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.

星期四, 九月 30, 2010

Sekiguchi, Yuichiro 2010 坍缩星中的黑洞吸积盘的形成

主要内容:
数值模拟盘的形成。还提到了伽马暴喷流的形成。

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文章信息:



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· arXiv e-print (arXiv:1009.5303)
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Title:
Formation of black hole and accretion disk in collapsar
Authors:
Sekiguchi, Yuichiro; Shibata, Masaru
Publication:
eprint arXiv:1009.5303
Publication Date:
09/2010
Origin:
ARXIV
Keywords:
Astrophysics - High Energy Astrophysical Phenomena
Comment:
28 pages, 26 figures with low resolution, abstract is shortened, submitted to ApJ
Bibliographic Code:
2010arXiv1009.5303S

Abstract

We present the first numerical result of full-GR simulations for the collapse of a rotating high-entropy stellar core to a BH and accretion disk. The simulations are performed taking into account the relevant microphysics such as nuclear-theory-based finite-temperature EOS, weak interaction processes, and neutrino cooling in a general relativistic leakage scheme. The initial core is modeled by a spherical configuration with a constant $Y_e = 0.5$ and s = 8 $k_B$, with rotational profiles added. In all models, collapse to a BH proceeds as follows: In the early phase, the core collapses and then experiences a gas-pressure-dominated bounce. Because the bounce is too weak to halt the collapse, a BH with the initial mass of $\sim 6$--$7M_{\odot}$ is eventually formed. Subsequent evolution depends sensitively on the amount of rotation. For the case that the rotation is not fast, a geometrically thin accretion disk is formed around the BH, and a standing shock wave is formed in the inner part of the disk. For the moderately rotating case, the thin disk expands eventually to be a geometrically thick torus after sufficient accumulation of the thermal energy generated at the shocks, and then, convection occurs inside the torus, because a region with negative entropy gradient emerges due to the interplay of the shock heating, neutrino cooling, and the neutrino trapping. In the long-term evolution of the torus, neutrino luminosities vary violently with time because of the convective motion. For the rapidly rotating case, by contrast, a geometrically thick torus is immediately formed soon after the BH formation. Based on our results, we describe a scenario for the generation of relativistic jets of long gamma-ray bursts in the collapse of a population III star. We also estimate GW due to anisotropic emission of neutrinos, and find that it may have a larger amplitude than previously estimated.

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Asano, Katsuaki 2010 暴本身阶段的光学和X射线超以及GeV辐射可能是超高能量质子的贡献

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· arXiv e-print (arXiv:1009.5178)
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Title:
Prompt X-ray and Optical Excess Emission due to Hadronic Cascades in Gamma-Ray Bursts
Authors:
Asano, Katsuaki; Inoue, Susumu; Meszaros, Peter
Publication:
eprint arXiv:1009.5178
Publication Date:
09/2010
Origin:
ARXIV
Keywords:
Astrophysics - High Energy Astrophysical Phenomena
Comment:
12 pages, 2 figures
Bibliographic Code:
2010arXiv1009.5178A

Abstract

A fraction of gamma-ray bursts exhibit distinct spectral features in their prompt emission below few 10s of keV that exceed simple extrapolations of the low-energy power-law portion of the Band spectral model. This is also true for the prompt optical emission observed in several bursts. Through Monte Carlo simulations, we model such low-energy spectral excess components as hadronic cascade emission initiated by photomeson interactions of ultra-high-energy protons accelerated within GRB outflows. Synchrotron radiation from the cascading, secondary electron-positron pairs can naturally reproduce the observed soft spectra in the X-ray band, and in some cases the optical spectra as well. These components can be directly related to the higher energy radiation at GeV energies due to the hadronic cascades. Depending on the spectral shape, the total energy in protons is required to be comparable to or appreciably larger than the observed total photon energy. In particular, we apply our model to the excess X-ray and GeV emission of GRB 090902B, and the bright optical emission of the "naked-eye" GRB 080319B. Besides the hard GeV components detected by {\it Fermi}, such X-ray or optical spectral excesses are further potential signatures of ultra-high-energy cosmic ray production in gamma-ray bursts.

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星期日, 九月 26, 2010

Melandri, A. 2010 GRB 090313的余辉观测

主要内容:


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多波段的光变

光学多波段的光变,有意思的是JHK这几个红外波段没有峰值


谱,不过为什么光变不同的那段没显示出来呢?
一些有光学峰的暴,以及对洛仑兹因子的估计


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Title:
GRB 090313 and the Origin of Optical Peaks in GRB Light Curves: Implications for Lorentz Factors and Radio Flares
Authors:
Melandri, A.; Kobayashi, S.; Mundell, C. G.; Guidorzi, C.; de Ugarte Postigo, A.; Pooley, G.; Yoshida, M.; Bersier, D.;Castro-Tirado, A. J.; Jelinek, M.; Gomboc, A.; Gorosabel, J.; Kubanek, P.; Bremer, M.; Winters, J. M.; Steele, I. A.;Smith, R. J.; de Gregorio-Monsalvo, I.; Garcia-Appadoo, D.; Sota, A.; Lundgren, A.
Publication:
eprint arXiv:1009.4361
Publication Date:
09/2010
Origin:
ARXIV
Keywords:
Astrophysics - High Energy Astrophysical Phenomena
Comment:
30 pages, 4 tables, 8 figures, accepted for publication on the Astrophysical Journal
Bibliographic Code:
2010arXiv1009.4361M

