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1.
R. N. Manchester 《Astrophysics and Space Science》2005,297(1-4):101-108
A total of eight gamma-ray sources are identified with pulsars and these include some of the strongest gamma-ray sources in
the sky. About 20 of the unidentified gamma-ray sources are very likely to be associated with currently known pulsars and
there is little doubt that many of the others, at least those at low Galactic latitudes, will ultimately be identified with
pulsars. How many of these and future gamma-ray detections will be detectable at radio wavelengths depends on the details
of the radio and gamma-ray beaming. There is good evidence that the radio beams in young and millisecond pulsars are very
wide, implying that most gamma-ray pulsars will be detectable in the radio band. 相似文献
2.
The Seyfert galaxy NGC 1275 is the central, dominant galaxy in the Perseus cluster of galaxies. NGC1275 is known as a powerful source of radio and X-ray emission. The well-known extragalactic object NGC 1275 has been observed by the SHALON high-altitude mirror Cherenkov telescopes within the framework of long-term studies of metagalactic gamma-ray sources. In 1996, the SHALON observations revealed a new metagalactic source of very high energy gamma-ray emission coincident in its coordinates with the galaxy NGC 1275. Having analyzed the SHALON data, we have determined such characteristics of NGC 1275 as the spectral energy distributions and images at energies >800 GeV for the first time. The results obtained at high and very high energies are needed for understanding the emission generation processes in an entire wide energy range. 相似文献
3.
We present a comprehensive study of the gamma-ray luminosity function (GLF) of blazars and their contribution to the extragalactic
diffuse gamma-ray background (EGRB). Radio and gamma-ray luminosity correlation is introduced with a modest dispersion, consistent
with observations, to take into account the radio detectability, which is important for blazar identification. Previous studies
considered only pure luminosity evolution (PLE) or pure density evolution, but here we introduce the luminosity-dependent
density evolution (LDDE) model, which is favored on the basis of the evolution of the X-ray luminosity function (XLF) of AGNs.
The model parameters are constrained by likelihood analyses of the observed redshift and gamma-ray flux distributions of the
EGRET blazars. Interestingly, we find that the LDDE model gives a better fit to the observed distributions than the PLE model,
indicating that the LDDE model is also appropriate for gamma-ray blazars and that the jet activity is universally correlated
with the accretion history of AGNs. We then find that only 25–50% of the EGRB can be explained by unresolved blazars with
the best-fit LDDE parameters. Unresolved blazars can account for all the EGRB only with a steeper index of the faint-end slope
of the GLF, which is marginally consistent with the EGRET data but inconsistent with XLF data. Therefore, unresolved AGNs
cannot be the dominant source of the EGRB, unless there is a new population of gamma-ray emitting AGNs that evolves differently
from the XLF of AGNs. Predictions for the GLAST mission are made, and we find that the best-fit LDDE model predicts about 3000 blazars in the entire sky, which is considerably
fewer (by a factor of more than 3) than a previous estimate. 相似文献
4.
Cyg X-3 is actively studied in the entire range of the electromagnetic spectrum from the radio band to ultrahigh energies. Based on the detection of ultrahigh-energy gamma-ray emission, it has been suggested that Cyg X-3 could be one of the most powerful sources of charged cosmic-ray particles in the Galaxy. We present the results of long-term observations of the Cygnus Х-3 region at energies 800 GeV–100 TeV by the SHALON mirror Cherenkov telescope. In 1995 the SHALON observations revealed a new Galactic source of very high energy gamma-ray emission coincident in its coordinates with the microquasar Cyg X-3. To reliably identify the detected source with Cyg X-3, an analysis has been performed and an orbital period of 4.8 h has been found, which is a signature of Cyg X-3. A series of flares in Cyg X-3 at energies >800 GeV and their correlation with the activity in the X-ray and radio bands have been observed. The results obtained in a wide energy range for Cyg X-3, including those during the periods of relativistic jet events, are needed to find the connection and to understand the different components of an accreting binary system. 相似文献
5.
