逆康普顿散射对中等银纬区银河弥漫γ射线的贡献

使用最近期的ＧＲＯ库中ＥＧＲＥＴ的γ射线数据，研究了逆康普顿散射对中等银纬区银河弥漫γ射线的贡献。采用了两种分析方法：其一为本的新分析方法，其中银河宇宙线与星际气体相互作用的γ射线的发射率ｑ／４π由γ射线数据本身确定；其二为通常的分析方法，即ｑ／４π由使用了局部银河宇宙线强度的观测值的理论估计给出。通过分析，我们获得了两种方法中逆康普顿散射的贡献与能量的依赖关系。结果表明，逆康普顿散射的贡献是大     

宇宙信息

宇宙信息第一幅γ射线天图美国宇航局于１９９１年４月７日向空间释放的康普顿Ｙ射线天文台卫星（ＣＧＲＯ）首次完成了全天γ射线源的普查任务。这一幅假彩色图表示的是卫星上的高能γ射线实验望远镜（ＥＧＲＥＴ）第一年的探测结果：宇宙中能量大于１００兆电子伏的γ射...     

坦谱射电源PKS 0528 134中γ射线爆发和毫米波射电爆发的演化关系

在１９９１—１９９３年期间,Ｃｏｍｐｔｏｎγ射线天文台（ＣＧＲＯ）在射电源ＰＫＳ０５２８＋１３４中观测到两次很强的射线爆发,都伴随有毫米波射电大爆发．本文详细分析了高能γ－Ｘ射线波段和红外－光学波段的辐射能量分布（ＳＥＤ）．结果表明,高能γ射线辐射可能主要是由喷流相对论电子对周围ＵＶ－软Ｘ射线光子的逆康普顿散射所产生的．同时,通过毫米波射电大爆发的频谱演化特性与γ射线源的同步辐射频谱特性的比较,对γ辐射等离子团和射电等离子团之间可能的演化联系作了讨论．     

逆康普顿散射对γ暴余辉的影响

γ暴余辉的发现是γ暴研究史上的一个重大突破,火球模型几乎可以较好地解释γ暴余辉的观测特性。但在标准的火球模型中,通常只考虑电子的同步加速辐射,没有考虑电子逆康普顿散射的贡献。这里我们详细计算了逆康普顿散射对γ暴余辉的影响,发现在一定的条件下,逆康普顿散射的影响是很重要的,它可以显著地改变辐射能谱,进而改变γ暴余辉的光变特性。     

发生在遥远星系中的γ射线爆

γ射线爆,简称ＧＲＢ或γ爆,是一种短时标(通常1～2秒)、突发性的高能γ射线爆发现象。第一例γ爆是由美国国防部发射的Ｖｅｌａ卫星于1967年偶然发现的。1991年4月5日,康普顿γ射线天文台(简称ＣＧＲＯ)发射上天后,平均每天可发现一个γ爆,但由于ＣＧＲＯ对天空出现事件...     

用位相相关方法测量Geminga脉冲星的守时参数

利用γ射线脉冲星Ｇｅｍｉｎｇａ自旋及频率变化的稳定性，采用位相相关的方法分析了ＥＧＲＥＴ对脉冲星Ｇｅｍｉｎｇａ四次观测间隔较长的数据，得到较为准确的守时参数ｆ，位相相关的结果与更长数据段折叠搜索的结果较为接近，对于自旋和频率变化都较为稳定的γ射线脉冲星，位相相关分析方法可以作为提高脉冲星参数精度的有效方法。     

用位相相关方法测量Geminga脉冲星的守时参数

利用γ射线脉冲星Ｇｅｍｉｎｇａ自旋及频率变化的稳定性，采用位相相关的方法分析了ＥＧＲＥＴ对脉冲星Ｇｅｍｉｎｇａ四次观测间隔较长的数据，得到较为准确的守时参数ｆ．位相相关的结果与更长数据段折叠搜索的结果较为接近，表明对于自旋和频率变化都较为稳定的γ射线脉冲星，位相相关分析方法可以作为提高脉冲星参数精度的有效方法．     

宇宙信息

宇宙信息γ暴的新品种宇宙γ射线爆发（ｃｏｓｍｉｃＣａｍｍａ－ｒａｙＢｕｒｓｔ，简称γ暴）是一种短时标、突发性的高能γ射线爆发现象。首例γ暴是由美国国防部发射的Ｖｅｌａ卫星于１９６７年突然发现的。１９９１年４月７日康普顿γ射线天文台（ＣｏｍｐｔｏｎＧａ...     

