Borgonovo 2007 长暴variability的分类

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astro-ph/0701920 [abs, ps, pdf, other] :

Title: On the temporal variability classes found in long gamma-ray bursts with known redshift
Authors: L. Borgonovo, F. Frontera, C. Guidorzi, E. Montanari, L. Vetere, P. Soffitta
Comments: 13 pages, 10 figures. Accepted for publication in A&A

Based on the analysis of a small sample of BATSE and Konus gamma-ray bursts (GRBs) with know redshift it has been reported that the width of the autocorrelation function (ACF) shows a remarkable bimodal distribution in the rest-frame of the source. However, the origin of these two well-separated ACF classes remains unexplained.We complement previous ACF analysis studying the corresponding power density spectra (PDS). With the addition of Beppo-SAX data and taken advantage of its broad-band capability, we not only increase the burst sample but we extend the analysis to X-ray energies. The rest-frame PDS analysis at gamma-ray energies shows that the two ACF classes are not simply characterised by a different low frequency cut-off, but they have a distinct variability as a whole in the studied frequency range. Both classes exhibit average PDS with power-law behaviour at high frequencies (f' > 0.1 Hz) but significantly different slopes, with index values close to those of Brownian (-2) and Kolmogorov (-5/3) spectra for the narrow and broad classes respectively. The latter spectrum presents an additional PDS component, a low-frequency noise excess with a sharp cut-off. At X-ray energies we find the power-law index unchanged for the broad class, but a significantly steeper slope in the narrow case (~ -3). We interpret this as an indication that the broad class bursts have weaker spectral evolution than the narrow ones, as suggested also by our analysis of the ACF energy dependence. The low and high frequency PDS components may then arise from two radiating regions involving different emission mechanisms.

Meszaros 2007 暗暴的起源可能是正常的

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astro-ph/0701905 [abs, ps, pdf, other] :

Title: On the Origin of the Dark Gamma-Ray Bursts
Authors: A. Meszaros, Z. Bagoly, S. Klose, F. Ryde, S. Larsson, L. G. Balazs, I. Horvath, L. Borgonovo
Comments: published in Nuovo Cimento

The origin of dark bursts - i.e. that have no observed afterglows in X-ray, optical/NIR and radio ranges - is unclear yet. Different possibilities - instrumental biases, very high redshifts, extinction in the host galaxies - are discussed and shown to be important. On the other hand, the dark bursts should not form a new subgroup of long gamma-ray bursts themselves.

Cui 2007 伽玛暴对中子星的kick

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astro-ph/0701888 [abs, ps, pdf, other] :

Title: Pulsar's kicks and Gamma-ray bursts
Authors: X. H. Cui (PKU), H. G. Wang (GZU), R. X. Xu (PKU), G. J. Qiao (PKU)
Comments: 3 pages, 1 figure

The supernova-GRB (Gamma-ray burst) association is tested by showing the consistence of the distributions of pulsar's kick velocities and GRB energies, under the assumption that cosmic GRBs are related to supernova explosions that form pulsars. These two distributions are derived from observations, and are checked by K-S test. The deduced distribution of kick velocity from the total energy of GRBs and the observed distribution of radio pulsars are found to come from a same parent population. This result may indicate that GRBs could be really related to supernovae, and that the asymmetry of GRB fireballs would cause the kick of pulsars.

Lee 2007 短暴的前身星

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astro-ph/0701874 [abs, ps, pdf, other] :

Title: The Progenitors of Short Gamma-Ray Bursts
Authors: William H. Lee, Enrico Ramirez-Ruiz
Comments: 76 pages, 26 figures, review article to appear in the GRB Focus Issue of New Journal of Physics

Recent months have witnessed dramatic progress in our understanding of SGRBs. There is now general agreement that SGRBs can produce directed outflows of relativistic matter with a kinetic luminosity exceeding by many millions that of AGN. The requirements of energy and compactness indicate that SGRB activity can be ascribed to a modest fraction of a solar mass of gas accreting onto a stellar mass BH or to a precursor stage leading inevitably to such an object. Scenarios involving the birth of a rapidly rotating NS, or an accreting BH in a merging binary driven by gravitational waves are reviewed, along with possible alternatives (collisions or collapse of compact objects). If a BH lies at the center of this activity, the fundamental pathways through which mass, angular momentum and energy can flow around and away from it play a key role in understanding how these prime movers can form collimated relativistic outflows. Hypercritical flows near BHs, where photons cannot supply the cooling, but neutrinos do so efficiently, are discussed in detail, and we believe that they offer the best hope of understanding the central engine. On the other hand, statistical investigations of SGRB niches provide valuable information on their nature and evolutionary behavior. In addition, compelling evidence now points to the continuous fueling of SGRB sources. We suggest that the observed late flaring activity could be due to a secondary accretion episode induced by the fall back of material stripped from a compact object during a merger or collision. Important open questions are identified, along with the types of observation that would discriminate among various models. SGRB jets may be one of the few observable consequences of how flows near nuclear density behave under the influence of strong gravitational fields. (abridged)

Troja 2007 GRB 051109B的观测

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astro-ph/0701855 [abs, ps, pdf, other] :

Title: Swift Observations of GRB 051109B
Authors: E. Troja, G. Cusumano, V. LaParola, V.Mangano, T. Mineo (INAF - IASFPA)
Comments: 2 pages, 1 figure. Proceedings of "SWIFT and GRBs: Unveiling the Relativistic Universe" June 5-9, 2006 Venice (Italy)

We present Swift observations of GRB 051109B, a soft long burst triggered by the Burst Alert Telescope (BAT). The soft photon index of the prompt emission suggest it is a X-ray Flash (XRF) or, at least, a X-ray Rich (XRR) burst. The X-ray lightcurve displays the canonical shape of many other GRBs, a double b roken power law with a small flare superimposed at ~T_0+1500 s, and its extrapolation to early times smoothly joins with the BAT lightcurve. On the basis of the derived optical to X-ray flux ratio, it cannot be classified as a dark burst.

Huang 2007 等时面的详细研究

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astro-ph/0701846 [abs, ps, pdf, other] :

Title: A Detailed Study on the Equal Arrival Time Surface Effect in Gamma-Ray Burst Afterglows
Authors: Y.F. Huang, Y. Lu, A.Y.L. Wong, K.S. Cheng
Comments: Accepted for publication in: Chin. J. Astron. Astrophys., 15 pages, 8 embedded eps figures

Due to the relativistic motion of gamma-ray burst remnant and its deceleration in the circumburst medium, the equal arrival time surfaces at any moment are not spherical, but should be distorted ellipsoids. This will leave some imprints in the afterglows. In this article, we study the effect of equal arrival time surfaces numerically under various conditions, i.e., for isotropic fireballs, collimated jets, density jump conditions, and energy injection events. For each condition, direct comparison between the two instances when the effect is and is not included, is presented. For isotropic fireballs and jets viewed on axis, the effect slightly hardens the spectra and postpones the peak time of afterglows, but does not change the shapes of the spectra and light curves significantly. In the cases when a density jump or an energy injection is involved, the effect smears the variability of the afterglows markedly.

