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1.
We discuss the implications of the recent X-ray and TeV γ-ray observations of the PSR B1259–63 system (a young rotation powered pulsar orbiting a Be star) for the theoretical models
of interaction of pulsar and stellar winds. We show that previously considered models have problems to account for the observed
behaviour of the system. We develop a model in which the broad band emission from the binary system is produced in result
of collisions of GeV–TeV energy protons accelerated by the pulsar wind and interacting with the stellar disk. In this model
the high energy γ-rays are produced in the decays of secondary neutral pions, while radio and X-ray emission are synchrotron and inverse Compton
emission produced by low-energy (≤100 MeV) electrons from the decays of secondary charged π
± mesons. This model can explain not only the observed energy spectra, but also the correlations between TeV, X-ray and radio
emission components.
相似文献
2.
Luigi Costamante 《Astrophysics and Space Science》2007,309(1-4):487-495
The study of the TeV emission from extragalactic sources is hindered by the uncertainties on the diffuse Extragalactic Background
Light (EBL). The recent H.E.S.S. results on the blazars 1ES 1101-232 and H 2356-309 represent a breakthrough on this issue.
Their unexpectedly hard spectra allow an upper limit to be derived on the EBL in the optical/near-infrared range, which is
very close to the lower limit given by the resolved galaxy counts. This result seems to exclude a large contribution to the
EBL from other sources (e.g. Population III stars) and indicates that the intergalactic space is more transparent to γ-rays than previously thought. A discussion of EBL absorption effects and further observational tests with Cherenkov telescopes
are presented.
For the H.E.S.S. collaboration. 相似文献
3.
There are indications now that globular clusters contain a large number of low magnetic field millisecond pulsars. Since millisecond
pulsars are expected to emit γ-rays due to curvature radiation, it is likely that globular clusters will themselves be sources
of γ-rays bright enough to be detectable by present day instruments. Using the expression derived by Scharlemann, Arons &
Fawley (1978) of the energy acquired by the electrons moving along the open magnetic field lines of the pulsars we have calculated
the likely luminosity of γ-rays from globular clusters. We discuss our results in the light of the calculations reported in
the literature based on some of the other models. 相似文献
4.
P. R. Vishwanath 《Journal of Astrophysics and Astronomy》1987,8(1):69-78
The Ooty data on VHE (> 600 GeV) γ-rays from the Crab pulsar have been used to look at possible emission on three different
timescales,viz. years, minutes and hours. When averaged over three years of observation, there is no significant time-averaged emission.
But interesting aspects are revealed when the data are subdivided into miniruns of one-minute duration. Minutes with moderate
γ-ray activity were isolated with a κ2 analysis. The summed phasogram of such minutes shows two strong peaks coinciding with the radio main pulse and the interpulse
respectively. The probability that these are due to chance is small. The phasogram has a bimodal distribution which indicates
some emission from the middle region between the two phases. In general, there is no significant emission on the timescale
of a few hours. However, the main pulse, as well as the bimodal distribution, were seen also in the total data of two nights
of simultaneous observation at two sites during 1984–1985. 相似文献
5.
M. Lemoine-Goumard F. Aharonian D. Berge B. Degrange D. Hauser N. Komin O. Reimer U. Schwanke 《Astrophysics and Space Science》2007,309(1-4):379-384
In 2004 and 2005, the shell-type supernova remnants RX J1713.7–3946 and RX J0852.0–4622 were observed and detected with the
complete H.E.S.S. array, a system of four Imaging Cherenkov Telescopes located in Namibia and dedicated to the observations
of γ-rays above 100 GeV. The energy spectra of these two sources have been measured over a wide energy range and revealed an integral
flux above 1 TeV similar to that of the Crab Nebula. Their morphologies were resolved with high accuracy with H.E.S.S. and
exhibit a striking correlation with the X-ray images, thereby pioneering a technique of unambiguously identifying spatially
extended γ-ray sources. The results of the observations will be presented. Similarities and differences between these two sources will
be pointed out as well as possible implications.
M. Lemoine-Goumard, F. Aharonian, D. Berge, B. Degrange, D. Hauser, N. Komin, O. Reimer, U. Schwanke for the H.E.S.S. Collaboration 相似文献
6.
Josep M. Paredes J. Martí D. F. Torres G. E. Romero J. A. Combi V. Bosch-Ramon J. García-Sáanchez 《Astrophysics and Space Science》2005,297(1-4):223-233
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
7.
