碰撞星系的照片

Hubble 为庆祝升空18周年，刚刚发布的几个碰撞星系的照片
http://www.nasa.gov/mission_pages/hubble/science/hst_img_20080424.html
http://www.nasa.gov/images/content/223974main_wildgalaxies1_20080424_HI.jpg

Covino 2008 GRB071010A的复杂光变

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· arXiv e-print (arXiv:0804.4367)

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Title:		The complex light-curve of the afterglow of GRB071010A
Authors:		Covino, S.; D'Avanzo, P.; Klotz, A.; Perley, D. A.; Amati, L.; et al
Publication:		eprint arXiv:0804.4367
Publication Date:		04/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		11 pages, 3 figures, MNRAS, in press
Bibliographic Code:		2008arXiv0804.4367C

Abstract

We present and discuss the results of an extensive observational campaign devoted to GRB071010A, a long-duration gamma-ray burst detected by the Swift satellite. This event was followed for almost a month in the optical/near-infrared (NIR) with various telescopes starting from about 2min after the high-energy event. Swift-XRT observations started only later at about 0.4d. The light-curve evolution allows us to single out an initial rising phase with a maximum at about 7min, possibly the afterglow onset in the context of the standard fireball model, which is then followed by a smooth decay interrupted by a sharp rebrightening at about 0.6d. The rebrightening was visible in both the optical/NIR and X-rays and can be interpreted as an episode of discrete energy injection, although various alternatives are possible. A steepening of the afterglow light curve is recorded at about 1d. The entire evolution of the optical/NIR afterglow is consistent with being achromatic. This could be one of the few identified GRB afterglows with an achromatic break in the X-ray through the optical/NIR bands. Polarimetry was also obtained at about 1d, just after the rebrightening and almost coincident with the steepening. This provided a fairly tight upper limit of 0.9% for the polarized-flux fraction.

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Yuksel 2008 Revealing the High-Redshift Star Formation Rate

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· arXiv e-print (arXiv:0804.4008)

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Title:		Revealing the High-Redshift Star Formation Rate with Gamma-Ray Bursts
Authors:		Yuksel, Hasan; Kistler, Matthew D.; Beacom, John F.; Hopkins, Andrew M.
Publication:		eprint arXiv:0804.4008
Publication Date:		04/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		4 pages, 2 figures
Bibliographic Code:		2008arXiv0804.4008Y

Abstract

While the high-z frontier of star formation rate (SFR) studies has advanced rapidly, direct measurements beyond z ~ 4 remain difficult, as shown by significant disagreements among different results. Gamma-ray bursts, owing to their brightness and association with massive stars, offer hope of clarifying this situation, provided that the GRB rate can be properly related to the SFR. The Swift GRB data reveal an increasing evolution in the GRB rate relative to the SFR at intermediate z; taking this into account, we use the highest-z GRB data to make a new determination of the SFR at z = 4-7. Our results exceed the lowest direct SFR measurements, and imply that no steep drop exists in the SFR up to at least z ~ 6.5. We discuss the implications of our result for cosmic reionization, the efficiency of the universe in producing stellar-mass black holes, and ``GRB feedback'' in star-forming hosts.

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Guida 2008 GRB 060124 的解释

主要内容:
这个暴是第一个Swift的BAT XRT和UVOT同时观测了瞬时辐射和余辉的暴。作者们想要用前兆是内激波、瞬时辐射是外激波的模型解释它。

这个暴有precusor
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文章信息:

· arXiv e-print (arXiv:0804.3983)

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Title:		Theoretical interpretation of GRB060124: preliminary results
Authors:		Guida, Roberto; Grazia Bernardini, Maria; Bianco, Carlo Luciano; Caito, Letizia; Giovanna Dainotti, Maria; Ruffini, Remo
Publication:		eprint arXiv:0804.3983
Publication Date:		04/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		6 pages, 2 figures, to appear on the Proceedings of the Eleventh Marcel Grossmann Meeting, Berlin (Germany), July 2006
Bibliographic Code:		2008arXiv0804.3983G

Abstract

We show the preliminary results of the application of our "fireshell" model to GRB060124. This source is very peculiar because it is the first event for which both the prompt and the afterglow emission were observed simultaneously by the three Swift instruments: BAT (15-350 keV), XRT (0.2-10 keV) and UVOT (170-650 nm), due to the presence of a precursor ~ 570 s before the main burst. We analyze GRB060124 within our "canonical" GRB scenario, identifying the precursor with the P-GRB and the prompt emission with the afterglow peak emission. In this way we reproduce correctly the energetics of both these two components. We reproduce also the observed time delay between the precursor (P-GRB) and the main burst. The effect of such a time delay in our model will be discussed.