Pulsars play a crucial astrophy sical role as highly energetic compact radio, X-ray and gammaray sources. Our previous works show that radio pulsars identified as pulsing gamma-ray sources by the Large Area Telescope(LAT) on board the Fermi Gamma-Ray Space Telescope have high values of magnetic field near the light cylinder, two-three orders of magnitude stronger compared with the magnetic fields of radio pulsars: log B_(lc)(G) are 3.60-3.95 and 1.75 correspondingly. Moreover,their losses of rotational energy are also three orders higher than the corresponding values for the main group of radio pulsars on average: log E(erg s~(-1)) = 35.37-35.53 and 32.64. The correlation between gammaray luminosities and radio luminosities is found. It allows us to select those objects from all sets of known radio pulsars that can be detected as gamma-ray pulsars with high probability. We provide a list of such radio pulsars and propose to search for gamma emission from these objects. On the other hand,the known catalog of gamma-ray pulsars contains some sources which are not currently identified as radio pulsars. Some of them have large values of gamma-ray luminosities and according to the obtained correlation, we can expect marked radio emission from these objects. We give the list of such pulsars and expected flux densities to search for radiation at frequencies 1400 and 111 MHz. 相似文献
6.
David L. Jauncey Lucyna Kedziora-Chudczer James E.J. Lovell Jean-Pierre Macquart George D. Nicolson Rick A. Perley John E. Reynolds Anastasios K. Tzioumis Mark H. Wieringa Hayley E. Bignall 《Astrophysics and Space Science》2001,278(1-2):87-92
Intra-day variability (IDV) of active galactic nuclei (AGN) has been detected from gamma-ray energies to radio wavelengths.
At high energies, such variability appears to be intrinsic to the sources themselves. However, at radio wavelengths, brightness
temperatures as high as1018 to 1021 K are encountered if the IDV is intrinsic to the source. We discuss here the accumulating evidence showing that, at radio
wavelengths where the highest brightness temperatures are encountered, interstellar scintillation (ISS) is the principal mechanism
causing IDV. While ISS reduces the implied brightness temperatures, they still remain uncomfortably high.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
O. Reimer † K.T.S. Brazier A. Carramiñana G. Kanbach P.L. Nolan D.J. Thompson 《Monthly notices of the Royal Astronomical Society》2001,324(3):772-780
The EGRET telescope aboard the NASA Compton Gamma-Ray Observatory ( CGRO ) has repeatedly detected 3EG J1835+5918, a bright and steady source of high-energy gamma-ray emission which has not yet been identified. The absence of any likely counterpart for a bright gamma-ray source located 25° off the Galactic plane initiated several attempts of deep observations at other wavelengths. We report on counterparts in X-rays on a basis of a 60-ks ROSAT HRI image. In order to conclude on the plausibility of the X-ray counterparts, we reanalysed data from EGRET at energies above 100 MeV and above 1 GeV, including data up to CGRO observation cycle 7. The gamma-ray source location represents the latest and probably the final positional assessment based on EGRET data. We especially address the question of flux and spectral variability, here discussed using the largest and most homogeneous data set available at high-energy gamma-rays for many years. The results from X-ray and gamma-ray observations were used in a follow-up optical identification campaign at the 2.2-m Guillermo Haro Telescope at Cananea, Mexico. VRI imaging has been performed at the positions of all of the X-ray counterpart candidates, and spectra were taken where applicable. The results of the multifrequency identification campaign toward this enigmatic unidentified gamma-ray source are given, especially on the one object which might be associated with the gamma-ray source 3EG J1835+5918. This object has the characteristics of an isolated neutron star and possibly of a radio-quiet pulsar. 相似文献
8.
