Fermi伽玛射线望远镜是一个备受瞩目的空间望远镜项目，自去年6月发射升空大约一年半以来，其表现也相当不俗，很多重要的成果陆续发表。我前一段时间在ADS上检索了一下Fermi合作组(主要是LAT)正式发表的论文，借此机会也了解一下全世界做高能天体物理的人都关注的一些焦点问题以及Fermi给出的可能的答案。
这里搜集了20篇论文，其中5篇Science，1篇PRL，其余都是ApJ, ApJL, ApJS文章。但这应该不是完整的列表，像预印本网上还贴出来一些接受发表但还未正式刊出的文章，还有一些是Fermi成员在一些会议上给的报告，没有包括在内。而且，随着Fermi数据分析的不断进展，可以预期还会有一大批成果将陆续面世，这些可以在以后作补充。
大致总结一下这20篇文章，其中8篇是关于脉冲星的(2篇毫秒脉冲星，其余为普通脉冲星)，6篇AGN，1篇GRB，1篇亮源列表，1篇伽玛射线双星，1篇球状星团，1篇弥散伽玛射线辐射，1篇正负电子。我大致翻译了一下摘要。
1. The Fermi Gamma-Ray Space Telescope Discovers the Pulsar in the Young Galactic Supernova Remnant CTA 1
Science, 2008, 322, 1218
Energetic young pulsars and expanding blast waves [supernova remnants (SNRs)] are the most visible remains after massive stars, ending their lives, explode in core-collapse supernovae. The Fermi Gamma-Ray Space Telescope has unveiled a radio quiet pulsar located near the center of the compact synchrotron nebula inside the supernova remnant CTA 1. The pulsar, discovered through its gamma-ray pulsations, has a period of 316.86 milliseconds and a period derivative of 3.614E-13 seconds per second. Its characteristic age of 1E4 years is comparable to that estimated for the SNR. We speculate that most unidentified Galactic gamma-ray sources associated with star-forming regions and SNRs are such young pulsars.
Fermi伽玛射线空间望远镜在年轻超新星遗迹CTA1中发现脉冲星
高能脉冲星和膨胀的爆轰波[超新星遗迹(SNRs)]是大质量恒星通过核坍缩超新星爆炸结束其生命之后残留的最可能的可见遗迹。Fermi伽玛射线空间望远镜揭示了一个位于超新星遗迹CTA1中，靠近其致密的同步辐射星云中心的射电宁静脉冲星。这颗伽玛射线脉冲星周期为316.86毫秒，其周期变化率为3.614E-13秒每秒。其特征年龄为1E4年，和该超新星遗迹的估计年龄相当。我们推断很多此类和恒星形成区成协的未证认的银河伽玛射线源都是这样的年轻伽玛射线脉冲星。
2. Fermi Observations of High-Energy Gamma-Ray Emission from GRB 080916C
Science, 2009, 323, 1688
Gamma-ray bursts (GRBs) are highly energetic explosions signaling the death of massive stars in distant galaxies. The Gamma-ray Burst Monitor and Large Area Telescope onboard the Fermi Observatory together record GRBs over a broad energy range spanning about 7 decades of gamma-ray energy. In September 2008, Fermi observed the exceptionally luminous GRB 080916C, with the largest apparent energy release yet measured. The high-energy gamma rays are observed to start later and persist longer than the lower energy photons. A simple spectral form fits the entire GRB spectrum, providing strong constraints on emission models. The known distance of the burst enables placing lower limits on the bulk Lorentz factor of the outflow and on the quantum gravity mass.
Fermi对GRB 080916C的高能伽玛射线发射的观测
伽玛射线暴(GRBs)是反映遥远星系中大质量恒星死亡过程的剧烈爆发现象。Fermi天文台上的伽玛暴监测器和大面积望远镜可以同时记录GRBs的宽波段伽玛射线发射，其能段横跨7个数量级。在2008年9月，Fermi观测到了一个异常明亮的伽玛暴GRB 080916C，其表观能量是迄今为止观测到的GRB中最大的。该GRB的高能伽玛射线晚于低能光子发射，并且持续时间也更长。一个简单的能谱形式就足以拟合整个观测谱，据此我们对其辐射模型给出很强的限制。此外该GRB的距离已知，我们可以因此给出其喷流的Lorentz因子以及量子引力质量的下限。
3. Discovery of Pulsed gamma-Rays from the Young Radio Pulsar PSR J1028–5819 with the Fermi Large Area Telescope
ApJ, 2009, 695, L72
Radio pulsar PSR J1028–5819 was recently discovered in a high-frequency search (at 3.1 GHz) in the error circle of the Energetic Gamma-Ray Experiment Telescope (EGRET) source 3EG J1027–5817. The spin-down power of this young pulsar is great enough to make it very likely the counterpart for the EGRET source. We report here the discovery of gamma-ray pulsations from PSR J1028–5819 in early observations by the Large Area Telescope (LAT) on the Fermi Gamma-Ray Space Telescope. The gamma-ray light curve shows two sharp peaks having phase separation of 0.460 +/- 0.004, trailing the very narrow radio pulse by 0.200 +/- 0.003 in phase, very similar to that of other known gamma-ray pulsars. The measured gamma-ray flux gives an efficiency for the pulsar of ~10-20% (for outer magnetosphere beam models). No evidence of a surrounding pulsar wind nebula is seen in the current Fermi data but limits on associated emission are weak because the source lies in a crowded region with high background emission. However, the improved angular resolution afforded by the LAT enables the disentanglement of the previous COS-B and EGRET source detections into at least two distinct sources, one of which is now identified as PSR J1028–5819.