1ES1853—379的EGRET观测上限对其自转参数的限制

给出了来自新发现的孤立中子星１ＥＳ１８５３－３７９方向的γ射线上限为５×１０％－８ｐｈｃｍ＾－２ｓ＾－１。假设γ射线辐射的１／４π立体角的成束和１ＧｅＶ的平均光子能量,对应的γ光度上限为７．６×１０＾２３（Ｄ／１００ｐｃ）＾２Ｊ／ｓ。导出的γ射线辐射效率上限比极冠模型或外间隙模型所预期的辐射效率低两个量级。由此给出了这一中子星自转参数的限制。     

Compton γ射线望远镜的直接解调成像

Ｃｏｍｐｔｏｎγ射线望远镜ＣＯＭＰＴＥＬ／ＣＧＲＯ工作于０．７５－３０ＭｅＶ能区，本文应用直接解调方法分析ＣＧＲＯ＃１观测的ＣＯＭＰＴＥＬ数据，准确定出Ｃｒａｂγ射线源的位置，在１０－３０ＭｅＶ能区，分辨开最大似然法所不能完全分辨的Ｃｒａｂγ射线源和类星体ＰＫＳ０５２８＋１３４，得出优于传统成像方法所得的成像结果．应用直接成像方法处理γ射线脉冲星Ｇｅｍｉｎｇａ分位相数据，发现Ｇｅｍｉｎｇａ在１０－３０ＭｅＶ能区仍存在辐射，辐射集中在Ｇｅｍｉｎｇａ第一个峰的位相区域．结果表明，应用直接解调方法对Ｃｏｍｐｔｏｎ望远镜数据作成像分析是完全可行的     

Is the diffuse gamma background radiation generated by Galactic cosmic rays?

We explore the possibility that the diffuse gamma-ray background radiation (GBR) at high Galactic latitudes could be dominated by inverse Compton scattering of cosmic ray (CR) electrons on the cosmic microwave background radiation and on starlight from our own galaxy. Assuming that the mechanisms accelerating Galactic CR hadrons and electrons are the same, we derive simple and successful relations between the spectral indices of the GBR above a few MeV and the CR electrons and CR nuclei above a few GeV. We reproduce the observed intensity and angular dependence of the GBR, in directions away from the Galactic disc and centre, without recourse to hypothetical extragalactic sources.     

Intergalactic shock acceleration and the cosmic gamma-ray background

We investigate numerically the contribution to the cosmic gamma-ray background from cosmic-ray ions and electrons accelerated at intergalactic shocks associated with cosmological structure formation. We show that the kinetic energy of accretion flows in the low-redshift intergalactic medium is thermalized primarily through moderately strong shocks, which allow for an efficient conversion of shock ram pressure into cosmic-ray pressure. Cosmic rays accelerated at these shocks produce a diffuse gamma-ray flux which is dominated by inverse Compton emission from electrons scattering off cosmic microwave background photons. Decay of neutral π mesons generated in p–p inelastic collisions of the ionic cosmic-ray component with the thermal gas contribute about 30 per cent of the computed emission. Based on experimental upper limits on the photon flux above 100 MeV from nearby clusters we constrain the efficiency of conversion of shock ram pressure into relativistic CR electrons to  ≲1 per cent  . Thus, we find that cosmic rays of cosmological origin can generate an overall significant fraction of order 20 per cent and no more than 30 per cent of the measured gamma-ray background.     

Gamma rays from halos around stars and the Sun

Inverse Compton (IC) scattering by relativistic electrons produces a major component of the diffuse emission from the Galaxy. The photon fields involved are the cosmic microwave background and the interstellar radiation field (ISRF) from stars and dust. Calculations of the inverse Compton distribution have usually assumed a smooth ISRF, but in fact a large part of the Galactic luminosity comes from the most luminous stars, which are rare. Therefore we expect the ISRF, and hence the inverse Compton emission, to be clumpy at some level, which could be detectable by instruments such as GLAST. Even individual nearby luminous stars could be detectable assuming just the normal cosmic-ray electron spectrum. We present the basic formalism required and give possible candidate stars to be detected and make predictions for GLAST. Then we apply the formalism to the OB associations and the Sun, showing that the IC emission produced is not negligible compared to the sensitivity of current or coming detectors. We estimate that the gamma-ray flux from the halo around the Sun contributes to the diffuse background emission at the few percent level.     

