Zhao, Xiaohong 2013 磁场衰减对伽马暴谱的影响

主要内容:


精彩摘抄:


文章信息:

· Find Similar Abstracts (with default settings below)

· Electronic Refereed Journal Article (HTML)

· Full Refereed Journal Article (PDF/Postscript)

· arXiv e-print (arXiv:1310.0551)

· References in the article

· Also-Read Articles (Reads History)

·

· Translate This Page

Title:		Gamma-Ray Burst Spectrum with Decaying Magnetic Field
Authors:		Zhao, Xiaohong; Li, Zhuo; Liu, Xuewen; Zhang, Bin-bin; Bai, Jinming; Mészáros, Peter
Affiliation:		AA(Yunnan Observatory, Chinese Academy of Sciences, P.O. Box 110, 650011 Kunming, China ; Key Laboratory for the Structure and Evolution of Celestial Bodies, Chinese Academy of Sciences, P.O. Box 110, 650011 Kunming, China ; Department of Astronomy and Astrophysics and Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA; zhaoxh@ynao.ac.cn), AB(Department of Astronomy and Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, China ; Key Laboratory for the Structure and Evolution of Celestial Bodies, Chinese Academy of Sciences, P.O. Box 110, 650011 Kunming, China; zhuo.li@pku.edu.cn), AC(Department of Astronomy and Astrophysics and Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA ; Department of Physics, Sichuan University, Chengdu 610065, China), AD(Department of Astronomy and Astrophysics and Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA ; Center for Space Plasma and Aeronomic Research (CSPAR), University of Alabama in Huntsville, Huntsville, AL 35899, USA), AE(Yunnan Observatory, Chinese Academy of Sciences, P.O. Box 110, 650011 Kunming, China ; Key Laboratory for the Structure and Evolution of Celestial Bodies, Chinese Academy of Sciences, P.O. Box 110, 650011 Kunming, China), AF(Department of Astronomy and Astrophysics and Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA)
Publication:		The Astrophysical Journal, Volume 780, Issue 1, article id. 12, 6 pp. (2014). (ApJ Homepage)
Publication Date:		01/2014
Origin:		IOP
Astronomy Keywords:		gamma-ray burst: general, magnetic fields, radiation mechanisms: non-thermal
DOI:		10.1088/0004-637X/780/1/12
Bibliographic Code:		2014ApJ...780...12Z

Abstract

In the internal shock model for gamma-ray bursts (GRBs), the synchrotron spectrum from the fast cooling electrons in a homogeneous downstream magnetic field (MF) is too soft to produce the low-energy slope of GRB spectra. However, the MF may decay downstream with distance from the shock front. Here we show that the synchrotron spectrum becomes harder if electrons undergo synchrotron and inverse-Compton cooling in a decaying MF. To reconcile this with the typical GRB spectrum with low-energy slope νF _νvpropν, the postshock MF decay time must be comparable to the cooling time of the bulk electrons (corresponding to a MF decaying length typically of ~10⁵ skin depths); that the inverse-Compton cooling should dominate synchrotron cooling after the MF decay time; and/or that the MF decays with comoving time roughly as Bvpropt ^–1.5. An internal shock synchrotron model with a decaying MF can account for the majority of GRBs with low-energy slopes not harder than ν^4/3.

---

Bibtex entry for this abstract   Preferred format for this abstract (see Preferences)

Basak, Rupal 2013 高能GeV和MeV的幂律成分相关

主要内容:
他们把MeV的分成两种成分：黑体（双温）+幂律；然后发现幂律成分的光变和GeV瞬时阶段的光变一致（注意不是晚期的，他们还是同意晚期的还是外激波的同步辐射）(另外注意，这一点不是他们文章的主要内容，而是进一步的目标，他们发现的仅仅是：对于有很多GeV光子的暴，幂律的MeV光子和LAT的GeV光子一样，也有延迟，见下图)，以此说明瞬时阶段的辐射和瞬时阶段的幂律的MeV是同源的。

那么这么说的话，一共就有如下这些成分：瞬时的两个黑体成分，可能是来自光球辐射（为什么是两个呢？） ；瞬时幂律成分，来自内激波，这个延伸到了GeV；外激波余辉，延伸到了GeV。