Nakar 2007 短暴综述 4

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astro-ph/0701748 [abs, ps, pdf, other] :

Title: Short-Hard Gamma-Ray Bursts
Authors: Ehud Nakar
Comments: A review, 125 pages, 12 figures. Physics Reports - Bethe Centennial Volume, in press

Two types of Gamma-ray bursts (GRBs) are observed: short duration hard spectrum GRBs and long duration soft spectrum GRBs. For many years long GRBs were the focus of intense research while the lack of observational data limited the study of short-hard GRBs (SHBs). In 2005 a breakthrough occurred following the first detections of SHB afterglows, longer wavelength emission that follows the burst of gamma-rays. Similarly to long GRBs, afterglow detections led to the identification of SHB host galaxies and measurement of their redshifts. These observations established that SHBs are cosmological relativistic sources that, unlike long GRBs, do not originate from the collapse of massive stars, and therefore constitute a distinct physical phenomenon. One viable model for SHB origin is the coalescence of compact binary systems (double neutron stars or a neutron star and a black hole), in which case SHBs are the electromagnetic counterparts of strong gravitational-wave sources. The theoretical and observational study of SHBs following the recent pivotal discoveries is reviewed, along with new theoretical results that are presented here for the first time.

Courty 2007 对伽玛暴宿主星系的数值模拟

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astro-ph/0701762 [abs, ps, pdf, other] :

Title: Numerical counterparts of GRB host galaxies
Authors: Stephanie Courty, Gunnlaugur Bjornsson, Einar H. Gudmundsson
Comments: 11 pages, 11 figures. Accepted for publication in MNRAS

We explore galaxy properties in general and properties of host galaxies of gamma-ray bursts (GRBs) in particular, using N-body/Eulerian hydrodynamic simulations and the stellar population synthesis model, Starburst99, to infer observable properties. We identify simulated galaxies that have optical star formation rate (SFR) and SFR-to-luminosity ratio similar to those observed in a well-defined sample of ten host galaxies. Each of the numerical counterparts are found in catalogs at the same redshifts as the observed hosts. The counterparts are found to be low-mass galaxies, with low mass-to-light ratio, recent epoch of formation, and high ratio between the SFR and the average of the SFR. When compared to the overall galaxy population, they have colors much bluer than the high-mass star-forming galaxy population. Although their SFRs span a range of values, the specific rates of the numerical counterparts are equal to or higher than the median values estimated at the different redshifts. We also emphasize the strong relationships between the specific star formation rate (SFR) and quantities known to reflect the star formation history of galaxies, i.e. color and mass-to-light ratio: At intermediate redshift, the faintest and bluest galaxies are also the objects with the highest specific rates. These results suggest that GRB host galaxies are likely to be drawn from the high specific SFR sub-population of galaxies, rather than the high SFR galaxy population. Finally, as indicated by our catalogs, in an extended sample, the majority of GRB host galaxies is expected to have specific SFRs higher than found in the magnitude-limited sample studied here.

Tanvir 2007 高红移伽玛暴的观测

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astro-ph/0701777 [abs, ps, pdf, other] :

Title: Observations of GRBs at High Redshift
Authors: N. R. Tanvir, P. Jakobsson
Comments: 8 pages, 2 figures. Proceedings of the Royal Society Discussion meeting on Gamma-ray Bursts, September 18-20, 2006. To appear in Phil. Trans. Roy. Soc. A

The extreme luminosity of gamma-ray bursts (GRBs) and their afterglows means they are detectable, in principle, to very high redshifts. Although the redshift distribution of GRBs is difficult to determine, due to incompleteness of present samples, we argue that for Swift-detected bursts the median redshift is between 2.5 and 3, with a few percent likely at z > 6. Thus, GRBs are potentially powerful probes of the era of reionization, and the sources responsible for it. Moreover, it seems likely that they can provide constraints on the star formation history of the universe, and may also help in the determination of the cosmological parameters.

La Parola 2007 短暴GRB051210的观测

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astro-ph/0701818 [abs, ps, pdf, other] :

Title: The short GRB 051210 observed by Swift
Authors: V. La Parola, V. Mangano, B. Zhang, G. Cusumano, T. Mineo, E. Troja, D.N. Burrows, S. Campana, M. Capalbi, G.Chincarini, P.Giommi, A. Moretti, M. Perri, P. Romano, G. Tagliaferri
Comments: 2 pages, 1 figure. Proceedings of "SWIFT and GRBs: Unveiling the Relativistic Universe" June 5-9, 2006 Venice (Italy)

We report on the short GRB051210 detected by the Swift-BAT. The light curve, on which we focus mainly, shows a hint of extended emission in the BAT energy range, a steep decay of the X-ray emission, without any flattening or break, and two small flares in the first 300 sec. The emission fades out after ~1000 s.

Mineo 2007 XRT的WT模式中对pile-up的改正

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astro-ph/0701815 [abs, ps, pdf, other] :

Title: Pile-up correction for the Swift-XRT observations in WT mode
Authors: T. Mineo (1), P. Romano (2), V. Mangano (1), A. Moretti (2), G. Cusumano (1), V. La Parola (1), E. Troja (1), S.Campana (2), G. Chincarini (2), G. Tagliaferri (2), M. Capalbi (3), M. Perri (3), P. Giommi (3), D. Burrows (4); ((1) INAF - IASFPA, (2) INAF - Osservatorio Astronomico di Brera, (3) ASI - Science Data Center, (4) PSU - Department of Astronomy & Astrophysics)
Comments: 2 pages, 3 figures. Proceedings of "SWIFT and GRBs: Unveiling the Relativistic Universe" June 5-9, 2006 Venice (Italy)

The detector at the focal plane of the Swift X-ray Telescope (XRT) supports four readout modes, automatically changed on board, to cover the dynamical range of fluxes and rapid variability expected from GRB afterglows. The Windowed Timing (WT) mode is used for sources with flux higher than a few mCrab and is obtained by compressing 10 rows into a single row, and then reading out only the central 200 columns of the CCD. Point sources with a rate above ~300 c/s produce severe pile-up in the central region of the Point Spread Function. This paper presents three methods to correct the effects of the pile-up in WT mode. On ground calibration results and data from the very bright GRB 060124 are used to define and test these methods.

