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1.
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
2.
Vasiliki Pavlidou Jennifer M. Siegal-Gaskins Carolyn Brown Brian D. Fields Angela V. Olinto 《Astrophysics and Space Science》2007,309(1-4):81-87
The large majority of EGRET point sources remain to this day without an identified low-energy counterpart. Whatever the nature of the EGRET unidentified sources, faint unresolved objects of the same class must have a contribution to the diffuse gamma-ray background: if most unidentified objects are extragalactic, faint unresolved sources of the same class contribute to the background, as a distinct extragalactic population; on the other hand, if most unidentified sources are Galactic, their counterparts in external galaxies will contribute to the unresolved emission from these systems. Understanding this component of the gamma-ray background, along with other guaranteed contributions from known sources, is essential in any attempt to use gamma-ray observations to constrain exotic high-energy physics. Here, we follow an empirical approach to estimate whether a potential contribution of unidentified sources to the extragalactic gamma-ray background is likely to be important, and we find that it is. Additionally, we comment on how the anticipated GLAST measurement of the diffuse gamma-ray background will change, depending on the nature of the majority of these sources. 相似文献
3.
The discovery of the microquasar LS 5039 well within the 95% confidence contour of the Unidentified EGRET Source (UES) 3EG
J1824−1514 was a major step towards the possible association between microquasars (MQs) and UESs. The recent discovery of
precessing relativistic radio jets in LS I +61 303, a source associated for long time with 2CG 135+01 and with the UES 3EG
J0241+6103, has given further support to this idea. Finally, the very recently proposed association between the microquasar
candidate AX J1639.0−4642 and the UES 3EG J1639−4702 points towards a population of High Mass X-ray Binary (HMXB)/Neutron
Star (NS) microquasars as counterparts of low-latitude unidentified EGRET sources. 相似文献
4.
Some unidentified EGRET sources have been reported to have probable X-ray counterparts. Periodicities in the X-ray data of
those sources, if found, may help to strengthen the identification and to reveal their nature. We performed a detailed search
of periodicities with a photon-counting method, the H-test, in the XMM and ASCA data of RX J0007.0+7302, which is the most probable X-ray counterpart to the EGRET source 3EG J0010+7309.
Although no periods with enough significance were found, a possible one, at 0.1275433± 0.0000001 s (MJD 52327.03399), is quite
intriguing based on results of cross-checking the two data sets. We suggest future analysis with other data to search the
vicinity of this period. 相似文献
5.
6.
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
7.
Blazars are the only (with one or two exceptions) extragalactic objects which were detected and identified at gamma-ray energies
so far. It is suspected that most of the unidentified gamma-ray sources may be the blazars as well. Because the entire electromagnetic
spectrum of these objects is dominated by non-thermal radiation from relativistically moving jets, the effects such as the
Klein–Nishina regime in the Compton scattering may play a major role in shaping some parts of the blazar spectrum. Within
the framework of external radiation Compton model, we present how these effect influence the spectra of blazars for which
the production of gamma rays is dominated by Comptonization of external radiation. 相似文献
8.
Fermi卫星对GeV能段的河外伽马射线背景(Extragalactic Gamma-ray Background, EGB)进行了较为精确的测量, 极大提高了对高能伽马射线背景的认识, 但是在TeV能段, 使用空间探测器进行观测非常困难, 只能依赖地面伽马射线探测器, 如成像大气切伦科夫望远镜. 目前, 对于TeV能段的河外伽马射线背景的认识还不完善. 使用有低活跃状态能谱的61个TeV源(包含2个星暴星系、6个射电星系以及53个耀变体)的累计流量给出河外TeV伽马射线背景的下限. 结果显示, 低能段(0.5--4.5TeV)流量由两个临近的耀变体Mrk 421和Mrk 501主导, 贡献了大约58%的累计背景流量; 而大于4.5TeV的能段, 由3个已观测到10TeV以上能段流量的极端耀变体H 1426+428、1ES 1959+650以及1ES 0229+200主导. 最后分别探究了星暴星系、射电星系以及耀变体对河外TeV伽马射线背景的贡献, 不同耀变体子类对河外TeV伽马射线背景的贡献以及不同红移区间TeV源对河外伽马射线背景的贡献. 相似文献
9.
We present a calculation of the blazar contribution to the extragalactic diffuse γ -ray background (EGRB) in the EGRET energy range. Our model is based on inverse-Compton scattering as the dominant γ -ray production process in the jets of flat spectrum radio quasars (FSRQs) and BL Lac objects, and on the unification scheme of radio-loud AGN. According to this picture, blazars represent the beamed fraction of the Fanaroff–Riley radio galaxies (FR galaxies).