于是紧接着可以做的一件事情：分析幂律MeV光子和瞬时阶段的GeV光子的光变曲线的关联程度（但是估计很难，因为不知道怎么在光变上区分幂律和非幂律的光子）。

嗯，也许把MeV的分出几个不同的成分是解释GeV以及MeV自身的一个办法。

精彩摘抄:
幂律部分的MeV光子应该和GeV的track

文章信息:

---

· Find Similar Abstracts (with default settings below)

· arXiv e-print (arXiv:1308.2819)

· References in the Article

· Also-Read Articles (Reads History)

·

· Translate This Page

Title:		A lingering non-thermal component in the GRB prompt emission: predicting GeV emission from the MeV spectrum
Authors:		Basak, Rupal; Rao, A. R.
Publication:		eprint arXiv:1308.2819
Publication Date:		08/2013
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		9 Pages, 2 Figures, ApJ Accepted
Bibliographic Code:		2013arXiv1308.2819B

Abstract

The high energy GeV emission of gamma-ray bursts (GRBs), detected by \emph{Fermi}/LAT, has a significantly different morphology compared to the lower energy MeV emission, detected by \emph{Fermi}/GBM. Though the late time GeV emission is believed to be synchrotron radiation produced via an external shock, this emission as early as the prompt phase is puzzling. Meaningful connection between these two emissions can be drawn only by an accurate description of the prompt MeV spectrum. We perform a time-resolved spectroscopy of the GBM data of long GRBs having significant GeV emission, using a model consisting of 2 blackbodies and a power-law. We examine in detail the evolution of the spectral components and found that GRBs having high GeV emission (GRB 090902B and GRB 090926A) have a delayed onset of the power-law component, in the GBM spectrum, which lingers at the later part of the prompt emission. This behaviour mimics the flux evolution in LAT. In contrast, bright GBM GRBs with an order of magnitude lower GeV emission (GRB 100724B and GRB 091003) show a coupled variability of the total and the power-law flux. Further, by analyzing the data for a set of 17 GRBs, we find a strong correlation between the power-law fluence in the MeV and the LAT fluence (Pearson correlation: r=0.88 and Spearman correlation: $\rho=0.81$). We demonstrate that this correlation is not influenced by the correlation between the total and the power-law fluences at a confidence level of 2.3$\sigma$. We speculate the possible radiation mechanisms responsible for the correlation.

---

Bibtex entry for this abstract   Preferred format for this abstract (see Preferences)

2012 Levinson 光球层的热辐射

主要内容:
也能产生Band 谱。
这篇文章应该仔细读。

精彩摘抄:


文章信息:

· Find Similar Abstracts (with default settings below)

· arXiv e-print (arXiv:1205.3227)

· References in the Article

· Also-Read Articles (Reads History)

·

· Translate This Page

Title:		Observational signatures of sub-photospheric radiation mediated shocks in the prompt phase of GRBs
Authors:		Levinson, Amir
Publication:		eprint arXiv:1205.3227
Publication Date:		05/2012
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		23 pages, 5 figures, revised version with an error corrected and additional results presented
Bibliographic Code:		2012arXiv1205.3227L

Abstract

A shock that form below the photosphere of a GRB outflow is mediated by Compton scattering of radiation advected into the shock by the upstream fluid. The characteristic scale of such a shock, a few Thomson depths, is larger than any kinetic scale involved by several orders of magnitudes, hence, unlike collisionless shocks, radiation mediated shocks cannot accelerate particles to non-thermal energies. The spectrum emitted by a shock that emerges from the photosphere of a GRB jet, reflects the temperature profile downstream of the shock, with a possible contribution at the highest energies from the shock transition layer itself. We study the properties of radiation mediated shocks that form during the prompt phase of GRBs, and compute the time integrated spectrum emitted by the shocked fluid following shock breakout. We show that the time integrated emission from a single shock exhibits a prominent thermal peak, with the location of the peak depending on the shock velocity profile. We also point out that multiple shock emission can produce a spectrum that mimics a Band spectrum.