Cusumano 2007 XRT的校准

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astro-ph/0701813 [abs, ps, pdf, other] :

Title: In-flight calibration of the SWIFT XRT
Authors: G. Cusumano (INAF - IASF Palermo, on behalf of the XRT Calibration Team)
Comments: 2 pages, 2 figures. Proceedings of "SWIFT and GRBs: Unveiling the Relativistic Universe" June 5-9, 2006 Venice (Italy)

The calibration of the Swift XRT effective area has been performed by analyzing cosmic sources observed during the in-flight calibration phase and by using laboratory results and ray-tracing simulations as a starting point. This work describes performance of the recent release of ancillary response files (ARF v8).

Mangano 2007 共动系的光变曲线

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astro-ph/0701812 [abs, ps, pdf, other] :

Title: Rest frame light curves of Swift GRBs
Authors: V. Mangano (1), V. La Parola (1), E. Troja (1), G. Cusumano (1), T. Mineo (1), D. Burrows (2), S. Campana (3), M.Capalbi (4), G. Chincarini (3,5), N.Gehrels (6), P. Giommi (4), A. Moretti (3), M. Perri (4), P. Romano (3); ((1) INAF-IASF PA, (2) Dept of Astronomy & Astrophysics, PSU, (3) INAF-Osservatorio Astronomico di Brera, (4) ASI-Science Data Center, (5) Universita degli Studi di Milano, Bicocca)
Comments: 5 pages, 7 figures. Proceedings of "SWIFT and GRBs: Unveiling the Relativistic Universe" June 5-9, 2006 Venice (Italy)

We have computed the luminosity rest frame light curves of the first 40 Gamma-ray bursts (GRBs) detected by Swift with well established redshift. We studied average properties of the light curves in the four subsamples of bursts given by z<1,>=4. We conclude that all the last three subsamples share the same morphology and the same luminosity range. Very high redshift (z>=4) GRBs detected up to now are not intrinsically longer than lower redshift long GRBs. Nearby long GRBs (z<1)>

O'Brien 2007 用swift的瞬时和余辉观测对伽玛暴分类

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astro-ph/0701811 [abs, ps, pdf, other] :

Title: Using Swift observations of prompt and afterglow emission to classify GRBs
Authors: P.T. O'Brien, R. Willingale
Comments: 10 pages. 8 figures. Proceedings of the Royal Society Discussion meeting on Gamma-ray Bursts, September 18-20, 2006. To appear in Phil. Trans. Roy. Soc. A

We present an analysis of early BAT and XRT data for 107 gamma--ray bursts (GRBs) observed by the Swift satellite. We use these data to examine the behaviour of the X-ray light curve and propose a classification scheme for GRBs based on this behaviour. As found for previous smaller samples, the earliest X-ray light curve can be well described by an exponential which relaxes into a power law, often with flares superimposed. The later emission is well fit using a similar functional form and we find that these two functions provide a good description of the entire X-ray light curve. For the prompt emission, the transition time between the exponential and the power law gives a well-defined timescale, T_p, for the burst duration. We use T_p, the spectral index of the prompt emission, beta_p, and the prompt power law decay index, alpha_p to define four classes of burst: short, slow, fast and soft. Bursts with slowly declining emission have spectral and temporal properties similar to the short bursts despite having longer durations. Some of these GRBs may therefore arise from similar progenitors including several types of binary system. Short bursts tend to decline more gradually than longer duration bursts and hence emit a significant fraction of their total energy at times greater than T_p. This may be due to differences in the environment or the progenitor for long, fast bursts.

Blustin 2007 伽玛暴预示着超新星的诞生

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astro-ph/0701804 [abs, ps, pdf, other] :

Title: Shock break-out: how a GRB revealed the beginnings of a supernova
Authors: A. J. Blustin
Comments: 6 pages, 4 figures, to appear in Phil. Trans. Roy. Soc. A, Proceedings of the Royal Society Discussion meeting on Gamma-Ray Bursts, September 18-20, 2006

In February 2006, Swift caught a GRB in the act of turning into a supernova, and made the first ever direct observations of the break-out and early expansion of a supernova shock wave. GRB 060218 began with an exceptionally long burst of non-thermal gamma-rays, lasting over 2000 s, as a jet erupted through the surface of the star. While this was in progress, an optically-thick thermal component from the shock wave of the supernova explosion grew to prominence, and we were able to track the mildly relativistic expansion of this shell as the blackbody peak moved from the X-rays into the UV and optical bands. The initial radius of the shock implied that it was a blue supergiant which had exploded, but the lack of Hydrogen emission lines in the supernova spectrum indicated a more compact star. The most likely scenario is that the shock ploughed into the massive stellar wind of a Wolf-Rayet progenitor, with the shock breaking out and becoming visible to us once it reached the radius where the wind became optically-thin. I present the Swift observations of this landmark event, and discuss the new questions and answers it leaves us with.

Sollerman 2007 XRF050824的观测

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astro-ph/0701736 [abs, ps, pdf, other] :

Title: The nature of the X-Ray Flash of August 24 2005
Authors: J. Sollerman, J. P. U. Fynbo, J. Gorosabel, J. P. Halpern, J. Hjorth, P. Jakobsson, N. Mirabal, D. Watson, D. Xu, A. J. Castro-Tirado, C. Feron, A. O. Jaunsen, M. Jelinek, B. L. Jensen, D. A. Kann, J.E. Ovaldsen, A. Pozanenko, M. Stritzinger, C. C. Thoene, A. de Ugarte Postigo, S. Guziy, M. Ibrahimov, S. P. Jaervinen, A. Levan, V. Rumyantsev, N. Tanvir
Comments: Accepted for publication in Astronomy & Astrophysics

We present comprehensive photometric R-band observations of the fading optical afterglow of the X-Ray Flash XRF050824, from 11 minutes to 104 days after the burst. The R-band lightcurve of the afterglow resembles the lightcurves of long duration Gamma-Ray Bursts (GRBs), i.e., a power-law albeit with a rather shallow slope of alpha=0.6. Our late R-band images reveal the host galaxy with a rest-frame B-band luminosity corresponding to roughly 0.5 Lstar. The star-formation rate as determined from the [O II] emission line luminosity is about 1.8 Msun per year. When accounting for the host contribution, the slope is alpha=0.65+-0.01 and a break in the lightcurve is also suggested. A potential lightcurve bump at 2 weeks can be interpreted as a supernova only if this is a supernova with a fast rise and a fast decay. However, the overall fit still show excess scatter in the lightcurve due to wiggles and bumps. The flat lightcurves in the optical and X-rays could be explained by a continuous energy injection scenario with an on-axis viewing angle and a wide jet opening angle (theta_j>10 deg). If the energy injections are episodic, this could potentially help explain the bumps and wiggles. Spectroscopy of the afterglow give a redshift of z=0.828+-0.005 from both absorption and emission lines. The spectral energy distribution (SED) of the afterglow has a power-law shape with slope beta=0.56+-0.04. This can be compared to the X-ray spectral index which is betaX=1.0+-0.1. The curvature of the SED constrain the dust reddening towards the burst to Av<0.5>