Ryo Yamazaki Kazunori Kohri Aya Bamba Tatsuo Yoshida Toru Tsuribe Fumio Takahara 《Monthly notices of the Royal Astronomical Society》2006,371(4):1975-1982
We study the emission from an old supernova remnant (SNR) with an age of around 105 yr and that from a giant molecular cloud (GMC) encountered by the SNR. When the SNR age is around 105 yr, proton acceleration is efficient enough to emit TeV γ-rays both at the shock of the SNR and that in the GMC. The maximum energy of primarily accelerated electrons is so small that TeV γ-rays and X-rays are dominated by hadronic processes, π0 -decay and synchrotron radiation from secondary electrons, respectively. However, if the SNR is older than several 105 yr, there are few high-energy particles emitting TeV γ-rays because of the energy-loss effect and/or the wave-damping effect occurring at low-velocity isothermal shocks. For old SNRs or SNR–GMC interacting systems capable of generating TeV γ-ray emitting particles, we calculated the ratio of TeV γ-ray (1–10 TeV) to X-ray (2–10 keV) energy flux and found that it can be more than ∼102 . Such a source showing large flux ratio may be a possible origin of recently discovered unidentified TeV sources. 相似文献
8.
Dmitry Khangulyan Slavomir Hnatic Felix Aharonian 《Astrophysics and Space Science》2007,309(1-4):261-265
The inverse Compton (IC) scattering of ultrarelativistic electrons accelerated at the pulsar wind termination shock is generally
believed to be responsible for TeV gamma-ray signal recently reported from the binary system PSR B1259-63/SS2883. In such
a system the acceleration takes place in the presence of a dense radiation field provided by a companion Be2-type star. Thus
it is natural to expect an orbital phase dependence of the acceleration efficiency in the system. The HESS collaboration reported
the tendency of reduction of TeV γ-rays around the periastron. In this paper we study a possible explanation of this effect by the “early” (sub-TeV) cutoffs
in the energy spectrum of accelerated electrons due to the enhanced rate of Compton losses close to the periastron. 相似文献
9.
P. R. Vishwanath 《Journal of Astrophysics and Astronomy》2002,23(1-2):45-51
The field of Very High Energy (VHE) gamma ray astronomy using the Atmospheric Cerenkov Technique has entered an interesting
phase with detection of various galactic and extragalactic sources. Among galactic sources, only the Crab nebula has been
established as a standard candle. Most observations on pulsars are in agreement as to the necessity for the GeV spectra to
steepen at < 200 GeV. While the Imaging method for increase of sensitivity has been successful with many results, an alternate
technique —Wavefront Sampling Technique- is also being used by an increasing number of experiments. The recently commissioned experiment at Pachmarhi (PACT) in India
is presented as an example of this technique. Preliminary results from this experiment show detection of VHE γ-ray emission
from (a) the Crab nebula at a high significance and (b) Crab and Geminga pulsars at > 1.5 TeV which could be the second component of the Outer Gap pulsar models. 相似文献
10.
Nonlinear kinetic theory of cosmic ray (CR) acceleration in supernova remnants (SNRs) is used to investigate the properties
of Kepler’s SNR and, in particular, to predict the γ-eay spectrum expected from this SNR. Observations of the nonthermal radio and X-ray emission spectra as well as theoretical
constraints for the total supernova (SN) explosion energy E
sn are used to constrain the astronomical and particle acceleration parameters of the system. Under the assumption that Kepler’s
SN is a type Ia SN we determine for any given explosion energy E
sn and source distance d the mass density of the ambient interstellar medium (ISM) from a fit to the observed SNR size and expansion speed. This makes
it possible to make predictions for the expected γ-eay flux. Exploring the expected distance range we find that for a typical explosion energy E
sn=1051 erg the expected energy flux of TeV γ-rays varies from 2×10−11 to 10−13 erg/(cm2 s) when the distance changes from d=3.4 kpc to 7 kpc. In all cases the γ-eay emission is dominated by π
0-decay γ-rays due to nuclear CRs. Therefore Kepler’s SNR represents a very promising target for instruments like H.E.S.S., CANGAROO
and GLAST. A non-detection of γ-rays would mean that the actual source distance is larger than 7 kpc. 相似文献
11.
L. G. Kocharov G. A. Kovaltsov G. E. Kocharov E. I. Chuikin I. G. Usoskin M. A. Shea D. F. Smart V. F. Melnikov T. S. Podstrigach T. P. Armstrong H. Zirin 《Solar physics》1994,150(1-2):267-283
Data on X-,γ-ray, optical and radio emission from the 1991 June 15 solar flare are considered. We have calculated the spectrum of protons
that producesγ-rays during the gradual phase of the flare. The primary proton spectrum can be described as a Bessel-function-type up to
0.8 GeV and a power law with the spectral index ≈3 from 0.8 up to 10 GeV or above. We have also analyzed data on energetic
particles near the Earth. Their spectrum differed from that of primary protons producingγ-ray line emission. In the gradual phase of the flare additional pulses of energy release occurred and the time profiles of
cm-radio emission andγ-rays in the 0.8–10 MeV energy band and above 50 MeV coincided. A continuous and simultaneous stochastic acceleration of the
protons and relativistic electrons at the gradual phase of the flare is considered as a natural explanation of the data. 相似文献
12.