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Lazzati 2008 X-ray flares中心引擎晚期能量注入

主要内容:
发现flares的能量随时间是呈幂律下降的。

精彩摘抄:
In this paper we show that the energy emitted in the form of flares decreases with time as a power-law


文章信息:

· arXiv e-print (arXiv:0804.2895)

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Title:		X-ray flares and their relation to the inner engine activity of GRBs
Authors:		Lazzati, Davide; Morsony, Brian J.; Perna, Rosalba; Begelman, Mitchell C.
Publication:		eprint arXiv:0804.2895
Publication Date:		04/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		Solicited paper to appear in Proceedings of Gamma Ray Bursts 2007 Meeting, Santa Fe, New Mexico
Bibliographic Code:		2008arXiv0804.2895L

Abstract

Flares overlaid on the smooth power-law decay of Swift X-ray afterglows are rather common, appearing in roughly half the observed light curves. They are a manifestation of the late time activity of the inner engine, since their temporal evolution is too fast to be linked to activity taking place in the external shock blastwave. In this paper we show that the energy emitted in the form of flares decreases with time as a power-law. We discuss several possibilities in which the flares can be powered and the source of the observed variability. We show that late time accretion from a disk can provide the necessary energy input in both classes of short duration and long duration gamma-ray bursts.

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Falcone 2008 伽玛暴甚高能辐射白皮书

主要内容:
介绍当前和将来在甚高能方面的情况

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文章信息:

· arXiv e-print (arXiv:0804.2256)

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Title:		The Gamma Ray Burst section of the White Paper on the Status and Future of Very High Energy Gamma Ray Astronomy: A Brief Preliminary Report
Authors:		Falcone, A. D.; Williams, D. A.; Baring, M. G.; Blandford, R.; Connaughton, V.; Coppi, P.; Dermer, C.; Dingus, B.; Fryer, C.; Gehrels, N.; Granot, J.; Horan, D.; Katz, J. I.; Kuehn, K.; Meszaros, P.; Norris, J.; Saz Parkinson, P.; Peer, A.; Ramirez-Ruiz, E.; Razzaque, S.; Wang, X.; Zhang, B.
Publication:		eprint arXiv:0804.2256
Publication Date:		04/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		to appear in Proceedings of Gamma Ray Bursts 2007 Meeting, Santa Fe, New Mexico; 5 pages, 4 figures
Bibliographic Code:		2008arXiv0804.2256F

Abstract

This is a short report on the preliminary findings of the gamma ray burst (GRB) working group for the white paper on the status and future of very high energy (VHE; >50 GeV) gamma-ray astronomy. The white paper discusses the status of past and current attempts to observe GRBs at GeV-TeV energies, including a handful of low-significance, possible detections. The white paper concentrates on the potential of future ground-based gamma-ray experiments to observe the highest energy emission ever recorded for GRBs, particularly for those that are nearby and have high Lorentz factors in the GRB jet. It is clear that the detection of VHE emission would have strong implications for GRB models, as well as cosmic ray origin. In particular, the extended emission phase (including both afterglow emission and possible flaring) of nearby long GRBs could provide the best possibility for detection. The difficult-to-obtain observations during the prompt phase of nearby long GRBs and short GRBs could also provide particularly strong constraints on the opacity and bulk Lorentz factors surrounding the acceleration site. The synergy with upcoming and existing observatories will, of course, be critical for both identification of GRBs and for multiwavelength/multimessenger studies.