R. P. Fender K. Southwell & A. K. Tzioumis 《Monthly notices of the Royal Astronomical Society》1998,298(3):692-696
We present a radio survey of X-ray sources in the Large and Small Magellanic Clouds with the Australia Telescope Compact Array at 6.3 and 3.5 cm. Specifically, we have observed the fields of five LMC and two SMC supersoft X-ray sources, the X-ray binaries LMC X-1, X-2, X-3 and X-4, the X-ray transient Nova SMC 1992, and the soft gamma-ray repeater SGR 0525-66. None of the targets are detected as point sources at their catalogued positions. In particular, the proposed supersoft jet source RXJ 0513-69 is not detected, placing constraints on its radio luminosity compared to Galactic jet sources. Limits on emission from the black hole candidate systems LMC X-1 and X-3 are consistent with the radio behaviour of persistent Galactic black hole X-ray binaries, and a previous possible radio detection of LMC X-1 is found to be almost certainly a result of nearby field sources. The SNR N49 in the field of SGR 0525-66 is mapped at higher resolution than it has been previously, but there is still no evidence for any enhanced emission or disruption of the SNR at the location of the X-ray source. 相似文献
9.
从Fermi 3期源表(3FGL)中选择了一个含935个耀变体(blazar)的样本, 包括415个平谱射电源(Flat Spectrum Radio Quasar, FSRQ), 520个蝎虎天体(BL Lac object, BL Lac), 其中高同步峰BL Lac (HBL) 233个, 中同步峰BL Lac (IBL) 144个, 低同步峰BL Lac (LBL) 143个. 研究了总样本、FSRQ、BL Lac及其子类HBL、LBL的射电1.4GHz 与gamma射线在0.1、0.3、1、3、10GeV处辐射流量密度的关系. 结果显示: 所有样本的射电1.4GHz与5个波段gamma射线的辐射流量都有强相关, 相关系数在0.48--0.81之间, 机会概率均小于$10^{-4; 对于不同的样本相关系数随着gamma射线辐射频率的变化有不同的变化趋势, 所有样本在5个波段的相关系数平均值随gamma射线频率的增加而减小. 该结果暗示, 随着频率的升高, blazar的gamma射线辐射主导机制在发生变化, 在相同频率处, 不同类型天体的辐射主导机制存在差异; HBL的gamma射线辐射主要由同步自康普顿主导, 而LBL的其他成份比HBL的更复杂; FSRQ的gamma射线起源较BL Lac的复杂. 相似文献
10.
We collect a sample of 51 Fermi-detected gamma-ray loud blazars with known radio Doppler factors and study properties of the Doppler factors of blazars at optical,X-ray and gamma-ray bands.A basic assumption is that the emission from the radio to gamma-ray bands of the blazars are produced by the nonthermal radiation of accelerated particles in a jet.Our results show that (1) the Doppler factors of blazars are a function of frequency,with the Doppler factor decreasing with frequency from the radio to X-ray ... 相似文献
11.
We discuss a possible generation of radio bursts preceding final stages of binary neutron star mergings which can be accompanied
by short gamma-ray bursts. Detection of such bursts appear to be advantageous in the low-frequency radio band due to a time
delay of ten to several hundred seconds required for radio signal to propagate in the ionized intergalactic medium. This delay
makes it possible to use short gamma-ray burst alerts to promptly monitor specific regions on the sky by low-frequency radio
facilities, especially by LOFAR. To estimate the strength of the radio signal, we assume a power-law dependence of the radio
luminosity on the total energy release in a magnetically dominated outflow, as found in millisecond pulsars. Based on the
planned LOFAR sensitivity at 120 MHz, we estimate that the LOFAR detection rate of such radio transients could be about several
events per month from redshifts up to z∼1.3 in the most optimistic scenario. The LOFAR ability to detect such events would crucially depend on exact efficiency of
low-frequency radio emission mechanism. 相似文献
12.
