华工已基本可下载三大天文杂志的全文了

刚才我试了一下，天文的三大杂志都基本可以直接下载了，只有AA只能下2004年以前的。（现在是可以直接上国际网的。）

http://www.journals.uchicago.edu/ApJ/issues.html
http://www.blackwell-synergy.com/loi/MNR
http://www.aanda.org/index.php?option=com_base_ora&access=allissues&Itemid=39&lang=en

至于为什么可以直接下载还不知道。

Mimica 2006 1D数值模拟伽玛暴内激波的碰撞 2

主要内容:
对于两个shell之间的碰撞， 考虑到辐射效率不能直接把两个shell当作整体，然后利用能量和动量守恒计算产生的内能，而应该是一个积分形式。计算了辐射效率，伽玛暴在6%-10%之间。

类似的还有：Mimica et al. 2005, A&A 441, 103

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文章信息:

astro-ph/0611765 [abs, ps, pdf, other] :

Title: Internal shocks in relativistic outflows: collisions of magnetized shells
Authors: Petar Mimica (1), Miguel-Angel Aloy (1, 2), Ewald Mueller (2) ((1) Departamento de Astronomia y Astrofisica, Universidad de Valencia, (2) MPA Garching)
Comments: 17 pages, 18 figures. 2 new references have been added. Accepted for publication in Astronomy and Astrophysics

(Abridged): We study the collision of magnetized irregularities (shells) in relativistic outflows in order to explain the origin of the generic phenomenology observed in the non-thermal emission of both blazars and gamma-ray bursts. We focus on the influence of the magnetic field on the collision dynamics, and we further investigate how the properties of the observed radiation depend on the strength of the initial magnetic field and on the initial internal energy density of the flow. The collisions of magnetized shells and the radiation resulting from these collisions are calculated using the 1D relativistic magnetohydrodynamics code MRGENESIS. The interaction of the shells with the external medium prior to their collision is also determined using an exact solver for the corresponding 1D relativistic magnetohydrodynamic Riemann problem. Our simulations show that two magnetization parameters - the ratio of magnetic energy density and thermal energy density, \alpha_B, and the ratio of magnetic energy density and mass-energy density, \sigma - play an important role in the pre-collision phase, while the dynamics of the collision and the properties of the light curves depend mostly on the magnetization parameter \sigma. The interaction of the shells with the external medium changes the flow properties at their edges prior to the collision. For sufficiently dense shells moving at large Lorentz factors (\simgt 25) these properties depend only on the magnetization parameter \sigma. Internal shocks in GRBs may reach maximum efficiencies of conversion of kinetic into thermal energy between 6% and 10%, while in case of blazars, the maximum efficiencies are \sim 2%.

McGlynn 2007 GRB 041219a的偏振观测

主要内容:
有高偏振。

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文章信息:

astro-ph/0702738 [abs, ps, pdf, other] :

Title: Polarisation studies of the prompt gamma-ray emission from GRB 041219a using the Spectrometer aboard INTEGRAL
Authors: S. McGlynn (1), D. J. Clark (2), A. J. Dean (2), L. Hanlon (1), S. McBreen (3), D. R. Willis (3), B. McBreen (1), A. J. Bird (2), S. Foley (1) ((1) University College Dublin, (2) University of Southampton, (3) MPE Garching)
Comments: 11 pages, 10 figures, accepted by A&A

