De Pasquale 2009 GRB090510的早期余辉观测

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Title:		Swift and Fermi Observations of the Early Afterglow of the Short Gamma-Ray Burst 090510
Authors:		De Pasquale, M.; Schady, P.; Kuin, N. P. M.; Page, M. J.; Curran, P. A.; Zane, S.; Oates, S. R.; Holland, S. T.; Breeveld, A. A.; Hoversten, E. A.; Chincarini, G.; Grupe, D.; Abdo, A. A.; Ackermann, M.; Ajello, M.; Axelsson, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Baring, M. G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Berenji, B.; Bissaldi, E.; Blandford, R. D.; Bloom, E. D.; Bonamente, E.; Borgland, A. W.; Bouvier, A.; Bregeon, J.; Brez, A.; Briggs, M. S.; Brigida, M.; Bruel, P.; Burnett, T. H.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Caraveo, P. A.; Carrigan, S.; Casandjian, J. M.; Cecchi, C.; Çelik, Ö.; Chekhtman, A.; Chiang, J.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Connaughton, V.; Conrad, J.; Dermer, C. D.; de Angelis, A.; de Palma, F.; Dingus, B. L.; Silva, E. do Couto e.; Drell, P. S.; Dubois, R.; Dumora, D.; Farnier, C.; Favuzzi, C.; Fegan, S. J.; Fishman, G.; Focke, W. B.; Frailis, M.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Gehrels, N.; Germani, S.; Giglietto, N.; Giordano, F.; Glanzman, T.; Godfrey, G.; Granot, J.; Greiner, J.; Grenier, I. A.; Grove, J. E.; Guillemot, L.; Guiriec, S.; Harding, A. K.; Hayashida, M.; Hays, E.; Horan, D.; Hughes, R. E.; Jackson, M. S.; Jóhannesson, G.; Johnson, A. S.; Johnson, W. N.; Kamae, T.; Katagiri, H.; Kataoka, J.; Kawai, N.; Kerr, M.; Kippen, R. M.; Knödlseder, J.; Kocevski, D.; Kuss, M.; Lande, J.; Latronico, L.; Lemoine-Goumard, M.; Longo, F.; Loparco, F.; Lott, B.; Lovellette, M. N.; Lubrano, P.; Makeev, A.; Mazziotta, M. N.; McEnery, J. E.; McGlynn, S.; Meegan, C.; Mészáros, P.; Meurer, C.; Michelson, P. F.; Mitthumsiri, W.; Mizuno, T.; Monte, C.; Monzani, M. E.; Moretti, E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Nolan, P. L.; Norris, J. P.; Nuss, E.; Ohno, M.; Ohsugi, T.; Omodei, N.; Orlando, E.; Ormes, J. F.; Paciesas, W. S.; Paneque, D.; Panetta, J. H.; Parent, D.; Pelassa, V.; Pepe, M.; Pesce-Rollins, M.; Piron, F.; Porter, T. A.; Preece, R.; Rainò, S.; Rando, R.; Razzano, M.; Reimer, A.; Reimer, O.; Reposeur, T.; Ritz, S.; Rochester, L. S.; Rodriguez, A. Y.; Roth, M.; Ryde, F.; Sadrozinski, H. F.-W.; Sander, A.; Saz Parkinson, P. M.; Scargle, J. D.; Schalk, T. L.; Sgrò, C.; Siskind, E. J.; Smith, P. D.; Spandre, G.; Spinelli, P.; Stamatikos, M.; Starck, J.-L.; Stecker, F. W.; Strickman, M. S.; Suson, D. J.; Tajima, H.; Takahashi, H.; Tanaka, T.; Thayer, J. B.; Thayer, J. G.; Thompson, D. J.; Tibaldo, L.; Toma, K.; Torres, D. F.; Tosti, G.; Tramacere, A.; Uchiyama, Y.; Uehara, T.; Usher, T. L.; van der Horst, A. J.; Vasileiou, V.; Vilchez, N.; Vitale, V.; von Kienlin, A.; Waite, A. P.; Wang, P.; Winer, B. L.; Wood, K. S.; Wu, X. F.; Yamazaki, R.; Ylinen, T.; Ziegler, M.
Affiliation:		AA(Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking Surrey, RH5 6NT, UK ; Corresponding authors.; mdp@mssl.ucl.ac.uk ), )
Publication:		The Astrophysical Journal Letters, Volume 709, Issue 2, pp. L146-L151 (2010). (ApJL Homepage)
Publication Date:		02/2010
Origin:		IOP
ApJ Keywords:		gamma-ray burst: individual: GRB090510, relativistic processes, shock waves
DOI:		10.1088/2041-8205/709/2/L146
Bibliographic Code:		2010ApJ...709L.146D