The INTEGRAL – HESS/MAGIC connection: A new class of cosmic high energy accelerators from keV to TeV
P. Ubertini 《Experimental Astronomy》2005,20(1-3):75-83
The recent completion and operation of the High Energy Stereoscopic System [1], an array of ground based imaging Cherenkov telescopes, has provided a survey with unprecedented sensitivity of the inner part of the Galaxy and revealed a new population of very high energy gamma-rays sources emitting at E > 100 GeV. Most of them were reported to have no known radio or X-ray counterpart and hypothesised to be representative of a new class of dark nucleonic cosmic sources. In fact, very high energy gamma-rays with energies E > 1011 eV are the best proof of non-thermal processes in the universe and provide a direct in-site view of matter-radiation interaction at energies by far greater than producible in ground accelerators. At lower energy INTEGRAL has regularly observed the entire galactic plane during the first 1000 day in orbit providing a survey in the 20–100 keV range resulted in a soft gamma-ray sky populated with more than 200 sources, most of them being galactic binaries, either Black Hole Candidates (BHC) or Neutron Stars (NS) [5]. Very recently, the INTEGRAL new source IGR J18135-1751 has been identified as the soft gamma-ray counterpart of HESS J1813-178 [18] and AXJ1838.0-0655 as the X/gamma-ray counterpart of HESS J1837-069 [14].Detection of non-thermal radio, X and gamma-ray emission from these TeV sources is very important to discriminate between various emitting scenarios and, in turn, to fully understand their nature.The implications of these new findings in the high energy Galactic population will be addressed.On behalf of the IBIS Survey Team 相似文献
13.
14.
In a novel approach in observational high-energy gamma-ray astronomy, observations carried out by imaging atmospheric Cherenkov
telescopes provide necessary templates to pinpoint the nature of intriguing, yet unidentified EGRET gamma-ray sources. Using
GeV-photons detected by EGRET and taking advantage of high spatial resolution images from H.E.S.S. observations, we were able
to shed new light on the EGRET observed gamma-ray emission in the Kookaburra complex, whose previous coverage in the literature
is somewhat contradictory. 3EG J1420–6038 very likely accounts for two GeV gamma-ray sources (E>1 GeV), both in positional coincidence with the recently reported pulsar wind nebulae (PWN) by HESS in the Kookaburra/Rabbit
complex. PWN associations at VHE energies, supported by accumulating evidence from observations in the radio and X-ray band,
are indicative for the PSR/plerionic origin of spatially coincident, but still unidentified Galactic gamma-ray sources from
EGRET. This not only supports the already suggested connection between variable, but unidentified low-latitude gamma-ray sources
with pulsar wind nebulae (3EG J1420–6038 has been suggested as PWN candidate previously), it also documents the ability of
resolving apparently confused EGRET sources by connecting the GeV emission as measured from a large-aperture space-based gamma-ray
instrument with narrow field-of-view but superior spatial resolution observations by ground-based atmospheric Cherenkov telescopes,
a very promising identification technique for achieving convincing individual source identifications in the era of GLAST-LAT.
相似文献
15.
M. Chiaberge † A. Capetti † A. Celotti † 《Monthly notices of the Royal Astronomical Society》2001,324(4):L33-L37
We have observed emission from the nucleus of the closest radio galaxy, Centaurus A, from the radio to the gamma-ray band. We construct, for the first time, its overall spectral energy distribution (SED) which appears to be intriguingly similar to those of blazars, showing two broad peaks located in the far-infrared band and at ∼0.1 MeV respectively. The whole nuclear emission of Centaurus A is successfully reproduced with a synchrotron self-Compton model. The estimated physical parameters of the emitting source are similar to those of BL Lacs, except for a much smaller beaming factor, as qualitatively expected when a relativistic jet is orientated at a large angle to the line of sight. These results represent strong evidence that Centaurus A is indeed a misoriented BL Lac, and provide strong support in favour of the unification scheme for low-luminosity radio-loud active galactic nuclei. Modelling of the SED of Centaurus A also provides further and independent indications of the presence of velocity structures in sub-parsec-scale jets. 相似文献
16.