The spectrometer aboard INTEGRAL, SPI, has the capability to detect the signature of polarised emission from a bright gamma-ray source. GRB 041219a is the most intense burst localised by INTEGRAL and is an ideal candidate for such a study. Polarisation can be measured using multiple events scattered into adjacent detectors because the Compton scatter angle depends on the polarisation of the incoming photon. A search for linear polarisation in the most intense pulse of duration 66 seconds and in the brightest 12 seconds of GRB 041219a was performed in the 100-350keV, 100-500keV and 100keV-1MeV energy ranges. The multiple event data from the spectrometer was analysed and compared with the predicted instrument response obtained from Monte-Carlo simulations using the GEANT 4 INTEGRAL mass model. The chi^2 distribution between the real and simulated data as a function of the percentage polarisation and polarisation angle was calculated for all three energy ranges. The degree of linear polarisation in the brightest pulse of duration 66s was found to be 63+/-31% at an angle of 70+/-14 degrees in the 100-350keV energy range. The degree of polarisation was also constrained in the brightest 12s of the GRB and a polarisation fraction of 96+/-40% at an angle of 60+/-14 degrees was determined over the same energy range. However, despite extensive analysis and simulations, a systematic effect that could mimic the weak polarisation signal could not be definitively excluded. Our results over several energy ranges and time intervals are consistent with a polarisation signal of about 60% at a low level of significance (2 sigma). We conclude that the procedure described here demonstrates the effectiveness of using SPI as a polarimeter, and is a viable method of measuring polarisation levels in intense gamma--ray bursts.

Coward 2007 关于伽玛暴的红移分布的一些问题

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文章信息:

astro-ph/0702704 [abs, ps, pdf, other] :

Title: Open issues with the gamma-ray burst redshift distribution
Authors: David Coward
Comments: 26 pages, 4 figures, submitted to New Astronomy Reviews, accepted subject to minor revision

Cosmological gamma ray bursts (GRBs) are the brightest explosions in the Universe. Satellite detectors, such as Beppo-SAX, HETE2 and more recently Swift, have provided a wealth of data, including the localization and redshifts of subsets of GRBs. The redshift distribution has been utilized in several studies in attempts to constrain the evolving star formation rate and to probe GRB rate evolution in the high-redshift Universe. These studies find that the GRB luminosity function and/or the rate density evolve with redshift. We present a short review of the problems of constraining GRB rate evolution in the context of the complex mix of biases inherent in the redshift measurements. To disentangle GRB rate evolution from the biases prevalent in the redshift distribution will require accounting for the incompleteness of the observed redshift sample. We highlight the importance of formulating a `complete GRB selection function' to account for the main sources of bias.

Berger 2007 短暴和X射线余辉的总结

主要内容:
总结了17个有余辉的短暴。

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文章信息:

astro-ph/0702694 [abs, ps, pdf, other] :

Title: The Prompt Gamma-Ray and Afterglow Energies of Short-Duration Gamma-Ray Bursts
Authors: E. Berger (Carnegie Observatories, Princeton)
Comments: Submitted to ApJ; 9 pages, 2 figures, 1 table

I present an analysis of the gamma-ray and afterglow energies of the complete sample of 17 short duration GRBs with prompt X-ray follow-up. I find that 80% of the bursts exhibit a linear correlation between their gamma-ray fluence and the afterglow X-ray flux normalized to t=1 d, a proxy for the kinetic energy of the blast wave ($F_{X,1}~F_{gamma}^1.01). An even tighter correlation is evident between E_{gamma,iso} and L_{X,1} for the subset of 13 bursts with measured or constrained redshifts. The remaining 20% of the bursts have values of F_{X,1}/F_{gamma} that are suppressed by about three orders of magnitude, likely because of low circumburst densities (Nakar 2007). These results have several important implications: (i) The X-ray luminosity is generally a robust proxy for the blast wave kinetic energy, indicating nu_X>nu_c and hence a circumburst density n>0.05 cm^{-3}; (ii) most short GRBs have a narrow range of gamma-ray efficiency, with ~0.85 and a spread of 0.14 dex; and (iii) the isotropic-equivalent energies span 10^{48}-10^{52} erg. Furthermore, I find tentative evidence for jet collimation in the two bursts with the highest E_{gamma,iso}, perhaps indicative of the same inverse correlation that leads to a narrow distribution of true energies in long GRBs. I find no clear evidence for a relation between the overall energy release and host galaxy type, but a positive correlation with duration may be present, albeit with a large scatter. Finally, I note that the outlier fraction of 20% is similar to the proposed fraction of short GRBs from dynamically-formed neutron star binaries in globular clusters. This scenario may naturally explain the bimodality of the F_{X,1}/F_{gamma} distribution and the low circumburst densities without invoking speculative kick velocities of several hundred km/s.

