TeV Gamma-ray Sources Research Articles

Galactic TeV Gamma-Ray Sources and Cosmic-Ray Origin

CANGAROO group has observed TeV gamma-ray sources in the southern hemisphere since 1992 at Woomera in South Australia [M. Mori, Prog. Theor. Phys. Suppl. No. 151 (2003), 85]. The southern hemisphere provides us a good chance of the observation for lots of galactic objects. Here we present a brief summary about established TeV gamma-ray galactic sources, Supernova Remnants and pulsar nebulae based on our results.

The Subluminal Parsec-Scale Jet of Markarian 501

We have combined very long baseline interferometry (VLBI) data from several programs in order to resolve differences in reported parsec-scale jet speeds for the TeV gamma-ray source Markarian 501. Data from the Very Long Baseline Array (VLBA) 2 cm survey, and 8 and 15 GHz data from the Radio Reference Frame Image Database, have been combined with data from a 5 GHz VLBI Space Observatory Programme observation to determine the apparent motions of jet components in this source. The combined data set consists of 12 observations between 1995 April and 1999 July. Four jet components are detected at most epochs, all of which are clearly subluminal (i.e., with apparent speeds less than the speed of light) and two of which appear stationary. The established TeV gamma-ray sources Mrk 501 and Mrk 421 thus both have subluminal parsec-scale jets, in contrast to the apparently superluminal jets of the majority of GeV sources detected by EGRET. No new VLBI component has emerged from the core following the extended TeV high state in 1997, again in contrast to the general behavior of GeV gamma-ray sources.

Possible High-Energy Neutrinos from the Cosmic Accelerator RX J1713.7−3946

The observation of TeV-gamma rays of neutral pion origin from the supernova remnant RX J1713.7-3946 might have revealed the first specific site where protons are accelerated to energies typical of the main component of the cosmic rays. In this letter we calculate the high-energy neutrino flux associated with this source to be at least 40 muon-type neutrinos per kilometer-squared per year. We perform the same calculations for other known sources of TeV-gamma rays and show how neutrino observations can establish whether the TeV-gamma rays emitted by blazars and supernova remnants are the decay products of neutral pions and thus unequivocally establish the sources as cosmic accelerators.

Evidence for TeV gamma ray emission from Cassiopeia A

232 hours of data were accumulated from 1997 to 1999, using the HEGRA Stereoscopic Cherenkov Telescope System to observe the supernova remnant Cassiopeia A. TeV gamma ray emission was detected at the 5 sigma level, and a flux of (5.8 +- 1.2(stat) +- 1.2(syst)) 10^(-9) ph m^(-2) s^(-1) above 1 TeV was derived. The spectral distribution is consistent with a power law with a differential spectral index of -2.5 +- 0.4(stat) +- 0.1(syst) between 1 and 10 TeV. As this is the first report of the detection of a TeV gamma ray source on the "centi-Crab" scale, we present the analysis in some detail. Implications for the acceleration of cosmic rays depend on the details of the source modeling. We discuss some important aspects in this paper.

Sub-TeV Gamma-Ray Astrophysics Using Large Air Čerenkov Telescopes

In 1990’s Very High Energy Gamma-ray Astrophysics has dramatically advanced due to the advent of Imaging Air Cerenkov Telescopes (IACTs), and has been widely recognized as an important field of astronomy. After the first detection of persistent TeV gamma-ray emission from the Crab in 1989, several types of TeV gamma-ray sources have been detected and established. Successive discoveries of active galactic nuclei emitting TeV gamma rays after 1992 especially astonished and enabled us directly to watch the high energy phenomena around the huge black holes at the center of galaxies. Recent detections of TeV gamma-ray emission from several supernova remnants have been reported in both southern and northern skies, which had been eagerly looked forward to since the beginning of cosmic-ray physics. Those are expected to be a clue of not only the galactic cosmic-ray origin but also the understanding of the particle acceleration due to a diffusive shock. At first we present the recent observational results and the understanding of high energy phenomena in gamma-ray sources, particularly galactic TeV gamma-ray sources. A brief review of experimental aspect of Very High Energy Gamma-ray Astronomy are also described including the perspective of TeV gamma-ray astronomy in the next decade.

VLBI Observations of Extragalactic TeV Gamma-ray Sources

VLBI observations of reported TeV gamma-ray sources are described and the inferences that can be drawn on the jet behaviour between the TeV variability-scale and the VLBI parsec-scale discussed.

