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.