伽玛暴(Gamma-Ray Burst)笔记。记录有关伽玛暴的新文章,另外也包括看的老文章、自己的想法、以及跟天文相关的一些东西。 Feel free to leave me a message by comments or by email.

星期五, 九月 30, 2011

Augusto 2011 疑似找到和GRB 991112成协的mu子中微子

主要内容:


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文章信息:



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· arXiv e-print (arXiv:1109.5156)
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Title:
Search for GeV gamma ray burst signal in the field of view of muon telescopes
Authors:
Augusto, C. R. A.Kopenkin, V.Navia, C. E.Shigueoka, H.Tsui, K. H.
Publication:
eprint arXiv:1109.5156
Publication Date:
09/2011
Origin:
ARXIV
Keywords:
Astrophysics - High Energy Astrophysical Phenomena
Comment:
9 pages, 9 figures
Bibliographic Code:
2011arXiv1109.5156A

Abstract

We present a search for the muon excess associated in time (preceding or following) with the trigger of gamma ray burst (GRB) detected by the satellite borne instruments. The 1 Hz rate data was collected at the sea level in the area located at 22S and 43W, inside the South Atlantic Anomaly (SAA) region and close to its center. Using 1 sec amd 10 sec time binning, we found the muon excess with significance $>5\sigma$ associated with the gamma ray burst GRB091112 observed by Swift BAT, Fermi GBM and Suzaku-WAM satellites. The detected muon time profile shows a rough peak at $\sim T+223$ sec ($5.2\sigma$), and with a duration of 7 sec. The FLUKA Monte Carlo simulation of the photon-to-muon conversion in the atmosphere shows that the observed muon excess can be explained by progenitor photons with energies above 10 GeV. This energy value is above the limits expected from the maximum synchrotron emission combined with the shock wave evolution. It shows constrains on the external shock synchrotron model for GRB emission in the GeV energy band and favors scenarios with overall afterglow spectrum, ranging from the optical-to-GeV photons. On the basis of the observed associations with the satellite data, we report confidence analysis of the background fluctuations and fluencies in the GeV energy region, that is important for better understanding of the GRB physics.
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Greco 2011 在伽马暴的“随机”光变里发现混沌现象

主要内容:
在随机光变里找到短时标的“吸引子”,是否说明存在内在的规律性。

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文章信息:

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· arXiv e-print (arXiv:1109.5891)
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Title:
Evidence of Deterministic Components in the Apparent Randomness of GRBs: Clues of a Chaotic Dynamic
Authors:
Greco, G.Rosa, R.Beskin, G.Karpov, S.Romano, L.Guarnieri, A.Bartolini, C.Bedogni, R.
Publication:
eprint arXiv:1109.5891
Publication Date:
09/2011
Origin:
ARXIV
Keywords:
Astrophysics - High Energy Astrophysical Phenomena
Comment:
13 pages, 6 figures; The article is published by Scientific Report. The original version is available at the following address: http://www.nature.com/srep/2011/110914/srep00091/full/srep00091.html
Bibliographic Code:
2011arXiv1109.5891G

Abstract

Prompt {\gamma}-ray emissions from gamma-ray bursts (GRBs) exhibit a vast range of extremely complex temporal structures with a typical variability time-scale significantly short - as fast as milliseconds. This work aims to investigate the apparent randomness of the GRB time profiles making extensive use of nonlinear techniques combining the advanced spectral method of the Singular Spectrum Analysis (SSA) with the classical tools provided by the Chaos Theory. Despite their morphological complexity, we detect evidence of a non stochastic short-term variability during the overall burst duration - seemingly consistent with a chaotic behavior. The phase space portrait of such variability shows the existence of a well-defined strange attractor underlying the erratic prompt emission structures. This scenario can shed new light on the ultra-relativistic processes believed to take place in GRB explosions and usually associated with the birth of a fast-spinning magnetar or accretion of matter onto a newly formed black hole.
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Maeder 2011 旋转的大质量恒星的演化

主要内容:

就个人而言,可以通过这篇综述查看WR星的星风,知道星风的轮廓(应该不是-2).