A Spectral Index Map from VSOP Observations of Markarian 501

Abstract One of the features of VSOP observations is the ability to make contemporaneous, matched-resolution images at different frequencies in order to produce spectral index maps. We have combined VSOP observations made at 4.8 GHz on 1998 April 7 and 1.6 GHz on 1998 April 8 to make such a map of the variable X-ray and TeV gamma-ray source Mkn 501. The spectral index map reveals considerably more information than a single frequency total intensity image, and shows significant spectral variation along and across the milli-arcsecond scale jet. We interpret this in terms of models for the jet involving an inner fast spine and slower outer shear layer.

Galactic TeV gamma-ray sources

The observations of galactic TeV objects are summarized with emphasis on the astrophysical significance of recent positive detections from three pulsar driven nebulae, Crab Nebula, Vela, PSR 1706-44, and a historical supernova remnant, SN 1006.

Discovery of Gamma‐Ray Emission above 350 GeV from the BL Lacertae Object 1ES 2344+514

We present the discovery of >350 GeV gamma-ray emission from the BL Lacertae object 1ES 2344+514 with the Whipple Observatory 10m gamma-ray telescope. This is the third BL Lac object detected at gamma-ray energies above 300 Gev, the other two being Markarian 421 (Mrk 421) and Mrk501. These three active galactic nuclei are all X-ray selected and have the lowest known redshifts of any BL Lac objects currently identified. The evidence for emission derives primarily from an apparent flare on December 20, 1995 when a 6 sigma excess was detected with a flux approximately 63% of the very high energy gamma-ray emission from the Crab Nebula, the standard candle for TeV gamma-ray sources. Excluding the flare, observations between October 1995 and January 1996 yield a 4 sigma detection corresponding to 11% of the VHE Crab Nebula flux. Observations spanning September 1996 to January 1997 failed to yield a significant detection of a steady flux or any flaring. For this period, the 99.9% confidence level upper limit is <8% of the Crab Nebula. The low baseline emission level and variations in nightly and yearly flux of 1ES 22344+514 are the same as the VHE emission characteristics of Mrk 421 and Mrk 501

Measurement of TeV gamma-ray spectra with the Cherenkov imaging technique

In this paper, we seek to establish reliable methods for extracting energy spectra for TeV gamma-ray sources observed using the atmospheric Cherenkov Imaging Technique. Careful attention has been paid to the calculation of the telescope gain, and we obtain good agreement between direct measurements, with a statistical error of about 10%, and an absolute calibration from the background cosmic-ray trigger rate that has an overall error of 18%. Two independent analyses that are based on different Monte Carlo shower simulations, employ different selection criteria in order to retain a large fraction of gamma-ray events, and use different approaches to spectral estimation are presented here. The first is a fairly traditional method that builds on established image selection techniques and calculates the detector collection area and an energy estimation function. The error in measuring the enrgy of a single event is estimated at 36%, and we try to compensate for this poor energy resolution. The second analysis uses more elegant gamma-ray selection criteria and implicity incorporates the properties of the detector into the simulations that are then compared with the data in order to obtain source spectra. The two simulations are compared to each other and to the data, with the aim of establishing that each method is robust and insensitive to simulation details. Finally, we consider the main sources of systematic errors, the largest of which is in the telescope gain calibration, arising from an incomplete knowledge of the relevant factors, and is estimated to be 16%. The effect of possible errors in the simulations is also considered. Both methods have been applied to a part of the Whipple observatory database on the Crab Nebula for the 1988/89 observing season, while the first method has also been applied to data taken in 1995/96. The statistical error in the flux constant is about 8% and that in the spectral index is about 5%, while the corresponding systematic errors are estimated to be 18% and 2%, respectively. The results presented here show good agreement between the two methods as well as between the two seasons. However, a comprehensive consideration of the implications of the derived spectra and a comparison to other work is addressed in another paper.

Discovery of T[CLC]e[/CLC]V Gamma Rays from SN 1006: Further Evidence for the Supernova Remnant Origin of Cosmic Rays

This paper reports the first discovery of TeV gamma-ray emission from a supernova remnant made with the CANGAROO 3.8 m Telescope. TeV gamma rays were detected at the sky position and extension coincident with the north-east (NE) rim of shell-type Supernova remnant (SNR) SN1006 (Type Ia). SN1006 has been a most likely candidate for an extended TeV Gamma-ray source, since the clear synchrotron X-ray emission from the rims was recently observed by ASCA (Koyama et al. 1995), which is a strong evidence of the existence of very high energy electrons up to hundreds of TeV in the SNR. The observed TeV gamma-ray flux was $(2.4\pm 0.5(statistical) \pm 0.7(systematic)) \times 10^{-12}$ cm$^{-2}$ s$^{-1}$ ($\ge 3.0\pm 0.9$ TeV) and $ (4.6\pm 0.6 \pm 1.4) \times 10^{-12}$ cm$^{-2}$ s$^{-1}$ ($\ge 1.7\pm 0.5$ TeV) from the 1996 and 1997 observations, respectively. Also we set an upper limit on the TeV gamma-ray emission from the SW rim, estimated to be $ 1.1 \times 10^{-12}$ cm$^{-2}$ s$^{-1}$ ($\ge 1.7\pm 0.5$ TeV, 95% CL) in the 1997 data. The TeV gamma rays can be attributed to the 2.7 K cosmic background photons up-scattered by electrons of energies up to about 10$^{14}$ eV by the inverse Compton (IC) process. The observed flux of the TeV gamma rays, together with that of the non-thermal X-rays, gives firm constraints on the acceleration process in the SNR shell; a magnetic field of $6.5\pm2$ $\mu$G is inferred from both the synchrotron X-rays and inverse Compton TeV gamma-rays, which gives entirely consistent mechanisms that electrons of energies up to 10$^{14}$ eV are produced via the shock acceleration in SN1006.

