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1.
An analysis of our observations of the Geminga object with the GT-48 ground-based gamma-ray telescope has shown that its very-high-energy gamma-ray flux is modulated with a 59-s period. The 59-s period and its time derivative previously inferred from satellite data have been confirmed. According to our data, the period was 61.94 s in 1997 at MSD=50573. The statistical significance of this result is (1?4.5)×10?4.  相似文献   

2.
A statistical analysis of the spectral and temporal parameters for 546 triggering events on the APEX gamma-ray detector onboard the Phobos-2 spacecraft has revealed a group of 28 events that are probably short cosmic gamma-ray bursts (GRBs). The distribution of the full group of 74 events of the APEX experiment in duration parameter is bimodal in shape, which is in good agreement with the bimodal shape of the BATSE GRB distribution. A search for the detected group of short events using data from the LILAS X-ray and soft gamma-ray detector onboard the same spacecraft has yielded no positive result. A comparison of the APEX and LILAS data has led us to conclude that the short GRBs have a significantly reduced soft gamma-ray flux at energies <100 keV relative to the power law dN/dE=CE?α with the average index α=2.62.  相似文献   

3.
We computed the thermal time-dependent X-ray spectrum of a hot plasma in the vicinity of a gamma-ray burst (GRB). An allowance for time-dependent processes in a hot rarefied plasma is shown to strongly affect the observed spectrum. These computations can give an alternative explanation for the observed X-ray emission lines in the early afterglows of GRBs (e.g., GRB 011211). Our technique allows the GRB collimation angle and the environment clumpiness parameters to be independently constrained.  相似文献   

4.
The spatial positions of unidentified gamma-ray sources ( E>100 MeV) were analyzed. This analysis shows that gamma-ray sources with fluxes >5×10?7 cm?2 s?1 correlate with Wolf-Rayet stars, while gamma-ray sources with fluxes <5×10?7 cm?2 s?1 may be associated with flaring stars.  相似文献   

5.
Observational parameters of the optical and gamma-ray emissions from 58 gamma-ray bursts (GRBs) with discovered afterglows and known redshifts are analyzed. The distributions of these parameters and pair correlations between them are studied. Approximately half of the objects exhibit a relatively slow decrease in the optical flux at initial afterglow phases (with a power-law index in the decay law α < 1). Correlations have been found between the luminosities, energies, and durations of the optical and gamma-ray emissions, which can be explained by the presence of universal features in the light curves. A correlation of the peak luminosity for afterglows with the redshift and an anticorrelation of their durations with the redshift have been found for the first time. Against the background of a weak z dependence of the total afterglow energy, this effect can be explained by cosmological evolution of the GRB environment, which determines the rate of optical energy release.  相似文献   

6.
On March 11, 2007, the INTEGRAL observation discovered and localized a gamma-ray burst in the sky from which an early infrared afterglow was then detected. We present our timing and spectral analyses of the data from the ISGRI detector of the IBIS telescope. The burst consists of one ～40-s-long peak during which a fluence of ～3 × 10?6 erg cm?2 was released in the energy range 20–200 keV. The 18–300-keV spectrum is characterized by a slope Γ ≈ ?0.8 at the rise phase and Γ ≈ ?1.4 at the maximum and decay phase. The basic characteristics of GRB 070311 suggest that it is a typical cosmological gamma-ray burst.  相似文献   

7.
In the relativistic fireball model, the afterglow of a gamma-ray burst (GRB) is produced by synchrotron radiation of the electrons accelerated in the external shock that emerges as the relativistic flow moves. According to this model, the afterglow peaks on a time scale of ～10 s when observed in the soft gamma-ray band. The peak flux can be high enough to be detected by modern all-sky monitors. We investigate the emission from short (ΔT<1 s) GRBs on a time scale t≈10 s using BATSE/CGRO data. A significant flux is recorded for ～20% of the events. In most cases, the observed persistent emission can be explained in terms of the model as an early burst afterglow. No early afterglows of most short GRBs are observed. The model parameters for these bursts are constrained.  相似文献   

8.
The detection efficiency of the atmospheric Cerenkov flashes in searching for very high energy (VHE) gamma-ray sources using the multichannel imaging cameras (MIC) are compared for various technique. Here the detection efficiency is regarded as the time needed for gamma-ray source detection with the preset flux at a certain confidence level. The shorter the time the higher the efficiency.The Monte Carlo simulation of the flashes detection process by MIC has been used for the comparison of various observational methods. The analysis has shown that the tracking of the source followed by the background tracking is the most efficient. Scanning and off-axis observations are 1.5–2.0 times less efficient.  相似文献   