Abstract

We present the observations of GRB090510 performed by the Fermi Gamma-Ray Space Telescope and the Swift observatory. This is a bright, short burst that shows an extended emission detected in the GeV range. Furthermore, its optical emission initially rises, a feature so far observed only in long bursts, while the X-ray flux shows an initial shallow decrease, followed by a steeper decay. This exceptional behavior enables us to investigate the physical properties of the gamma-ray burst outflow, poorly known in short bursts. We discuss internal and external shock models for the broadband energy emission of this object.

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Levinson 2009 相对论自相似解的Rayleigh-Taylor不稳定性

主要内容:
有不稳定性, 可能可以解释早期余辉的变平.

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Title:		Relativistic Rayleigh-Taylor Instability of a Decelerating Shell and its Implications for Gamma Ray Bursts
Authors:		Levinson, Amir
Publication:		eprint arXiv:0909.1636
Publication Date:		09/2009
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		18 pages
Bibliographic Code:		2009arXiv0909.1636L

Abstract

Global linear stability analysis of a self-similar solution describing the interaction of a relativistic shell with an ambient medium is performed. The solution is shown to be unstable to convective Rayleigh-Taylor modes having angular scales smaller than the causality scale. Longer wavelength modes are stable and decay with time. For modes of sufficiently large spherical harmonic degree $l$ the dimensionless growth rate scales as $\sqrt{l/\Gamma}$, where $\Gamma$ is the Lorentz factor of the shell. The instability commences at the contact interface separating the shocked eject a and shocked ambient gas and propagates to the shocks. The reverse shock front responds promptly to the in stability and exhibits rapidly growing distortions at early times. Propagation to the forward shock is slower, and it is anticipated that the region near the contact will become fully turbulent before the instability is communicated to the forward shock. The non-universality of the Blandford-McKee blast wave solution suggests that turbulence generated by the instability in the shocked ambient medium may decay slowly with time and may be the origin of magnetic fields over a long portion of the blast wave evolution. It is also speculated that the instability may affect the emission from the shocked ejecta in the early post-prompt phase of GRBs.

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Ghisellini 2009 早期余辉的中心能源继续活动解释

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arXiv:0908.0732 [ps, pdf, other]

Title: Prolonged activity of the central engine of Gamma Ray Bursts

Authors: G. Ghisellini (1), M. Nardini (2), G. Ghirlanda (1) ((1) INAF - Brera Obs., (2) SISSA)

Comments: 6 pages, 7 figures, to be published in the proceedings of the conference: Neutron Stars and Gamma Ray Bursts: Recent Developments and Future Directions" - March 30 - April 4, 2009 (Cairo and Alexandria, Egypt)

Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE)