The observed log N –log S distribution and redshift distribution of both FSRQs and BL Lacs constrain our model. Depending slightly on the evolutionary behaviour of blazars, we find that unresolved AGN underproduce the intensity of the extragalactic background radiation. With our model only 20–40 per cent of the extragalactic background emission can be explained by unresolved blazars if we integrate to a maximum redshift of Zmax =3. For Z max =5, blazars could account for 40–80 per cent of the EGRB. Roughly 70–90 per cent of the AGN contribution to the EGRB would result from BL Lacs. While the systematic uncertainties in our estimate for the FSRQ contribution appear small, in the case of BL Lacs our model parameters are not consistent with the results from studies in other wavelength regimes, and therefore may have larger systematic uncertainties. Thus we end up with two possibilities, depending on whether we underpredict or overpredict the BL Lac contribution: either unresolved AGN cannot account for the entire EGRB, or unresolved BL Lacs produce the observed background.
We predict a significant flattening of the γ -ray log N –log S function in the next two decades of flux below the EGRET threshold. 相似文献
The observed log N –log S distribution and redshift distribution of both FSRQs and BL Lacs constrain our model. Depending slightly on the evolutionary behaviour of blazars, we find that unresolved AGN underproduce the intensity of the extragalactic background radiation. With our model only 20–40 per cent of the extragalactic background emission can be explained by unresolved blazars if we integrate to a maximum redshift of Z
We predict a significant flattening of the γ -ray log N –log S function in the next two decades of flux below the EGRET threshold. 相似文献
10.
Jennifer M. Siegal-Gaskins Vasiliki Pavlidou Angela V. Olinto Carolyn Brown Brian D. Fields 《Astrophysics and Space Science》2007,309(1-4):43-49
The third EGRET catalog contains a large number of unidentified sources. This subset of objects is expected to include known gamma-ray emitters of Galactic origin such as pulsars and supernova remnants, in addition to an extragalactic population of blazars. However, current data allows the intriguing possibility that some of these objects may represent a new class of yet undiscovered gamma-ray sources. Many theoretically motivated candidate emitters (e.g. clumps of annihilating dark matter particles) have been suggested to account for these detections. We take a new approach to determine to what extent this population is Galactic and to investigate the nature of the possible Galactic component. By assuming that galaxies similar to the Milky Way should host comparable populations of objects, we constrain the allowed Galactic abundance and distribution of various classes of gamma-ray sources using the EGRET data set. We find it is highly improbable that a large number of the unidentified sources are members of a Galactic halo population, but that a distribution of the sources entirely in the disk and bulge is plausible. Finally, we discuss the additional constraints and new insights that GLAST will provide. 相似文献
11.
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
12.
Alberto Carramiñana 《Astrophysics and Space Science》2007,309(1-4):373-378
The Cygnus region of the Milky Way is prolific in star formation and presents extended diffuse γ-ray emission with a few γ-ray point sources. Among them is 3EG J2020+4017, the brightest of the unidentified EGRET sources, positionally coincident
with the supernova remnant G78.2+2.1. Even though the EGRET and multi-wavelength data have not provided a conclusive identification
for this γ-ray loud, but otherwise faint object, the evidence favors a pulsar like source. The EGRET photon data lack the signal-to-noise
ratio required for a period search, but will serve as a valuable timing baseline extension in the case that GLAST confirms the pulsar nature of the γ-Cygni source.
Work sponsored by CONACyT grant SEP-2003-C02-42611. 相似文献
13.
Nicola La Palombara Patrizia Caraveo Roberto Mignani Evanthia Hatziminaoglou Giovanni F. Bignami Mischa Schirmer 《Astrophysics and Space Science》2005,297(1-4):335-344
Most counterparts of the identified low-latitude γ-ray sources are isolated neutron stars (INSs). Since INSs are characterized by an extremely high value of f
X/f
opt, a systematic X-ray/optical coverage of the fields of unidentified low-latitude γ-ray sources is the best way to unveil INS
counterparts of unidentified sources. Since the low-latitude sources are heavily affected by the interstellar absorption in
both the X-ray and optical bands, we decided to apply the above strategy to two middle-latitude EGRET sources, which could belong to a local galactic population: 3EG J0616-3310 and 3EG J1249-8330. Here we report on the global
X-ray characterization of about 300 objects, on their candidate optical counterparts and on the preliminary results of their
identification. 相似文献
14.