---

Bibtex entry for this abstract   Preferred format for this abstract (see Preferences)

Beniamini, P. 2011 通过假设GeV和MeV光子的比例，来限制GeV的流量

主要内容:
通过假设GeV的能量是MeV的0.1，Le T., & Dermer C. D., 2009, ApJ, 700, 1026.他们得到过GeV的流量，不过和观测有些不符。

他们应该是用一个更加复杂一点的办法（没看明白，但大意应该是和上面类似），得到GeV辐射的上限，也就是给出二者比例的上限。这个上限还可以和观测到了GeV流量的暴比较，见下图，红色部分，都还吻合呢。

精彩摘抄:

文章信息:

· Find Similar Abstracts (with default settings below)

· Electronic On-line Article (HTML)

· arXiv e-print (arXiv:1103.0745)

· References in the Article

· Also-Read Articles (Reads History)

·

· Translate This Page

Title:		Limits on the GeV Emission from Gamma-Ray Bursts
Authors:		Beniamini, P.; Guetta, D.; Nakar, E.; Piran, T.
Publication:		eprint arXiv:1103.0745
Publication Date:		03/2011
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		Accepted for publication in MNRAS
Bibliographic Code:		2011arXiv1103.0745N

Abstract

The Large Area Telescope (LAT) on board of the Fermi satellite detected emission above 30 MeV only in a small fraction of the long gamma-ray bursts (GRBs) detected by the Fermi Gamma-ray Burst Monitor (GBM) at 8 keV - 10 MeV. Those bursts that were detected by the LAT were among the brightest GBM bursts. We examine a sample of the most luminous GBM bursts with no LAT detection and obtain upper limits on their high energy fluence. We find an average upper limit of LAT/GBM fluence ratio of 0.13 for GeV fluence during $T_{90}$ and an average upper limit ratio of 0.45 for GeV fluence during the first 600 seconds after the trigger. These ratios strongly constrain various emission models and in particular rule out SSC models for the prompt emission. In about a third of both LAT detected and LAT non-detected bursts, we find that the extrapolation of the MeV range Band spectrum to the GeV range is larger than the observed GeV fluence (or its upper limit). While this excess is not highly significant for any specific burst, the overall excess in a large fraction of the bursts suggests a decline in the high energy spectral slope in at least some of these bursts. Possibly an evidence for the long sought after pair creation limit.

---

Bibtex entry for this abstract   Preferred format for this abstract (see Preferences)

Gruber 2011 GBM观测到的32个暴

主要内容:
由于GBM和BATSE差不多，观测到的暴的性质也差不多，峰值能量在800keV，不想Swift的BAT。

精彩摘抄:


文章信息:

· Find Similar Abstracts (with default settings below)

· arXiv e-print (arXiv:1104.5495)

· References in the Article

·

· Translate This Page

Title:		Rest-frame properties of 32 gamma-ray bursts observed by the Fermi Gamma-Ray Burst Monitor
Authors:		Gruber, D.; Greiner, J.; von Kienlin, A.; Rau, A.; Briggs, M. S.; Connaughton, V.; Goldstein, A.; van der Horst, A. J.; Nardini, M.; Bhat, P. N.; Bissaldi, E.; Burgess, J. M.; Chaplin, V. L.; Diehl, R.; Fishman, G. J.; Fitzpatrick, G.; Foley, S.; Gibby, M. H.; Giles, M. M.; Guiriec, S.; Kippen, R. M.; Kouveliotou, C.; Lin, L.; McBreen, S.; Meegan, C. A.; Olivares E., F.; Paciesas, W. S.; Preece, R. D.; Tierney, D.; Wilson-Hodge, C.
Publication:		eprint arXiv:1104.5495
Publication Date:		04/2011
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		accepted by A&A
Bibliographic Code:		2011arXiv1104.5495G