Fermi伽玛射线望远镜发现年轻射电脉冲星PSR J1028–5819的脉冲伽玛射线辐射
射电脉冲星PSR J1028–5819于近期在一个高频(3.1 GHz)射电搜寻中发现，其位置位于高能伽玛射线实验望远镜(EGRET)发现的源3EG J1027-5817的误差圆圈之内。这颗年轻脉冲星的自转变慢所释放的功率很高，因此很可能是那个EGRET源的对应天体。我们在此报道Fermi伽玛射线望远镜上的大面积望远镜(LAT)在早期观测中发现的PSR J1028–5819的脉冲伽玛射线辐射。其伽玛射线光变曲线体现出两个尖锐的峰，相位相差0.460+/-0.004个周期，比起窄射电脉冲落后0.200+/-0.003个周期，这和很多已知的伽玛射线脉冲星非常相似。观测到的伽玛射线流强表明该脉冲星的高能辐射效率为~10-20% (针对外磁球束流模型)。从现有的Fermi数据中没有发现外围的脉冲星风星云，由于这个源正好处于一个高背景区域，我们只能对于脉冲星风星云的辐射给出一个宽松的上限。尽管如此，LAT的高角分辨率使得我们能够确认此前COS-B和EGRET的观测至少为两个独立的源，其中之一如今被证认为PSR J1028–5819。
4. Fermi Large Area Telescope Observations of the Vela Pulsar
ApJ, 2009, 696, 1084
The Vela pulsar is the brightest persistent source in the GeV sky and thus is the traditional first target for new gamma-ray observatories. We report here on initial Fermi Large Area Telescope observations during verification phase pointed exposure and early sky survey scanning. We have used the Vela signal to verify Fermi timing and angular resolution. The high-quality pulse profile, with some 32,400 pulsed photons at E >= 0.03 GeV, shows new features, including pulse structure as fine as 0.3 ms and a distinct third peak, which shifts in phase with energy. We examine the high-energy behavior of the pulsed emission; initial spectra suggest a phase-averaged power-law index of Gamma = 1.51+0.05-0.04 with an exponential cutoff at Ec = 2.9 +/- 0.1 GeV. Spectral fits with generalized cutoffs of the form e^{-(E/E_c)^b} require b <= 1, which is inconsistent with magnetic pair attenuation, and thus favor outer-magnetosphere emission models. Finally, we report on upper limits to any unpulsed component, as might be associated with a surrounding pulsar wind nebula.
Fermi大面积望远镜对Vela脉冲星的观测
Vela脉冲星是GeV能段最亮的持续源，正因如此它也常常被当作新建伽玛射线天文台的第一个观测目标。我们在此报道Fermi大面积望远镜在运行初期校准阶段的定点曝光和巡天扫描的观测结果。我们运用Vela信号来校验Fermi的时间分辨率和角度分辨率。由Fermi记录到大约32400个高于0.03GeV的脉冲光子构建出的高质量脉冲轮廓揭示出新的特征，包括精细至0.3毫秒的脉冲结构，显著的第三峰，以及该峰相位随着能量的移动等。我们研究了其脉冲辐射的高能行为，测得其周期平均能谱为带e指数截断的幂律能谱，幂指数为Gamma = 1.51+0.05-0.04，截断能量为Ec = 2.9 +/-0.1 GeV。当使用更一般的截断形式e^{-(E/E_c)^b}拟合能谱时我们发现b<=1，这和磁场对产生所致的吸收行为是不一致的，而是更倾向于外磁球辐射模型。最后，我们给出非脉冲辐射上限，这将可能联系于外围的脉冲星风星云。
5. Simultaneous Observations of PKS 2155–304 with HESS, Fermi, RXTE, and Atom: Spectral Energy Distributions and Variability in a Low State
ApJ, 2009, 696, 150
We report on the first simultaneous observations that cover the optical, X-ray, and high-energy gamma-ray bands of the BL Lac object PKS 2155–304. The gamma-ray bands were observed for 11 days, between 2008 August 25 and 2008 September 6 (MJD 54704–54715), jointly with the Fermi Gamma-ray Space Telescope and the HESS atmospheric Cherenkov array, providing the first simultaneous MeV-TeV spectral energy distribution (SED) with the new generation of gamma-ray telescopes. The ATOM telescope and the RXTE and Swift observatories provided optical and X-ray coverage of the low-energy component over the same time
period. The object was close to the lowest archival X-ray and very high energy (VHE; >100 GeV) state, whereas the optical flux was much higher. The light curves show relatively little (~30%) variability overall when compared to past flaring episodes, but we find a clear optical/VHE correlation and evidence for a correlation of the X-rays with the high-energy spectral index. Contrary to previous observations in the flaring state, we do not find any correlation between the X-ray and VHE components. Although synchrotron self-Compton models are often invoked to explain the SEDs of BL Lac objects, the most common versions of these models are at odds with the correlated variability we find in the various bands for PKS 2155–304.
HESS, Fermi, RXTE和Atom关于PKS 2155-304的同时观测：低活动态的能谱分布和光变
我们报道对于BL lac天体PKS 2155–304的首次覆盖光学，X射线和高能伽玛射线波段的同时观测。伽玛波段的观测从2008年8月25日到9月6日(MJD 54704-54715)持续了11天，由Fermi伽玛射线望远镜和HESS大气切伦科夫阵列的联合观测给出从MeV-TeV的能谱分布，这对于新一代伽玛射线望远镜来说尚属首次。与此同时，ATOM, RXTE和Swift望远镜也给出其光学和X波段的低能观测。在这次观测期内，该源X射线和甚高能伽玛波段(VHE; >100 GeV)发射接近于历史最低记录，然而光学流强却处于很高水平。和历次耀发态相比，其光变曲线只体现出相对微弱的光变(~30%)，但是我们观测到了明显的光学/甚高能相关性，同时也发现X射线光度－高能谱指数存在相关的迹象。和历次耀发态不同的是我们没有发现X波段和甚高能成分的相关性。虽然同步自康普顿模型常被成功地用于解释BL Lac天体的能谱分布，然而对于PKS 2155-304常规的同步自康普顿模型却很难解释我们所发现的不同波段之间的关联性。
6. Fermi/Large Area Telescope Discovery of Gamma-Ray Emission from the Flat-Spectrum Radio Quasar PKS 1454–354
ApJ, 2009, 697, 934
We report the discovery by the Large Area Telescope (LAT) onboard the Fermi Gamma-Ray Space Telescope of high-energy gamma-ray (GeV) emission from the flat-spectrum radio quasar PKS 1454–354 (z = 1.424). On 2008 September 4, the source rose to a peak flux of (3.5 +/- 0.7) E-6 ph cm–2 s–1 (E > 100 MeV) on a timescale of hours and then slowly dropped over the following 2 days. No significant spectral changes occurred during the flare. Fermi/LAT observations also showed that PKS 1454–354 is the most probable counterpart of the unidentified EGRET source 3EG J1500–3509. Multiwavelength measurements performed during the following days (7 September with Swift; 6-7 September with the ground-based optical telescope Automated Telescope for Optical Monitoring; 13 September with the Australia Telescope Compact Array) resulted in radio, optical, UV, and X-ray fluxes greater than archival data, confirming the activity of PKS 1454–354.