Malacrino 2007 CFHTLS Very Wide巡天找孤儿余辉 3

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找到了一个可能的孤儿余辉。

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astro-ph/0701722 [abs, ps, pdf, other] :

Title: Constraining the rate of GRB visible afterglows with the CFHTLS Very Wide Survey
Authors: Frederic Malacrino (LATT), Jean-Luc Atteia (LATT), Michel Boer (OHP), Alain Klotz (OHP, CESR), Christian Veillet (CFHT), Jean-Charles Cuillandre (CFHT)
Comments: 4 pages, 3 figures, 2 tables. Accepted by A&A Letter

We analyze images of the CFHTLS Very Wide Survey to search for visible orphan afterglows from gamma-ray bursts (GRBs). We have searched 490 square degrees down to magnitude r'=22.5 for visible transients similar to GRB afterglows. We translate our observations into constraints on the number of GRB visible afterglows in the sky, by measuring the detection efficiency of our search with a simulation reproducing the characteristics of our observational strategy and the properties of on-axis GRB afterglows. We have found only three potential candidates, of which two are most probably variable stars, and one presents similarities to an orphan afterglow. We constrain the number of visible afterglows to be less than 220 down to r'=22.5 in the whole sky at any time. Our observations are marginally consistent with the most optimistic model, which predicts orphan afterglows to be about 10 times more frequent than GRBs. This search has led to the detection of one possible GRB afterglow, and provides the strongest constraints on the rate of GRB visible afterglows as well as an estimation of the observing time required to detect a significant number of GRB afterglows.

Jin 2007 GRB 060418 and 060607A, 用反向激波解释

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astro-ph/0701715 [abs, ps, pdf, other] :

Title: GRB 060418 and 060607A: the medium surrounding the progenitor and the weak reverse shock emission
Authors: Zhi-Ping Jin (PMO), Yi-Zhong Fan (HU and PMO)
Comments: 5 pages, 1 figure

We constrain the circum-burst medium profile with the rise behavior of the very early afterglow light curves of gamma-ray bursts (GRBs). Using this method, we find a constant and low-density medium profile for GRB 060418 and GRB 060607A, which is consistent with the inference from the late afterglow data. In addition, we show that the absence of the IR flashes in these two GRB afterglows is consistent with the standard external reverse shock model, which thus renders models like the highly magnetized GRB outflow being unnecessary to a certain extent.

Eldridge 2007 WR星的非对称星风

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astro-ph/0701707 [abs, ps, pdf, other] :

Title: Asymmetric Wolf-Rayet winds: implications for GRB afterglows
Authors: J.J. Eldridge
Comments: 5 pages, 4 figures, version revised by referee's comments, resubmitted to MNRAS

Recent observations of Wolf-Rayet (WR) binaries WR151 and WR155 infer that their stellar winds are asymmetric. We show that such asymmetries can alter the stellar-wind bubble structure, bringing the wind-termination shock closer to the WR star. If the wind asymmetry is caused by rotation, the wind density and distance to the wind-termination shock are both decreased along the rotation axis by a factor of a few for the observed equator-to-pole wind density ratio of WR151. If this asymmetry lasts until core-collapse the time taken to reach the wind-termination shock by supernova ejecta or a gamma-ray burst jet is reduced. This leads to a distorted structure of the supernova ejecta and makes it more likely a constant density environment is inferred from gamma-ray burst afterglow observations.

Nava 2007 平降时间和其他量的统计关系

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T_a基本和其他量没什么关系。

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astro-ph/0701705 [abs, ps, pdf, other] :

Title: The time ending the shallow decay of the X-ray light curves of long GRBs
Authors: L. Nava (1,2), G. Ghisellini (1), G. Ghirlanda (1), J.I. Cabrera (3), C. Firmani (1,3), V. Avila-Reese (3) ((1)INAF-OAB, (2)Univ. Insubria, (3)U.N.A.M.)
Comments: 10 pages, 8 figures, submitted to MNRAS

The early X-ray light curve of Gamma Ray Bursts (GRBs) is complex, and shows a typical steep-flat-steep behaviour. The time T_a at which the flat (plateau) part ends may bear some important physical information, especially if it plays the same role of the so called jet break time t_jet. To this aim, stimulated by the recent analysis of Willingale et al., we have assembled a sample of GRBs of known redshifts, spectral parameters of the prompt emission, and T_a. By using T_a as a jet angle indicator, and then estimating the collimation corrected prompt energetics, we find a correlation between the latter quantity and the peak energy of the prompt emission. However, this correlation has a large dispersion, similar to the dispersion of the Amati correlation and it is not parallel to the Ghirlanda correlation. Furthermore, we show that the correlation itself results mainly from the dependence of the jet opening angle on the isotropic prompt energy, with the time T_a playing no role, contrary to what we find for the jet break time t_jet. We also find that for the bursts in our sample T_a weakly correlates with E_iso of the prompt emission, but that this correlation disappears when considering all bursts of known redshift and T_a. There is no correlation between T_a and the isotropic energy of the plateau phase.

“收缩战线”的设想

以后不要每天看astro－ph了，一个月或者一周看一次，把感兴趣的整理下来。

Nakagawa 2007 SGR1806-20 SGR1900+14的系统研究

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astro-ph/0701701 [abs, ps, pdf, other] :

Title: A Comprehensive Study of Short Bursts from SGR 1806-20 and SGR 1900+14 Detected by HETE-2
Authors: Yujin E. Nakagawa, Atsumasa Yoshida, Kevin Hurley, Jean-Luc Atteia, Miki Maetou, Toru Tamagawa, Motoko Suzuki, Tohru Yamazaki, Kaoru Tanaka, Nobuyuki Kawai, Yuji Shirasaki, Alexandre Pelangeon, Masaru Matsuoka, Roland Vanderspek, Geoff B. Crew, Joel S. Villasenor, Rie Sato, Satoshi Sugita, Jun'ichi Kotoku, Makoto Arimoto, Graziella Pizzichini, John P. Doty, George R. Ricker
Comments: 48 pages, 14 figures, submitted to publication in PASJ