B.B. Singh V.R. Chitnis D. Bose M.A. Rahman S.S. Upadhya K.S. Gothe B.K. Nagesh P.N. Purohit Shobha K. Rao Kamesh K. Rao S.K. Sharma P.V. Sudersan B.L. Venkateshmurthy P.R. Vishwanath B.S. Acharya 《Astroparticle Physics》2009,32(2):120-128
We present the results of observation of the Geminga pulsar carried out in the TeV energy band during the 6 year period spanning 2000–2006 using the Pachmarhi Array of Cherenkov Telescopes (PACT). A long stretch of data, new computer codes and the “Tempo” package have been used in the present analysis. We have searched for evidence of pulsed emission of γ-rays from the Geminga pulsar using the post-glitch pulsar elements obtained by Jackson and Halpern from X-ray/γ-ray satellite data. We do not see any significant evidence for pulsed emission from the Geminga pulsar at a threshold energy of 825 GeV. In this paper we present our results on the light curve in the TeV energy band, set an upper limit on the time averaged flux of γ-rays, and compare our results with other ground based observations. 相似文献
13.
Results are reported from a study of the variability of the x-ray and very high energy (VHE) γ -ray emission from Mrk 421 during a 10-day period of enchanced source activity at the end of 2005. The TeV data were taken
from observations with the Whipple 10-m Cerenkov telescope and the soft x-ray data, from the ASM on board the RXTE orbital
observatory. Light curves for this source indicated an obvious variability in the form of flares in both energy ranges. During
the flares, the flux of VHE γ -rays exceeded that from the Crab nebula and correlated positively with the observed x-ray emission. The flux of VHE γ - rays varied almost linearly with the soft x-ray flux. The statistical characteristics of the variability were independent
of energy and the two emission components were detected quasi-simultaneously. The observed temporal properties of the source
can be interpreted in terms of the rapid acceleration of leptons in a jet using a synchrotron self-Compton model. Our studies
confirm a flare activity intrinsic to this source on the scale of a day found in earlier studies. 相似文献
14.
P. L. Gonthier R. Van Guilder A. K. Harding I. A. Grenier C. A. Perrot 《Astrophysics and Space Science》2005,297(1-4):71-80
We present results of a population synthesis study of radio-loud and radio-quiet γ-ray pulsars from the Galactic plane and
the Gould Belt. The simulation includes the Parkes multibeam pulsar survey, realistic beam geometries for radio and γ-ray
emission from neutron stars and the new electron density model of Cordes and Lazio. Normalizing to the number of radio pulsars
observed by a set of nine radio surveys, the simulation suggests a neutron star birth rate of 1.4 neutron stars per century
in the Galactic plane. In addition, the simulation predicts 19 radio-loud and 7 radio-quiet γ-ray pulsars from the plane that
EGRET should have observed as point sources. Assuming that during the last 5 Myr the Gould Belt produced 100 neutron stars,
only 10 of these would be observed as radio pulsars with three radio-loud and four radio-quiet γ-ray pulsars observed by EGRET.
These results are in general agreement with the recent number of about 25 EGRET error boxes that contain Parkes radio pulsars.
Since the Gould Belt pulsars are relatively close by, the selection of EGRET radio-quiet γ-ray pulsars strongly favors large
impact angles, β, in the viewing geometry where the off-beam emission from curvature radiation provides the γ-ray flux. Therefore,
the simulated EGRET radio-quiet γ-ray pulsars, being young and nearby, most closely reflect the current shape of the Gould
Belt suggesting that such sources may significantly contribute to the EGRET unidentified γ-ray sources correlated with the
Gould Belt. 相似文献
15.
We have attempted to devise a scheme by which it may be possible to identify pulsars which are likely to be γ-ray pulsars.
We apply this test to a representative population of pulsars and identify the likely candidates for γ emission. We also discuss
some individual cases including the Crab and Vela pulsars. 相似文献
16.