Fermi大面积望远镜发现平谱射电类星体PKS 1454-354的伽玛射线发射
我们报道Fermi伽玛射线空间望远镜上的大面积望远镜(LAT)发现来自于平谱射电类星体PKS 1454-354 (z=1.424)的高能(GeV)伽玛辐射。2008年9月4日该源辐射流强在数小时内上升至最大值，高达(3.5 +/- 0.7) E-6 ph cm–2 s–1 (E > 100 MeV)，在随后的两天内辐射缓慢下降。在此次耀发期间辐射能谱没有明显变化。Fermi/LAT观测还表明PKS 1454-354很可能就对应于EGRET的未证认源3EG J1500-3509。接下来几天在射电，光学，紫外和X射电能断的多波段观测(9月7日，Swift; 9月6－7日，地面光学望远镜Automated Telescope；9月13日，澳大利亚致密望远镜阵)证实了PKS 1454-354的活动性。
7. Measurement of the Cosmic Ray e++e- Spectrum from 20GeV to 1TeV with the Fermi Large Area Telescope
PRL, 2009, 102, 1101
Designed as a high-sensitivity gamma-ray observatory, the Fermi Large Area Telescope is also an electron detector with a large acceptance exceeding 2m2sr at 300 GeV. Building on the gamma-ray analysis, we have developed an efficient electron detection strategy which provides sufficient background rejection for measurement of the steeply falling electron spectrum up to 1 TeV. Our high precision data show that the electron spectrum falls with energy as E-3.0 and does not exhibit prominent spectral features. Interpretations in terms of a conventional diffusive model as well as a potential local extra component are briefly discussed.
Fermi大面积望远镜测量20GeV至1TeV的宇宙线正负电子总能谱
虽然设计目标是高灵敏度伽玛射线天文台，Fermi大面积望远镜同时也可以作为电子探测器，其接收度在300GeV时超过2m2sr。基于伽玛射线分析技术，我们发展出有效的电子探测方案，足以排除足够的本底以测量快速下降的电子能谱直到1TeV。高精度的数据表明电子能谱随着能量以E-3.0的幂律下降，并没有明显的谱结构。我们简要讨论了对该能谱的可能解释，包括传统的宇宙线扩散模型以及潜在的邻近额外成分。
8. Fermi Discovery of Gamma-ray Emission from NGC 1275
ApJ, 2009, 699, 31
We report the discovery of high-energy (E > 100 MeV) gamma-ray emission from NGC 1275, a giant elliptical galaxy lying at the center of the Perseus cluster of galaxies, based on observations made with the Large Area Telescope (LAT) of the Fermi Gamma-ray Space Telescope. The positional center of the gamma-ray source is only ~3' away from the NGC 1275 nucleus, well within the 95% LAT error circle of ~5'. The spatial distribution of gamma-ray photons is consistent with a point source. The average flux and power-law photon index measured with the LAT from 2008 August 4 to 2008 December 5 are F_gamma = (2.10 +/- 0.23)E-7
ph (>100 MeV) cm–2 s–1 and Gamma = 2.17 +/- 0.05, respectively. The measurements are statistically consistent with constant flux during the four-month LAT observing period. Previous EGRET observations gave an upper limit of F_gamma < 3.72 E-8 ph (>100 MeV) cm–2 s–1 to the gamma-ray flux from NGC 1275. This indicates that the source is variable on timescales of years to decades, and therefore restricts the fraction of emission that can be produced in extended regions of the galaxy cluster. Contemporaneous and historical radio observations are also reported. The broadband spectrum of NGC 1275 is modeled with a simple one-zone synchrotron/synchrotron self-Compton model and a model with a decelerating jet flow.
Fermi发现来自于NGC 1275的伽玛射线辐射
基于Fermi伽玛射线望远镜大面积望远镜的观测，我们发现来自于位于英仙星系团中心的巨椭圆星系NGC 1275的高能(E>100MeV)射线辐射。伽玛源的位置中心仅仅偏离NGC 1275核心大约3'，位于LAT的95%指向误差(~5')以内。伽玛射线光子的空间分布和一个点源相符。LAT从2008年8月4日至12月5日的观测得到的平均流强和幂律谱指数分别为F_gamma = (2.10 +/- 0.23)E-7 ph (>100 MeV) cm–2 s–1 和 Gamma = 2.17 +/- 0.05。在LAT 4个月的观测期内，NGC 1275的发射流强统计上符合常数发射。此前的EGRET观测得到NGC 1275伽玛射线辐射上限为F_gamma < 3.72 E-8 ph (>100 MeV) cm–2 s–1。这表明该源在从年到数十年的时间尺度上是变化的，并且我们可以由此限制来源于星系团延展区域的贡献的比例。我们一并报道了同期以及以往的射电观测。NGC 1275的宽波段能谱可以用一个简单的单区域同步自康普顿模型和一个减速喷流模型描述。
9. Early Fermi Gamma-ray Space Telescope Observations of the Quasar 3C 454.3
ApJ, 2009, 699, 817
This is the first report of Fermi Gamma-Ray Space Telescope observations of the quasar 3C 454.3, which has been undergoing pronounced long-term outbursts since 2000. The data from the Large Area Telescope, covering 2008 July 7-October 6, indicate strong, highly variable gamma-ray emission with an average flux of ~3E-6 photons cm–2 s–1, for energies >100 MeV. The gamma-ray flux is variable, with strong, distinct, symmetrically shaped flares for which the flux increases by a factor of several on a timescale of about 3 days. This variability indicates a compact emission region, and the requirement that the source is optically thin to pair production implies relativistic beaming with Doppler factor delta>8, consistent with the values inferred from Very Long Baseline Interferometry observations of superluminal expansion (delta~25). The observed gamma-ray spectrum is not consistent with a simple power law, but instead steepens strongly above ~2 GeV, and is well described by a broken power law with photon indices of ~2.3 and ~3.5 below and above the break, respectively. This is the first direct observation of a break in the spectrum of a high-luminosity blazar above 100 MeV, and it is likely direct evidence for an intrinsic break in the energy distribution of the radiating particles. Alternatively, the spectral softening above 2 GeV could be due to gamma-ray absorption via photon-photon pair production on the soft X-ray photon field of the host active galactic nucleus, but such an interpretation would require the dissipation region to be located very close (l~100 gravitational radii) to the black hole, which would be inconsistent with the X-ray spectrum of the source.