We present the results of temporal and spectral studies of the short burst (less than a few hundred milliseconds) from the soft gamma repeaters (SGRs) 1806-20 and 1900+14 using the HETE-2 samples. In five years from 2001 to 2005, HETE-2 detected 50 bursts which were localized to SGR 1806-20 and 5 bursts which were localized to SGR 1900+14. Especially SGR 1806-20 was active in 2004, and HETE-2 localized 33 bursts in that year. The cumulative number-intensity distribution of SGR 1806-20 in 2004 is well described by a power law model with an index of -1.1+/-0.6. It is consistent with previous studies but burst data taken in other years clearly give a steeper distribution. This may suggest that more energetic bursts could occur more frequently in periods of greater activity. A power law cumulative number-intensity distribution is also known for earthquakes and solar flares. It may imply analogous triggering mechanisms. Although spectral evolution during bursts with a time scale of > 20 ms is not common in the HETE-2 sample, spectral softening due to the very rapid (<> 11 keV) photons from an emission region near the stellar surface.

Vergani 2007 GRB 060418 的红外余辉观测

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astro-ph/0701688 [abs, ps, pdf, other] :

Title: REM observations of GRB 060418: the fireball Lorentz factor determination
Authors: S.D. Vergani (on behalf of the REM collaboration)
Comments: 2 pages, 1 eps figure. Proceedings of the "Swift and GRBs: Unveiling the Relativistic Universe" meeting, Venice, June 5-9, 2006, to be published by "Il Nuovo Cimento"

We measured the fireball Lorentz factor of GRB 060418 by the direct observation of the onset of the NIR afterglow carried with the REM telescope. We found a value of about 400.

Lieu 2007 宇宙空间引力对伽玛暴光变的影响

主要内容:
在jet不同位置（哪怕是相同纬度处）的光子在经过宇宙空间传播到观测者的过程中，由于引力势的不同，导致到达的时间会不同。

精彩摘抄:
示意图

文章信息:

astro-ph/0701659 [abs, ps, pdf, other] :

Title: The gravitational time delay effect of primordial matter on the light curve of a Gamma Ray Burst
Authors: Richard Lieu
Comments: 8 pages, 1 figure

The `rise time' of a gamma-ray burst, which may be defined as the radiation pulse width from a small segment of a fireball's spherical shell wherein second order effects like shell curvature are unimportant, is conventionally attributed to photon time delay across the thickness of the shell. If the intervening space between the observer and the fireball is inhomogeneous at the minimum level given by primordial density variations, two photons propagating towards us from opposite ends of this small segment along different directions will not arrive simultaneously even when they were emitted at the same depth, because of the gravitational potential gradient transverse to the light paths. The phenomenon is {\it first order} in the `off-axis' angle of the photon wavevector, and should not be ignored. We demonstrate that, for bulk fireball Lorentz factors of $\Gamma \sim$ 100 -- 300 this delay is usually much longer than that due to shell thickness, and can therefore potentially be used to scrutinize the standard cosmological model, by investigating whether a GRB emission code that incorporates the extra delay can still match observational data. If $\Gamma \gtrsim 10^3$, even the decaying tail of the GRB light curve will be a function of cosmology, because curvature delay at the shell will no longer be the only influence on the arrival times of photons emitted from angles $\sim 1/\Gamma$ near the edge of the jet.

Thulasidas 2007 GRB和射电源的Luminal Boom

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astro-ph/0701634 [abs, ps, pdf, other] :

Title: Are Radio Sources and Gamma Ray Bursts Luminal Booms?
Authors: Manoj Thulasidas
Comments: Accepted for publication in IJMP-D (International Journal of Modern Physics D). 16 pages and 10 figures

The softening of a Gamma Ray Burst (GRB) afterglow bears remarkable similarities to the frequency evolution in a sonic boom. At the front end of the sonic boom cone, the frequency is infinite, much like a GRB. Inside the cone, the frequency rapidly decreases to infrasonic ranges and the sound source appears at two places at the same time, mimicking the double-lobed radio sources. Although a "luminal" boom violates the Lorentz invariance and is therefore forbidden, it is tempting to work out the details and compare them with existing data. This temptation is further enhanced by the observed superluminality in the celestial objects associated with radio sources and some GRBs. In this article, we calculate the temporal and spatial variation of observed frequencies from a hypothetical luminal boom and show remarkable similarity between our calculations and current observations.

Massey 2007 暗物质在宇宙中的分布 3

主要内容:
通过引力透镜效应，给出了暗物质在宇宙中角向和径向的分布。

精彩摘抄:
重子物质和暗物质（contour图）的大尺度结构对比。

文章信息:

Letter

Nature 445, 286-290 (18 January 2007) | doi:10.1038/nature05497; Received 14 November 2006; Accepted 30 November 2006; Published online 7 January 2007

Dark matter maps reveal cosmic scaffolding

Richard Massey¹, Jason Rhodes^1,2, Richard Ellis¹, Nick Scoville¹, Alexie Leauthaud³, Alexis Finoguenov⁴, Peter Capak¹, David Bacon⁵, Hervé Aussel⁶, Jean-Paul Kneib³, Anton Koekemoer⁷, Henry McCracken⁸, Bahram Mobasher⁷, Sandrine Pires⁹, Alexandre Refregier⁶, Shunji Sasaki¹⁰, Jean-Luc Starck⁹, Yoshi Taniguchi¹⁰, Andy Taylor⁵ and James Taylor¹¹

Abstract

Ordinary baryonic particles (such as protons and neutrons) account for only one-sixth of the total matter in the Universe^{1, 2, 3}. The remainder is a mysterious 'dark matter' component, which does not interact via electromagnetism and thus neither emits nor reflects light. As dark matter cannot be seen directly using traditional observations, very little is currently known about its properties. It does interact via gravity, and is most effectively probed through gravitational lensing: the deflection of light from distant galaxies by the gravitational attraction of foreground mass concentrations^{4, 5}. This is a purely geometrical effect that is free of astrophysical assumptions and sensitive to all matter—whether baryonic or dark^{6, 7}. Here we show high-fidelity maps of the large-scale distribution of dark matter, resolved in both angle and depth. We find a loose network of filaments, growing over time, which intersect in massive structures at the locations of clusters of galaxies. Our results are consistent with predictions of gravitationally induced structure formation^{8, 9}, in which the initial, smooth distribution of dark matter collapses into filaments then into clusters, forming a gravitational scaffold into which gas can accumulate, and stars can be built¹⁰.