Abstract

Aims: In this paper we study the main spectral and temporal properties of gamma-ray bursts (GRBs) observed by Fermi/GBM. We investigate these key properties of GRBs in the rest-frame of the progenitor and test for possible intra-parameter correlations to better understand the intrinsic nature of these events. Methods: Our sample comprises 32 GRBs with measured redshift that were observed by GBM until August 2010. 28 of them belong to the long-duration population and 4 events were classified as short/hard bursts. For all of these events we derive, where possible, the intrinsic peak energy in the $\nu F_{\nu}$ spectrum (\eprest), the duration in the rest-frame, defined as the time in which 90% of the burst fluence was observed (\tninetyrest) and the isotropic equivalent bolometric energy (\eiso). Results: The distribution of \eprest has mean and median values of 1.1 MeV and 750 keV, respectively. A log-normal fit to the sample of long bursts peaks at ~800 keV. No high-\ep population is found but the distribution is biased against low \ep values. We find the lowest possible \ep that GBM can recover to be ~ 15 keV. The \tninetyrest distribution of long GRBs peaks at ~10 s. The distribution of \eiso has mean and median values of $8.9\times 10^{52}$ erg and $8.2 \times 10^{52}$ erg, respectively. We confirm the tight correlation between \eprest and \eiso (Amati relation) and the one between \eprest and the 1-s peak luminosity ($L_p$) (Yonetoku relation). Additionally, we observe a parameter reconstruction effect, i.e. the low-energy power law index $\alpha$ gets softer when \ep is located at the lower end of the detector energy range. Moreover, we do not find any significant cosmic evolution of neither \eprest nor \tninetyrest.

---

Bibtex entry for this abstract   Preferred format for this abstract (see Preferences)

Luchkov 2011 有些伽马暴可能是来自银河系内恒星的闪耀

主要内容:
通过暴的坐标和恒星的坐标对比，发现有四个位置对得上。而他们计算的巧合的可能性只有4E-5.

精彩摘抄:


文章信息:

· Find Similar Abstracts (with default settings below)

· arXiv e-print (arXiv:1104.3351)

· References in the Article

·

· Translate This Page

Title:		Stellar Sources of Gamma-ray Bursts
Authors:		Luchkov, B. I.
Publication:		eprint arXiv:1104.3351
Publication Date:		04/2011
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Galaxy Astrophysics
Comment:		2 pages
Bibliographic Code:		2011arXiv1104.3351L

Abstract

Correlation analysis of Swift gamma-ray burst coordinates and nearby star locations (catalog Gliese) reveals 4 coincidences with good angular accuracy. The random probability is 4\times 10^{-5}, so evidencing that coincident stars are indeed gamma-ray burst sources. Some additional search of stellar gamma-ray bursts is discussed.

---

Bibtex entry for this abstract   Preferred format for this abstract (see Preferences)

Beloborodov 2010 极端相对论外流在光球层的辐射转移

主要内容:
分物质为主和辐射为主两种情形。

应该是辐射转移的一个很好的应用的例子。

精彩摘抄:


文章信息:

· Find Similar Abstracts (with default settings below)

· arXiv e-print (arXiv:1011.6005)

· References in the Article

·

· Translate This Page

Title:		Radiative transfer in ultra-relativistic outflows and photospheres of gamma-ray bursts
Authors:		, Andrei M.
Publication:		eprint arXiv:1011.6005
Publication Date:		11/2010
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		13 pages, 8 figures, submitted to ApJ
Bibliographic Code:		2010arXiv1011.6005B

Abstract

Emission of gamma-ray bursts involves radiative transfer in ultra-relativistic jets. The corresponding transfer equation is solved. The solution describes the initial trapping of radiation in the opaque outflow, its adiabatic cooling, and the transition to transparency. Two opposite regimes are examined: (1) Baryon-dominated outflow. Surprisingly, radiation develops enormous anisotropy in the fluid frame before decoupling from the fluid. The radiation is strongly polarized. (2) Radiation-dominated outflow. The transfer occurs as if radiation propagated in vacuum, preserving the angular distribution and the blackbody shape of the spectrum. The observed photospheric spectrum is blackbody if (and only if) the outflow energy is dominated by radiation up to the photospheric radius.

