3.0 nu_e cm^-2 s^-1 > 16 MeV total positron energy (17.3 MeV E_nu).

hep-ex↗

arXiv2011

Search for Differences in Oscillation Parameters for Atmospheric Neutrinos and Antineutrinos at Super-Kamiokande

We present a search for differences in the oscillations of antineutrinos and neutrinos in the Super-Kamiokande -I, -II, and -III atmospheric neutrino sample. Under a two-flavor disappearance model with separate mixing parameters between neutrinos and antineutrinos, we find no evidence for a difference in oscillation parameters. Best fit antineutrino mixing is found to be at (dm2bar, sin2 2 thetabar) = (2.0x10^-3 eV^2, 1.0) and is consistent with the overall Super-K measurement.

hep-ex↗

arXiv2011

Letter of Intent: The Hyper-Kamiokande Experiment --- Detector Design and Physics Potential ---

We propose the Hyper-Kamiokande (Hyper-K) detector as a next generation underground water Cherenkov detector. It will serve as a far detector of a long baseline neutrino oscillation experiment envisioned for the upgraded J-PARC, and as a detector capable of observing -- far beyond the sensitivity of the Super-Kamiokande (Super-K) detector -- proton decays, atmospheric neutrinos, and neutrinos from astronomical origins. The baseline design of Hyper-K is based on the highly successful Super-K, taking full advantage of a well-proven technology. (to be continued)

hep-ex↗

arXiv2011

Study of Non-Standard Neutrino Interactions with Atmospheric Neutrino Data in Super-Kamiokande I and II

In this paper we study non-standard neutrino interactions as an example of physics beyond the standard model using atmospheric neutrino data collected during the Super-Kamiokande I(1996-2001) and II(2003-2005) periods. We focus on flavor-changing-neutral-currents (FCNC), which allow neutrino flavor transitions via neutral current interactions, and effects which violate lepton non-universality (NU) and give rise to different neutral-current interaction-amplitudes for different neutrino flavors. We obtain a limit on the FCNC coupling parameter, varepsilon_{mu tau}, |varepsilon_{mu tau}|<1.1 x 10^{-2} at 90%C.L. and various constraints on other FCNC parameters as a function of the NU coupling, varepsilon_{e e}. We find no evidence of non-standard neutrino interactions in the Super-Kamiokande atmospheric data.

hep-ex↗

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↗

arXiv2011

Scintillation-only Based Pulse Shape Discrimination for Nuclear and Electron Recoils in Liquid Xenon

In a dedicated test setup at the Kamioka Observatory we studied pulse shape discrimination (PSD) in liquid xenon (LXe) for dark matter searches. PSD in LXe was based on the observation that scintillation light from electron events was emitted over a longer period of time than that of nuclear recoil events, and our method used a simple ratio of early to total scintillation light emission in a single scintillation event. Requiring an efficiency of 50% for nuclear recoil retention we reduced the electron background to 7.7\pm1.1(stat)\pm1.2 0.6(sys)\times10-2 at energies between 4.8 and 7.2 keVee and to 7.7\pm2.8(stat)\pm2.5 2.8(sys)\times10-3 at energies between 9.6 and 12 keVee for a scintillation light yield of 20.9 p.e./keV. Further study was done by masking some of that light to reduce this yield to 4.6 p.e./keV, the same method results in an electron event reduction of 2.4\pm0.2(stat)\pm0.3 0.2(sys)\times10-1 for the lower of the energy regions above. We also observe that in contrast to nuclear recoils the fluctuations in our early to total ratio for electron events are larger than expected from statistical fluctuations.

physics.ins-det↗

arXiv2011

Towards an Axiomatic Formulation of Noncommutative Quantum Field Theory

We propose new Wightman functions as vacuum expectation values of products of field operators in the noncommutative space-time. These Wightman functions involve the $\star$-product among the fields, compatible with the twisted Poincaré symmetry of the noncommutative quantum field theory (NC QFT). In the case of only space-space noncommutativity ($θ_{0i}=0$), we prove the CPT theorem using the noncommutative form of the Wightman functions. We also show that the spin-statistics theorem, demonstrated for the simplest case of a scalar field, holds in NC QFT within this formalism.

hep-th↗

arXiv2009

Self-shielding effect of a single phase liquid xenon detector for direct dark matter search

Liquid xenon is a suitable material for a dark matter search. For future large scale experiments, single phase detectors are attractive due to their simple configuration and scalability. However, in order to reduce backgrounds, they need to fully rely on liquid xenon's self-shielding property. A prototype detector was developed at Kamioka Observatory to establish vertex and energy reconstruction methods and to demonstrate the self-shielding power against gamma rays from outside of the detector. Sufficient self-shielding power for future experiments was obtained.

astro-ph.CO↗

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

Reanalysis of Data Taken by the CANGAROO 3.8 Meter Imaging Atmospheric Cherenkov Telescope: PSR B1706-44, SN 1006, and Vela

