GRB 090510

有UVOT的光学观测, 在600s附近峰值.

有LAT的GeV光子

Finke 2009 Modeling the Extragalactic Background Light from Stars and Dust

主要内容:
说20GeV以下的光子在宇宙中是透明的

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Title:		Modeling the Extragalactic Background Light from Stars and Dust
Authors:		Finke, Justin D.; Razzaque, Soebur; Dermer, Charles D.
Publication:		eprint arXiv:0905.1115
Publication Date:		05/2009
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Extragalactic Astrophysics
Comment:		12 pages, 9 figures, 3 tables, emulateapj. Submitted to ApJ
Bibliographic Code:		2009arXiv0905.1115F

Abstract

The extragalactic background light (EBL) from the far infrared through the visible and extending into the ultraviolet is thought to be dominated by starlight, either through direct emission or through absorption and reradiation by dust. This is the most important energy range for absorbing $\g$-rays from distant sources such as blazars and gamma-ray bursts and producing electron positron pairs. In previous work we presented EBL models in the optical through ultraviolet by consistently taking into account the star formation rate (SFR), initial mass function (IMF) and dust extinction, and treating stars on the main sequence as blackbodies. This technique is extended to include post-main sequence stars and self-consistently describe dust absorption and reradiation. We find our best fit model combining the Hopkins and Beacom SFR using the Cole et al. parameterization with the Baldry and Glazebrook IMF agrees with available luminosity density data at a variety of redshifts. Our resulting EBL energy density is quite close to the lower limits from galaxy counts and in some cases below the lower limits, and agrees fairly well with other recent EBL models shortward of about 5 $\mu$m. Deabsorbing TeV $\g$-ray spectra of various blazars with our EBL model gives results consistent with simple shock acceleration theory. We also find that the universe should be optically thin to $\g$-rays with energies less than 20 GeV.

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Fan 2009 Fermi未探测到GeV的可能解释

主要内容:
讨论了现有模型不能得到高能辐射的原因. 以及偏振和高能中微子辐射.

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Title:		Interpretation and implication of the non-detection of GeV spectrum excess by Fermi gamma-ray Space Telescope in most GRBs
Authors:		Fan, Yi-Zhong
Publication:		eprint arXiv:0905.0908
Publication Date:		05/2009
Origin:		ARXIV
Keywords:		Astrophysics - Cosmology and Extragalactic Astrophysics, Astrophysics - High Energy Astrophysical Phenomena
Comment:		10 pages including 2 tables and 7 figures, accepted by MNRAS
Bibliographic Code:		2009arXiv0905.0908F

Abstract

Since the launch of the Fermi Gamma-ray Space Telescope on 11 June 2008, significant detections of high energy emission have been reported only in six Gamma-ray Bursts (GRBs) until now. In this work we show that the lack of detection of a GeV spectrum excess in almost all GRBs, though somewhat surprisingly, can be well understood within the standard internal shock model and several alternatives like the photosphere-internal shock (gradual magnetic dissipation) model and the magnetized internal shock model. The delay of the arrival of the >100 MeV photons from some Fermi bursts can be interpreted too. We then show that with the polarimetry of prompt emission these models may be distinguishable. In the magnetized internal shock model, high linear polarization level should be typical. In the standard internal shock model, high linear polarization level is still possible but much less frequent. In the photosphere-internal shock model, the linear polarization degree is expected to be roughly anti-correlated with the weight of the photosphere/thermal component, which may be a unique signature of this kind of model. We also briefly discuss the implication of the current Fermi GRB data on the detection prospect of the prompt PeV neutrinos. The influences of the intrinsic proton spectrum and the enhancement of the neutrino number at some specific energies, due to the cooling of pions (muons), are outlined.

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测试一下新的图片上传

From pictures

Cenko 2009 Swift最亮的几个暴都有jet break

主要内容:
说明喷流模型是对的, 其他没有jet break的可能是选择效应

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GRB 050820A, 从上到下分别是X射线, 光学, 和射电


GRB 060418
GRB 080319B

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Title:		The Collimation and Energetics of the Brightest Swift Gamma-Ray Bursts
Authors:		Cenko, S. B.; Frail, D. A.; Harrison, F. A.; Kulkarni, S. R.; Nakar, E.; Chandra, P.; Butler, N. R.; Fox, D. B.; Gal-Yam, A.; Kasliwal, M. M.; Kelemen, J.; Moon, D. -S.; Price, P. A.; Rau, A.; Soderberg, A. M.; Teplitz, H. I.; Werner, M. W.; Bock, D. C. -J.; Bloom, J. S.; Starr, D. A.; Filippenko, A. V.; Chevalier, R. A.; Gehrels, N.; Nousek, J. N.; Piran, T.
Publication:		eprint arXiv:0905.0690
Publication Date:		05/2009
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		Submitted to ApJ, comments welcome
Bibliographic Code:		2009arXiv0905.0690C