Bissaldi 2007 检验GRB和Ib/c型超新星的成协

主要内容:


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文章信息:

astro-ph/0702652 [abs, ps, pdf, other] :

Title: The connection between Gamma-ray bursts and Supernovae Ib/c
Authors: Elisabetta Bissaldi (1), Francesco Calura (2), Francesca Matteucci (2,3), Francesco Longo (1,4), Guido Barbiellini (1,4) (1: Dip. di Fisica, Universita' di Trieste; 2: INAF-Osservatorio Astronomico di Trieste; 3: Dip. di Astronomia, Universita' di Trieste; 4: INFN, sezione di Trieste)
Comments: A&A, in press, 15 pages, 11 figures

It has been established that Gamma-Ray Bursts (GRBs) are connected to Supernovae (SNe) explosions of Type Ib/c. We intend to test whether the hypothesis of Type Ib/c SNe from different massive progenitors can reproduce the local GRB rate as well as the GRB rate as a function of redshift. We aim to predict the GRB rate at very high redshift under different assumptions about galaxy formation and star formation histories in galaxies. We assume different star formation histories in galaxies of different morphological type: ellipticals, spirals and irregulars. We explore different hypotheses concerning the progenitors of Type Ib/c SNe. We find an excellent agreement between the observed GRB local rate and the predicted Type Ib/c SN rate in irregular galaxies, when a range for single Wolf-Rayet stars of 40-100 M_sun is adopted. We also predict the cosmic Type Ib/c SN rate by taking into account all the galaxy types in an unitary volume of the Universe and we compare it with the observed cosmic GRB rate as a function of redshift. By assuming the formation of spheroids at high redshift, we predict a cosmic Type Ib/c SN rate, which is always higher than the GRB rate, suggesting that only a small fraction (0.1-1 %) of Type Ib/c SNe become GRBs. In particular, we find a ratio between the cosmic GRB rate and the cosmic Type Ib/c rate in the range 0.001-0.01, in agreement with previous estimates. Finally, due to the high star formation in spheroids at high redshift, which is our preferred scenario for galaxy formation, we predict more GRBs at high redshift than in the hierarchical scenario for galaxy formation, a prediction which awaits to be proven by future observations.

Burrows 200 7 SwiftX射线余辉无喷流拐折

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文章信息:

astro-ph/0702633 [abs, ps, pdf, other] :

Title: Swift X-ray Afterglows: Where are the X-ray Jet Breaks?
Authors: David N. Burrows, Judith Racusin
Comments: 13 pages; 15 figures; Proceeding of the "Swift and GRBs: Unveiling the Relativistic Universe" meeting,Venice, June 5-9,2006, to be published by "Il Nuovo Cimento"

We examine the Swift/X-ray Telescope (XRT) light curves from the first ~150 gamma-ray burst (GRB) afterglows. Although we expected to find jet breaks at typical times of 1-2 days after the GRB, we find that these appear to be extremely rare. Typical light curves have a break in the slope at about 10^4s, followed by a single power-law decay whose slope is much too shallow to be consistent with expectations for jet breaks. X-ray light curves typically extend out to ~10 days without any further breaks, until they become too faint for the XRT to detect. In some extreme cases, light curves extend out to more than two months without evidence for jet breaks. This raises concerns about our understanding of afterglow and jet dynamics, and of GRB energetics.

Tagliaferri 2007 早期X射线余辉

主要内容:
小综述。

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文章信息:

astro-ph/0702620 [abs, ps, pdf, other] :

Title: The early X-ray afterglows of Gamma Ray Bursts
Authors: G. Tagliaferri
Comments: 8 pages, 4 figures. Invited talk at the conference "The Multicoloured Landscape of Compact Objects and their Explosive Origins" held in Cefalu', June 2006