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Falcone 2008 X射线耀发的观测大致特征

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文章信息:

· arXiv e-print (arXiv:0804.2260)

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Title:		Observations of X-ray Flares from Gamma Ray Bursts
Authors:		Falcone, A. D.; Morris, D.; Racusin, J.; Chincarini, G.; Moretti, A.; Romano, P.; Burrows, D. N.; Pagani, C.; Stroh, M.; Grupe, D.; Campana, S.; Covino, S.; Tagliaferri, G.; Gehrels, N.
Publication:		eprint arXiv:0804.2260
Publication Date:		04/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		Solicited paper to appear in Proceedings of Gamma Ray Bursts 2007 Meeting, Santa Fe, New Mexico; 6 pages, 4 figures
Bibliographic Code:		2008arXiv0804.2260F

Abstract

Swift-XRT observations of the X-ray emission from gamma ray bursts (GRBs) and during the GRB afterglow have led to many new results during the past two years. One of these exciting results is that approximately 1/3-1/2 of GRBs contain detectable X-ray flares. The mean fluence of the X-ray flares is ~10 times less than that of the initial prompt emission, but in some cases the flare is as energetic as the prompt emission itself. The flares display fast rises and decays, and they sometimes occur at very late times relative to the prompt emission (sometimes as late as 10^5 s after T_0) with very high peak fluxes relative to the underlying afterglow decay that has clearly begun prior to some flares. The temporal and spectral properties of the flares are found to favor models in which flares arise due to the same GRB internal engine processes that spawned the prompt GRB emission. Therefore, both long and short GRB internal engine models must be capable of producing high fluences in the X-ray band at very late times.

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Ferrero 2008 GRB 060605 的余辉观测

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精彩摘抄:
余辉的位置
余辉光变曲线，上面的是光学，下面的是X射线。
光学在其它暴中的位置

文章信息:

· arXiv e-print (arXiv:0804.2457)

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Title:		Analysing afterglows using integral field spectroscopy: GRB 060605, the first practical example
Authors:		Ferrero, Patrizia; Klose, Sylvio; Kann, David Alexander; Savaglio, Sandra; Palazzi, Eliana; Maiorano, Elisabetta; Böhm, Petra; Schulze, Steve; Grupe, Dirk; Oates, Samantha R.; Sánchez, Sebastián F.; Amati, Lorenzo; Greiner, Jochen; Hjorth, Jens; Malesani, Daniele; Barthelmy, Scott D.; Gorosabel, Javier; Masetti, Nicola; Roth, Martin M.
Publication:		eprint arXiv:0804.2457
Publication Date:		04/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		Submitted to A&A
Bibliographic Code:		2008arXiv0804.2457F

Abstract

GRB 060605 was a long and relatively faint gamma-ray burst detected by \emph{Swift}/BAT with a duration of about 20 sec. Its afterglow could be observed with \emph{Swift}/XRT for nearly 1 day while \emph{Swift}/UVOT could detect the afterglow during the first 6 hours after the event. Here, we report on integral field spectroscopy of its afterglow performed with PMAS/PPak mounted at the Calar Alto 3.5 m telescope. In addition, we report on a detailed analysis of XRT and UVOT data and on the results of deep late-time VLT observations, which reveal the GRB host galaxy. We find that the burst occured at a redshift of $z$=3.773, possibly associated with a faint, $R_C=26.4 \pm 0.3$ host. Based on the optical and X-ray data we deduce information on the SED of the afterglow, the position of the cooling frequency in the SED, the nature of the circumburst environment, its collimation factor, and its energetics. We find that the GRB fireball was expanding into a constant-density medium and that the explosion was collimated with a narrow half-opening angle of about 2.3 degrees. The initial Lorentz factor of the fireball was about 250, its beaming-corrected energy release in the gamma-ray band was comparably low, however. The optical as well as the X-ray afterglow, on the other hand, were rather luminous. Finally, we find that within the error bars the data is consistent with an achromatic evolution of the afterglow during the suspected jet break time at about 0.24 days after the burst.}

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Kann 2008 ELT era的伽玛暴余辉

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文章信息:

· arXiv e-print (arXiv:0804.1979)