We call "prompt" emission of Gamma Ray Bursts (GRBs) the erratic and violent phase of hard X-ray and soft gamma-ray emission, usually lasting for tens of seconds in long GRBs. However, the central engine of GRBs may live much longer. Evidence of it comes from the strange behaviour of the early "afterglow", seen especially in the X-ray band, characterised by a "steep-flat-steep" light curve, very often not paralleled by a similar behaviour in the optical band. This difference makes it hard to explain both the optical and the X-ray emission with a unique component. Two different mechanisms seem to be required. One can well be the standard emission from the forward shock of the fireball running through the interstellar medium. The second one is more elusive, and to characterise its properties we have studied those GRBs with well sampled data and known redshift, fitting at the same time the optical and the X-ray light curves by means of a composite model, i.e. the sum of the standard forward shock emission and a phenomenological additional component with a minimum of free parameters. Some interesting findings have emerged, pointing to a long activity of the central engine powered by fallback material.

Xue 2009 用早期X射线定初始Lorentz factor

主要内容:
假设第一个突起是外激波产生的

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Title:		The initial Lorentz factors of fireballs inferred from the early X-ray data of SWIFT GRBs
Authors:		Xue, Rongrong; Fan, Yizhong; Wei, Daming
Publication:		eprint arXiv:0902.2613
Publication Date:		02/2009
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		6 pages,1 figure,3 tables,accepted for publication in Astronomy & Astrophysics
Bibliographic Code:		2009arXiv0902.2613X

Abstract

We intend to determine the type of circumburst medium and measure directly the initial Lorentz factor $\Gamma_0$ of GRB outflows. If the early X-ray afterglow lightcurve has a peak and the whole profile across the peak is consistent with the standard external shock model, the early rise profile of light curves can be used to differentiate whether the burst was born in interstellar medium (ISM) or in stellar wind. In the thin shell case, related to a sub-relativistic reverse shock, the peak time occurring after the end of the prompt emission, can be used to derive an accurate $\Gamma_0$, especially for the ISM case. The afterglow lightcurves for a flat electron spectrum $p ~ (1,2)$ have been derived analytically. In our GRB sample, we obtain $\Gamma_0 \sim 300$ for the bursts born in ISM. We did not find any good case for bursts born in stellar wind and behaving as a thin shell that can be used to constrain $\Gamma_0$ reliably.

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Genet 2008 测试高维辐射

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考虑多个pulses的和之后, 下降指数可以很大. 指数见右图. 其根本原因是最后一个pulse的时间零点被提前了很多.

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arXiv:0812.4677 [ps, pdf, other]

Title: Testing High Latitude Emission in GRBs

Authors: F. Genet, J. Granot

Subjects: Astrophysics (astro-ph)

Most gamma-ray bursts (GRBs) observed by the Swift satellite show an early rapid decay phase (RDP) in their X-ray lightcurve, which is usually a smooth continuation of the prompt gamma-ray emission, strongly suggesting that it is its tail. However, the mechanism behind it is still not clear. The most popular model for this RDP is High Latitude Emission (HLE). While HLE is expected in many models for the prompt GRB emission, such as the popular internal shocks model, there are models in which it is not expected, such as sporadic magnetic reconnection events. Therefore, testing whether the RDP is consistent with HLE can help distinguish between different prompt emission models. We address this question by modeling the prompt emission as the sum of its individual pulses with their HLE tails. Analytic expressions for the observed flux density are obtained for power-law and Band function emission spectra. For internal shocks the observed instantaneous spectrum is very close to the emitted one, and should be well described by a Band function also during the RDP. Our model naturally produces, the observed spectral softening and steepening of the flux decay. The observed flux during the RDP is initially dominated by the tail of the last pulse, but the tails of one or more earlier pulses can become dominant later on. Moreover, modeling several overlapping pulses as a single wider pulse would over-predict the emission tail. Thus, one should be very careful when testing the predictions of HLE and do a combined temporal and spectral fit of the prompt GRB emission and the RDP.

Curran 2008 多参数拟合余辉

主要内容:
为解释Swift的早期余辉(就是一系列的新问题), 考虑多个参数: 电子指数p, 能量注入参数q, 星风参数k. 貌似解释的还不错, 但也有不能解释的.