Fermi伽玛射线空间望远镜对类星体3C 454.3的早期观测
这是Fermi伽玛射线空间望远镜对2000年以来一直持续活动的类星体3C 454.3的观测的首次报道。从2008年7月7日至10月6日大面积望远镜搜集的数据表明3C 454.3呈现着剧烈的，高度光变的伽玛射线发射，能量高于100 MeV的平均流强为~3E-6 photons cm–2 s–1。伽玛射线流强高度变化，体现出强的，明显的而且形状对称的耀发，在大约3天的时间尺度辐射流强增大了数倍。其快速光变表明辐射区域很致密，而伽玛光子能够避免对产生而逃出辐射区则需要Doppler因子delta>8的相对论性集束效应，这和甚长基线干涉仪通过观测该源视超光速膨胀得到的结论(delta~25)一致。观测到的伽玛射线能谱不是单一幂律形式，而是在大约2 GeV以上变得更陡。利用在拐点(~2 GeV)前后幂指数分别为~2.3和~3.5的分段幂律函数可以很好的描述观测数据。对于高光度blazar而言这是首次在100 MeV以上观测到谱的拐折，而且它很可能直接反映了辐射伽玛光子的高能粒子的内禀拐折。另外的关于2 GeV以上能谱变软的可能解释是高能光子和寄主活动星系核的软X射线辐射场通过电子对产生反应而被吸收，但是这个解释要求反应区域要很靠近中心黑洞(1~100倍引力半径)，这和3C 454.3的X射线测量谱相矛盾。
10. Fermi/Large Area Telescope Discovery of Gamma-Ray Emission from a Relativistic Jet in the Narrow-Line Quasar PMN J0948+0022
ApJ, 2009, 699, 976
We report the discovery by the Large Area Telescope (LAT) onboard the Fermi Gamma-Ray Space Telescope of high-energy gamma-ray emission from the peculiar quasar PMN J0948+0022 (z = 0.5846). The optical spectrum of this object exhibits rather narrow Hbeta (FWHM(Hbeta) ~1500 km s–1), weak forbidden lines, and is therefore classified as a narrow-line type I quasar. This class of objects is thought to have relatively small black hole mass and to accrete at a high Eddington ratio. The radio loudness and variability of the compact radio core indicate the presence of a relativistic jet. Quasi-simultaneous radio/optical/X-ray and gamma-ray observations are presented. Both radio and gamma-ray emissions (observed over five months)
are strongly variable. The simultaneous optical and X-ray data from Swift show a blue continuum attributed to the accretion disk and a hard X-ray spectrum attributed to the jet. The resulting broadband spectral energy distribution (SED) and, in particular, the gamma-ray spectrum measured by Fermi are similar to those of more powerful Flat-Spectrum Radio Quasars (FSRQs). A comparison of the radio and gamma-ray characteristics of PMN J0948+0022 with the other blazars detected by LAT shows that this source has a relatively low radio and gamma-ray power with respect to other FSRQs. The physical parameters obtained from modeling the SED also fall at the low power end of the FSRQ parameter region discussed in Celotti & Ghisellini. We suggest that the similarity of the SED of PMN J0948+0022 to that of more massive and more powerful quasars can be
understood in a scenario in which the SED properties depend on the Eddington ratio rather than on the absolute power.