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Title:		GRB afterglows in the ELT era
Authors:		Kann, D. A.; Klose, S.
Publication:		eprint arXiv:0804.1979
Publication Date:		04/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		Submitted to the conference proceedings of the ESO workshop "Science with the VLT in the ELT Era"; 2 pages, 1 figure
Bibliographic Code:		2008arXiv0804.1979K

Abstract

This is a very short conference proceeding based on a poster shown at the ESO workshop "Science with the VLT in the ELT Era". For more information, see "The Afterglows of Swift-era Gamma-Ray Bursts. I. Comparing pre-Swift and Swift era Long/Soft (Type II) GRB Optical Afterglows" (arXiv:0712.2186) as well as "The Afterglows of Swift-era Gamma-Ray Bursts. II. Short/Hard (Type I) vs. Long/Soft (Type II) Optical Afterglows" (arXiv:0804.1959)

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Kann 2008 详细的长短暴余辉比较

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· arXiv e-print (arXiv:0804.1959)

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Title:		The Afterglows of Swift-era Gamma-Ray Bursts. II. Short/Hard (Type I) vs. Long/Soft (Type II) Optical Afterglows
Authors:		Kann, D. A.; Klose, S.; Zhang, B.; Wilson, A. C.; Butler, N. R.; Malesani, D.; Nakar, E.; Antonelli, L. A.; Chincarini, G.; Cobb, B. E.; Covino, S.; D'Avanzo, P.; D'Elia, V.; Della Valle, M.; Ferrero, P.; Fugazza, D.; Gorosabel, J.; Israel, . L.; Mannucci, F.; Piranomonte, S.; Schulze, S.; Stella, L.; Tagliaferri, G.; Wiersema, K.
Publication:		eprint arXiv:0804.1959
Publication Date:		04/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		Submitted to ApJ; 70 pages in referee format; 28 pages main text, 13 pages Appendix, 15 pages references, 2 tables, 10 figures; Figures 1 and 2 downgraded to fit arXiv space restrictions
Bibliographic Code:		2008arXiv0804.1959K

Abstract

We use a large sample of Gamma-Ray Burst (GRB) afterglow and prompt emission data to compare the optical afterglows (or the lack thereof) of ``short/hard'' Type I GRBs (those that are assumed not to be due to the death of massive stars, but, e.g., merger of compact objects) with those of ``long/soft'' Type II GRBs (those due to the core collapse of massive stars). In comparison to the afterglows of Type II GRBs, we find that those of Type I GRBs have a lower average luminosity and show a larger intrinsic spread of luminosities. From late and deep upper limits on the optical transients, we establish limits on the maximum optical luminosity of any associated supernova, confirming older works and adding new results. We use deep upper limits on Type I GRB optical afterglows to constrain the parameter space of possible Mini-SN emission associated with a compact-object merger. Using the prompt emission data, we search for correlations between the parameters of the prompt emission and the late optical afterglow luminosities. We find trends between the bolometric isotropic energy release and the optical afterglow luminosity at a fixed time after trigger, and between the host offset and the luminosity, bit no significant trend between the isotropic energy release and the duration of the GRBs. We also discuss three anomalous GRBs, GRB 060121, GRB 060505, and GRB 060614, in the light of their optical afterglow luminosities.

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Piran 2008 Paczy'nski对伽玛暴理解的贡献

主要内容:
总结Paczy'nski对伽玛暴的贡献，实际上也应该是Piran对伽玛暴的思考。

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文章信息:

· arXiv e-print (arXiv:0804.2074)

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Title:		Bohdan's Impact on Our Understanding of Gamma-ray Bursts
Authors:		Piran, Tsvi
Publication:		eprint arXiv:0804.2074
Publication Date:		04/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		A talk given at The Variable Universe A Celebration of Bohdan Paczy'nski. To appear at the proccedings edited by Kris Stanek
Bibliographic Code:		2008arXiv0804.2074P

Abstract

Bohdan Paczy'nski was one of the pioneers of the cosmological GRB model. His ideas on how GRBs operate and what are their progenitors have dominated the field of GRBs in the hectic nineties during which the distances and the origin of GRBs were revealed. I discuss here Bohdan's contributions in some historical perspective.