The source of TeV gamma-rays in Cen X-3 and Vela X-1

An experimentally verifiable model is developed to explain the discrepancy between detected TeV γ-ray pulsed periods and neutron star spin periods in X-ray binary systems. It assumes that the TeV γ-rays are produced at the X-ray period and not on the neutron star itself, but somewhere else in the orbital plane. It was successfully applied to both Cen X-3 and Vela X-1. In the case of Cen X-3, an emission region was identified, with a 99.5% significance. This region trails the neutron star by 70° and is situated between the neutron star orbit and the companion. For Vela X-1 an emission region outside the orbit of the neutron star was found, with a probability for chance occurrence of 4 × 10 −5 . This region leads the neutron star by 90°. These detections were used to illustrate the characteristics of the model, especially parameters determining its applicability and possible limitations.

TeV gamma ray astronomy

The atmospheric Cherenkov technique has been used to study TeV gamma-ray sources for over 30 years; it is the only viable technique in the energy band from 0.1 to 10 TeV and at least three sources have been detected.

TeV radiation from galactic sources

The detection of the Crab Nebula as a steady source of TeV gamma rays puts the field of Very High Energy Gamma-Ray Astronomy on a firm observational basis and permits a critical re-assessment of the claims for the detection of a multitude of episodic binary sources. A new generation of detectors in the TeV and PeV energy regions is coming on-line; together with the telescopes of the Gamma-Ray Observatory these instruments will present a new perspective on one of the last frontiers of astronomy.

A search for the 2.223 MeV neutron capture gamma-ray line from the directions of Cygnus and the Galactic center

view Abstract Citations (11) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Search for the 2.223 MeV Neutron Capture Gamma-Ray Line from the Directions of Cygnus and the Galactic Center Harris, Michael J. ; Share, Gerald H. Abstract Free neutrons produced by nuclear reactions in high-temperature plasmas may undergo proton capture in ambient material, giving rise to gamma-ray emisison in a line at 2.223 MeV. Plausible settings for this process include accretion disks around black holes, material accreting onto neutron stars, and the binary companions of TeV gamma-ray sources. Data accumulated by the Solar Maximum Mission Gamma Ray Spectrometer (GRS) between 1980 and 1989 have been searched for evidence of this line, during periods when the black hole candidates Cygnus X-1 and the Galactic center were in transit across the GRS aperture. During these periods the neutron-star X-ray binaries Cygnus X-3 and Scorpius X-1 were also in the respective GRS fields of view. A 3-sigma upper limit of 0.0001/sq cm s has been placed on the steady emission in the 2.223 MeV line from the Galactic center and Scorpius X-1. Upper limits in the range 0.00012-0.00022 gamma/sq cm s have been set for Cygnus X-1 according to different models of the origin of the emission. The 3-sigma upper limit to the phase-averaged steady emission from Cygnus X-3 was found to be 0.00012 gamma/sq cm s. Publication: The Astrophysical Journal Pub Date: November 1991 DOI: 10.1086/170666 Bibcode: 1991ApJ...381..439H Keywords: Cygnus Constellation; Galactic Nuclei; Gamma Ray Astronomy; Neutron Distribution; Capture Effect; Milky Way Galaxy; Nuclear Astrophysics; X Ray Binaries; Astrophysics; GAMMA RAYS: GENERAL; GALAXIES: NUCLEI; GALAXIES: THE GALAXY; X-RAYS: BINARIES full text sources ADS | data products SIMBAD (5)

Sensitivity and consistency in statistical analysis of TeV gamma-ray observations

Statistical tests which are sensitive to the full distribution of Rayleigh powers for a set of observations of a TeV gamma-ray source are considered and compared with the standard approach of considering only the highest powers. For sources with duty factors of more than about 2%, the global tests can be more effective. Tests for consistency between the apparent strength of a periodic signal with measured dc excess are reviewed.