9.
Observations of the gamma-ray sky reveal the most powerful sources and the most violent events in the Universe. While at lower wavebands the observed emission is generally dominated by thermal processes, the gamma-ray sky provides us with a view on the non-thermal Universe. Here particles are accelerated to extreme relativistic energies by mechanisms which are still poorly understood, and nuclear reactions are synthesizing the basic constituents of our world. Cosmic accelerators and cosmic explosions are the major science themes that are addressed in the gamma-ray regime.With the INTEGRAL observatory, ESA has provided a unique tool to the astronomical community revealing hundreds of sources, new classes of objects, extraordinary views of antimatter annihilation in our Galaxy, and fingerprints of recent nucleosynthesis processes. While INTEGRAL provides the global overview over the soft gamma-ray sky, there is a growing need to perform deeper, more focused investigations of gamma-ray sources. In soft X-rays a comparable step was taken going from the Einstein and the EXOSAT satellites to the Chandra and XMM/Newton observatories. Technological advances in the past years in the domain of gamma-ray focusing using Laue diffraction and multilayer-coated mirror techniques have paved the way towards a gamma-ray mission, providing major improvements compared to past missions regarding sensitivity and angular resolution. Such a future Gamma-Ray Imager will allow to study particle acceleration processes and explosion physics in unprecedented detail, providing essential clues on the innermost nature of the most violent and most energetic processes in the Universe.  相似文献   

10.
We review the particle-in-cell simulation results related to the recently discovered particle acceleration mechanism called the Diamagnetic Relativistic Pulse Accelerator, or DRPA. This mechanism may be relevant to the prompt gamma-ray emission of gamma-ray bursts. It may also be testable with future laboratory experiments using ultra-intense lasers.  相似文献   

11.
Observations of several active galactic nuclei were performed with the GT-48 gamma-ray telescope at CrAO in 2004: 3C 66A, Mk 421, Mk 501, 1H 1426, 1ES 1959, and BL Lac. Very-high-energy (E ≥ 1012 eV) gamma-ray fluxes were recorded from 3C 66A, Mk 421, Mk 501, and 1H 1426 at a confidence level of more than 4σ. Upper limits for the flux of very-high-energy gamma rays are presented for 1ES 1959 and BL Lac. The 2004 observational data for 3C 66A (z = 0.44) confirm the results obtained previously at CrAO.  相似文献   

12.
With ESA’s INTEGRAL mission gamma-ray astronomy has advanced to the point where major scientific advances must be expected from detailed studies of the many new point sources. The interest in developing focusing telescopes operating in the soft gamma-ray regime up to 1 MeV is therefore mounting rapidly. Telescopes based on Laue diffraction of gamma-rays from crystals appear as one promising route, although the practical difficulties of realizing a large scale Laue lens are certainly not small. In this paper I have attempted to develop an optimized lens design considering the size and mass constraints of a specific medium size launch vehicle. The introduction of the lens mass as a primary design driver has some surprising effects for the choice of material for the crystals and new tradeoff considerations are introduced.  相似文献   

13.
The active galactic nuclei BL Lac, 3C66A, and Mk501, as well as the Crab nebula and the Cyg γ-2 source were observed in 2006 at the Crimean Astrophysical Observatory using the GT-48 gamma-ray telescope. Very high energy (VHE) gamma-ray fluxes at a high confidence level (Q > 4) were detected from the active galactic nuclei and the Crab nebula. VHE gamma-ray fluxes from the unidentified gamma-ray source Cyg γ-2 and the X-ray source Cyg X-3 were recorded during observations of Cyg γ-2.  相似文献   

14.
Recent developments of cerium-doped lanthanum-halide scintillators like LaBr3:Ce show a remarkable performance in gamma-ray spectroscopy. When high energy resolution in combination with stopping power is required they provide excellent gamma-ray detector candidates for the use in space missions. Moreover, irradiation tests have shown that such detectors are radiation tolerant. In this paper we discuss a possible application of LaBr in nuclear astrophysics missions. We show results on recent proton irradiation tests at KVI in Groningen (NL) and discuss the damage and activation effects after irradiation. A possible implementation for a focal plane detector in a gamma-ray telescope and the expected performance is presented.  相似文献   