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Qin 2008 全面考虑曲率效应

主要内容:
由于曲率效应导致的高纬辐射在光变上的表现f_nu ~ t^{-2-\beta}，只是在辐射时标很短的情况下成立。文章更仔细地考虑的曲率效应。

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文章信息:

· arXiv e-print (arXiv:0804.2175)

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Title:		The full curvature effect expected in early X-ray afterglow emission of gamma-ray bursts
Authors:		Qin, Y. -P.
Publication:		eprint arXiv:0804.2175
Publication Date:		04/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		28 pages, 9 figures. Accepted for publication in ApJ
Bibliographic Code:		2008arXiv0804.2175Q

Abstract

We explore the influence of the full curvature effect on the flux of early X-ray afterglow of gamma-ray bursts (GRBs) in cases when the spectrum of the intrinsic emission is a power-law. We find that the well-known $t^{-(2+\beta)}$ curve is present only when the intrinsic emission is extremely short or the emission arises from an exponential cooling. The time scale of this curve is independent of the Lorentz factor. The resulting light curve would contain two phases when the intrinsic emission has a power-law spectrum and a temporal power-law profile with infinite duration. The first phase is a rapid decay one where the light curve well follows the $t^{-(2+\beta)}$ curve. The second is a shallow decay phase where the power-law index of the light curve is obviously smaller than that in the first phase. The start of the shallow phase is strictly constrained by the fireball radius, which in turn, can put a lower limit to the latter. In the case when the temporal power-law emission lasts a limited interval of time, there will be a third phase after the $t^{-(2+\beta)}$ curve and the shallow decay phase, which is much steeper than the shallow phase. As an example of application, we fit the XRT data of GRB 050219A with our model and show that the curvature effect alone can roughly account for this burst. Although fitting parameters can not be uniquely determined due to various choices of fitting, a lower limit of the fireball radius of this burst can be estimated, which is $\sim 10^{14}cm$.

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Kann 2008 长短暴余辉比较

主要内容:
对长暴和短暴的余辉进行了统计

精彩摘抄:
光变曲线，黑线是短暴（或者是I型暴）的

文章信息:

· arXiv e-print (arXiv:0804.1980)

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Title:		Afterglows of Gamma-Ray Bursts: Short vs. Long GRBs
Authors:		Kann, D. A.; Klose, S.
Publication:		eprint arXiv:0804.1980
Publication Date:		04/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		Conference Proceedings, "Gamma-Ray Bursts 2007", Santa Fe, shortened poster presentation; 4 pages, 3 figures; for full updated papers, go here to arXiv:0712.2186 and also here to arXiv:0804.1959
Bibliographic Code:		2008arXiv0804.1980K

Abstract

We compiled a large sample of Swift-era photometric data on long (Type II) and short (Type I) GRB afterglows. We compare the luminosity and energetics of the different samples to each other and to the afterglows of the pre-Swift era. Here, we present the first results of these studies.

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D'Elia 2008 GRB 080319B的高分辨谱

主要内容:
余辉阶段的谱，有多个成分，可能是外部介质环境的吸收

精彩摘抄:


文章信息:

· arXiv e-print (arXiv:0804.2141)

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Title:		The prompt, high resolution spectroscopic view of the "naked-eye" GRB080319B
Authors:		D'Elia, V.; Fiore, F.; Perna, R.; Krongold, Y.; Covino, S.; Fugazza, D.; Lazzati, D.; Nicastro, F.; Antonelli, L. A.; Campana, S.; Chincarini, G.; D'Avanzo, P.; Della Valle, M.; Goldoni, P.; Guetta, D.; Guidorzi, C.; Meurs, E. J. A.; Molinari, E.; Norci, L.; Piranomonte, S.; Stella, L.; Stratta, G.; Tagliaferri, G.; Ward, P.
Publication:		eprint arXiv:0804.2141
Publication Date:		04/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		5 pages, 4 .ps figures, ApJL, submitted
Bibliographic Code:		2008arXiv0804.2141D