Fermi/大面积望远镜发现来自于窄线类星体PMN J0948+0022的相对论性喷流的伽玛射线发射
我们报道Fermi伽玛射线望远镜上的大面积望远镜(LAT)发现来自于类星体PMN J0948+0022 (z = 0.5846)的高能伽玛射线辐射。该类星体的光谱呈现出很窄的Hbeta线(FWHM(Hbeta) ~1500 km s–1)和弱的禁线，因此被划分为窄线I类类星体。这类类星体通常被认为具有相对小的黑洞质量以及高Eddington比率的吸积率。其致密核心的高射电光度和变化特征表明该类星体存在相对论喷流。我们给出准同时的射电/光学/X射线和伽玛射线的观测结果。其中射电和伽玛射线发射(超过5个月的观测)是高度变化的。与此同时Swift观测的光学和X射线数据表明存在一个来自于吸积盘的蓝色连续谱成分和来自于喷流的硬X射线成分。测量得到的宽波段能谱分布(SED)，特别是来自于Fermi的伽玛射线谱，和更加高功率的平谱射电类星体(FSRQs)类似。比较PMN J0948+0022和LAT发现的其它blazar的射电和伽玛射线特征，我们发现这个源的射电和伽玛光度较低。通过模型拟合SED得到的参数值也落在Celotti & Ghisellini讨论的FSRQs参数空间的低功率端。我们认为PMN J0948+0022和那些更大质量和更高功率的类星体的SED的相似性可以解释为其SED依赖于Eddington比率而不是绝对功率。
11. Pulsed Gamma Rays from the Millisecond Pulsar J0030+0451 with the Fermi Large Area Telescope
ApJ, 2009, 699, 1171
We report the discovery of gamma-ray pulsations from the nearby isolated millisecond pulsar (MSP) PSR J0030+0451 with the Large Area Telescope on the Fermi Gamma-ray Space Telescope (formerly GLAST). This discovery makes PSR J0030+0451 the second MSP to be detected in gamma rays after PSR J0218+4232, observed by the EGRET instrument on the Compton Gamma-Ray Observatory. The spin-down power dE/dt = 3.5E33 erg s–1 is an order of magnitude lower than the empirical lower bound of previously known gamma-ray pulsars. The emission profile is characterized by two narrow peaks, 0.07 +/- 0.01 and 0.08 +/- 0.02 wide,
respectively, separated by 0.44 +/- 0.02 in phase. The first gamma-ray peak falls 0.15 +/- 0.01 after the main radio peak. The pulse shape is similar to that of the "normal" gamma-ray pulsars. An exponentially cutoff power-law fit of the emission spectrum leads to an integral photon flux above 100 MeV of (6.76 +/- 1.05 +/- 1.35)E–8 cm–2 s–1 with cutoff energy (1.7 +/- 0.4 +/- 0.5) GeV. Based on its parallax distance of (300 +/- 90) pc, we obtain a gamma-ray efficiency L_gamma / (dE/dt) ~ 15% for the conversion of spin-down energy rate into gamma-ray radiation, assuming isotropic emission.
Fermi大面积望远镜对于毫秒脉冲星PSR J0030+0451的脉冲伽玛射线发射观测
我们在此报道Fermi伽玛射线望远镜(之前叫GLAST)的大面积望远镜发现来自于邻近孤立的毫秒脉冲星(MSP)PSR J0030+0451的脉冲伽玛射线辐射。这是继康普顿伽玛射线天文台的EGRET探测器发现PSR J0218+4232的伽玛射线发射之后第二个发现具有高能伽玛辐射的毫秒脉冲星。其自旋变慢功率为dE/dt = 3.5E33 erg s–1，这比已知的伽玛射线脉冲星的经验下限值低了一个量级。伽玛辐射光变轮廓由两个窄峰组成，宽度分别为0.07 +/- 0.01 和 0.08 +/- 0.02倍周期，两峰间距为0.44 +/- 0.02倍周期。第一个伽玛射线峰落后于主射电峰0.15 +/- 0.01 倍周期。其脉冲形状和"正常"伽玛射线脉冲星类似。我们可以用一个带e指数截断的幂律函数拟合能谱，得到100 MeV以上的积分光子流强为(6.76 +/- 1.05 +/- 1.35)E–8 cm–2 s–1，截断能量为(1.7 +/- 0.4 +/- 0.5) GeV。根据PSR J0030+0451的距离(300 +/- 90) pc，并且假设辐射是各向同性的，我们得到自转变慢能量转移给伽玛射线辐射的效率为L_gamma / (dE/dt) ~ 15%。
12. Discovery of Pulsations from the Pulsar J0205+6449 in SNR 3C 58 with the Fermi Gamma-Ray Space Telescope
ApJ, 2009, 699, L102
We report the discovery of gamma-ray pulsations (>=0.1 GeV) from the young radio and X-ray pulsar PSR J0205 + 6449 located in the Galactic supernova remnant 3C 58. Data in the gamma-ray band were acquired by the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope (formerly GLAST), while the radio rotational ephemeris used to fold gamma-rays was obtained using both the Green Bank Telescope and the Lovell telescope at Jodrell Bank. The light curve consists of two peaks separated by 0.49 +/- 0.01 +/- 0.01 cycles which are aligned with the X-ray peaks. The first gamma-ray peak trails the radio pulse by 0.08
+/- 0.01 +/- 0.01, while its amplitude decreases with increasing energy as for the other gamma-ray pulsars. Spectral analysis of the pulsed gamma-ray emission suggests a simple power law of index –2.1 +/- 0.1 +/- 0.2 with an exponential cutoff at 3.0+1.1-0.7 +/- 0.4 GeV. The first uncertainty is statistical and the second is systematic. The integral gamma-ray photon flux above 0.1 GeV is (13.7 +/- 1.4 +/- 3.0)E–8 cm–2 s–1, which implies for a distance of 3.2 kpc and assuming a broad fan-like beam a luminosity of 8.3E34 erg s–1 and an efficiency yita of 0.3%. Finally, we report a 95% upper limit on the flux of 1.7E–8 cm–2 s–1 for off-pulse emission from the object.