Abstract

Long-duration gamma-ray bursts (GRBs) are widely believed to be highly-collimated explosions (opening angle theta ~ 1-10 deg). As a result of this beaming factor, the true energy release from a GRB is usually several orders of magnitude smaller than the observed isotropic value. Measuring this opening angle, typically inferred from an achromatic steepening in the afterglow light curve (a "jet" break), has proven exceedingly difficult in the Swift era. Here we undertake a study of five of the brightest (in terms of the isotropic prompt gamma-ray energy release, E(gamma, iso)) GRBs in the Swift era to search for jet breaks and hence constrain the collimation-corrected energy release. We present multi-wavelength (radio through X-ray) observations of GRBs 050820A, 060418, and 080319B, and construct afterglow models to extract the opening angle and beaming-corrected energy release for all three events. Together with results from previous analyses of GRBs 050904 and 070125, we find evidence for an achromatic jet break in all five events, strongly supporting the canonical picture of GRBs as collimated explosions. The most natural explanation for the lack of observed jet breaks from most Swift GRBs is therefore selection effects. However, the opening angles for the events in our sample are larger than would be expected if all GRBs had a canonical energy release of ~ 10e51 erg. The total energy release we measure for those "hyper-energetic" (E(total) >~ 10e52 erg) events in our sample is large enough to start challenging models with a magnetar as the compact central remnant.

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Horvath 2009 BeppoSAX也有"中等长度"的暴

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Title:		Classification of BeppoSAX's Gamma-Ray Bursts
Authors:		Horvath, I.
Publication:		eprint arXiv:0905.0860
Publication Date:		05/2009
Origin:		ARXIV
Keywords:		Astrophysics - Cosmology and Extragalactic Astrophysics, Astrophysics - High Energy Astrophysical Phenomena
Comment:		Accepted for publication in Astrophysics & Space Science
Bibliographic Code:		2009arXiv0905.0860H

Abstract

The BeppoSAX Catalog has been very recently published. In this paper we analyze - using the Maximum Likelihood (ML) method - the duration distribution of the 1003 GRBs listed in the catalog with duration. The ML method can identify the long and the intermediate duration groups. The short population of the bursts is identified only at a 96% significance level. MC simulation has been also applied and gives a similar significance level; 95%. However, the existence of the short bursts is not a scientific question after the Compton Gamma-Ray Observatory's observation. Our minor result is this well-known fact that in the BeppoSAX data the short bursts are underrepresented, mainly caused by the different triggering system. Our major result is the identification of the intermediate group in the BeppoSAX data. Therefore, four different satellites (CGRO, Swift, RHESSI and BeppoSAX) observed the intermediate type Gamma-Ray Burst.

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van der Horst 2009 光学亮暴和暗暴的分类新方法

主要内容:
用两个参数，x射线的谱 beta_x 和 x与光学之间的谱指数 beta_ox. 如果beta_ox .lt. beta_x-0.5, 就算暗暴。
(n_nu ~ nu^-beta)

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Title:		Optical Classification of Gamma-Ray Bursts in the Swift Era
Authors:		van der Horst, A. J.; Kouveliotou, C.; Gehrels, N.; Rol, E.; Wijers, R. A. M. J.; Cannizzo, J. K.; Racusin, J.; Burrows, D. N.
Publication:		eprint arXiv:0905.0524
Publication Date:		05/2009
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		6 pages, 3 figures; accepted for publication in ApJ
Bibliographic Code:		2009arXiv0905.0524V

Abstract

We propose a new method for the classification of optically dark gamma-ray bursts (GRBs), based on the X-ray and optical-to-X-ray spectral indices of GRB afterglows, and utilizing the spectral capabilities of Swift. This method depends less on model assumptions than previous methods, and can be used as a quick diagnostic tool to identify optically sub-luminous bursts. With this method we can also find GRBs that are extremely bright at optical wavelengths. We show that the previously suggested correlation between the optical darkness and the X-ray/gamma-ray brightness is merely an observational selection effect.