Abstract

GRB080319B reached 5th optical magnitude during the burst. Thanks to the VLT/UVES rapid response mode, we observed its afterglow just 8m:30s after the GRB onset when the magnitude was R ~ 12. This allowed us to obtain the best signal-to-noise, high resolution spectrum of a GRB afterglow ever (S/N per resolution element ~ 50). The spectrum is rich of absorption features belonging to the main system at z=0.937, divided in at least six components spanning a total velocity range of 100 km/s. The VLT/UVES observations caught the absorbing gas in a highly excited state, producing the strongest Fe II fine structure lines ever observed in a GRB. A few hours later the optical depth of these lines was reduced by a factor of 4-20, and the optical/UV flux by a factor of ~ 60. This proves that the excitation of the observed fine structure lines is due to ``pumping'' by the GRB UV photons. A comparison of the observed ratio between the number of photons absorbed by the excited state and those in the Fe II ground state suggests that the six absorbers are $\gs18-34$ kpc from the GRB site, with component I ~ 2 times closer to the GRB site than components III to VI. Component I is characterized also by the lack of Mg I absorption, unlike all other components. This may be due to a higher gas temperature, suggesting a structured ISM in this galaxy complex.

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Ostlin 2008 限制GRB 030329的前身星质量

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文章信息:

arXiv:0804.1856 [ps, pdf, other]

Title: Constraining the mass of the GRB 030329 progenitor

Authors: G. Ostlin, E. Zackrisson, J. Sollerman, S. Mattila, M. Hayes

Comments: Accepted to MNRAS

Subjects: Astrophysics (astro-ph)

The long-duration gamma-ray burst (GRB) 030329, associated with supernova (SN) 2003dh, occurred inside a star-forming dwarf galaxy at redshift $z=0.1685$. The low redshift, and a rich set of archival Hubble Space Telescope (HST) images, makes this GRB well-suited for a detailed study of the stellar population in the immediate vicinity of the explosion. Since the lifetime of a star is directly tied to its mass, the age of the stellar population can be used to put constraints on the GRB and SN progenitor mass. From the HST images we extract the colours of the precise site from which the GRB originated, and find that the colours are significantly different from those of the overall host galaxy and the surrounding starburst environment. We have used spectral evolutionary models, including nebular emission, to carefully constrain the age of the stellar population, and hence the progenitor, at the very explosion site. For instantaneous burst models we find that a population age of 5 Myr best matches the data, suggesting a very massive (M > 50 M_sun) star as the progenitor, with an upper limit of 8 Myr (M > 25 M_sun). For more extended star formation scenarios, the inferred progenitor age is in most cases still very young (age <> 25 M_sun), with an upper limit of 20 Myr (M > 12 M_sun). These age estimates are an order of magnitude lower than the ages inferred from the overall host galaxy colours, indicating that progenitor mass estimates based on data for spatially unresolved GRB host galaxies will in general be of limited use. Our results are consistent with the collapsar scenario.

Gomboc 2008 GRB 061126的详细观测

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文章信息:

· arXiv e-print (arXiv:0804.1727)

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Title:		Multiwavelength analysis of the intriguing GRB 061126: the reverse shock scenario and magnetization
Authors:		Gomboc, A.; Kobayashi, S.; Guidorzi, C.; Melandri, A.; Mangano, V.; Sbarufatti, B.; Mundell, C. G.; Schady, P.; Smith, R. J.; Updike, A. C.; Kann, D. A.; Misra, K.; Rol, E.; Pozanenko, A.; Castro-Tirado, A. J.; Anupama, G. C.; Bersier, D.; Bode, M. F.; Carter, D.; Curran, P.; Fruchter, A.; Graham, J.; Hartmann, D. H.; Ibrahimov, M.; Levan, A.; Monfardini, A.; Mottram, C. J.; O'Brien, P. T.; Prema, P.; Sahu, D. K.; Steele, I. A.; Tanvir, N. R.; Wiersema, K.
Publication:		eprint arXiv:0804.1727
Publication Date:		04/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		Submitted to ApJ
Bibliographic Code:		2008arXiv0804.1727G