《天文和天体物理学研究(英文版)》2016,(11)
Transcontinental e-VLBI observations were conducted in June 2008 with telescopes in Australia,China and Japan. Detections were made of the radio-loud quasar PKS B0727-115, which shows superluminal motion, and the intra-day variable quasar PKS B0524+034. The latter source was used as a phase reference calibrator for observations at the position of the gamma-ray burst GRB 080409, for which an upper limit to the radio emission is set. Australia Telescope Compact Array data were also used to derive a limit on the radio flux density of the GRB afterglow. These observations demonstrate the capability to form a large Australasian radio telescope network for e-VLBI, with data transported and processed in realtime over high capacity networks. This campaign represents the first step towards more regular e-VLBI observations in this region. 相似文献
17.
Using the generic hydrodynamic model of gamma-ray burst(GRB) afterglows, we calculate the radio afterglow light curves of low luminosity, high luminosity,failed and standard GRBs in different observational bands of FAST’s energy window.The GRBs are assumed to be located at different distances from us. Our results rank the detectability of GRBs in descending order as high luminosity, standard, failed and low luminosity GRBs. We predict that almost all types of radio afterglows except those of low luminosity GRBs could be observed by a large radio telescope as long as the domains of time and frequency are appropriate. It is important to note that FAST can detect relatively weak radio afterglows at a higher frequency of 2.5 GHz for very high redshift up to z = 15 or even more. Radio afterglows of low luminosity GRBs can only be detected after the completion of the second phase of FAST. FAST is expected to significantly expand the sample of GRB radio afterglows in the near future. 相似文献
18.
Lupin Chun-Che Lin Hsiang-Kuang Chang 《Monthly notices of the Royal Astronomical Society》2008,387(2):729-734
A periodicity search of gamma-ray data is usually difficult because of the small number of detected photons. A periodicity in the timing signal at other energy bands from the counterpart to the gamma-ray source may help to establish the periodicity in the gamma-ray emission and strengthen the identification of the source in different energy bands. However, it may still be difficult to find the period directly from X-ray data because of limited exposure. We have developed a procedure, by cross-checking two X-ray data sets, to find candidate periods for X-ray sources that are possible counterparts to gamma-ray pulsar candidates. Here, we report on the results of this method obtained with all the currently available X-ray data of eight X-ray sources. Some attractive periodicity features were found. These candidate periods can serve as the target periods for a future search when new data become available, so that a blind search with a huge number of trials can be avoided. 相似文献
19.
Having analyzed high-resolution observations of extragalactic compact radio sources with modern systems of radio telescopes, we obtained an estimate of the upper limit for the photon electric charge, eγ ? 3×10?33 of the elementary charge (assuming the photon charge to be energy independent). This is three orders of magnitude better than the limit obtained from radio pulsar timing. We also set a limit on the charge of a gamma-ray (energy ～0.1 MeV) photon. In the future, the estimate based on extragalactic sources can be improved significantly. 相似文献
20.
We calculate the reverse shock (RS) synchrotron emission in the optical and the radio wavelength bands from electron–positron pair-enriched gamma-ray burst ejecta with the goal of determining the pair content of gamma-ray bursts (GRBs) using early-time observations. We take into account an extensive number of physical effects that influence radiation from the RS-heated GRB ejecta. We find that optical/infrared flux depends very weakly on the number of pairs in the ejecta, and there is no unique signature of ejecta pair enrichment if observations are confined to a single wavelength band. It may be possible to determine if the number of pairs per proton in the ejecta is ≳100 by using observations in optical and radio bands; the ratio of flux in the optical and radio at the peak of each respective RS light curve is dependent on the number of pairs per proton. We also find that over a large parameter space, RS emission is expected to be very weak; GRB 990123 seems to have been an exceptional burst in that only a very small fraction of the parameter space produces optical flashes this bright. Also, it is often the case that the optical flux from the forward shock is brighter than the RS flux at deceleration. This could be another possible reason for the paucity of prompt optical flashes with a rapidly declining light curve at early times as was seen in GRBs 990123 and 021211. Some of these results are a generalization of similar results reported in Nakar & Piran. 相似文献