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1.
《New Astronomy Reviews》2002,46(8-10):475-480
We present γ-ray spectra for a set of Type Ia supernovae. Our study is based on a detailed Monte Carlo transport scheme for both spherical and full 3-D geometries. Classical and new challenges of the γ-ray astronomy are addressed. We find that γ-rays are very suitable to reveal the structure of the envelope and, thus, they allow to probe properties of the nuclear burning front and the progenitor, namely its central density and global asphericities. The potential problems are discussed for the quantitative comparison between theoretical and observed line fluxes during the first few months after the explosion.  相似文献   

2.
The MACE (Major Atmospheric Cherenkov Experiment) is an upcoming Very High Energy (VHE) γ-ray telescope, based on imaging atmospheric Cherenkov technique, being installed at Hanle, a high altitude astronomical site in Ladakh, India. Here we present Monte Carlo simulation studies of trigger rates and threshold energies of MACE in the zenith angle range of 0°–60° for on-axis γ-ray coming from point source and various cosmic ray species. We have simulated the telescope’s response to γ-rays, proton, electron and alpha initiated atmospheric Extensive Air Showers (EAS) in the broad energy range of 5 GeV to 20 TeV. For γ-rays we consider power law and log parabolic spectra while other particles are simulated with their respective cosmic ray spectrum. Trigger rates and threshold energies are estimated for the trigger configuration of 4 Close Cluster Nearest Neighbour(CCNN) pixels as implemented in MACE hardware, in combination with single channel discriminator threshold ranging from 6–10 photo electrons (pe). We find that MACE can achieve the γ-ray trigger energy threshold of ∼ 17 GeV (4 CCNN, 9 pe) at 0° zenith angle for power law spectrum. The total trigger rate at 0° zenith is expected to be ∼650 Hz, with protons contributing ∼ 80% to it. For the zenith range of 0°-40° we find that the telescope can achieve γ-ray trigger threshold energies of ∼22 GeV at 20° zenith angle and ∼40 GeV at 40° zenith angle. Integral rates are also almost constant for this zenith angle range. At zenith angle of 60°, trigger energy threshold increases to ∼173 GeV and total integral rate falls down to ∼305 Hz.  相似文献   

3.
Very high energy γ-rays have recently been detected from the microquasar LS I +61 303 using the MAGIC telescope. A phenomenological study on the concomitant neutrinos that would be radiated if the γ-ray emission is hadronic in origin is herein presented. Neutrino oscillations are considered, and the expected number of events in a km-scale detector such as ICECUBE is computed under different assumptions including orbital periodicity and modulation, as well as different precision in the modeling of the detector. We argue that the upper limits already imposed on the neutrino emission of LS I +61 303 using AMANDA-II and the forthcoming measurements by ICECUBE may significantly constrain – in an independent and unbiased way – the γ-ray to neutrino flux ratio, and thus the possibility of a hadronic origin of the γ-rays. The viability of hadronic models based on wind–jet interactions in the LS +61 303 system after MAGIC measurements is discussed.  相似文献   

4.
The recent advances in TeV γ-ray astronomy using imaging Cerenkov telescopes is mainly due to the good separation between the properties of γ-ray and hadronic showers. A new method for this discrimination is described. The method is mainly based on the change of the image's Size and Surface Brightness (Size/Area) with energy and the differences in these parameters between those initiated by γ-rays and hadrons. The application of the method to the Whipple's 10 m telescope database from the Crab Nebula and Markarian 421 demonstrates its sensitivity to gamma-hadron separation. This study shows the importance of the image Surface Brightness, in addition to the previously used Shape and Orientation parameters.  相似文献   

5.
During its Cycle I (2005/2006), the MAGIC telescope targeted about 250 hours several galactic γ-ray sources detected previously by other experiments or expected to emit in the same energy domain. This paper reviews some results of such MAGIC observations. We cover, among others, supernova remnants, the Galactic Center and microquasars. We will concentrate on the recent discovery of very high energy γ-rays from the microquasar LS I +61 303.  相似文献   

6.
The propagation of γ-rays through metagalactic space is associated with pair creation and subsequent inverse-Compton scattering off low-energy background radiation. As a consequence, γ-rays of very high energy emitted by remote sources are reprocessed into the window from 10 MeV to 30 GeV conserving the injected energy. Any cosmologically distributed population of γ-ray sources therefore contributes to the diffuse γ-ray background in this energy band which is well-determined from recent observations with the Compton Gamma Ray Observatory (CGRO). Since the γ-rays trace accelerated particles, the observed flux of diffuse γ-rays also constrains the global efficiency for particle acceleration. Radio galaxies can account for the γ-ray background if their particle acceleration efficiency considerably exceeds ∼ 18% implying that particle acceleration is an essential part of the thermodynamics in these sources. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