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Title:		Testing the blast wave model with Swift GRBs
Authors:		Curran, P. A.; Starling, R. L. C.; van der Horst, A. J.; Wijers, R. A. M. J.
Publication:		eprint arXiv:0812.2813
Publication Date:		12/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		14 pages, submitted to MNRAS
Bibliographic Code:		2008arXiv0812.2813C

Abstract

The complex structure of the light curves of Swift GRBs has made the identification of breaks, and the interpretation of the blast wave caused by the burst, more difficult than in the pre-Swift era. We aim to identify breaks, which are possibly hidden, and to constrain the blast wave parameters; electron energy distribution, p, density profile of the circumburst medium, k, and the continued energy injection index, q. We do so by comparing the observed multi-wavelength light curves and X-ray spectra of our sample to the predictions of the blast wave model. We can successfully interpret all of the bursts in our sample of 10, except two, within this framework and we can estimate, with confidence, the electron energy distribution index for 6 of the sample. Furthermore we identify jet breaks in a number of the bursts. A statistical analysis of the distribution of p reveals that, even in the most conservative case of least scatter, the values are not consistent with a single, universal value. The values of k suggest that the circumburst density profiles are not drawn from only one of the constant density or wind-like media populations.

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Barniol 2008 早期快降的绝热膨胀解释

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Title:		Adiabatic expansion, early x-ray data and the central engine in GRBs
Authors:		Barniol Duran, R.; Kumar, P.
Publication:		eprint arXiv:0806.1226
Publication Date:		06/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		6 pages, 2 figures, submitted for publication on MNRAS
Bibliographic Code:		2008arXiv0806.1226B

Abstract

The Swift satellite early x-ray data shows a very steep decay in most of the Gamma-Ray Bursts light curves. This decay is either produced by the rapidly declining continuation of the central engine activity or by some left-over radiation starting right after the central engine shuts off. The latter scenario consists of the emission from an "ember" that cools via adiabatic expansion and, if the jet angle is larger than the inverse of the source Lorentz factor, the large angle emission. In this work, we calculate the temporal and spectral properties of the emission from such a cooling ember, providing a new treatment for the micro-physics of the adiabatic expansion. We compare the theoretical expectations of the adiabatic expansion (and the large angle emission) with the current observations of the early x-ray data and find that only about 20% of our sample of 107 bursts is potentially consistent with this model. This leads us to believe that, for most bursts, the central engine does not turn off completely during the steep decay of the x-ray light curve; therefore, this phase is produced by the continued rapidly declining activity of the central engine.

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Mao 2008 stochastic acceleration for the shellow decay phase

主要内容:
Using a micro-physical process to explain the shallow decay phase. In fact, is the variation of micro parameters.

I fear that 1. why it stops to a normal decay; 2. if it stops, it should come to a steep and than normal, because of that the E_0.

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文章信息:
A New Scenario on X-ray Shallow Decay of Gamma-ray Bursts

Authors: Jirong Mao, Jiancheng Wang

(Submitted on 6 Jan 2008)

Abstract: In this Letter, we propose that a microphysical process takes a vital role in the shocked region in which the prompt emission of GRBs is emitted. The turbulent energy is included in the internal energy transferred by the kinetic energy of the shock. It dissipates through stochastic acceleration for the electrons to supply the early X-ray emission in the phase of shallow decay. We put the constraints on the time evolution of microphysical parameters. The early X-ray fluxes can be obtained by this scenario and these results are consistent with the Swift observation

Comments:	ApJL submitted, comments are welcome
Subjects:	Astrophysics (astro-ph)
Cite as:	arXiv:0801.0855v1 [astro-ph]

Moretti 2007 spectra of Swift early afterglow

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Although the data do not allow an unequivocal interpretation, the importance of this analysis consists in the fact that we show that a simple power law model or a Band model are insufficient to describe the X-ray spectra of a small homogeneous sample of GRBs at the end of their prompt phase.