Doi 2007 早期光学辐射的内激波模型 3

主要内容:
用内激波，同步辐射加高纬辐射来解释早期的光学辐射。

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astro-ph/0701603 [abs, ps, pdf, other] :

Title: A Unified Model of Prompt Optical Emission of Gamma-Ray Bursts
Authors: Hirotsugu Doi, Kentaro Takami, Ryo Yamazaki
Comments: 8 pages, 1 figure, submitted to ApJL

The observational diversity of the optical emission simultaneous with the prompt gamma-ray bursts (GRBs) has been found in the recent Swift era. We show that on the assumption of the synchrotron radiation for the observed energy range below the X-ray band, the observed diversity can be explained in the internal shock model taking into account a high-latitude emission and the spectral change due to the synchrotron self-absorption. It may even be possible in our model to include bright optical flashes found in, e.g., GRB 990123. The prediction of our model is that the spectral index in the optical band depends on whether the optical light curve correlates with those in the X-rays and/or gamma-rays or not, which will be tested in the near future observations.

Tagliaferri 2007 Swift暴早期余辉的谱

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astro-ph/0701591 [abs, ps, pdf, other] :

Title: Swift GRBs: the early afterglow spectral energy distribution
Authors: G.Tagliaferri, D.Malesani, S.D.Vergani, S.Campana, G.Chincarini, S.Covino, C.Guidorzi, A.Moretti, P.Romano, L.A.Antonelli, M.Capalbi, M.L.Conciatore, G.Cusumano, P.Giommi, V.La Parola, V.Mangano, T.Mineo, M.Perri, E.Troja
Comments: 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, 8 pages, 5 figures

We present the first results of a program to systematically study the optical-to-X-ray spectral energy distribution (SED) of Swift GRB afterglows with known redshift. The goal is to study the properties of the GRB explosion and of the intervening absorbing material. In this report we present the preliminary analysis on 23 afterglows. Thanks to Swift, we could build the SED at early times after the GRB (minutes to hours). We derived the Hydrogen column densities and the spectral slopes from the X-ray spectrum. We then constrained the visual extinction by requiring that the combined optical/X-ray SED is due to synchrotron, namely either a single power law or a broken power law with a slope change by 0.5. We confirm a low dust-to-metal ratio, smaller than in the SMC, even from the analysis of data taken significantly earlier than previously possible. Our analysis does not support the existence of ``grey'' dust. We also find that the synchrotron spectrum works remarkably well to explain afterglow SEDs. We clearly see, however, that during the X-ray steep decay phases and the flares, the X-ray radiation cannot be due only to afterglow emission.

Wright 2007 多方法限制宇宙暗能量

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astro-ph/0701584 [abs, ps, pdf, other] :

Title: Constraints on Dark Energy from Supernovae, Gamma Ray Bursts, Acoustic Oscillations, Nucleosynthesis and Large Scale Structure and the Hubble constant
Authors: Edward L. Wright (UCLA)
Comments: 16 pages Latex with 8 Postscript figure files

The luminosity distance vs. redshift law is now measured using supernovae and gamma ray bursts, and the angular size distance is measured at the surface of last scattering by the CMB and at z = 0.35 by baryon acoustic oscillations. In this paper this data is fit to models for the equation of state with w = -1, w = const, and w(z) = w_0+w_a(1-a). The last model is poorly constrained by the distance data, leading to unphysical solutions where the dark energy dominates at early times unless the large scale structure and acoustic scale constraints are modified to allow for early time dark energy effects. A flat LambdaCDM model is consistent with all the data.

Piranomonte 2007 射电高分辨谱观测

主要内容:
是他们前一篇的补充

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文章信息:

astro-ph/0701563 [abs, ps, pdf, other] :

Title: UVES/VLT High Resolution Spectroscopy of Gamma Ray Burst Afterglows
Authors: S. Piranomonte, V. D'Elia, P. Ward, F. Fiore, E.J.A. Meurs
Comments: 2 pages, 1 ps figure. Proceedings of the Swift-Venice 2006 meeting to be published by "Il Nuovo Cimento"

We present early time, high resolution spectroscopy of three GRB afterglows: GRB050730, 050922C and 060418. These data give us precious information on the kinematics, ionization and metallicity of the interstellar matter of GRB host galaxies up to a redshift z = 4, and of intervening absorbers along the line of sight.

Larsson 2007 伽玛暴前身星质量限制

主要内容:
伽玛暴和超新星在星系中的分布明显不同，伽玛暴（长暴）比超新星更集中于星系中心。暗示这长暴的前身星质量更大，最终形成黑洞。

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文章信息:

astro-ph/0701562 [abs, ps, pdf, other] :

Title: A new constraint for gamma-ray burst progenitor mass
Authors: Josefin Larsson, Andrew J. Levan, Melvyn B. Davies, Andrew S. Fruchter
Comments: 7 pages, 4 figures, accepted by MNRAS

Recent comparative observations of long duration gamma-ray bursts (LGRBs) and core collapse supernovae (cc SN) host galaxies demonstrate that these two, highly energetic transient events are distributed very differently upon their hosts. LGRBs are much more concentrated on their host galaxy light than cc SN. Here we explore the suggestion that this differing distribution reflects different progenitor masses for LGRBs and cc SN. Using a simple model we show that, assuming cc SN arise from stars with main sequence masses $>$8 M$_{\odot}$, GRBs are likely to arise from stars with initial masses $>$ 20 M$_{\odot}$. This difference can naturally be explained by the requirement that stars which create a LGRB must also create a black hole.

D'Elia 2007 伽玛暴余辉的射电高分辨谱观测

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astro-ph/0701558 [abs, ps, pdf, other] :

Title: UVES - VLT High Resolution Spectroscopy of GRB Afterglows
Authors: V. D'Elia, S. Piranomonte, P. Ward, F. Fiore, E.J.A. Meurs, L. Norci, S.D. Vergani
Comments: 8 pages, 11 figure, To appear in "The Multicoloured Landscape of Compact Objects and their Explosive Progenitors: Theory vs Observations" (Cefalu, Sicily, June 2006). Eds. L. Burderi et al. (New York: AIP)

We present early time, high resolution spectroscopy of three GRB afterglows: GRB050730, GRB050922C and GRB060418. These data give us precious information on the kinematics, ionization and metallicity of the interstellar matter of GRB host galaxies up to a redshift z = 4, and of intervening absorbers along the line of sight. The absorption spectra show that elements are present both with high and low ionization states, and even forbidden, fine structure levels are commonly observed. These features allow us to evaluate the physical parameters of the absorbing gas. In details, the density of the gas regions lie in the range n = 10 - 10^6 cm-3, and the temperatures are of the order of T = 10^3 - 10^4 K. The metallicity of the GRB host galaxies is computed using the hydrogen absorption features. We find undersolar abundances for our GRBs, namely, Z = 0.001 - 0.01. However, depletion has not been considered. It can be taken into account using as metallicity indicators Zn and Cr, which tend to remain in the gas phase. We find metallicities higher than the previous values and in agreement with other measurements for GRB host galaxies. Finally, the observed [C/Fe] ratio for GRB050730 (z = 3.967) agrees with values expected for a galaxy younger than a Gyr undergoing bursts of star-formation. In addition, the [C/Fe] ratio evaluated component by component can give informations on the relative distances of the components from the GRB explosion site, since Fe dust is more efficiently destroyed than graphite.