Abstract

We present a detailed study of the prompt and afterglow emission from Swift GRB 061126 using BAT, XRT, UVOT data and multi-color optical imaging from ten ground-based telescopes. GRB 061126 was a long burst ($T_{90}=191$ s) with four overlapping peaks in its $\gamma$-ray light curve. The X-ray afterglow, observed from 26 min to 20 days after the burst, shows a simple power-law decay with $\alpha_{\rm X}=1.290\pm0.008$. Optical observations presented here cover the time range from 258 s (Faulkes Telescope North) to 15 days (Gemini North) after the burst; the decay rate of the optical afterglow shows a steep-to-shallow transition (from $\alpha_1=1.48\pm 0.06$ to $\alpha_2=0.89\pm0.03$) approximately 12 min after the burst. We suggest the early, steep component is due to a reverse shock and show that the original ejecta from the central engine is highly magnetized. The optical light curve implies a late-time break at about 1.5 days after the burst, while there is no evidence of the simultaneous break in the X-ray light curve. We model the broad band emission and show that some afterglow characteristics (the steeper decay in X-ray and the shallow spectral index from optical to X-ray) are difficult to explain in the framework of the standard fireball model. This might imply that the X-ray afterglow is due to an additional emission process, such as late time central engine activity rather than blast-wave shock emission. Possible chromatic break at 1.5 days after the burst would give support to the additional emission scenario.

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Ghirlanda 2008 Epeak-Eiso的选择效应

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文章信息:

· arXiv e-print (arXiv:0804.1675)

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Title:		The Epeak-Eiso plane of long Gamma Ray Bursts and selection effects
Authors:		Ghirlanda, G.; Nava, L.; Ghisellini, G.; Firmani, C.; Cabrera, J. I.
Publication:		eprint arXiv:0804.1675
Publication Date:		04/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		To appear in MNRAS
Bibliographic Code:		2008arXiv0804.1675G

Abstract

We study the distribution of long Gamma Ray Bursts in the Ep-Eiso and in the Ep,obs-Fluence planes through an updated sample of 76 bursts, with measured redshift and spectral parameters, detected up to September 2007. We confirm the existence of a strong rest frame correlation Ep ~ Eiso^0.54+-0.01. Contrary to previous studies, no sign of evolution with redshift of the Ep-Eiso correlation (either its slope and normalisation) is found. The 76 bursts define a strong Ep,obs-Fluence correlation in the observer frame (Ep,obs ~ F^0.32+-0.05) with redshifts evenly distributed along this correlation. We study possible instrumental selection effects in the observer frame Ep,obs-Fluence plane. In particular, we concentrate on the minimum peak flux necessary to trigger a given GRB detector (trigger threshold) and the minimum fluence a burst must have to determine the value of Ep,obs (spectral analysis threshold). We find that the latter dominates in the Ep,obs-Fluence plane over the former. Our analysis shows, however, that these instrumental selection effects do not dominate for bursts detected before the launch of the Swift satellite, while the spectral analysis threshold is the dominant truncation effect of the Swift GRB sample (27 out of 76 events). This suggests that the Ep,obs-Fluence correlation defined by the pre--Swift sample could be affected by other, still not understood, selection effects. Besides we caution about the conclusions on the existence of the Ep,obs-Fluence correlation based on our Swift sample alone.

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Resmi 2008 电子能谱分布p小于2的情况

主要内容:
认为电子也是分段的幂律谱，有p1和p2, p1小于2,但p2肯定大于2的。（即使同步辐射不也可以修正单一幂律到两段幂律吗，p和p+1. 不过可能这里是原始分部就是两段，加上同步修正就可能变成三段了。）

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文章信息:

arXiv:0804.1378 [ps, pdf, other]

Title: Hard Electron Energy Distribution in the Relativistic Shocks of GRB Afterglows

Authors: L. Resmi, D. Bhattacharya

Comments: 17 pages, 6 figures. Accepted for publication in MNRAS

Subjects: Astrophysics (astro-ph)

Particle acceleration in relativistic shocks is not a very well understood subject. Owing to that difficulty, radiation spectra from relativistic shocks, such as those in GRB afterglows, have been often modelled by making assumptions about the underlying electron distribution. One such assumption is a relatively soft distribution of the particle energy, which need not be true always, as is obvious from observations of several GRB afterglows. In this paper, we describe modifications to the afterglow standard model to accommodate energy spectra which are `hard'. We calculate the overall evolution of the synchrotron and compton flux arising from such a distribution. We also model two afterglows, GRB010222 and GRB020813, under this assumption and estimate the physical parameters.