文章信息:

arXiv:0711.3739 [ps, pdf, other]

Title: When GRB afterglows get softer, hard components come into play

Authors: A. Moretti (1), R. Margutti (1,2), F. Pasotti (1,2), A.P. Beardmore (3), S. Campana (1), G. Chincarini (2,1), S. Covino (1), O. Godet (3), C. Guidorzi (2,1) J.P. Osborne (3), P. Romano (2,1), G. Tagliaferri (1) ((1) INAF-OAB; (2) U. Bicocca; (3) U. Leicester)

Comments: 10 pages, accepted for publication in A&A

Subjects: Astrophysics (astro-ph)

We aim to investigate the ability of simple spectral models to describe the GRB early afterglow emission. We performed a time resolved spectral analysis of a bright GRB sample detected by the Swift Burst Alert Telescope and promptly observed by the Swift X-ray Telescope,with spectroscopically measured redshift in the period April 2005 -- January 2007. The sample consists of 22 GRBs and a total of 214 spectra. We restricted our analysis to the softest spectra sub--sample which consists of 13 spectra with photon index > 3. In this sample we found that four spectra, belonging to GRB060502A, GRB060729, GRB060904B, GRB061110A prompt--afterglow transition phase, cannot be modeled neither by a single power law nor by the Band model. Instead we find that the data present high energy (> 3 keV, in the observer frame) excesses with respect to these models. We estimated the joint statistical significance of these excesses at the level of 4.3 sigma. In all four cases, the deviations can be modeled well by adding either a second power law or a blackbody component to the usual synchrotron power law spectrum. The additional power law would be explained by the emerging of the afterglow, while the blackbody could be interpreted as the photospheric emission from X-ray flares or as the shock breakout emission. In one case these models leave a 2.2 sigma excess which can be fit by a Gaussian line at the energy the highly ionized Nickel recombination. Although the data do not allow an unequivocal interpretation, the importance of this analysis consists in the fact that we show that a simple power law model or a Band model are insufficient to describe the X-ray spectra of a small homogeneous sample of GRBs at the end of their prompt phase.

Giannios 2007 magnetized reverse shock

主要内容:
Optical flashes may come from the magnetized reverse shock, not the normal reverse shock.

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arXiv:0711.1980 [ps, pdf, other]

Title: On the existence of a reverse shock in magnetized GRB ejecta

Authors: D. Giannios, P. Mimica, M. A. Aloy

Comments: 8 pages, 1 figure, A&A submitted

Subjects: Astrophysics (astro-ph)

The role of magnetic fields in gamma-ray burst (GRB) flows remains controversial. The study of the early afterglow phases and, in particular, of the reverse shock dynamics and associated emission offers a promising probe of the magnetization of the ejecta. In this paper, we derive the conditions for the existence of a reverse shock in arbitrarily magnetized ejecta that decelerate interacting with external medium of constant density. We show, in contrast to previous estimates, that ejecta with magnetization larger than unity are not crossed by a reverse shock for a large fraction of the parameter space relevant for GRB flows. Allowing for shell spreading, there is always a relativistic or mildly relativistic reverse shock forming in sigma_o < 0.3 ejecta. Thereby, we conclude that the paucity of optical flashes, believed to be a distinctive signature of a reverse shock, may be explained by the existence of dynamically important magnetic fields in the ejecta.