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Liang 2009 共动系中的Plynting流的辐射

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Title:		Radiation from Comoving Poynting Flux Acceleration
Authors:		Liang, Edison; Noguchi, Koichi
Publication:		eprint arXiv:0905.0160
Publication Date:		05/2009
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		30 pages 8 figures, resubmitted to ApJ, replaces earlier preprint titled "Radiation from Kinetic Poynting Flux Acceleration" (arXiV:0704.1843); most of the paper has been rewritten
Bibliographic Code:		2009arXiv0905.0160L

Abstract

We derive analytic formulas for the radiation power output when electrons are accelerated by a relativistic comoving kinetic Poynting flux, and validate these analytic results with Particle-In-Cell simulations. We also derive analytically the critical frequency of the radiation spectrum. Potential astrophysical applications of these results are discussed. A quantitative model of gamma-ray bursts based on the breakout of kinetic Poynting flux is presented.

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Perley 2009 暗暴的宿主星系

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Title:		The Host Galaxies of Swift Dark Gamma-Ray Bursts: Observational Constraints on Highly Obscured and Very High-Redshift GRBs
Authors:		Perley, D. A.; Cenko, S. B.; Bloom, J. S.; Chen, H. -W.; Butler, N. R.; Kocevski, D.; Prochaska, J. X.; Brodwin, M.; Glazebrook, K.; Kasliwal, M. M.; Kulkarni, S. R.; Lopez, S.; Ofek, E. O.; Pettini, M.; Soderberg, A. M.; Starr, D.
Publication:		eprint arXiv:0905.0001
Publication Date:		05/2009
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Extragalactic Astrophysics
Comment:		20 pages, 11 figures. Submitted to AJ
Bibliographic Code:		2009arXiv0905.0001P

Abstract

In this work we present the first results of our imaging campaign at Keck Observatory to identify the host galaxies of "dark" gamma-ray bursts (GRBs), events with no detected optical afterglow or with detected optical flux significantly fainter than expected from the observed X-ray afterglow. We find that out of a uniform sample of 29 Swift bursts rapidly observed by the Palomar 60-inch telescope through March 2008 (14 of which we classify as dark), all events have either a detected optical afterglow, a probable optical host-galaxy detection, or both. Our results constrain the fraction of Swift GRBs coming from very high redshift (z > 7), such as the recent GRB 090423, to between 0.2-7 percent at 80% confidence. In contrast, a significant fraction of the sample requires large extinction columns (host-frame A_V > 1 mag), with several events showing A_V > 2-5 mag, identifying dust extinction as the dominant cause of the dark GRB phenomenon. We infer that a significant fraction of GRBs (and, by association, of high-mass star formation) occurs in highly obscured regions. However, the host galaxies of dark GRBs seem to have normal optical colors, suggesting that the source of obscuring dust is local to the vicinity of the GRB progenitor or highly unevenly distributed within the host galaxy.

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Aoi 2009 通过高能cutoff来看，模拟结果伽玛暴的罗仑兹因子可能没那么高

主要内容:
主要观点是假设每个内激波都产生一个power law+cutoff，不同的内激波的辐射的求和是一个broken power law+cutoff，同时最小的罗仑兹因子也没那么高。像080916C，可以只有600.

不过不知道他的这个低频部分的谱指数（也就是他的每个pulse的真实谱指数）和观测到的低频谱指数是否相等哦

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Title:		Can we probe the Lorentz factor of gamma-ray bursts from GeV-TeV spectra integrated over internal shocks?
Authors:		Aoi, Junichi; Murase, Kohta; Takahashi, Keitaro; Ioka, Kunihito; Nagataki, Shigehiro
Publication:		eprint arXiv:0904.4878
Publication Date:		04/2009
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Extragalactic Astrophysics
Comment:		11 pages, 7 figures
Bibliographic Code:		2009arXiv0904.4878A

Abstract

We revisit the high-energy spectral cutoff originating from the electron-positron pair creation in the prompt phase of gamma-ray bursts (GRBs) with numerical and analytical calculations. We show that the conventional exponential cutoff should be drastically modified to a steepened power-law in practical observations that integrate emissions from different internal shocks. Since the steepening is tiny for observations, this "smearing" effect can generally reduce the previous estimates of the Lorentz factor of the GRB outflows. We apply our formulation to GRB 080916C, recently detected by the LAT detector on the Fermi satellite, and find that the minimum Lorentz factor can be ~600 (or even smaller values), which is below but consistent with the previous result of ~900. Observing the steepening energy (so-called "pair-break energy") is crucial to diagnose the Lorentz factor and/or the emission site in the future observations.

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