Fujimoto 2008 喷流中的核合成

主要内容:
考虑磁场主导的喷流中的核合成，认为喷流的能量越高，产生的Ni56越多。而象060614和060605这样的低能量的暴，产生的Ni56就比较少，因为没有超新星成分。 也就是说他们还是认为这两个暴是大质量恒星坍缩引起的。

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· arXiv e-print (arXiv:0804.0969)

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Title:		Nucleosynthesis in Magnetically Driven Jets from Collapsars
Authors:		Fujimoto, Shin-ichiro; Nishimura, Nobuya; Hashimoto, Masa-aki
Publication:		eprint arXiv:0804.0969
Publication Date:		04/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		10 pages, 14 figures, 1 table, Accepted for publication in the Astroph ysical Journal
Bibliographic Code:		2008arXiv0804.0969F

Abstract

We have made detailed calculations of the composition of magnetically driven jets ejected from collapsars, or rapidly rotating massive stars, based on long-term magnetohydrodynamic simulations of their core collapse with various distributions of magnetic field and angular momentum before collapse. We follow the evolution of the abundances of about 4000 nuclides from the collapse phase to the ejection phase and through the jet generation phase using a large nuclear reaction network. We find that the r-process successfully operates only in energetic jets (> 1e51 ergs), such that U and Th are synthesized abundantly, even when the collapsar has a relatively weak magnetic field (1e10 G) and a moderately rotating core before the collapse. The abundance patterns inside the jets are similar to those of the r-elements in the solar system. About 0.01-0.06 Msun neutron-rich, heavy nuclei are ejected from a collapsar with energetic jets. The higher energy jets have larger amounts of Ni56, varying from 0.00037 to 0.06Msun. Less energetic jets, which eject small amounts of Ni56, could induce a gamma-ray burst (GRB) a supernova, such as GRB 060505 or GRB 060614. Considerable amounts of r-elements are likely to be ejected from GRBs with hypernovae, if both the GRB and hypernova are induced by jets that are driven near the black hole.

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Melandri 2008 伽玛暴早期光学余辉统计

主要内容:
给出了63个暴的早期光学余辉（这些是最近所能看到的）

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四种光学和X-ray光变的可能情形，示意图

文章信息:

· arXiv e-print (arXiv:0804.0811)

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Title:		The Early-time Optical Properties of Gamma-Ray Burst Afterglows
Authors:		Melandri, A.; Mundell, C. G.; Kobayashi, S.; Guidorzi, C.; Gomboc, A.; Steele, I. A.; Smith, R. J.; Bersier, D.; Mottram, C. J.; Carter, D.; Bode, M. F.; O'Brien, P. T.; Tanvir, N. R.; Rol, E.; Chapman, R.
Publication:		eprint arXiv:0804.0811
Publication Date:		04/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		51 pages, 9 figures, 4 tables, submitted to ApJ
Bibliographic Code:		2008arXiv0804.0811M

Abstract

We present a multiwavelength analysis of 63 Gamma-Ray Bursts observed with the world's three largest robotic optical telescopes, the Liverpool and Faulkes Telescopes (North and South). Optical emission was detected for 24 GRBs with brightnesses ranging from R = 10 to 22 mag in the first 10 minutes after the burst. By comparing optical and X-ray light curves from t = 100 to about 10^6 seconds, we introduce four main classes, defined by the presence or absence of temporal breaks at optical and/or X-ray wavelengths. While 15/24 GRBs can be modelled with the forward-shock model, explanation of the remaining nine is very challenging in the standard framework even with the introduction of energy injection or an ambient density gradient. Early X-ray afterglows, even segments of light curves described by a power-law, may be due to additional emission from the central engine. 39 GRBs in our sample were not detected and have deep upper limits (R <> Bibtex entry for this abstract Preferred format for this abstract (see Preferences)