15.
We consider temporal, spectral, and polarization parameters of the hard X-ray and gamma-ray radiation observed during the solar flare of May 20, 2002, in the course of experiments with the SONG and SPR-N instruments onboard the Coronas-F spacecraft. This flare is one of the most intense gamma-ray events among all of the bursts of solar hard electromagnetic radiation detected since the beginning of the Coronas-F operation (since July 31, 2001) and one of the few gamma-ray events observed during solar cycle 23. A simultaneous analysis of the Coronas-F and GOES data on solar thermal X-ray radiation suggests that, apart from heating due to currents of matter in the the flare region, impulsive heating due to the injection of energetic electrons took place during the near-limb flare S21E65 of May 20, 2002. These electrons produced intense hard X-ray and gamma-ray radiation. The spectrum of this radiation extends up to energies ≥7 MeV. Intense gamma-ray lines are virtually unobservable against the background of the nonthermal continuum. The polarization of the hard X-ray (20–100 keV) radiation was estimated to be ≤15–20%. No significant increase in the flux of energetic protons from the flare under consideration was found. At the same time, according to ACE data, the fluxes of energetic electrons in interplanetary space increased shortly (～25 min) after the flare.  相似文献   

16.
We present the observations of Cygnus X-3 carried out with the GT-48 gamma-ray telescope at the Crimean Astrophysical Observatory in 1994–1995. The mean gamma-ray flux at energy E>1012 eV is shown to be approximately equal to 1.3×10?11 cm?2 s?1. The flux in 1994 was much lower than that in 1995, being (6.2±2.6)×10?12 cm?2 s?1; i.e., it was statistically insignificant. The flux in 1995 was (2.7±0.7)×10?11 cm?2 s?1. Thus, the very high energy gamma-ray emission from Cyg X-3 is variable. These measurement results can be used to obtain upper limits on the flux from Cyg X-3 in 1994–1995.  相似文献   

17.
The 17 m Major Atmospheric Gamma Imaging Cherenkov (MAGIC) telescope for gamma-ray astronomy between 30 and 300 GeV started operations in its final configuration in October 2003 and is currently well into its calibration phase. Here I report on its present status and its first gamma-ray source detections.  相似文献   

18.
We present the observations of cosmic gamma-ray bursts (GRBs) with the main detector of the SIGMA telescope onboard the Granat Observatory from January 1990 through September 1994. The observations were carried out in the energy range 35–1300 keV. We detected 36 GRBs and 31 high-energy solar flares during this period. No GRB fell within the main field of view; they were all recorded by the “secondary optics” of the telescope. The SIGMA telescope recorded relatively bright bursts with peak fluxes of 10?6–10?4 erg s?1 cm?2 in the 100–500-keV energy band. Stable detector background allows the long-term variability of GRB sources on a time scale of ～1000 s to be studied. The results of our search for early afterglows of GRBs are presented. The flux averaged over all bursts in the interval 100–800 s after the main event is 0.36±0.14 counts s?(35–300 keV), suggesting that there is soft gamma-ray emission on this time scale after a considerable number of GRBs.  相似文献   

19.
The galaxy Mrk 421 was observed with the GT-48 Cherenkov telescope in 2004. The observations revealed a very-high-energy gamma-ray flux at a confidence level of 4.8 σ. Comparison with the constant gamma-ray flux from the Crab Nebula yielded an estimate of the total flux from Mrk 421, 1.7 ± 0.7 Crab (E ≥ 1 TeV).  相似文献   

20.
Gamma-ray lines are the fingerprints of nuclear transitions, carrying the memory of high energy processes in the universe. Setting out from what is presently known about line emission in gamma-ray astronomy, requirements for future telescopes are outlined. The inventory of observed line features shows that sources with a wide range of angular and spectral extent have to be handled: the scientific objectives for gamma-ray spectroscopy are spanning from compact objects as broad class annihilators, over longlived galactic radioisotopes with hotspots in the degree-range to the extremely extended galactic disk and bulge emission of the narrow e– e+ line.The instrumental categories which can be identified in the energy range of nuclear astrophysics have their origins in the different concepts of light itself: geometrical optics is the base of modulating aperture systems-these methods will continue to yield adequate performances in the near future. Beyond this, focusing telescopes and Compton telescopes, based on wave- and quantum- optics respectively, may be capable to further push the limits of resolution and sensitivity.  相似文献   

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