The contribution to the Galactic diffuse gamma-ray spectrum from unresolved rotation-powered pulsars

We consider the contribution to the Galactic diffuse γ-ray emission from unresolved γ-ray pulsars. Based on the thick outer gap model, Monte Carlo methods are used to simulate the properties (period, distance, magnetic field, etc.) of the Galactic population of rotation-powered pulsars the gamma-ray flux of which is lower than the threshold sensitivity of the EGRET detector on the Compton Gamma-Ray Observatory . Furthermore, the contribution to the Galactic diffuse γ-ray spectrum from the unresolved γ-ray pulsars is calculated. Our results indicate that the unresolved γ-ray pulsars contribute ∼5 to ∼10 per cent to the measured Galactic diffuse γ-ray emission if the birth rate of neutron stars in the Galaxy is 1 to 2 per century, and that these pulsars contribute significantly to the observed Galactic diffuse γ-ray emission above 1 GeV. Comparing the model spectrum with the observed spectrum, we show that the unresolved γ-ray pulsars contribute very little to the diffuse emission at lower energies but can account for ∼50 per cent of the observed spectrum above 1 GeV if the product of the birth rate of neutron stars and the γ-ray beaming fraction is about unity. Such a large pulsar contribution can explain the difference (∼60 per cent) between the intensity of the Galactic diffuse emission as measured by EGRET above 1 GeV and model predictions based on cosmic ray–matter interaction only.     

Gamma-Ray lines from the galaxy: the GRO revolution

The Compton Gamma-Ray Observatory (GRO) functioned flawlessly for more than8 years. Its accomplishments, both in novelty and breadth, have virtuallyrevolutionized the field of gamma-ray astrophysics. Since the review ofits entire palette of results would be outside the scope of the presentreview, we will limit ourselves to the sub-field of Galactic gamma-raylines; furthermore, we will have to neglect the minor topic of very-highenergy gamma-ray lines (pion decay, axion annihilation, etc.).This review is divided into three main parts, plus an introductionpresenting GRO and a summary in the form of a table showing the originalobjectives, GRO's accomplishments, and the remaining goals in eachsub-field. The first main part deals with the knowledge gained from longand extensive observations of the Galactic electron-positron annihilationline radiation; the second major section treats the Galactic lines fromradioactive isotope decay; the third major section discusses advances(and recent failures) in the very interesting field of Galactic nuclearde-excitation lines. In each case, an effort will be made not only topresent the current knowledge in the field, but to particularly highlightthe contribution made by GRO to our knowledge.     

Spatial distribution of high energy cosmic ray electrons perpendicular to the galactic plane

With the help of empirical data concerning the latitudinal distribution of galactic gamma rays the contribution of inverse Compton scattered gamma rays is calculated using various models concerning the distribution of high energy cosmic ray electrons perpendicular to the galactic plane. It is shown that gamma ray astronomy from regions with vanishing stellar and interstellar matter densities at energies greater than 100 MeV provides instructive information on the cosmic ray electron density. We find evidence for the existence of a broad galactic electron disk with a total thickness of at least 6.4 kpc. The uncertainties of the cosmic ray electron spectrum measurements above 100 GeV imply an additional uncertainty in the inverse Compton source function of at least a factor 6.     

The klein–nishina Effects in Blazar Jets

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.     

Multifrequency studies of the enigmatic gamma-ray source 3EG J1835+5918

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.     

Pionic photons and neutrinos from cosmic ray accelerators

Identifying the accelerators that produce the Galactic and extragalactic cosmic rays has been a priority mission of several generations of high energy gamma ray and neutrino telescopes; success has been elusive so far. Detecting the gamma-ray and neutrino fluxes associated with cosmic rays reaches a new watershed with the completion of IceCube, the first neutrino detector with sensitivity to the anticipated fluxes, and the construction of CTA, a ground-based gamma ray detector that will map and study candidate sources with unprecedented precision. In this paper, we revisit the prospects for revealing the sources of the cosmic rays by a multiwavelength approach; after reviewing the methods, we discuss supernova remnants, gamma ray bursts, active galaxies and GZK neutrinos in some detail.     

Constraining Galactic pγ Interactions with Cosmic Ray Electron and Positron Spectra

High energy protons produced by various sources of cosmic rays, e.g., supernova remnants, pulsar wind nebulae, active galactic nuclei and gamma-ray bursts, participate in Pγ and pp interactions. Although pp interactions may be the dominant mechanism in our Galaxy, it is unclear how important pγ process is. We show that the upper bound on the fraction of total number of protons participating in pγ interactions inside all Galactic astrophysical sources of cosmic rays is 10%.