Fermi伽玛射线空间望远镜发现来自于超新星遗迹SNR 3C 58中的脉冲星PSR J0205+6449的脉冲辐射
我们报道对位于银河超新星遗迹3C 58里的年轻射电和X射线脉冲星PSR J0205+6449的高能(>=0.1 GeV)脉冲伽玛射线辐射的发现。伽玛波段的数据来自于Fermi伽玛射线空间望远镜(以前称作GLAST)上的大面积望远镜的观测，用于折叠伽玛射线数据的射电旋转周期数据来自于Green Bank望远镜和位于Jodrell Bank的Lovell望远镜的观测。伽玛射线光变曲线由两个间隔0.49 +/- 0.01 +/- 0.01倍周期的峰组成，这两个峰和X射线峰位置重合。其中第一个峰落后射电脉冲0.08 +/- 0.01 +/- 0.01个周期，其幅度随着能量增加而下降，这和其余伽玛射线脉冲星一样。能谱分析表明其脉冲发射的能谱可以由一个带e指数截断的幂律能谱描述，幂律谱指数和截断能量分别为–2.1 +/- 0.1 +/- 0.2和3.0+1.1-0.7 +/- 0.4 GeV，其中第一项误差是统计误差，第二项为系统误差。0.1 GeV以上的积分流强为(13.7 +/- 1.4 +/- 3.0)E–8 cm–2 s–1，对于该源3.2kpc的距离这意味着其辐射光度为8.3E34 erg s–1，以及自转－辐射转换效率yita为0.3%。最后，我们给出该天体非脉冲辐射的95%流强上限为1.7E–8 cm–2 s–1。
13. Bright Active Galactic Nuclei Source List from the First Three Months of the Fermi Large Area Telescope All-Sky Survey
ApJ, 2009, 700, 597
The first three months of sky-survey operation with the Large Area Telescope (LAT) onboard the Fermi Gamma-Ray Space Telescope reveal 132 bright sources at |b|>10°with test statistic greater than 100 (corresponding to about 10 sigma). Two methods, based on the CGRaBS, CRATES, and BZCat catalogs, indicate high-confidence associations of 106 of these sources with known active galactic nuclei (AGNs). This sample is referred to as the LAT Bright AGN Sample (LBAS). It contains two radio galaxies, namely, Centaurus A and NGC 1275, and 104 blazars consisting of 58 flat spectrum radio quasars (FSRQs), 42 BL Lac objects, and 4 blazars with unknown classification. Four new blazars were discovered on the basis of the LAT detections. Remarkably, the LBAS includes 10 high-energy-peaked BL Lacs (HBLs), sources which were previously difficult to detect in the GeV range. Another 10 lower-confidence associations are found. Only 33 of the sources, plus two at |b| < 10°, were previously detected with Energetic Gamma-Ray Experiment Telescope(EGRET), probably due to variability. The analysis of the gamma-ray properties of the LBAS sources reveals that the average GeV spectra of BL Lac objects are significantly harder than the spectra of FSRQs. No significant correlation between radio and peak gamma-ray fluxes is observed. Blazar log N-log S distributions and luminosity functions are constructed to investigate the evolution of the different blazar classes, with
positive evolution indicated for FSRQs but none for BL Lacs. The contribution of LAT blazars to the total extragalactic gamma-ray intensity is estimated.
Fermi大面积望远镜前三个月全天巡天发现的亮活动星系核列表
Fermi伽玛射线空间望远镜上的大面积望远镜在其前三个月的巡天观测中发现了132个|b|>10°的亮源，每个源的统计计数都超过100 (对应于10 sigma显著性水平)。基于CGRaBS, CRATES, 和BZCat星表，我们运用的两种分析方法都以高置信水平表明这些源中的106个是已知的活动星系核(AGNs)。这个样本被称作LAT亮活动星系核样本(LBAS)。它由两个射电星系(Centaurus A和NGC 1275)和104个blazar组成，其中这104个blazar又包含58个射电平谱类星体，42个BL Lac天体以及4个未知分类的blazar。LAT的探测发现了4个新的blazar。特别值得一提的是LBAS包括了10个高频BL Lac天体(HBLs)，这些源以前通常认为是很难在GeV波段观测到的。另外还有10个源和AGN星表的天体成协，只是置信度稍低。Fermi发现的这些源中仅有33个，再加上另外两个|b| < 10°的源于此前被高能伽玛射线实验望远镜(EGRET)所探测到，这或许是源于这些源的变化特性。对于LBAS源的伽玛射线性质分析表明BL Lac天体的平均GeV能段能谱要明显硬于FSRQs。Fermi没有观测到明显的射电和伽玛射线峰值流强的相关性。我们构造了logN-logS分布和光度函数以研究不同类型的blazar的演化，发现FSRQs存在正演化而BL lacs没有明显演化特征。最后我们估计了LAT blazars对河外伽玛射线背景辐射的贡献。
14. Fermi/Large Area Telescope Bright Gamma-Ray Source List
ApJS, 2009, 183, 46
Following its launch in 2008 June, the Fermi Gamma-ray Space Telescope (Fermi) began a sky survey in August. The Large Area Telescope (LAT) on Fermi in three months produced a deeper and better resolved map of the gamma-ray sky than any previous space mission. We present here initial results for energies above 100 MeV for the 205 most significant (statistical significance greater than ~10sigma) gamma-ray sources in these data. These are the best characterized and best localized point-like (i.e., spatially unresolved) gamma-ray sources in the early mission data.
Fermi大面积望远镜亮伽玛源列表
Fermi伽玛射线空间望远镜自2008年6月发射后，于8月开始巡天观测。Fermi的大面积望远镜经过三个月左右的曝光，得到了比以往所有设备都要更深远并且分辨率更高的伽玛射线天图。我们在此给出能量大于100 MeV的205个最显著(统计显著性大于10 sigma)的伽玛射线源。相比较以前的实验数据而言，这是质量最高，定位最准确的伽玛点源(即未分辨出空间结构)列表。
15. Pulsed Gamma-rays from PSR J2021+3651 with the Fermi Large Area Telescope
ApJ, 2009, 700, 1059
We report the detection of pulsed gamma-rays from the young, spin-powered radio pulsar PSR J2021+3651 using data acquired with the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope (formerly GLAST). The light curve consists of two narrow peaks of similar amplitude separated by 0.468 +/- 0.002 in phase. The first peak lags the maximum of the 2 GHz radio pulse by 0.162 +/- 0.004 +/- 0.01 in phase. The integral gamma-ray photon flux above 100 MeV is (56 +/- 3 +/- 11) E–8 cm–2 s–1. The photon spectrum is well described by an exponentially cut-off power law of the form dF/dE = kE^{-Gamma } e^{(-E/E_c)}, where the energy E is expressed in GeV. The photon index is Gamma = 1.5 +/- 0.1 +/- 0.1 and the exponential cut-off is Ec = 2.4 +/- 0.3 +/- 0.5 GeV. The first uncertainty is statistical and the second is systematic. The integral photon flux of the bridge is approximately 10% of the pulsed emission, and the upper limit on off-pulse gamma-ray emission from a putative pulsar wind nebula is < 10% of the pulsed emission at the 95% confidence level. Radio polarization measurements yield a rotation measure of RM = 524 +/- 4 rad m–2 but a poorly constrained magnetic geometry. Re-analysis of Chandra X-ray Observatory data enhanced the significance of the weak X-ray pulsations, and the first peak is roughly phase aligned with the first gamma-ray peak. We discuss the emission region and beaming geometry based on the shape and spectrum of the gamma-ray light curve combined with radio and X-ray measurements, and the implications for the pulsar distance. Gamma-ray emission from the polar cap region seems unlikely for this pulsar.