The X-ray light curves of hundreds of bursts are now available, thanks to the X-ray Telescope on board the Swift satellite, on time scales from ~1 minute up to weeks and in some cases months from the burst explosion. These data allow us to investigate the physics of the highly relativistic fireball outflow and its interaction with the circumburst environment. Here we review the main results of the XRT observations, with particular regard to the evolution of the X-ray light curves in the early phases. Unexpectedly, they are characterised by different slopes, with a very steep decay in the first few hundred of seconds, followed by a flatter decay and, a few thousand of seconds later, by a somewhat steeper decay. Often strong flare activity up to few hours after the burst explosion is also seen. These flares, most likely, are still related to the central engine activity, that last much longer than expected and it is still dominating the X-ray light curve well after the prompt phase, up to a few thousand of seconds. The real afterglow emission (external shock) is dominating the X-ray light curve only after the flatter phase ends. The flatter phase is probably the combination of late-prompt emission and afterglow emission. When the late-prompt emission ends the light curve steepens again. Some flare activity can still be detected during these later phases. Finally, even the late evolution of the XRT light curves is puzzling, in particular many of them do not show a ``jet-break''. There are various possibilities to explain these observations (e.g.time evolution of the microphysical parameters, structured jet). However, a clear understanding of the formation and evolution of the jet and of the afterglow emission is still lacking.

Wang 2007 XRFs的逆康普顿产生高能射线

主要内容:


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文章信息:

astro-ph/0702617 [abs, ps, pdf, other] :

Title: High-Energy Gamma-Rays from GRB X-ray Flares
Authors: Xiang-Yu Wang, Zhuo Li, Peter Meszaros
Comments: 4 pages, Contributed talk presented at "The First GLAST Symposium", Feb.5-8 2007, Stanford University

The recent detection of X-ray flares during the afterglow phase of gamma-ray bursts (GRBs) suggests an inner-engine origin, at radii inside the forward shock. There must be inverse Compton (IC) emission arising from such flare photons scattered by forward shock afterglow electrons when they are passing through the forward shock. We find that this IC emission produces high energy gamma-ray flares, which may be detected by AGILE, GLAST and ground-based TeV telescopes. The anisotropic IC scattering between flare photons and forward shock electrons does not affect the total IC component intensity, but cause a time delay of the IC component peak relative to the flare peak. The anisotropic scattering effect may also weaken, to some extent, the suppression effect of the afterglow intensity induced by the enhanced electron cooling due to flare photons. We speculate that this IC component may already have been detected by EGRET from a very strong burst--GRB940217. Future observations by GLAST may help to distinguish whether X-ray flares originate from late central engine activity or from external shocks.

Krimm 2007 GRB060714的暴本身和XRFs并没有严格分界

主要内容:
（其实所有XRF，我觉得都个GRB一样）

精彩摘抄:


文章信息:

astro-ph/0702603 [abs, ps, pdf, other] :

Title: GRB 060714: No Clear Dividing Line Between Prompt Emission and X-ray Flares
Authors: H. A. Krimm, J. Granot, F. Marshal, M. Perri, S. D. Barthelmy, D. N. Burrows, N. Gehrels, P. Mészáros, D. Morris
Comments: Submitted to ApJ

The long gamma-ray burst GRB 060714 was observed to exhibit a series of five X-ray flares beginning ~70 s after the burst trigger T0 and continuing until T0 + ~200 s. The first two flares were detected by the Burst Alert Telescope (BAT) on the Swift satellite, before Swift had slewed to the burst location, while the last three flares were strongly detected by the X-Ray Telescope (XRT) but only weakly detected by the BAT. This burst provides an unusual opportunity to track a complete sequence of flares over a wide energy range. The flares were very similar in their light curve morphology, showing power-law rise and fall components, and in most cases significant sub-structure. The flares also showed strong evolution with time, both spectrally and temporally. The small time scale and large amplitude variability observed are incompatible with an external shock origin for the flares, and support instead late time sporadic activity either of the central source or of localized dissipation events within the outflow. We show that the flares in GRB 060714 cannot be the result of internal shocks in which the contrast in the Lorentz factor of the colliding shells is very small, and that this mechanism faces serious difficulties in most Swift GRBs. The morphological similarity of the flares and the prompt emission and the gradual and continual evolution of the flares with time makes it difficult and arbitrary to draw a dividing line between the prompt emission and the flares.

