Giannios 2009 激波加速电子的热成份

主要内容:
PIC模拟得到热电子, 解释早期光变的陡降. (不过任何一个绝热演化都可以陡降啊)

不过热电子, 热谱本身还是有意思的.

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Title:		Signatures of a Thermal Component in Shock-Accelerated Electrons in GRBs
Authors:		Giannios, Dimitrios; Spitkovsky, Anatoly
Publication:		eprint arXiv:0905.1970
Publication Date:		05/2009
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		6 pages, 8 figures, MNRAS submitted
Bibliographic Code:		2009arXiv0905.1970G

Abstract

Recent particle-in-cell simulations suggest that a large fraction of the energy dissipated in a relativistic shock is deposited into a thermal distribution of electrons that is connected to the high-energy power-law tail. Here, we explore the observational implications of such a mixed thermal-nonthermal particle distribution for the afterglow and prompt emission of gamma-ray bursts. When the thermal component dominates the energy budget, the afterglow lightcurves show a very steep decline phase followed by a more shallow decay when the characteristic synchrotron frequency crosses the observed band. The steep decay appears in the X-rays at ~100 sec after the burst and is accompanied by a characteristic hard-soft-hard spectral evolution that has been observed in a large number of early afterglows. If internal shocks produce a similar mixed electron distribution, a thermal-like bump is expected at the synchrotron peak of the nu*f_nu spectrum.

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Toma 2009 Cocoon的X射线做种子光子解释高能GeV辐射

主要内容:
基于080916C的观测, 总结出五个高能的观测特点(是否是普遍特点还有待进一步证实):
1. 从8keV到13GeV, 可以用简单的broken power law拟合；
2. 高能的光子比MeV的晚5秒左右到(但不是spectral time lag)；
3. 当考虑高能光子的时候, 时间向后移(也就是spectral time lag, 如果没理解错的话)；
4. 大于100MeV的光子比低能的持续更长时间, 对080916C来说, 高能的到了1400s, 低能的不到200s；
5. E_iso~1e55 erg, 很亮.

模型:
高能来自于EIC. Cocoon是恒星爆炸时候产生的一个张角更大光深更大但速度更慢的喷流, 可以产生X射线作为种子光子, 被内激波的相对论电子散射到GeV, 就是观测到的高能辐射了.

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Title:		An up-scattered cocoon emission model of Gamma-Ray Burst high-energy lags
Authors:		Toma, Kenji; Wu, Xue-Feng; Meszaros, Peter
Publication:		eprint arXiv:0905.1697
Publication Date:		05/2009
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		emulateapj 14 pages, 5 figures, submitted to ApJ
Bibliographic Code:		2009arXiv0905.1697T

Abstract

The Fermi Gamma-ray Space Telescope recently detected the most energetic gamma-ray burst so far, GRB 080916C, and reported its detailed temporal properties in an extremely broad spectral range: (i) the time-resolved spectra are well described by broken power-law forms over the energy range of $10 {\rm keV}-10$ GeV, (ii) the high-energy emission (at $\epsilon > 100$ MeV) is delayed by $\approx 5$s with respect to the $\epsilon \lesssim 1$ MeV emission, and (iii) the higher energy fluxes have the later onset times. We show that this behavior of the high-energy emission can be explained by a model in which the prompt emission consists of two components: one is the emission component peaking at $\epsilon \sim 1$ MeV due to the synchrotron-self-Compton radiation of electrons accelerated in the internal shock of the jet and the other is the component peaking at $\epsilon \sim 100$ MeV due to up-scattering of the photospheric X-ray emission of the expanding cocoon (i.e., the hot bubble produced by dissipation of the jet energy inside the progenitor star) off the same electrons in the jet. Based on this model, we derive some constraints on the radius of the progenitor star and the total energy and mass of the cocoon of this GRB, which may provide information on the structure of the progenitor star and the physical conditions of the jet propagating in the star. We discuss some predictions of this model, including a prompt bright optical emission and a soft X-ray excess.