Fermi大面积望远镜对PSR J2021+3651的脉冲伽玛射线辐射的观测
我们报道Fermi伽玛射线空间望远镜上的大面积望远镜对年轻的，自转能驱动的射电脉冲星PSR J2021+3651的脉冲伽玛辐射的探测。光变曲线由两个幅度相当，间距为0.468 +/- 0.002周期的窄峰构成。第一个峰落后2 GHz射电脉冲峰0.162 +/- 0.004 +/- 0.01倍周期。100 MeV以上的积分伽玛光子流强为(56 +/- 3 +/- 11) E–8 cm–2 s–1 (E以GeV为单位)。能谱可以由一个形式为dF/dE = kE^{-Gamma } e^{(-E/E_c)}的带e指数截断的幂律函数描述。其能谱幂指数为Gamma = 1.5 +/- 0.1 +/- 0.1，截断能量为Ec = 2.4 +/- 0.3 +/- 0.5 GeV，其中第一项误差为统计误差，第二项为系统误差。连接两个峰之间的部分积分流强小于脉冲辐射流强的10%，并且在95%置信水平下我们得到可能来自于其伴随脉冲星风星云的非脉冲辐射流强也小于脉冲辐射流强的10%。对该源的射电极化测量得到的旋转度量为RM = 524 +/- 4 rad m–2，但是关于磁场几何的限制还很匮乏。对于Chandra X射线天文台数据的重新分析增大了弱X射线脉冲发射存在的显著性，而且发现X射线第一个峰大致和伽玛射线第一峰位置相同。基于伽玛射线光变曲线的形状以及能谱，并且结合射电以及X射线波段测量数据，我们讨论该源的辐射区域，集束几何，以及对于其距离的预示。我们认为这颗脉冲星伽玛射线不大可能来自于极冠区域。
16. Fermi LAT Observations of LS I +61°303: First Detection of an Orbital Modulation in GeV Gamma Rays
ApJ, 2009, 701, L123
This Letter presents the first results from the observations of LS I +61°303 using Large Area Telescope data from the Fermi Gamma-Ray Space Telescope between 2008 August and 2009 March. Our results indicate variability that is consistent with the binary period, with the emission being modulated at 26.6 +/- 0.5 days. This constitutes the first detection of orbital periodicity in high-energy gamma rays (20 MeV-100 GeV, HE). The light curve is characterized by a broad peak after periastron, as well as a smaller peak just before apastron. The spectrum is best represented by a power law with an exponential cutoff, yielding an overall flux above 100 MeV of 0.82 +/- 0.03(stat) +/- 0.07(syst)E–6 ph cm–2 s–1, with a cutoff at 6.3 +/- 1.1(stat) +/- 0.4(syst) GeV and photon index Gamma = 2.21 +/- 0.04(stat) +/- 0.06(syst). There is no significant spectral change with orbital phase. The phase of maximum emission, close to periastron, hints at inverse Compton
scattering as the main radiation mechanism. However, previous very high-energy gamma ray (>100 GeV, VHE) observations by MAGIC and VERITAS show peak emission close to apastron. This and the energy cutoff seen with Fermi suggest that the link between HE and VHE gamma rays is nontrivial.
Fermi LAT对LS I+61°303的观测：首次探测到GeV伽玛射线的轨道调制
这篇通讯报道Fermi伽玛射线望远镜的大面积望远镜对LS I +61°303的首个观测结果，观测时间从2008年8月到2009年3月。我们的结果发现一个周期为26.6 +/- 0.5天的调制效应，和该双星的轨道周期一致。这是在高能伽玛射线波段(20 MeV-100 GeV)首次探测到轨道周期性。其光变曲线由一个位于近星点之后的宽峰和一个正好位于远星点之前的小峰组成。能谱可以由一个带e指数截断的幂律函数描述，其大于100 MeV的辐射流强为0.82 +/- 0.03(stat) +/- 0.07(syst)E–6 ph cm–2 s–1，截断能量为6.3 +/- 1.1(stat) +/- 0.4(syst) GeV，幂律谱指数为Gamma = 2.21 +/- 0.04(stat) +/- 0.06(syst)。不同的轨道周期之间没有明显的谱变化。伽玛辐射最大位置接近近星点，这表明逆康普顿散射过程或许是其主要辐射机制。但是，此前MAGIC和VERITAS的甚高能伽玛射线(>100 GeV, VHE)观测却发现辐射极大位置位于远星点附近。这个结果和Fermi看到的能谱截断表明高能和甚高能辐射之间联系并不直接。
17. Detection of 16 Gamma-Ray Pulsars Through Blind Frequency Searches Using the Fermi LAT
Science, 2009, 325, 840
Pulsars are rapidly rotating, highly magnetized neutron stars emitting radiation across the electromagnetic spectrum. Although there are more than 1800 known radio pulsars, until recently only seven were observed to pulse in gamma rays, and these were all discovered at other wavelengths. The Fermi Large Area Telescope (LAT) makes it possible to pinpoint neutron stars through their gamma-ray pulsations. We report the detection of 16 gamma-ray pulsars in blind frequency searches using the LAT. Most of these pulsars are coincident with previously unidentified gamma-ray sources, and many are associated with supernova remnants. Direct detection of gamma-ray pulsars enables studies of emission mechanisms, population statistics, and the energetics of pulsar wind nebulae and supernova remnants.