Vietri 2007 SGR1806-20和QPO

主要内容:


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文章信息:

astro-ph/0702598 [abs, ps, pdf, other] :

Title: SGR1806-20: evidence for a superstrong Magnetic Field from Quasi Periodic Oscillations
Authors: M. Vietri, L. Stella, G. Israel
Comments: Accepted for publication in the Astrophysical Journal, Part I

Fast Quasi-Periodic Oscillations (QPOs, frequencies of $\sim 20 - 1840$ Hz) have been recently discovered in the ringing tail of giant flares from Soft Gamma Repeaters (SGRs), when the luminosity was of order $10^{41}-10^{41.5}$ erg/s. These oscillations persisted for many tens of seconds, remained coherent for up to hundreds of cycles and were observed over a wide range of rotational phases of the neutron stars believed to host SGRs. Therefore these QPOs must have originated from a compact, virtually non-expanding region inside the star's magnetosphere, emitting with a very moderate degree of beaming (if at all). The fastest QPOs imply a luminosity variation of $\Delta L/\Delta t \simeq 6 \times 10^{43}$ erg s$^{-2}$, the largest luminosity variation ever observed from a compact source. It exceeds by over an order of magnitude the usual Cavallo-Fabian-Rees (CFR) luminosity variability limit for a matter-to-radiation conversion efficiency of 100%. We show that such an extreme variability can be reconciled with the CFR limit if the emitting region is immersed in a magnetic field $\gtrsim 10^{15}$ G at the star surface, providing independent evidence for the superstrong magnetic fields of magnetars.

Cantiello 2007 长暴的双星并合模型

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文章信息:

astro-ph/0702540 [abs, ps, pdf, other] :

Title: Binary star progenitors of long gamma-ray bursts
Authors: M. Cantiello, S.-C. Yoon, N. Langer, M. Livio
Comments: Accepted for publication in A&A Letters

We present a binary channel for the progenitors of long gamma-ray bursts. We test the idea of producing rapidly rotating Wolf-Rayet stars in massive close binaries through mass accretion and consecutive quasi-chemically homogeneous evolution. The binary channel presented here may provide a means for massive stars to obtain the required high rotation rates. Moreover, it suggests that a possibly large fraction of long gamma-ray bursts occurs in runaway stars. This can have important observational consequences for both the positions of GRBs, and their afterglow properties.

Watson 2007 伽玛暴的光学和X射线余辉被消光于不同地方

主要内容:
从X射线和光学所得到的介质柱密度不符，可能影响光学的主要是ISM。

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文章信息:

astro-ph/0702537 [abs, ps, pdf, other] :

Title: The optical and X-ray afterglows of gamma-ray bursts do not probe the same gas: ionisation in GRB environments
Authors: D. Watson, J. Hjorth, J. P. U. Fynbo (DARK, NBI, U. Copenhagen), P. Jakobsson (U. Herts.), S. Foley (UCD), R. A. M. J. Wijers (U. Amsterdam)
Comments: 5 pages, emulateapj, 2 figures, submitted to ApJL

We compare the HI column densities from Ly-alpha absorption to the metal column densities from soft X-ray absorption in gamma-ray burst (GRB) afterglows. Of the eight bursts for which useful measures are obtained we find a range in metallicities from sub-solar to a few hundred times the solar value. The lack of correlation in the column densities, and the large range and extreme values of these `metallicities', suggest that the column densities derived by one or both methods are not a reliable indication of the true total column densities towards GRBs. Ionisation of the GRB's gas cloud to large distances along the line of sight seems the most likely interpretation of these results. From the lower limit on the total column density and the UV luminosity of the GRBs we derive a maximum distance to the majority of the gas surrounding GRBs of ~3 pc, suggesting that the gas probed by optical afterglow spectra is not the cloud in which the burst occurs. This is an encouraging result for the use of GRB optical afterglows as probes of the interstellar medium (ISM) in their host galaxies, as the ISM observed is less likely to be strongly affected by the GRB or its progenitor.