---

Bibtex entry for this abstract   Preferred format for this abstract (see Preferences)

Zhang 2010 内部磁扰动产生伽马射线辐射

主要内容:
一个新的模型，企图解决內激波模型的困难。

精彩摘抄:


文章信息:

· Find Similar Abstracts (with default settings below)

· arXiv e-print (arXiv:1011.1197)

· References in the Article

· Citations to the Article (2) (Citation History)

· Refereed Citations to the Article

· Also-Read Articles (Reads History)

·

· Translate This Page

Title:		The Internal-Collision-Induced Magnetic Reconnection and Turbulence (ICMART) Model of Gamma-Ray Bursts
Authors:		Zhang, Bing; Yan, Huirong
Publication:		eprint arXiv:1011.1197
Publication Date:		11/2010
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		ApJ, in press (submitted on May 6, 2010). 27 emulateapj pages, 4 figures
Bibliographic Code:		2010arXiv1011.1197Z

Abstract

The recent Fermi observation of GRB 080916C shows that the bright photosphere emission associated with a putative fireball is missing, which suggests a Poynting-flux-dominated outflow. We propose a model of gamma-ray burst (GRB) prompt emission in the Poynting-flux-dominated regime, namely, the Internal-Collision-induced MAgnetic Reconnection and Turbulence (ICMART) model. It is envisaged that the GRB central engine launches an intermittent, magnetically-dominated wind, and that in the GRB emission region, the ejecta is still moderately magnetized. Similar to the internal shock (IS) model, the mini-shells interact internally at the traditional internal shock radius. Most of these early collision have little energy dissipation, but serve to distort the ordered magnetic field lines. At a certain point, the distortion of magnetic field configuration reaches the critical condition to allow fast reconnection seeds to occur, which induce relativistic MHD turbulence in the interaction regions. The turbulence further distorts field lines easing additional magnetic reconnections, resulting in a runway release of the stored magnetic field energy (an ICMART event). Particles accelerated in the ICMART region radiate synchrotron photons that power the observed gamma-rays. Each ICMART event corresponds to a broad pulse in the GRB lightcurve, and a GRB is composed of multiple ICMART events. This model retains the merits of the IS and other models, but may overcome several difficulties/issues faced by the IS model (e.g. low efficiency, fast cooling, electron number excess, Amati/Yonetoku relation inconsistency, and missing bright photosphere). It predicts two-component variability time scales, and a decreasing Ep and polarization degree during each ICMART event. The model may be applied to most Fermi LAT GRBs that have time-resolved, featureless Band-function spectra (abridged).

---

Bibtex entry for this abstract   Preferred format for this abstract (see Preferences)

Shen 2009 用瞬时辐射的光学流量限制暴本身的辐射半径

主要内容:
假设瞬时光学光子和伽玛光子来自相同的电子的同步辐射, 考虑光学流量应该和同步自吸收(即黑体低频段)一致, 可以给出半径和Gamma, B的关系, 得到对R的限制.

R > 10^14 (Gamma/300)^3/4 (B/10^5 G)^1/4 cm.

用了 GRBs - 041219A, 050820A, 051111 and 061121. 没有包括080319B.

精彩摘抄:


文章信息:

· Find Similar Abstracts (with default settings below)

· arXiv e-print (arXiv:0906.2597)

· References in the Article

·

· Translate This Page

Title:		Prompt optical emission and synchrotron self-absorption constraints on emission site of GRBs
Authors:		Shen, Rong-Feng; Zhang, Bing
Publication:		eprint arXiv:0906.2597
Publication Date:		06/2009
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		13 pages, 4 figures, accepted for publication on MNRAS
Bibliographic Code:		2009arXiv0906.2597S