We observed 3EG J1234-1318 with the CANGAROO-II telescope in March, 2002. This source is a steady unidentified EGRET gamma-ray
source at high Galactic latitude which has been associated with a dynamically merging clusters of galaxies, and is therefore
a candidate TeV source. TeV gamma-ray emission is also expected as a result of large-scale cosmological structure formation.
We here report the resulting upper limit on the TeV gamma-ray emission from 3EG J1234-1318.
For the CANGAROO Collaboration. 相似文献
15.
We discuss the contribution of the blazar population to the extragalactic background radiation across the electromagnetic (e.m.) spectrum with particular reference to the microwave, hard-X-ray and γ-ray bands. Our estimates are based on a recently derived blazar radio LogN-LogS that was built by combining several radio and multi-frequency surveys. We show that blazar emission integrated over cosmic time gives rise to a considerable broad-band non-thermal cosmic background that dominates the extragalactic brightness in the high-energy part of the e.m. spectrum. We also estimate the number of blazars that are expected to be detected by future planned or hypothetical missions operating in the X-ray and γ-ray energy bands. 相似文献
16.
Paolo Padovani 《Astrophysics and Space Science》2007,309(1-4):63-71
The “blazar sequence” posits that the most powerful BL Lacertae objects and flat-spectrum radio quasars should have relatively
small synchrotron peak frequencies, ν
peak, and that the least powerful such objects should have the highest ν
peak values. This would have strong implications for our understanding of jet formation and physics and the possible detection
of powerful, moderately high-redshift TeV blazars. I review the validity of the blazar sequence by using the results of very
recent surveys and compare its detailed predictions against observational data. I find that the blazar sequence in its simplest
form is ruled out. However, powerful flat-spectrum radio quasars appear not to reach the ν
peak typical of BL Lacs. This could indeed be related to some sort of sequence, although it cannot be excluded that it is instead
due to a selection effect.
相似文献
17.
A major legacy of the EGRET experiment aboard the Compton Gamma-Ray Observatory (CGRO) is the detection of a large number
of unidentified Gamma-ray sources. Out of the 271 EGRET sources are 170 not identified yet [Hartman et al. ApJS (123) (1999) 79]. To provide additional information on these unidentified EGRET sources, we derived simultaneous MeV fluxes
or flux limits for each source by analyzing the contemporaneous COMPTEL data. Then we compare these MeV fluxes to the extrapolations
of the published EGRET spectra. Our results can be grouped into 4 categories [Zhang et al. A&A (421) (2004) 983]: (1) non-constraining upper limits (∼120 sources), (2) hints (> 2 sigma) or detections with consistent
MeV fluxes (∼16 sources), (3) enhanced MeV emission (2 sources), and (4) constraining MeV flux limits, requiring a spectral
break (∼22 sources). In summary, for about 40 of the unidentified EGRET sources we can provide supplementary spectral information
in the neighboring gamma-ray band, which – together with other source parameters – might provide clues to the underlying source
nature. 相似文献
18.
Most of the extragalactic sources from which very-high-energy (VHE, E > 1011 eV) gamma-ray fluxes have been detected belong to the category of high-energy peaked BL Lacertae objects (HBLs)—the sources
in which the synchrotron radiation peaks in the UV or X-ray band. They often have higher X-ray luminosities than the VHE gamma-ray
energy output, which makes them the most valuable objects for studying the characteristic spectral and temporal variations
in the region of the synchrotron peak of the spectral energy distribution. The blazar 1ES 1426+428 belonging to this category
is a target of many multiwavelength studies, both orbital and ground-based ones. The properties of its X-ray emission have
also been investigated using RXTE/PCA, XMM-Newton, and SWIFT observations. Archival PCA/RXTE data with a total exposure time
in 2002 and 2004 of ≈120h and the most recent available background and calibration files have been used. The extracted light curves of 1ES 1426+428
in the 2.9–24 keV energy band have shown an intense flaring activity on various time scales. Analysis of the observational
data has also confirmed the spectral hardening with increasing X-ray intensity typical of blazars. The flaring state of the
object is also characterized by a flat spectrum, which steepens with decreasing flux. The previously detected evidence of
a spectral hysteresis in a separate flare has also been confirmed. Observations of 1ES 1426+428 with the SWIFT/XRT telescope
and the EPIC instrument onboard XMM-Newton have revealed several intermediate-intensity flares in the 1.5–12 keV energy band
with flux variations reaching a factor of 2, while analysis of the light curves has revealed a correlation between two components
of the X-ray emission from the object. 相似文献
19.
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
20.
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