Nomoto 2007 伽玛暴－超新星成协的分类

主要内容:
分为四类：GRB-SN,XRF-SN,noGRB-SN,GRB-nonSN。准备用统一的jet模型解释。

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文章信息:

astro-ph/0702472 [abs, ps, pdf, other] :

Title: Diversity of the Supernova - Gamma-Ray Burst Connection
Authors: K. Nomoto, N. Tominaga, M. Tanaka, K. Maeda, T. Suzuki, J.S. Deng, P.A. Mazzali
Comments: 16 pages, 12 figures. To be published in the proceedings of the conference "SWIFT and GRBs: Unveiling the Relativistic Universe", Venice, June 5-9, 2006. To appear in "Il Nuovo Cimento"

The connection between the long Gamma Ray Bursts (GRBs) and Type Ic Supernovae (SNe) has revealed interesting diversity. We review the following types of the GRB-SN connection. (1) GRB-SNe: The three SNe all explode with energies much larger than those of typical SNe, thus being called Hypernovae (HNe). They are massive enough for forming black holes. (2) Non-GRB HNe/SNe: Some HNe are not associated with GRBs. (3) XRF-SN: SN 2006aj associated with X-Ray Flash 060218 is dimmer than GRB-SNe and has very weak oxygen lines. Its progenitor mass is estimated to be small enough to form a neutron star rather than a black hole. (4) Non-SN GRB: Two nearby long GRBs were not associated SNe. Such ``dark HNe'' have been predicted in this talk (i.e., just before the discoveries) in order to explain the origin of C-rich (hyper) metal-poor stars. This would be an important confirmation of the Hypernova-First Star connection. We will show our attempt to explain the diversity in a unified manner with the jet-induced explosion model.

Tominaga 2007 伽玛暴和极端贫金属大质量恒星的成协

主要内容:
以期解释无超新星成协的长暴如GRB060614等。

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文章信息:

astro-ph/0702471 [abs, ps, pdf, other] :

Title: The Connection between Gamma-Ray Bursts and Extremely Metal-Poor Stars: Black Hole-forming Supernovae with Relativistic Jets
Authors: Nozomu Tominaga, Keiichi Maeda, Hideyuki Umeda, Ken'ichi Nomoto, Masaomi Tanaka, Nobuyuki Iwamoto, Tomoharu Suzuki, Paolo A. Mazzali
Comments: 7 pages, 3 figures. Accepted for publication in the Astrophysical Journal Letters (10 March 2007, v657n2 issue)

Long-duration gamma-ray bursts (GRBs) are thought to be connected to luminous and energetic supernovae (SNe), called hypernovae (HNe), resulting from the black-hole (BH) forming collapse of massive stars. For recent nearby GRBs~060505 and 060614, however, the expected SNe have not been detected. The upper limits to the SN brightness are about 100 times fainter than GRB-associated HNe (GRB-HNe), corresponding to the upper limits to the ejected $^{56}$Ni masses of $M({\rm ^{56}Ni})\sim 10^{-3}M_\odot$. SNe with a small amount of $^{56}$Ni ejection are observed as faint Type II SNe. HNe and faint SNe are thought to be responsible for the formation of extremely metal-poor (EMP) stars. In this Letter, a relativistic jet-induced BH forming explosion of the 40 $M_\odot$ star is investigated and hydrodynamic and nucleosynthetic models are presented. These models can explain both GRB-HNe and GRBs without bright SNe in a unified manner. Their connection to EMP stars is also discussed. We suggest that GRBs without bright SNe are likely to synthesize $\Mni\sim 10^{-4}$ to $10^{-3}M_\odot$ or $\sim 10^{-6}M_\odot$.