Abstract

We constrain the distance of the Gamma-Ray Burst (GRB) prompt emission site from the explosion centre, R, by determining the location of the electron's self absorption frequency in the GRB prompt optical-to-X/gamma-ray spectral energy distribution, assuming that the optical and the gamma-ray emissions are among the same synchrotron radiation continuum of a group of hot electrons. All possible spectral regimes are considered in our analysis. The method has only two assumed parameters, namely, the bulk Lorentz factor of the emitting source Gamma, and the magnetic field strength B in the emission region (with a weak dependence). We identify a small sample of 4 bursts that satisfy the following three criteria: (1) they all have simultaneous optical and gamma-ray detections in multiple observational time intervals; (2) they all show temporal correlations between the optical and gamma-ray light curves; and (3) the optical emission is consistent with belonging to the same spectral component as the gamma-ray emission. For all the time intervals of these 4 bursts, it is inferred that R \geq 10^{14} (Gamma/300)^{3/4} (B/10^5 Gauss)^{1/4} cm. For a small fraction of the sample, the constraint can be pinned down to R \approx 10^{14} - 10^{15} cm for Gamma ~ 300. For a second sample of bursts with prompt optical non-detections, only upper limits on R can be obtained. We find no inconsistency between the R-constraints for this non-detection sample and those for the detection sample.

---

Bibtex entry for this abstract Preferred format for this abstract (see Preferences)

Balazs 2009 伽玛暴的天区分布统计

主要内容:
中间类不是随机分布的(不过确定度不高).

精彩摘抄:


文章信息:

· Find Similar Abstracts (with default settings below)

· arXiv e-print (arXiv:0902.4812)

· References in the Article

·

· Translate This Page

Title:		New Statistical Results on the Angular Distribution of Gamma-Ray Bursts
Authors:		Balazs, L. G.; Horvath, I.; Vavrek, R.; Bagoly, Z.; Meszaros, A.
Publication:		eprint arXiv:0902.4812
Publication Date:		02/2009
Origin:		ARXIV
Keywords:		Astrophysics - Cosmology and Extragalactic Astrophysics, Astrophysics - High Energy Astrophysical Phenomena
Comment:		in GAMMA-RAY BURSTS 2007: Proceedings of the Santa Fe Conference
Bibliographic Code:		2009arXiv0902.4812B

Abstract

We presented the results of several statistical tests of the randomness in the angular sky-distribution of gamma-ray bursts in BATSE Catalog. Thirteen different tests were presented based on Voronoi tesselation, Minimal spanning tree and Multifractal spectrum for five classes (short1, short2, intermediate, long1, long2) of gamma-ray bursts, separately. The long1 and long2 classes are distributed randomly. The intermediate subclass, in accordance with the earlier results of the authors, is distributed non-randomly. Concerning the short subclass earlier statistical tests also suggested some departure from the random distribution, but not on a high enough confidence level. The new tests presented in this article suggest also non-randomness here.

---

Bibtex entry for this abstract Preferred format for this abstract (see Preferences)

Lazar 2009 用假设shell里有很多小的eddy来产生伽玛暴的光变

主要内容:
假设shell里有一些比较小的eddy, 它们辐射光子, 罗仑兹变换后到伽玛射线. 由于它们的尺寸比较小, 光变的pulse的时标就比较小, 而伽玛暴的持续时标是R/Gamma^2c.

精彩摘抄:


文章信息:

· Find Similar Abstracts (with default settings below)

· arXiv e-print (arXiv:0901.1133)

· References in the Article

·

· Translate This Page

Title:		GRB Light Curves in the Relativistic Turbulence Model
Authors:		Lazar, Ayah; Nakar, Ehud; Piran, Tsvi
Publication:		eprint arXiv:0901.1133
Publication Date:		01/2009
Origin:		ARXIV
Keywords:		Astrophysics
Bibliographic Code:		2009arXiv0901.1133L

Abstract

Relativistic Turbulence provides an alternative to internal shocks as a mechanism for producing GRBs' variable light curves with efficient conversion of energy to radiation. In this model the relativistic outflow is broken into small eddies moving relativistically in the outflow's rest frame. Variability arises because an observer sees an eddy only when its velocity points towards him and only a small fraction of the eddies are observed. Relativistic turbulence with a significant relativistic velocity requires converting and maintaing a large fraction of the over all energy into turbulent motion. While it is not clear how this is achieved, we explore here, using a toy model, the constraints the model parameters results in light curves comparable to the observations. We find that a tight relation between the size of the eddies and the bulk and turbulent Lorentz factors is needed and that the variability level determines the turbulent Lorentz factor. While the model successfully produces the observed variability there are several inconsistencies with other properties of the light curves. Most of which, but not all, might be resolved if the central engine is active for a long time producing a number of shells, resembling to some extent the internal shocks model.