7.
A PC-based drive-control system has been developed for the altitude-azimuth mounted TACTIC -ray telescope to control the speed and direction of motion of its 2-axes. Details of various hardware components chosen for the telescope, including hybrid-stepper motor, 16-bit absolute encoder and CAMAC-based programmable stepper motor controller, are discussed in this paper. The telescope-control strategy, based on the position-loop with a proportional type control for the source-seek mode and the on/off type control for the tracking mode, is explained in detail. Some important performance features of the telescope, including its blind-spot size, drive-system backlash and encoder-error compensation, are also presented. The drive system has been extensively field-tested and has been operating satisfactorily during observation campaigns carried out since March 1997 with the TACTIC Imaging Element. A tracking accuracy of ±3 arc-minutes has been achieved. A test report of its performance, with regard to its tracking accuracy on the basis of successful detection of TeV -rays from the active galaxy Markarian 501 in April–May 1997, is also presented.  相似文献   

8.
We study the contribution of young pulsars, with characteristic ages of less than 106 yr, to the diffuse γ-ray emission from the Large Magellanic Cloud (LMC). Based on the outer gap model for γ-ray emission proposed by Zhang & Cheng and pulsar properties in the LMC given by Hartmann, Brown & Schnepf, we simulate the properties of the young pulsars in the LMC. We show that γ-rays produced by the pulsars in the LMC may make an important contribution to the diffuse γ-rays in the LMC, especially in the high-energy range. We calculate the γ-ray energy spectrum of the pulsars in the LMC and show that the γ-ray component contributed by the pulsars to the diffuse γ-rays in the high-energy range (above ∼1 GeV) becomes dominant. We expect that none of the young pulsars should be detectable as an individual point source of γ-ray emission by EGRET. We also expect that pulsar contribution above ∼1 GeV in the SMC is very important.  相似文献   

9.
At least one massive binary system containing an energetic pulsar, PSR B1259−63/SS2883, has been recently detected in the TeV γ-rays by the HESS telescopes. These γ-rays are likely produced by particles accelerated in the vicinity of the pulsar and/or at the pulsar wind shock, in comptonization of soft radiation from the massive star. However, the process of γ-ray production in such systems can be quite complicated due to the anisotropy of the radiation field, complex structure of the pulsar wind termination shock and possible absorption of produced γ-rays which might initiate leptonic cascades. In this paper, we consider in detail all these effects. We calculate the γ-ray light curves and spectra for different geometries of the binary system PSR B1259−63/SS2883 and compare them with the TeV γ-ray observations. We conclude that the leptonic inverse-Compton model, which takes into account the complex structure of the pulsar wind shock due to the aspherical wind of the massive star, can explain the details of the observed γ-ray light curve.  相似文献   

10.
The explosion mechanism associated with thermonuclear supernovae (SNIa) is still a matter of debate. There is a wide agreement that high amounts of radioactive nuclei are produced during these events and they are expected to be strong γ-ray emitters. In the past, several authors have investigated the use of this γ-ray emission as a diagnostic tool. In this paper we have performed a complete study of the γ-ray spectra associated with all the different scenarios currently proposed. This includes detonation, delayed detonation, deflagration and the off-centre detonation. We have performed accurate simulations for this complete set of models in order to determine the most promising spectral features that could be used to discriminate among the different models. Our study is not limited to qualitative arguments. Instead, we have quantified the differences among the spectra and established distance limits for their detection. The calculations have been performed considering the best current response estimations of the SPI and IBIS instruments aboard INTEGRAL in such a way that our results can be used as a guideline to evaluate the capabilities of INTEGRAL in the study of Type Ia supernovae. For the purpose of completeness we have also investigated the nuclear excitation and spallation reactions as a possible secondary source of γ-rays present in some supernova scenarios. We conclude that this mechanism can be neglected because of its small contribution.  相似文献   