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文章信息:

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· arXiv e-print (arXiv:1109.6171)
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Title:
Rotating massive stars through the ages, with applications to WR stars, Pop III stars and Gamma Ray Bursts
Authors:
Maeder, AndreMeynet, Georges
Publication:
eprint arXiv:1109.6171
Publication Date:
09/2011
Origin:
ARXIV
Keywords:
Astrophysics - Solar and Stellar Astrophysics
Comment:
55 pages, 33 figures, 2 tables, accepted for publication in Review of Modern Physics
Bibliographic Code:
2011arXiv1109.6171M

Abstract

This article first reviews the basic physics of rotating stars and their evolution. We examine in particular the changes of the mechanical and thermal equilibrium of rotating stars. An important (predicted and observed) effect is that rotating stars are hotter at the poles and cooler at the equator. We briefly discuss the mass loss by stellar winds, which are influenced by the anisotropic temperature distribution. These anisotropies in the interior are also driving circulation currents, which transports the chemical elements and the angular momentum in stars. Internal differential rotation, if present, creates instabilities and mixing, in particular the shear mixing, the horizontal turbulence and their interactions. A major check of the model predictions concerns the changes of the surface abundances, which are modified by mass loss in the very massive stars and by rotational mixing in O- and B-type stars. We show that the observations confirm the existence of rotational mixing, with much larger effects at lower metallicities. We discuss the predictions of stellar models concerning the evolution of the surface velocities, the evolutionary tracks in the HR diagram and lifetimes, the populations of blue, red supergiants and Wolf-Rayet stars, and the progenitors of type Ibc supernovae. We show, that in many aspects, rotating models provide a much better fit than non-rotating ones. Using the same physical ingredients as those which fit the best the observations of stars at near solar metallicities, we explore the consequences of rotating models for the status of Be stars, the progenitors of Gamma Ray Bursts, the evolution of Pop III stars and of very metal poor stars, the early chemical evolution of galaxies, the origin of the C-enhanced Metal Poor stars (CEMP) and of the chemical anomalies in globular clusters.
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Granot 2011 关于侧向膨胀新的解析解

主要内容:
以前的解析解认为在gamma=1/theta_j的时候就开始进入指数阶段,侧向膨胀很显著;但数值模拟发现不是这样的。Granot和Piran给出了新的解析解,得到了和数值解一致的结果。

结果是再共动系中侧向膨胀的速度 beta_theta ~ 1/(Gamma^2 delta_theta) ~ 1/(Gamma^2 theta)

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文章信息:

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· arXiv e-print (arXiv:1109.6468)
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Title:
On the lateral expansion of GRB jets
Authors:
Granot, JonathanPiran, Tsvi
Publication:
eprint arXiv:1109.6468
Publication Date:
09/2011
Origin:
ARXIV
Keywords:
Astrophysics - High Energy Astrophysical Phenomena
Comment:
33 pages, 11 figures, submitted to MNRAS
Bibliographic Code:
2011arXiv1109.6468G

Abstract

The dynamics of GRB jets during the afterglow phase have an important effect on the interpretation of their observations and for inferring key physical parameters such as their true energy and event rate. Semi-analytic models generally predict a fast lateral expansion, where the jet opening angle asymptotically grows exponentially with its radius. Numerical simulations, however, show a much more modest lateral expansion, where the jet retains memory of its initial opening angle for a very long time, and the flow remains non-spherical until it becomes sub-relativistic, and only then gradually approaches spherical symmetry. Here we suggest a new analytic model based on a new physically derived recipe for the lateral expansion. We also generalize the model by relaxing the common approximations of ultra-relativistic motion and a narrow jet opening angle. We find that the new analytic model fits much better the results of numerical simulations, mainly because it remains valid also in the mildly relativistic, quasi spherical regime. This model shows that for modest initial jet half-opening angles, \theta_0, the outflow is not sufficiently ultra-relativistic when its Lorentz factor reaches \Gamma = 1/\theta_0 and therefore the sideways expansion is rather slow, showing no rapid, exponential phase. On the other hand, we find that jets with a very narrow initial half-opening angle, \theta_0 << 1, which are still ultra-relativistic at \Gamma = 1/\theta_0, do show a phase of rapid, exponential lateral expansion. However, even such jets that expand sideways exponentially are still not spherical when they become sub-relativistic.
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