---

Bibtex entry for this abstract Preferred format for this abstract (see Preferences)

Narayan 2008 Turbulent Model

主要内容:
主要是想抛弃 delta t = R/Gamma^2 c这个关系. 这个关系的限制太大, 导致和很多观测不符.

想法是在shell里有一个eddy, 也就是一个小的球体的样子, 在shell里辐射, 我们看到的delta t = R/Gamma^2/gamma_t^2/c, 其中gamma_t是eddy的LF.

但是我觉得可能不是很对. 其中(4)式的n_e的估算可能有问题. 如果eddy在自己系里是球形的, 那么在shell系里就不是. n_e~(r/r_e)^3就是不对的. 另外, 感觉整个模型貌似没什么意义 :P.

精彩摘抄:


文章信息:

· Find Similar Abstracts (with default settings below)

· arXiv e-print (arXiv:0812.0018)

· References in the Article

· Also-Read Articles (Reads History)

·

· Translate This Page

Title:		A Turbulent Model of Gamma-Ray Burst Variability
Authors:		Narayan, Ramesh; Kumar, Pawan
Publication:		eprint arXiv:0812.0018
Publication Date:		11/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		Submitted to MNRAS
Bibliographic Code:		2008arXiv0812.0018N

Abstract

A popular paradigm to explain the rapid temporal variability observed in gamma-ray burst (GRB) lightcurves is the internal shock model. We propose an alternative model in which the radiating fluid in the GRB shell is relativistically turbulent with a typical eddy Lorentz factor $\gamma_t$. In this model, all pulses in the gamma-ray lightcurve are produced at roughly the same distance $R$ from the center of the explosion. The burst duration is $\sim R/c\Gamma^2$, where $\Gamma$ is the bulk Lorentz factor of the expanding shell, and the duration of individual pulses in the lightcurve is $\sim R/c\Gamma^2\gamma_t^2$. The model naturally produces highly variable lightcurves with $\sim\gamma_t^2$ individual pulses. Even though the model assumes highly inhomogeneous conditions, nevertheless the efficiency for converting jet energy to radiation is high.

---

Bibtex entry for this abstract Preferred format for this abstract (see Preferences)

Kumar 2008 GRB 080319B可能来自于外激波的扰动

主要内容:
辐射机制还是SSC

他们从光变相似认为光学和伽玛来自同一个地方; 另外, 没有考虑黑体辐射的限制. 而且认为辐射半径~10^17cm, 可能超过了减速半径.

精彩摘抄:


文章信息:

· Find Similar Abstracts (with default settings below)

· arXiv e-print (arXiv:0812.0021)

· References in the Article

·

· Translate This Page

Title:		Gamma-ray Burst 080319B: Evidence for Relativistic Turbulence, Not Internal Shocks
Authors:		Kumar, Pawan; Narayan, Ramesh
Publication:		eprint arXiv:0812.0021
Publication Date:		11/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		submitted to MNRAS
Bibliographic Code:		2008arXiv0812.0021K

Abstract

We show that the excellent optical and gamma-ray data available for GRB 080319B rule out the internal shock model for the prompt emission. The data instead point to a model in which the observed radiation was produced close to the deceleration radius ($\sim10^{17}$ cm) by a turbulent source with random Lorentz factors $\sim10$ in the comoving frame. The optical radiation was produced by synchrotron emission from relativistic electrons, and the gamma-rays by inverse Compton scattering of the synchrotron photons. The gamma-ray emission originated both in eddies and in an inter-eddy medium, whereas the optical radiation was mostly from the latter. Therefore, the gamma-ray emission was highly variable whereas the optical was much less variable. The model explains all the observed features in the prompt optical and gamma-ray data of GRB 080319B. We are unable to determine with confidence whether the energy of the explosion was carried outward primarily by particles (kinetic energy) or magnetic fields. Consequently, we cannot tell whether the turbulent medium was located in the reverse shock (we can rule out the forward shock) or in a Poynting-dominated jet.

---

Bibtex entry for this abstract Preferred format for this abstract (see Preferences)