Pierre Kaufmann Gérard Trottet C. Guillermo Giménez de Castro Jean-Pierre Raulin Säm Krucker Albert Y. Shih Hugo Levato 《Solar physics》2009,255(1):131-142
The presence of a solar burst spectral component with flux density increasing with frequency in the sub-terahertz range, spectrally
separated from the well-known microwave spectral component, bring new possibilities to explore the flaring physical processes,
both observational and theoretical. The solar event of 6 December 2006, starting at about 18:30 UT, exhibited a particularly
well-defined double spectral structure, with the sub-THz spectral component detected at 212 and 405 GHz by the Solar Submilimeter
Telescope (SST) and microwaves (1 – 18 GHz) observed by the Owens Valley Solar Array (OVSA). Emissions obtained by instruments
onboard satellites are discussed with emphasis to ultra-violet (UV) obtained by the Transition Region And Coronal Explorer
(TRACE), soft X-rays from the Geostationary Operational Environmental Satellites (GOES) and X- and γ-rays from the Ramaty High Energy Solar Spectroscopic Imager (RHESSI). The sub-THz impulsive component had its closer temporal
counterparts only in the higher energy X- and γ-rays ranges. The spatial positions of the centers of emission at 212 GHz for the first flux enhancement were clearly displaced
by more than one arc-minute from positions at the following phases. The observed sub-THz fluxes and burst source plasma parameters
were difficult to be reconciled with a purely thermal emission component. We discuss possible mechanisms to explain the double
spectral components at microwaves and in the THz ranges. 相似文献
17.
A magnetic field model is constructed for the extremely slow rotator γEqu based on measurements of its magnetic field over
many years and using the “magnetic charge” method. An analysis of γEqu and of all the data accumulated up to the present on
the magnetic field parameters of chemically peculiar stars leads to some interesting conclusions, of which the main ones are:
the fact that the axis of rotation and the dipole axis are not parallel in γEqu and the other slowly rotating magnetic stars
which we have studied previously is one of the signs that the braking of CP stars does not involve the participation of the
magnetic field as they evolve “to the main sequence.” The axes of the magnetic field dipole in slow rotators are oriented
arbitrarily with respect to their axes of rotation. The substantial photometric activity of these CP stars also argues against
these axes being close. The well-known absence of sufficiently strong magnetic fields in the Ae/Be Herbig stars also presents
difficulties for the hypothesis of “magnetic braking” in the “pre-main sequence” stages of evolution. The inverse relation
between the average surface magnetic field Bs and the rotation period P is yet another fact in conflict with the idea that
the magnetic field is involved in the braking of CP stars. We believe that angular momentum loss involving the magnetic field
can hardly have taken place during evolution immediately prior “to the main sequence,” rather the slow rotation of CP stars
most likely originates from protostellar clouds with low angular momentum. Some of the slowly rotating stars have a central
dipole magnetic field configuration, while others have a displaced dipole configuration, where the displacement can be toward
the positive or the negative magnetic pole.
__________
Translated from Astrofizika, Vol. 49, No. 2, pp. 251–262 (May 2006). 相似文献
18.
Alice K. Harding Isabelle A. Grenier Peter L. Gonthier 《Astrophysics and Space Science》2007,309(1-4):221-230
Radio-quiet γ-ray pulsars like Geminga may account for a number of the unidentified EGRET sources in the Galaxy. The number of Geminga-like
pulsars is very sensitive to the geometry of both the γ-ray and radio beams. Recent studies of the shape and polarization of pulse profiles of young radio pulsars have provided
evidence that their radio emission originates in wide cone beams at altitudes that are a significant fraction (1–10%) of their
light cylinder radius. Such wide radio emission beams will be visible at a much larger range of observer angles than the narrow
core components thought to originate at lower altitude. Using 3D geometrical modeling that includes relativistic effects from
pulsar rotation, we study the visibility of such radio cone beams as well as that of the γ-ray beams predicted by slot gap and outer gap models. From the results of this study, one can obtain revised predictions
for the fraction of Geminga-like, radio quiet pulsars present in the γ-ray pulsar population.
相似文献
19.
In the atmospheric Čerenkov technique γ-rays are detected against the abundant background produced by hadronic showers. In
order to improve the signal to noise ratio of theexperiment, it is necessary to reject a significant fraction of hadronic
showers. Traditional background rejection methods based on image shape parameters have been extensively used for the data
from imaging telescopes. However, non-imaging Čerenkov telescopes have to develop very different means of statistically identifying
and removing cosmic ray events. Some of the parameters, which could be potentially important for non-imaging arrays, are the
temporal and spectral differences, the lateral distributions and density fluctuations of Čerenkov photons generated by γ-ray
and hadron primaries. Here we study the differences in fluctuations of Čerenkov photon density in the light pool at the observation
level from showers initiated by photons and those initiated by protons or heavier nuclei. The database of simulated events
for the PACT array has been used to evaluate the efficiency of the new technique. Various types of density fluctuations like
the short range and medium range fluctuations as well as flatness parameter are studied. The estimated quality factors reflect
the efficiencies with which the hadrons can be rejected from the data. Since some of these parameters are independent, the
cuts may be applied in tandem and we demonstrate that the proton rejection efficiency of ∼90% can be achieved. Use of density
fluctuations is particularly suited for wavefront sampling observations and it seems to be a good technique to improve the
signal to noise ratio.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
20.
K. Mannheim 《Astrophysics and Space Science》1998,264(1-4):471-479
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