Sakamoto 2007 Swift暴快下降阶段的数据统计

主要内容:
不是像其他人将BAT延伸到XRT再作光变曲线，而是反过来。说下降用指数衰减比用幂律衰减更好拟合。得到的结论说快下降阶段不支持曲率效应的解释，给出可能是早期外激波的。（主要还是给出了很多处理过的数据）

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横坐标是时间幂律指数alpha，纵坐标是光子谱指数gamma，如果是曲率效应，则alpha＝gamma＋1，应该是虚线所表示的。但这些暴没有一个经过虚线。

对X射线的幂律拟合，如果只看后面的红线，选择不同的t0，和时间指数alpha都能很好地拟合！

文章信息:

arXiv:0707.2170 [ps, pdf, other]

Title: Evidence of Exponential Decay Emission in the Swift Gamma-ray Bursts

Authors: T. Sakamoto, J. E. Hill, R. Yamazaki, L. Angelini, H. A. Krimm, G. Sato, S. Swindell, K. Takami, J. P. Osborne

Comments: 33 pages, 34 figures; accepted for publication in ApJ

Subjects: Astrophysics (astro-ph)

We present a systematic study of the steep decay emission from gamma-ray bursts (GRBs) observed by the Swift X-Ray Telescope (XRT). In contrast to the analysis described in recent literature, we produce composite Burst Alert Telescope (BAT) and XRT light curves by extrapolating the XRT data (2-10 keV) into the BAT energy range (15-25 keV) rather than extrapolating the BAT data into the XRT energy band (0.3-10 keV). Based on the fits to the composite light curves, we have confirmed the existence of an exponential decay component which smoothly connects the BAT prompt data to the XRT steep decay for several GRBs. We also find that the XRT steep decay for some of the bursts can be well fit by a combination of a power-law with an exponential decay model. We discuss this exponential component within the frame work of both the internal and the external shock model.

Murase 2007 早期余辉阶段的高能中微子

主要内容:
考虑各种模型在早期余辉阶段的高能中微子辐射，以及探测到的可能性。认为正反激波不能产生。

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arXiv:0707.1140 [ps, pdf, other]

Title: High energy neutrino early afterglows gamma-ray bursts revisited

Authors: Kohta Murase

Comments: 17 pages, 11 figures

Subjects: Astrophysics (astro-ph)

High energy neutrino emission from gamma-ray bursts (GRBs) has been expected in various scenarios. In this paper, we study neutrino emission under the various models for early afterglows of GRBs, and discuss implications for neutrino signals from recent Swift observations. Future neutrino detectors such as IceCube might detect neutrino signals from early afterglows under the late prompt emission model, but it would be difficult under the reverse-forward shock model. Neutrino-detections are inviting because they could provide us with not only information on baryon acceleration but also one of the clues to the model of early afterglows. They also lead to motivating neutrino telescopes that are larger than IceCube. Finally, we compare various predictions for the neutrino background from GRBs.

Malesani 2007 GRB 060418 and GRB 060607A的早期余辉观测

主要内容:
给出了用REM对GRB 060418 and GRB 060607A的早期余辉观测，估算早期的Lorentz因子有400。而余辉的流量有暴本身的16%，对GRB 060418来说的话。

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文章信息:
arXiv:0706.1772 [ ps, pdf, other] : Title: The GRB afterglow onset observed by REM: fireball Lorentz factor and afterglow fluence
Authors: Daniele Malesani (DARK), Emilio Molinari (INAF/Brera), Susanna Vergani (DIAS and DCU), Stefano Covino (INAF/Brera), for the REM team
Comments: 4 pages, 1 figure, to appear in New Astronomy Reviews, proceedings of "070228: The Next Decade of Gamma-Ray Burst Afterglows", Amsterdam, 2007 March 19-23, eds. R.A.M.J. Wijers, L. Kaper, E. van Eerten

We report observations of the early light curves of GRB 060418 and GRB 060607A, carried out with the pink robotic telescope REM. A clear peak is detected for both events, which is interpreted as the onset of the afterglow, that is the time at which the fireball starts decelerating. This detection allows to directly measure the initial fireball Lorentz factor, which was found to be Gamma_0 ~ 400 for both events, fully confirming the ultrarelativistic nature of gamma-ray burst fireballs. Sampling the light curve before the peak also allows to compute the bolometric fluence of the afterglow, which is 16% of the prompt one in the case of GRB 060418.