11.
We discuss the capability of ‘100 GeV’ class imaging atmospheric Cherenkov telescope (IACT) arrays as future powerful instruments of ground-based gamma-ray astronomy. It is assumed that the array is gathered from individually triggered quadrangular 4-IACT ‘cells’ with a linear size of about 100 m. The multi-cell concept allows coverage of large detection areas economically, and at the same time the effective exploitation of the stereoscopic approach of determination of the shower parameters using information obtained by several IACTs simultaneously. Determination of arrival directions of γ-ray primaries on an event-by-event basis with accuracy δθ ≤ 0.1° combined with high suppression efficiency (at both the hardware and software levels) of the background hadronic showers by a factor of ≈ 103, and large, up to 1 km2 collection areas, can provide minimum detectable energy fluxes of ≥ 100 GeV γ-rays from point sources down to 10−13 erg/cm2 s which is about 3 orders of magnitude lower than the current sensitivities achieved by the satellite-borne detectors at MeV and GeV energies. High sensitivities of multi-IACT arrays would partially compensate the limited efficiency of the technique for all-sky surveys, as well as allow study of moderately extended (≤ 1°) γ-ray sources. IACT arrays with minimum detectable fluence of ≥ 100 GeV γ-rays Sγ < 10−8 erg/cm2 are well suited for effective exploration of highly sporadic nonthermal phenomena from different classes of astrophysical objects on time-scales from ≤ 1 s to several minutes.  相似文献   

12.
HESS J1616−508 is one of the brightest emitters in the TeV sky. Recent observations with the IBIS/ISGRI telescope onboard the INTEGRAL spacecraft have revealed that a young, nearby and energetic pulsar, PSR J1617−5055, is a powerful emitter of soft γ-rays in the 20–100 keV domain. In this paper, we present an analysis of all available data from the INTEGRAL , Swift , BeppoSAX and XMM–Newton telescopes with a view to assessing the most likely counterpart to the High Energy Stereoscopic System (HESS) source. We find that the energy source that fuels the X/γ-ray emissions is derived from the pulsar, both on the basis of the positional morphology, the timing evidence and the energetics of the system. Likewise the 1.2 per cent of the pulsar's spin-down energy loss needed to power the 0.1–10 TeV emission is also fully consistent with other HESS sources known to be associated with pulsars. The relative sizes of the X/γ-ray and very high energy sources are consistent with the expected lifetimes against synchrotron and Compton losses for a single source of parent electrons emitted from the pulsar. We find that no other known object in the vicinity could be reasonably considered as a plausible counterpart to the HESS source. We conclude that there is good evidence to assume that the HESS J1616−508 source is driven by PSR J1617−5055 in which a combination of synchrotron and inverse-Compton processes combine to create the observed morphology of a broad-band emitter from keV to TeV energies.  相似文献   

13.
The Fermi γ-ray space telescope reported the observation of several Galactic supernova remnants recently, with the γ-ray spectra well described by hadronic pp collisions. The possible neutrino emissions from these Fermi detected supernova remnants are discussed in this work, assuming the hadronic origin of the γ-ray emission. The muon event rates induced by the neutrinos from these supernova remnants on typical km3 neutrino telescopes, such as the IceCube and the KM3NeT, are calculated. The results show that for most of these supernova remnants the neutrino signals are too weak to be detected by the on-going or up-coming neutrino experiment. Only for the TeV bright sources RX J1713.7-3946 and possibly W28 the neutrino signals can be comparable with the atmospheric background in the TeV region, if the protons can be accelerated to very high energies. The northern hemisphere based neutrino telescope might detect the neutrinos from these two sources.  相似文献   

14.
《Astroparticle Physics》2010,32(6):431-436
We consider Vela Jr. as being the old Supernova Remnant (SNR) at the beginning of the transition from adiabatic to radiative stage of evolution. According to our model, Vela Jr. is situated outside Vela SNR at the distance of ∼600 pc and its age is 17500 yr. We model the high energy fluxes from Vela Jr. and its broadband spectrum. We find our results compatible with experimental data in radio waves, X- and γ-rays. Our hydrodynamical model of Vela Jr. explains the observed TeV γ-ray flux by hadronic mechanism. The proposed model does not contradict to the low density environment of the SNR and does not need extreme fraction of the explosion energy to be transferred to Cosmic Rays.  相似文献   

15.
We present preliminary results of a campaign undertaken with different radio interferometers to observe a sample of the most variable unidentified EGRET sources. We expect to detect which of the possible counterparts of the γ-ray sources (any of the radio emitters in the field) varies in time with similar timescales as the γ-ray variation. If the γ-rays are produced in a jet-like source, as we have modelled theoretically, synchrotron emission is also expected at radio wavelengths. Such radio emission should appear variable in time and correlated with the γ-ray variability.  相似文献   