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看样子GBM的数据还没available

软件(RMFIT)也还没ready, 数据(.rsp, .bak)都还没准备好

From http://blog.astromiror.org/
http://blog.astromiror.org/2009/04/01/gammaray-analysis-update.aspx

I'm still suck on the Fermi Gamma-ray Burst Monitor (GBM) response file creation problem. Like the BAT, the GBM slews, which means I need to create several GBM response files for each GRB just like with BAT. In order to create my own response files, I need access to a specific computer located somewhere in my workplace which contains information vital to creating correct response files. Last week, I was denied an account on this computer because I was told that a free-standing response file generating program would soon be available, but I don't know when “soon” is (could be next week or next year for all I know – our group is understaffed and overworked, and the main software program RMFIT isn't even finished yet). I don't even like using the response files I download from the trigger catalog because I don't know how they were created and during which lengths of time they're good for. At this point, I'm going to forgo using GBM data altogether until I master BAT analysis, then bug my group members enough until either I get that free standing response generator or I get an account on that necessary computer. My research cannot be put on pause for something like this if I want to graduate by fall/winter 2010.

Posted by Laura at 4/1/2009 5:00 PM | Add Comment

Asano 2009 辐射的慢加热模型

主要内容:
认为电子被激波加热是需要一段时间的, 可以用来解释伽玛暴的低能段为什么偏离同步预言的1/3. 并解释为什么有个延迟的高能辐射尾巴.

个人觉得模型本身如果是对的, 其他很多别的辐射机制也可以用过来了.

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Title:		Slow Heating Model of Gamma-Ray Burst: Photon Spectrum and Delayed Emission
Authors:		Asano, K.; Terasawa, T.
Publication:		eprint arXiv:0905.1392
Publication Date:		05/2009
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		20 pages, 7 figures
Bibliographic Code:		2009arXiv0905.1392A

Abstract

We propose a new mechanism for the prompt emission of gamma-ray burst. In our model electrons are continuously accelerated in the post shock region via plasma turbulance. Using Monte Carlo technique, we mimic the 2$^{\rm nd}$ order Fermi acceleraion due to plasma turbulance and obtain photon spectra. Since the acceleration balances with the synchrotron cooling, the observed low-energy spectral index is naturally explained. The resultant spectra can be consistent with observed spectra at least below $\sim 1$ MeV. The model also predicts delayed GeV-TeV emission due to inverse Compton and broad pulse profile of optical emission in some cases. Although nontrivial assumptions are required to reproduce MeV-GeV power-law spectra, the model implies the possibility to explain various kinds of luminosity correlations.

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Niino 2009 用宿主星系的Lyman-alpha发射线来探测伽玛暴的前身星性质

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Title:		Probing the Gamma-Ray Burst Progenitor by Lyman-Alpha Emission of Host Galaxies
Authors:		Niino, Yuu; Totani, Tomonori; Kobayashi, Masakazu A. R.
Publication:		eprint arXiv:0905.1525
Publication Date:		05/2009
Origin:		ARXIV
Keywords:		Astrophysics - Cosmology and Extragalactic Astrophysics, Astrophysics - High Energy Astrophysical Phenomena
Comment:		8 pages, 5 figures, submitted to ApJ
Bibliographic Code:		2009arXiv0905.1525N

Abstract

Theoretical and observational studies suggest that long gamma-ray bursts (GRBs) preferentially occur in low metallicity environment. We discuss the possibility and theoretical aspects of using Lyman alpha emission properties of GRB host galaxies as a metallicity indicator of high redshift GRB environments, where direct metallicity measurements are not easy. We consider the fraction of Lyman-alpha emitters (LAEs) in GRB host galaxies as a function of UV luminosity, which can be compared with star-formation-rate weighted LAE fraction of Lyman-break galaxies as the standard in the case of no metallicity dependence. According to recent observational and theoretical studies of LAEs, we argue that there are two important effects of metallicity dependence of GRB rate to change the LAE fraction of host galaxies. One is the enhancement of intrinsic Lyman-alpha EW by stronger ionizing UV luminosity of low metallicity stellar population, and the other is extinction by interstellar dust to change the observable EW. We argue that the latter is likely to work in the opposite direction to the former, i.e., to decrease LAE fraction by the low metallicity preference of GRBs through the clumpy inter-stellar medium effect. The relative importance of the two effects changes by different UV luminosity ranges. The selection effect of GRB host galaxies by extinction of optical afterglows also works to decrease LAE fraction. We find that the observed high LAE fraction of GRB host galaxies can quantitatively be explained if GRBs occur predominantly in low metallicity environments of Z ~ 0.1Z_sun, although statistics is still limited and we need more systematic studies by future data sets.