Kocevski 2007 XRFs脉冲宽度的内激波解释

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文章信息:

astro-ph/0702452 [abs, ps, pdf, other] :

Title: Pulse Width Evolution of Late Time X-rays Flares in GRBs: Evidence For Internal Shocks
Authors: Daniel Kocevski, Nathaniel Butler, Joshua S. Bloom
Comments: 26 pages, 5 figures, 1 table. Submitted to ApJ. This work expands upon and formalizes our previous report at the October 2006 AAS HEAD Meeting of the discovery of pulse width evolution

We study the duration and variability of late time X-ray flares following gamma-ray bursts (GRBs) observed by the narrow field X-ray telescope (XRT) aboard the {\it Swift} spacecraft. These flares are thought to be indicative of late time activity by the central engine that powers the GRB and produced by means similar to those which produce the prompt emission. We use a non-parametric procedure to study the overall temporal properties of the flares and a structure function analysis to look for an evolution of the fundamental variability time-scale between the prompt and late time emission. We find a strong correlation in 28 individual x-ray flares in 18 separate GRBs between the flare duration and their time of peak flux since the GRB trigger. We also find a qualitative trend of decreasing variability as a function of time since trigger, with a characteristic minimum variability timescale $\Delta t/t=0.1$ for most flares. We interpret these results as evidence of internal shocks at collision radii that are larger than those that produced the prompt emission. Contemporaneous detections of high energy emission by GLAST could be a crucial test in determining if indeed these X-ray flares originate as internal shocks behind the afterglow, as any X-ray emission originating from behind the afterglow is expected to undergo inverse Compton scattering as it passes through the external shock.

Waxman 2007 GRB060218的余辉的解释

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文章信息:

astro-ph/0702450 [abs, ps, pdf, other] :

Title: GRB060218: A Relativistic Supernova Shock Breakout
Authors: E. Waxman, P. Meszaros, S. Campana

We show that the prompt and afterglow X-ray emission of GRB060218, as well as its early (t<=1 d) optical-UV emission, can be explained by a model in which a radiation- mediated shock propagates through a compact progenitor star into a dense wind. The prompt thermal X-ray emission is produced in this model as the mildly relativistic shock, v/c=0.85 carrying few x 10^49 erg, reaches the wind (Thomson) photosphere, where the post-shock thermal radiation is released and the shock becomes collisionless. Adopting this interpretation of the thermal X-ray emission, a subsequent X-ray afterglow is predicted, due to synchrotron emission and inverse-Compton scattering of SN UV photons by electrons accelerated in the collisionless shock. Early optical-UV emission is also predicted, due to the cooling of the outer \delta M ~10^{-3} M_sun envelope of the star, which was heated to high temperature during shock passage. The observed X-ray afterglow and the early optical-UV emission are both consistent with those expected in this model. Detailed analysis of the early optical-UV emission may provide detailed constraints on the density distribution near the stellar surface.

Wang 2007 回落盘模型下的前兆时标

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文章信息:

astro-ph/0702441 [abs, ps, pdf, other] :

Title: GRB Precursors in the Fallback Collapsar Scenario
Authors: Xiang-Yu Wang, Peter Meszaros
Comments: 6 pages, submitted to ApJ

Precursor emission has been observed in a non-negligible fraction of gamma-ray bursts, the time gap between the precursor and the main burst extending up to hundreds of seconds in some cases, such as in GRB041219A, GRB050820A and GRB060124. We have investigated the maximum possible time gaps arising from the jet propagation inside the progenitor star, in models which assume that the precursor is produced by the jet bow shock or the cocoon breaking out of the progenitor. Due to the pressure drop ahead of the jet head after it reaches the stellar surface, a rarefaction wave propagates back into the jet at the sound speed, which re-accelerates the jet to a relativistic velocity and therefore limits the gap period to within about ten seconds. This scenario therefore cannot explain gaps which are hundreds of seconds long. Instead, we ascribe such long time gaps to the behavior of the central engine, and suggest a fallback collapsar scenario for these bursts. In this scenario, the precursor is produced by a weak jet formed during the initial core collapse, possibly related to MHD process associated with a short-lived proto-neutron star, while the main burst is produced by a stronger jet fed by the fallback disk accreting onto the black hole resulting from the collapse of the neutron star. We have examined the propagation times of the weak precursor jet through the stellar progenitor. We find that the initial weak jet can break out of the progenitor in a time less than ten seconds provided that it has a moderately high relativistic Lorentz factor (Gamma>10). The longer time gap following this is dictated by the fall-back timescale, which is long enough for the exit channel to close after the precursor activity ceases, allowing for the collimation of the main jet by the cocoon pressure as it propagates outward.