Schaefer 2007 跟光度相关的八个统计关系

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astro-ph/0701548 [abs, ps, pdf, other] :

Title: Generalized Tests for Eight GRB Luminosity Relations
Authors: Bradley E. Schaefer, Andrew C. Collazzi
Comments: Ap.J. Letters in press, 11 pages

Long duration Gamma-Ray Bursts (GRBs) have eight luminosity relations where observable burst properties can yield the burst luminosity and hence distance. This turns GRBs into useful tools of cosmology. Recently, two tests have been proposed (by Nakar & Piran and by Li) for which one of the eight relations is claimed to have significant problems. In this paper, we generalize these tests and apply them to all eight GRB luminosity relations. (a) All eight relations pass the Nakar & Piran test after accounting for the uncertainties on the data and the dispersions of the correlations. (b) All eight relations are good when the GRB redshifts are known, for example for calibration of the relations and for GRB Hubble diagram purposes. (c) We confirm the earlier results that the E_gamma,iso - E_peak Amati relation must produce very large error bars whenever an unknown redshift being sought is >1.4. (d) The E_gamma - E_peak relation of Ghirlanda et al. must produce very large error bars whenever an unknown redshift being sought is >3.4. (e) The other six relations have no problem at all from the ambiguity test of Li.

Zhang 2007 Swift时代伽玛暴研究 4

主要内容:
综述给出了目前伽玛暴研究最活跃的方向：伽玛暴的新分类；余辉的4段光变；统计关系，宇宙学等。

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astro-ph/0701520 [abs, ps, pdf, other] :

Title: Gamma-Ray Bursts in the Swift Era
Authors: Bing Zhang (UNLV)
Comments: Invited review for Chinese Journal of Astronomy & Astrophysics, 60 pages, to appear in 2007, ChJAA, 7, 1-50

Since the successful launch of NASA's dedicated gamma-ray burst (GRB) mission, Swift, the study of cosmological GRBs has entered a new era. Here I review the rapid observational and theoretical progress in this dynamical research field during the first two-year of the Swift mission, focusing on how observational breakthroughs have revolutionized our understanding of the physical origins of GRBs. Besides summarizing how Swift helps to solve some pre-Swift mysteries, I also list some outstanding problems raised by the Swift observations. An outlook of GRB science in the future, especially in the GLAST era, is briefly discussed.

Nava 2007 星风环境下的E_p-E_gamma关系 3

主要内容:
在星风环境假设下，Ghirlanda关系变成线性的，E_p正比于E_gamma。其中E_gamma于\theta_j有关，而\theta_j来自于t_j，又与外部环境有关。

精彩摘抄:
二者之间的线性关系。

文章信息:

astro-ph/0701496 [abs, ps, pdf, other] :

Title: Wind circumburst density profile: a linear E_p-E_gamma correlation
Authors: L. Nava (1,2), G. Ghisellini (1), G. Ghirlanda (1), F. Tavecchio (1), C. Firmani (1,3) ((1)INAF-OAB, (2)Univ. Insubria, (3)U.N.A.M.)
Comments: 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"

Ghirlanda et al. (2004) derived the collimation-corrected energy E_gamma for a sample of 15 bursts under the assumption of a homogeneous circumburst density profile. They found a correlation (the so-called Ghirlanda correlation) between E_gamma and the rest frame peak energy of the nuF_nu prompt spectrum (E_p). Nava et al. (2006) showed that, assuming a circumburst density distribuited with a r^-2 wind profile, the Ghirlanda correlation remains tight and becomes linear. This implies that: i) it remains linear also in the comoving frame, no matter the distribution of bulk Lorentz factors, ii) it entails that different bursts have the same number of relevant photons. We have updated these findings including recently detected bursts (21 in total), stressing the two important implications.

Meynet 2007 伽玛暴前身星的星风各向异性

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astro-ph/0701494 [abs, ps, pdf, other] :

Title: Wind anisotropies and GRB progenitors
Authors: Georges Meynet, Andre Maeder
Comments: 5 pages, 4 figures, accepted for publication in A&A Letter

We study the effect of wind anisotropies on the stellar evolution leading to collapsars. Rotating models of a 60 M$_\odot$ star with $\Omega/\Omega_{\rm crit}=0.75$ on the ZAMS, accounting for shellular rotation and a magnetic field, with and without wind anisotropies, are computed at $Z$=0.002 until the end of the core He-burning phase. Only the models accounting for the effects of the wind anisotropies retain enough angular momentum in their core to produce a Gamma Ray Burst (GRB). The chemical composition is such that a type Ic supernova event occurs. Wind anisotropies appear to be a key physical ingredient in the scenario leading to long GRBs.

Bisnovatyi-Kogan 2007 伽玛暴的观测与模型

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astro-ph/0701461 [abs, ps, pdf, other] :

Title: Cosmic gamma-ray bursts: observations and modeling
Authors: G.S.Bisnovatyi-Kogan
Journal-ref: Physics of Particles and Nuclei, 2006, Vol.37, No.5, pp.647-676

The present common view about GRB origin is related to cosmology, what is based on statistical analysis, and on measurements of the redshifts in the GRB optical afterglows of long GRB. Models of radiation, and models of the central machine for GRB are critically analyzed. Most of these models cannot produce the amount of energy required for the cosmological GRB. Collimation is needed to reduce GRB energy output. No correlation is found between redshifts, GRB spectrum, and total GRB fluence. Comparison of KONUS and BATSE data about statistics and hard X-ray lines is done, and some differences are noted. Hard gamma-ray afterglows, prompt optical spectra, hard X-ray lines measurements could be important for farther insight into GRB origin. Two bright optical afterglows had been detected, indicating that initial bright optical emission is directly connected with the GRB itself, and has a different origin from the subsequent faint optical emission. Results of these observations are represented. Observations indicate that GRB originate in star forming regions of galaxies with a high matter density. Interaction of the mighty gamma ray flux from the cosmological GRB with the dense surrounding molecular cloud lead to long optical afterglow, lasting up to 10 years, due to reradiation of the cloud. Results of numerical simulations of such reradiation for different forms of clouds are represented. Possible connection of short GRB with soft gamma repeaters is discussed.