Fermi LAT通过频率盲扫探测到16个伽玛射线脉冲星
脉冲星是快速旋转，高度磁化的中子星，其辐射覆盖电磁波谱各个波段。虽然已经发现超过1800颗射电脉冲星，但迄今为止只观测到其中7颗具有脉冲伽玛射线辐射，而且它们均是在别的波段发现的。Fermi大面积望远镜(LAT)使得通过伽玛射线脉冲发射精确定位中子星成为可能。我们报道LAT通过频率盲扫观测到16个伽玛射线脉冲星。其中绝大多数和此前的未证认伽玛射线源位置相符，并且很多和超新星遗迹成协。直接地观测伽玛射线脉冲星使得我们可以研究其辐射机制，族类统计，以及脉冲星风星云和超新星遗迹的高能过程。
18. Detection of High-Energy Gamma-Ray Emission from the Globular Cluster 47 Tucanae with Fermi
Science, 2009, 325, 845
We report the detection of gamma-ray emissions above 200 megaelectron volts at a significance level of 17sigma from the globular cluster 47 Tucanae, using data obtained with the Large Area Telescope onboard the Fermi Gamma-ray Space Telescope. Globular clusters are expected to emit gamma rays because of the large populations of millisecond pulsars that they contain. The spectral shape of 47 Tucanae is consistent with gamma-ray emission from a population of millisecond pulsars. The observed gamma-ray luminosity implies an upper limit of 60 millisecond pulsars present in 47 Tucanae.
Fermi对来自于球状星团47 Tucanae的高能伽玛射线发射的探测
根据Fermi伽玛射线空间望远镜的大面积望远镜数据，我们报道对于球状星团47 Tucanae的伽玛射线发射的探测，Fermi的探测结果在200 MeV以上达到17sigma的显著性。球状星团含有大量的毫秒脉冲星，因此也被认为应该发射伽玛射线。观测到的47 Tucanae的辐射能谱和一族毫秒脉冲星的期望辐射相一致。根据测量的伽玛射线光度我们得到47 Tucanae中毫秒脉冲星的数量上限为60个。
19. A Population of Gamma-Ray Millisecond Pulsars Seen with the Fermi Large Area Telescope
Science, 2009, 325, 848
Pulsars are born with subsecond spin periods and slow by electromagnetic braking for several tens of millions of years, when detectable radiation ceases. A second life can occur for neutron stars in binary systems. They can acquire mass and angular momentum from their companions, to be spun up to millisecond periods and begin radiating again. We searched Fermi Large Area Telescope data for pulsations from all known millisecond pulsars (MSPs) outside of globular clusters, using rotation parameters from radio telescopes. Strong gamma-ray pulsations were detected for eight MSPs. The gamma-ray pulse profiles and spectral properties resemble those of young gamma-ray pulsars. The basic emission mechanism seems to be the same for MSPs and
young pulsars, with the emission originating in regions far from the neutron star surface.
Fermi大面积望远镜看到的一族伽玛射线毫秒脉冲星
脉冲星刚形成时旋转周期在亚秒左右，通过电磁辐射过程在几千万年时间内逐渐变慢，直到看不见辐射为止。然而在双星系统中中子星可以出现二次生命。它们可以从伴星获取质量和角动量，然后自转加速，周期达到毫秒量级并且重新发出辐射。利用射电望远镜给出的周期信息，我们在Fermi大面积望远镜观测数据中寻找球状星团之外的所有已知毫秒脉冲星(MSPs)的脉冲辐射。我们发现8颗MSPs具有强的脉冲伽玛射线辐射。这些MSPs的伽玛射线脉冲轮廓和能谱性质和年轻伽玛射线脉冲星一致。MSPs和年轻脉冲星的基本辐射机制看来是相同的，即起源于远离中子星表面的区域。
20. Fermi LAT Observation of Diffuse Gamma Rays Produced Through Interactions Between Local Interstellar Matter and High-energy Cosmic Rays
ApJ, 2009, 703, 1249
Observations by the Large Area Telescope (LAT) on the Fermi mission of diffuse gamma-rays in a mid-latitude region in the third quadrant (Galactic longitude l from 200° to 260° and latitude |b| from 22°to 60°) are reported. The region contains no known large molecular cloud and most of the atomic hydrogen is within 1 kpc of the solar system. The contributions of gamma-ray point sources and inverse Compton scattering are estimated and subtracted. The residual gamma-ray intensity exhibits a linear correlation with the atomic gas column density in energy from 100 MeV to 10 GeV. The measured integrated gamma-ray emissivity is (1.63 +/- 0.05) E–26 photons s–1sr–1 H-atom–1 and (0.66 +/- 0.02) E–26 photons s–1sr–1 H-atom–1 above 100 MeV and above 300 MeV, respectively, with an additional systematic error of ~10%. The differential emissivity
from 100 MeV to 10 GeV agrees with calculations based on cosmic ray spectra consistent with those directly measured, at the 10% level. The results obtained indicate that cosmic ray nuclei spectra within 1 kpc from the solar system in regions studied are close to the local interstellar spectra inferred from direct measurements at the Earth within ~10%.
Fermi对产生于本地星际介质和高能宇宙线相互作用的弥散伽玛射线的观测
我们在此报道Fermi天文台大面积望远镜对于银河中纬度天区第3象限(银经200<l<260, 银纬22<|b|<60)的弥散伽玛射线的观测。该天区没有大分子云，而且大多数原子氢也距离太阳系在1kpc以内。我们估计并且扣除了伽玛射线点源和逆康普顿散射的贡献。剩余的伽玛射线辐射强度(100 MeV-10 GeV)体现出和原子气体柱密度的线性相关性。测量到的100 MeV和300 MeV以上的积分伽玛射线发射率分别为(1.63 +/- 0.05) E–26 photons s–1sr–1 H-atom–1 和 (0.66 +/- 0.02) E–26 photons s–1sr–1 H-atom–1，当然还有额外的~10%的系统误差。从100 MeV到10 GeV的微分发射率与根据直接测量的宇宙线能谱计算的结果在10%的水平上相一致。该结果表明在该研究区域距离太阳系1 kpc以内的宇宙线原子核能谱应该和从直接测量结果推断的本地星际空间宇宙线能谱差别在~10%之内。 |
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