We have reanalyzed data from observations of PSR B1706-44, SN 1006, and the Vela pulsar region made with the CANGAROO 3.8 m imaging atmospheric Cherenkov telescope between 1993 and 1998 in response to the results reported for these sources by the H.E.S.S. collaboration. In our reanalysis, in which gamma-ray selection criteria have been determined exclusively using gamma-ray simulations and OFF-source data as background samples, no significant TeV gamma-ray signals have been detected from compact regions around PSR B1706-44 or within the northeast rim of SN 1006. We discuss reasons why the original analyses gave the source detections. The reanalysis did result in a TeV gamma-ray signal from the Vela pulsar region at the 4.5 sigma level using 1993, 1994, and 1995 data. The excess was located at the same position, 0.13 deg. to the southeast of the Vela pulsar, as that reported in the original analysis. We have investigated the effect of the acceptance distribution in the field of view of the 3.8 m telescope, which rapidly decreases toward the edge of the field of the camera, on the detected gamma-ray morphology. The expected excess distribution for the 3.8 m telescope has been obtained by reweighting the distribution of HESS J0835-455 measured by H.E.S.S. with the acceptance of the 3.8 m telescope. The result is morphologically comparable to the CANGAROO excess distribution, although the profile of the acceptance-reweighted H.E.S.S. distribution is more diffuse than that of CANGAROO. The integral gamma-ray flux from HESS J0835-455 has been estimated for the same region as defined by H.E.S.S. from the 1993-1995 data of CANGAROO to be F(> 4.0 +/- 1.6 TeV) = (3.28 +/- 0.92) x 10^{-12} photons cm^{-2} s^{-1}, which is statistically consistent with the integral flux obtained by H.E.S.S.

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↗

arXiv2009

Distillation of Liquid Xenon to Remove Krypton

A high performance distillation system to remove krypton from xenon was constructed, and a purity level of Kr/Xe = $\sim 3 \times 10^{-12}$ was achieved. This development is crucial in facilitating high sensitivity low background experiments such as the search for dark matter in the universe.

physics.ins-det↗

arXiv2008

The implications from CANGAROO-III observations of TeV blazar PKS 2155-304

We have observed the high-frequency-peaked BL Lacertae object PKS2155-304 in 2004, 2005 and 2006 with the CANGAROO-III imaging atmospheric Cherenkov telescope, and have detected a signal above 660 GeV at the 4.8/sigma level during the 2006 outburst period. Intranight flux variability on time scale of half an hour is observed. From this variability time scale, the size of the TeV gamma-ray emission region is restricted to 5x10^13δcm, and the super massive black hole mass is estimated to be less than 1.9x10^8δM_{Solar}, where δis the beaming factor. The differential energy spectrum is obtained, and an upper limit of the extragalactic infrared background light (EBL) flux is derived under some assumption. We also fit a synchrotron self Compton (SSC) model to the spectral energy distribution (SED) and derive the beaming factor and magnetic field strength.

astro-ph↗

arXiv2008

Noncommutative Quantum Field Theory: A Confrontation of Symmetries

The concept of a noncommutative field is formulated based on the interplay between twisted Poincaré symmetry and residual symmetry of the Lorentz group. Various general dynamical results supporting this construction, such as the light-wedge causality condition and the integrability condition for Tomonaga-Schwinger equation, are presented. Based on this analysis, the claim of the identity between commutative QFT and noncommutative QFT with twisted Poincaré symmetry is refuted.

hep-th↗

arXiv2008

Scintillation yield of liquid xenon at room temperature

The intensity of scintillation light emission from liquid xenon at room temperature was measured. The scintillation light yield at 1 deg. was measured to be 0.64 +/- 0.02 (stat.) +/- 0.06 (sys.) of that at -100 deg. Using the reported light yield at -100 deg. (46 photons/keV), the measured light yield at 1 deg. corresponds to 29 photons/keV. This result shows that liquid xenon scintillator gives high light yield even at room temperature.

physics.ins-det↗

arXiv2007

CANGAROO-III Observations of the 2006 Outburst of PKS2155-304

We have used the CANGAROO-III imaging atmospheric Cherenkov telescopes to observe the high-frequency-peaked BL Lacertae (HBL) object PKS 2155-304 between 2006 July 28 (MJD 53944) 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 sigma level in an effective live time of 25.1 hours during the outburst period. The flux of Very High Energy gammarays from the CANGAROO-III observations shows the variability on the time scale of less than a few hours. The averaged integral flux above 660 GeV is (1.6 +/- 0.3_stat +/- 0.5_syst) x 10^-11 cm^-2 sec^-1 which corresponds to ~45% of the flux observed from the Crab nebula. Follow-up observations between August 17 (MJD 53964) and 25 indicate the source activity had decreased.

astro-ph↗