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Corsi 2009 GRB 081024B的GeV辐射的解释

主要内容:
认为是余辉的SSC

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Title:		GeV emission from short Gamma-Ray Bursts: the case of GRB 081024B
Authors:		Corsi, Alessandra; Guetta, Dafne; Piro, Luigi
Publication:		eprint arXiv:0905.1513
Publication Date:		05/2009
Origin:		ARXIV
Keywords:		Astrophysics - Cosmology and Extragalactic Astrophysics
Comment:		7 pages, 3 color figures, submitted to Astronomy and Astrophysics
Bibliographic Code:		2009arXiv0905.1513C

Abstract

We investigate the origin of the high energy tail detected by Fermi/LAT in the short GRB 081024B through synchrotron and self-Compton emission in either the internal or external shock models. In the internal shock scenario, we explore the possibility of generating the high energy photons directly through synchrotron process, or through inverse Compton emission in which target photons are synchrotron photons produced in internal shocks taking place either in the short prompt phase, or in a lately emitted shell (delayed internal shocks). In the external shock scenario, we consider the possibility of the high energy tail being the extension of the afterglow synchrotron emission, or alternatively the inverse Compton component associated to the afterglow synchrotron photons. For the internal shock scenario we conclude that, given the constraints set by the observations on the prompt emission spectrum, only an inverse Compton component from delayed internal shocks can accommodate the presence of a high energy tail extended up to the GeV range. In the external shock scenario, we show that interpreting the high energy tail as synchrotron-only afterglow emission, implies a bright late-time afterglow which was not observed by Swift. On the other hand, the observed high energy tail is consistent with an inverse Compton component of the afterglow, powered by a fireball with isotropic energy of the order of 10^{51} ergs, expanding in a uniform medium with density n \sim 5 particles/cm^{3}.

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Aielli 2009 羊八井没有观测到伽玛暴1-100GeV的辐射

主要内容:
给了上限: 10**{-5} erg cm**{-2} in the 1-100 GeV energy.

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Title:		Search for Gamma Ray Bursts with the Argo-YBJ Detector in Scaler Mode
Authors:		ARGO-YBJ Collaboration: G. Aielli
Publication:		eprint arXiv:0905.1189
Publication Date:		05/2009
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		accepted for publication in ApJ
Bibliographic Code:		2009arXiv0905.1189A

Abstract

We report on the search for Gamma Ray Bursts (GRBs) in the energy range 1-100 GeV in coincidence with the prompt emission detected by satellites using the Astrophysical Radiation with Ground-based Observatory at YangBaJing (ARGO-YBJ) air shower detector. Thanks to its mountain location (Yangbajing, Tibet, P.R. China, 4300 m a.s.l.), active surface (about 6700 m**2 of Resistive Plate Chambers), and large field of view (about 2 sr, limited only by the atmospheric absorption), the ARGO-YBJ air shower detector is particularly suitable for the detection of unpredictable and short duration events such as GRBs. The search is carried out using the "single particle technique", i.e. counting all the particles hitting the detector without measurement of the energy and arrival direction of the primary gamma rays. Between 2004 December 17 and 2009 April 7, 81 GRBs detected by satellites occurred within the field of view of ARGO-YBJ (zenith angle <>1 GeV counterpart in the ARGO-YBJ data finding no statistically significant emission. With a lack of detected spectra in this energy range fluence upper limits are profitable, especially when the redshift is known and the correction for the extragalactic absorption can be considered. The obtained fluence upper limits reach values as low as 10**{-5} erg cm**{-2} in the 1-100 GeV energy region. Besides this individual search for a higher energy counterpart, a statistical study of the stack of all the GRBs both in time and in phase was made, looking for a common feature in the GRB high energy emission. No significant signal has been detected.

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GRB 090417B

时间达到2000s的超长暴.

GRB 090424

谱变硬

光度流量也很大

GRB 090423

z=8.2 迄今为止最远的暴