X射线的平降阶段和外部介质分布

假设n \propto r^{-k}, 而且k>2. 这样喷流在往外运动的过程中基本不会被减速，自身也不会怎么被激波化，所以也不用计算辐射。只算正向激波的辐射，可能可以和早期平降阶段吻合。

然后也许进入ISM，成为标准余辉。

Yu 2007 Shallow decay相的星风泡解释

主要内容:
用磁星主导的外流星风泡作为能量注入的机制，星风的反向激波解释早期余辉的平降阶段。

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文章信息:
Shallow decay phase of GRB X-ray afterglows from relativistic wind bubbles

Authors: Yun-Wei Yu, Zi-Gao Dai

(Submitted on 8 May 2007)

Abstract: The postburst object of a GRB is likely to be a highly magnetized, rapidly rotating compact object (e.g., a millisecond magnetar), which could produce an ultrarelativistic electron-positron-pair wind. The interaction of such a wind with an outwardly expanding fireball ejected during the burst leads to a relativistic wind bubble (RWB). We numerically calculate the dynamics and radiative properties of RWBs and use this model to explain the shallow decay phase of the early X-ray afterglows observed by Swift. We find that RWBs can fall into two types: forward-shock-dominated and reverse-shock-dominated bubbles. Their radiation during a period of $\sim 10^{2}-10^{5}$ seconds is dominated by the shocked medium and the shocked wind, respectively, based on different magnetic energy fractions of the shocked materials. For both types, the resulting light curves always have a shallow decay phase. In addition, we provide an example fit to the X-ray afterglows of GRB 060813 and GRB 060814 and show that they could be produced by forward-shock-dominated and reverse-shock-dominated bubbles, respectively. This implies that, for some early afterglows (e.g., GRB 060814), the long-lasting reverse shock emission is strong enough to explain their shallow decay phase.

Comments:

5 pages, 4 figures, Accepted for Publication in A&A

Subjects:

Astrophysics (astro-ph)

Cite as:

arXiv:0705.1108v1 [astro-ph]

Takami 2007 通过X射线早期快下降阶段来推测喷流结构

主要内容:
细致研究不同结构的喷流的tail emission导致的光变曲线的下降指数。方法是蒙特卡罗模拟。

精彩摘抄:


文章信息:
Probing the Structure of Gamma-Ray Burst Jets with Steep Decay Phase of their Early X-ray Afterglows

Authors: Kentaro Takami (1), Ryo Yamazaki (1), Takanori Sakamoto (2), Goro Sato (2) ((1) Hiroshima Univ., (2) NASA/GSFC)

(Submitted on 9 Apr 2007 (v1), last revised 13 Apr 2007 (this version, v2))

Abstract: We show that the jet structure of gamma-ray bursts (GRBs) can be investigated with the tail emission of the prompt GRB. The tail emission which we consider is identified as a steep-decay component of the early X-ray afterglow observed by the X-ray Telescope onboard Swift. Using a Monte Carlo method, we derive, for the first time, the distribution of the decay index of the GRB tail emission for various jet models. The new definitions of the zero of time and the time interval of a fitting region are proposed. These definitions for fitting the light curve lead us an unique definition of the decay index, which is useful to investigate the structure of the GRB jet. We find that if the GRB jet has a core-envelope structure, the predicted distribution of the decay index of the tail has a wide scatter and has multiple peaks, which cannot be seen for the case of the uniform and the Gaussian jet. Therefore, the decay index distribution tells us the information on the jet structure. Especially, if we observe events whose decay index is less than about 2, both the uniform and the Gaussian jet models will be disfavored according to our simulation study.