Horvath 2007 中间型伽玛暴的特征与长、短暴的比较

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astro-ph/0701456 [abs, ps, pdf, other] :

Title: Properties of the intermediate type of gamma-ray bursts
Authors: I. Horvath, F. Ryde, L.G. Balazs, Z. Bagoly, A. Meszaros
Comments: In Sixteenth Maryland Astrophysics Conference

Gamma-ray bursts can be divided into three groups ("short", "intermediate", "long") with respect to their durations. The third type of gamma-ray bursts - as known - has the intermediate duration. We show that the intermediate group is the softest one. An anticorrelation between the hardness and the duration is found for this subclass in contrast to the short and long groups.

Chincarini 2007 从XRFs的形状研究其来源

主要内容:
从XRFs的形状看，可能来自于晚期内激波。

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astro-ph/0701450 [abs, pdf] :

Title: Attributes of flares in Gamma Ray Bursts: sample I
Authors: G. Chincarini, A. Moretti, P. Romano, A.D. Falcone, S. Campana, S. Covino, C. Guidorzi, G. Tagliaferri, D.N. Burrows, M. Capalbi, G. Cusumano, P. Giommi, V. Mangano, V. La Parola, T. Mineo, M. Perri, E. Troja
Comments: Paper presented at the GRB meeting in Venice: Swift and GRBs: Unveiling the relativistic Universe

We discuss some of the preliminary results and findings derived from the analysis of a first sample of flares detected by the XRT on board Swift. The analysis shows that the morphology of flares is the one we expect from the collision of ultra-relativistic shells as it happens during the internal shock model proposed by Rees and Meszaros in 1994. Furthermore the Delta(t)/t ratio and the decay-time to rise-time ratio have mean values that are in good agreement with the values observed in the prompt emission pulses that are believed to originate from internal shocks. The conclusion is that the flare analysis favors the internal shock as due to shells that have been ejected by the central engine after the prompt emission. The central engine seems to remain active and capable of generating large amounts of energy also at later times. More data are needed to establish whether or not some of the flares could be due to shells that have been emitted with small Lorentz factor at the time of the prompt emission and generate later time flares due to the catch up of these shells.

Ghirlanda 2007 短暴的硬度与距离

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astro-ph/0701448 [abs, ps, pdf, other] :

Title: On the spectra and distance scale of short Gamma Ray--Bursts
Authors: Giancarlo Ghirlanda (INAF - Osservatorio Astronomico di Brera)
Comments: 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"

I discuss the spectral properties of short GRBs detected by BATSE and compare them with long events. The detailed modeling of short GRB spectra shows that their being (on average) harder than long events (as it has been found by comparing their hardness ratios) is indeed due to a harder low energy spectral component (i.e. the powerlaw of the Band or cutoff-powerlaw model) in short GRBs which, instead, have a peak energy similar to long events. Another open issue is the distance scale to short GRBs. While the few redshift measurements suggests that they are at z<1,>

Meliani 2007 新的AMRVAC方法数值模拟余辉动力学

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astro-ph/0701434 [abs, ps, pdf, other] :

Title: AMRVAC and Relativistic Hydrodynamic simulations for GRB afterglow phases
Authors: Z. Meliani, R. Keppens, F. Casse, D. Giannios
Comments: 12 pages, accepted in MNRAS, 12/01/2007

We apply a novel adaptive mesh refinement code, AMRVAC, to numerically investigate the various evolutionary phases in the interaction of a relativistic shell with its surrounding cold Interstellar Medium (ISM). We do this for both 1D isotropic as well as full 2D jetlike fireball models. This is relevant for Gamma Ray Bursts, and we demonstrate that, thanks to the AMR strategy, we resolve the internal structure of the shocked shell-ISM matter, which will leave its imprint on the GRB afterglow. We determine the deceleration from an initial Lorentz factor $\gamma=100$ up to the almost Newtonian $\gamma\sim{\cal O}(2)$ phase of the flow. We present axisymmetric 2D shell evolutions, with the 2D extent characterized by their initial opening angle. In such jetlike GRB models, we discuss the differences with the 1D isotropic GRB equivalents. These are mainly due to thermally induced sideways expansions of both the shocked shell and shocked ISM regions. We found that the propagating 2D ultrarelativistic shell does not accrete all the surrounding medium located within its initial opening angle. Part of this ISM matter gets pushed away laterally and forms a wide bow-shock configuration with swirling flow patterns trailing the thin shell. The resulting shell deceleration is quite different from that found in isotropic GRB models. As long as the lateral shell expansion is merely due to ballistic spreading of the shell, isotropic and 2D models agree perfectly. As thermally induced expansions eventually lead to significantly higher lateral speeds, the 2D shell interacts with comparably more ISM matter and decelerates earlier than its isotropic counterpart.

Ghisellini 2007 伽玛暴余辉平下降阶段的晚期内激波模型

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astro-ph/0701430 [abs, ps, pdf, other] :

Title: "Late prompt" emission in Gamma Ray Bursts?
Authors: G. Ghisellini (1), G. Ghirlanda (1), L. Nava (1,2), C. Firmani (1,3) ((1) INAF-OAB; (2) Univ. Insubria; (3) U.N.A.M.)
Comments: Submitted to ApJ Letters

The flat decay phase in the first 100-1e4 seconds of the X-ray light curve of Gamma Ray Bursts (GRBs) has not yet found a convincing explanation. The fact that the optical and X-ray lightcurves are often different, with breaks at different times, makes contrived any explanation based on the same origin for both the X-ray and optical fluxes. We here propose that the central engine can be active for a long time, producing shells of decreasing kinetic energy and bulk Lorentz factor Gamma The internal dissipation of these late shells, at radii similar to what occurs for the early prompt, can produce radiation most often dominant in the X-ray band, and sometimes even in the optical. When Gamma of the late shells is larger than 1/theta_j, where theta_j is the jet opening angle, we see only a portion of the emitting surface. Eventually, Gamma becomes smaller than 1/theta_j, and the entire emitting surface is visible. Thus there is a break in the light curve when Gamma=1/theta_j, which we associate to the time at which the plateau ends. After a few hundreds seconds since the onset of the burst, i.e. after the steeply decaying phase which follows the early prompt, we see the sum of two emission components: the "late--prompt" emission (due to late internal dissipation), and the "real afterglow" emission (due to external shocks). A variety of different optical and X-ray light curves are then possible, explaining why the X-ray and the optical light curves often do not track each other (but sometimes do), and often they do not have simultaneous breaks.