16.
Neutrino energy spectra have been calculated based on the recently measured energy spectra of Galactic very high energy γ-ray sources. Based on these neutrino spectra the expected event rates in the ANTARES neutrino telescope and KM3NeT, a future neutrino telescope in the Mediterranean Sea with an instrumented volume of one km3, have been calculated. For the brightest γ-ray sources we find event rates of the order of one neutrino per year. Although the neutrino event rates are comparable to the background from atmospheric neutrinos the detection of individual sources seems possible.  相似文献   

17.
An array of seven atmospheric Cherenkov telescopes was commissioned at a high altitude site in Hanle in the Ladakh region of the Himalayas. The array called HAGAR has been designed to observe celestial γ-rays of energy >100 GeV. Each telescope is altitude-azimuth mounted and carries seven parabolic mirrors whose optic axes are co-aligned with the telescope axis. The telescopes point and track a celestial source using a PC-based drive control system. Two important issues in positioning of each HAGAR telescope are pointing accuracy of telescope axis and co-alignment of mirrors’ optic axes with the telescope axis. We have adopted a three pronged strategy to address these issues, namely use of pointing models to improve pointing accuracy of the telescopes, RA-DEC scan technique to measure the pointing offsets of the mirrors and mechanical fine-tuning of off-axis mirrors by sighting a distant stationary light source. This paper discusses our efforts in this regard as well as the current status of pointing and monitoring of HAGAR telescopes.  相似文献   

18.
The resonant inverse Compton scattering (RICS) of relativistic electrons in intense magnetic fields is an efficient mechanism for producing the highenergy γ-rays. In our previous work it is suggested that the early-stage γ-ray radiation of γ-ray bursts (GRBs) may be mainly produced by this mechanism. By using this mechanism, some puzzles in the study of GRBs can be clarified, e.g., the origin of the Amati relation obtained from the statistics of observations, the formation of the observed two-segment (broken) power-law spectra, the relevant “deadline problem”, the polarization property, etc. Herein our discussion will be focused on the formation of the broken power-law spectra. Based on the formula of the RICS spectral power of individual fast electrons, we have derived the simplified analytical formula of the collective RICS radiation spectrum (RICS spectral luminosity) produced by the assembly of relativistic electrons in an intense magnetic field when they pass through the ambient low-frequency radiation field, and applied it to several typical low-frequency radiation fields (e.g., the black-body radiation field, power-law radiation field and thermal bremsstrahlung field) around the central neutron star, for the convenience of comparison with the observed spectra. Our calculations indicate that the RICS radiation mechanism has a very high efficiency in the hard X-ray and γ-ray wavebands, if the matching condition (i.e., the condition approximate to resonance) is satisfied, and that independent of the ambient radiation field, the produced spectra are commonly the two-segment power-law spectra. Additionally, it is suggested that the RICS mechanism might be an ideal highly-efficient radiation mechanism for the high-energy emissions (hard X-rays and γ-rays) of the GRBs, soft γ-ray repeated bursts (SGRs) and γ-ray pulsars (GRPs).  相似文献   

19.
We present a calculation of a three-dimensional pulsar magnetosphere model to explain high-energy emission from the Geminga pulsar with a thick outer gap. High-energy γ -rays are produced by primary accelerated particles with a power-law energy distribution through curvature radiation inside the outer gap. We also calculate the emission pattern, pulse profile and phase-resolved spectra of high-energy γ -rays of the Geminga pulsar, and find that its pulse profile is consistent with the observed one if the magnetic inclination and viewing angle are ∼50° and ∼86° respectively. We describe the relative phases among soft (thermal) X-rays, hard (non-thermal) X-rays, and γ -rays. Our results indicate that X-ray and γ -ray emission from the Geminga pulsar may be explained by the single thick outer gap model. Finally, we discuss the implications of the radio and optical emission of the Geminga pulsar.  相似文献   

20.
We use a new self-consistent model to derive the conversion efficiency from rotation power to γ-ray power for pulsars (εth). Our result indicates that εth∝τ6/7 P 2, where τ and P are the characteristic age and period of the pulsar, which shows that although the efficiency increases with the characteristic age of the pulsar, it also depends on the pulsar period. We test our model results with the survey of high-energy γ-rays from pulsars by EGRET. Our model not only successfully explains the efficiency of the confirmed γ-ray pulsars but also explains why the γ-ray efficiency of millisecond pulsars is so low.  相似文献   

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