Comments:

21 pages, 10 figures, ApJ in press, the paper with full resolution images is this http URL

Subjects:

Astrophysics (astro-ph)

Cite as:

arXiv:0704.1055v2 [astro-ph]

Dado 2007 Cannonball模型下的shallow deacay的终止时间限定

主要内容:


精彩摘抄:


文章信息:
The time ending the shallow decay of the X-ray light curves of long GRBs

Authors: Shlomo Dado, Arnon Dar, A. De Rujula

(Submitted on 27 Mar 2007)

Abstract: We show that the mean values and distributions of the time ending the shallow decay of the light curve of the X-ray afterglow of long gamma ray bursts (GRBs), the equivalent isotropic energy in the X-ray afterglow up to that time and the equivalent isotropic GRB energy, as well as the correlations between them, are precisely those predicted by the cannonball (CB) model of GRBs. Correlations between prompt and afterglow observables are important in that they test the overall consistency of a GRB model. In the CB model, the prompt and afterglow spectra, the endtime, the complex canonical shape of the X-ray afterglows and the correlations between GRB observables are not surprises, but predictions.

Comments:

12 pages, 4 figures

Subjects:

Astrophysics (astro-ph)

Cite as:

arXiv:astro-ph/0703700v1

Mundell 2007 GRB 060418早期余辉的偏振观测

主要内容:
得到不大于8%的偏振度，排除了大尺度磁场的可能性。

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文章信息:
Early Optical Polarization of a Gamma Ray Burst Afterglow

Authors: Carole G. Mundell (1), Iain A. Steele (1), Robert J. Smith (1), Shiho Kobayashi (1) Andrea Melandri (1), Cristiano Guidorzi (1,2,3), Andreja Gomboc (4) Chris J. Mottram (1), David Clarke (5), Alessandro Monfardini (1,6), David Carter (1), David Bersier (1).

Abstract: We report the optical polarization of a gamma ray burst (GRB) afterglow, obtained 203 seconds after the initial burst of gamma rays from GRB 060418, using a ring polarimeter on the robotic Liverpool Telescope. Our robust (2-sigma) upper limit on the percentage of polarization, less than 8%, coincides with the fireball deceleration time at the onset of the afterglow. The combination of the rate of decay of the optical brightness and the low polarization at this critical time constrains standard models of GRB ejecta, ruling out the presence of a large-scale ordered magnetic field in the emitting region.

Comments:

8 pages including 1 figure. Accepted for publication in Science; published online 15 March 2007; 10.1126/science.1138484

Subjects:

Astrophysics (astro-ph)

Cite as:

arXiv:astro-ph/0703654v1

De Pasquale 2007 GRB 050801的早期余辉观测

主要内容:
包括光学、紫外和X射线。

精彩摘抄:


文章信息:
Early afterglow detection in the Swift observations of GRB 050801

Authors: Massimiliano De Pasquale, S. R. Oates, M.J.Page, D.N. Burrows, A.J.Blustin, S. Zane, K.O. Mason, P.W.A. Roming, D. Palmer, N. Gehrels, B. Zhang

(Submitted on 16 Mar 2007)

Abstract: We present results of Swift optical, UV and X-ray observations of the afterglow of GRB 050801. The source is visible over the full optical, UV and X-ray energy range of the Swift UVOT and XRT instruments.Both optical and X-ray lightcurves exhibit a broad plateau (\Delta t/t ~ 1) during the first few hundred seconds after the gamma-ray event. We investigate the multiwavelength spectral and timing properties of the afterglow, and we suggest that the behaviour at early times is compatible with an energy injection by a newly born magnetar with a period of a few tenths of a millisecond, which keeps the forward shock refreshed over this short interval by irradiation. Reverse shock emission is not observed. Its suppression might be due to GRB ejecta being permeated by high magnetic fields, as expected for outflows powered by a magnetar.Finally, the multiwavelength study allows a determination of the burst redshift, z=1.56.

Comments:

13 pages, 7 figs, Accepted for publication in MNRAS

Subjects:

Astrophysics (astro-ph)

Cite as:

arXiv:astro-ph/0703447v1