Abstract

We use a sample of 19 Gamma Ray Bursts (GRBs) that exhibit single-peaked optical light curves to test the standard fireball model by investigating the relationship between the time of the onset of the afterglow and the temporal rising index. Our sample includes GRBs and X-ray flashes for which we derive a wide range of initial Lorentz factors ($40 < \Gamma < 450$). Using plausible model parameters the typical frequency of the forward shock is expected to lie close to the optical band; within this low typical frequency framework, we use the optical data to constrain $\epsilon_e$ and show that values derived from the early time light curve properties are consistent with published typical values derived from other afterglow studies. We produce expected radio light curves by predicting the temporal evolution of the expected radio emission from forward and reverse shock components, including synchrotron self-absorption effects at early time. Although a number of the GRBs in this sample do not have published radio measurements, we demonstrate the effectiveness of this method in the case of {\it Swift} GRB 090313, for which millimetric and centrimetric observations were available, and conclude that future detections of reverse-shock radio flares with new radio facilities such as the EVLA and ALMA will test the low frequency model and provide constraints on magnetic models.
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Nakar, Ehud 2010 对伽马暴我们知道什么

主要内容:
在2009年威尼斯会议上的一个讨论。文章貌似有所改动,分为 前身星、外流、暴本身和余辉四部分。
可以肯定的基本上只有相对论性的外流和余辉来自于外流与介质相互作用。

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Title:
What do we know about gamma-gay bursts?
Authors:
Nakar, Ehud
Publication:
eprint arXiv:1009.4648
Publication Date:
09/2010
Origin:
ARXIV
Keywords:
Astrophysics - High Energy Astrophysical Phenomena
Comment:
proceedings of the The Shocking Universe meeting, Venice, September 2009
Bibliographic Code:
2010arXiv1009.4648N

Abstract

Decades of improving data and extensive theoretical research have led to a popular model of gamma-ray bursts. According to this model, a catastrophic event in a stellar system results in the formation of a compact central engine, which releases a fraction of a solar rest-mass energy within seconds in the form of ultra-relativistic jets. Dissipation of the jets energy leads first to prompt gamma-ray emission and later to a long lasting afterglow. Here I summarize the introduction that I gave to the debate "where do we stand?" in the conference ``The Shocking Universe" held in Venice. This is a very brief summary of my view of the facts that we are (almost) certain about, models that are popular but may need rethinking, and main open questions.
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星期三, 九月 22, 2010

Deng, J. 2010 GRB 060912A的光学余辉

主要内容:
光学一直下降,X射线有个平台。平台处二者的谱连不上,同事下降的地方谱能连上。

精彩摘抄:

光变


文章信息:

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· arXiv e-print (arXiv:0912.5435)
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Title:
The X-ray Asynchronous Optical Afterglow of GRB 060912A and Tentative Evidence of a 2175-A Host Dust Extinction Feature
Authors:
Deng, J.; Zheng, W.; Zhai, M.; Xin, L.; Qiu, Y.; Stefanescu, A.; Pozanenko, A.; Ibrahimov, M.; Volnova, A.
Publication:
eprint arXiv:0912.5435
Publication Date:
12/2009
Origin:
ARXIV
Keywords:
Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Extragalactic Astrophysics
Comment:
19 pages, 2 figures, 2 tables, submitted to ApJ
Bibliographic Code:
2009arXiv0912.5435D

Abstract

We present optical photometry of the GRB 060912A afterglow obtained with ground-based telescopes, from about 100 sec after the GRB trigger till about 0.3 day later, supplemented with the Swift optical afterglow data released in its official website. The optical light curve (LC) displays a smooth single power-law decay throughout the observed epochs, with a power-law index of about -1 and no significant color evolution. This is in contrast to the X-ray LC which has a plateau phase between two normal power-law decays of a respective index of about -1 and -1.2. It is shown by our combined X-ray and optical data analysis that this asynchronous behavior is difficult to be reconciled with the standard afterglow theory and energy injection hypothesis. We also construct an optical-to-X-ray spectral energy distribution at about 700 sec after the GRB trigger. It displays a significant flux depression in the B-band, reminding us of the possibility of a host-galaxy (at z=0.937) 2175-A dust absorption similar to the one that characterizes the Milky Way extinction law. Such an identification, although being tentative, may be confirmed by our detailed analysis using both template extinction laws and the afterglow theory. So far the feature is reported in very few GRB afterglows. Most seem to have a host galaxy either unusually bright for a GRB, just like this one, or of an early type, supporting the general suggestion of an anti-correlation between the feature and star-forming activities.
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Wang, F. Y. 2010 区分暗能量模型和修改引力模型

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Title:
Probing the cosmographic parameters to distinguish between dark energy and modified gravity models
Authors:
Wang, F. Y.; Dai, Z. G.; Qi, Shi
Affiliation:
AA(Department of Astronomy, Nanjing University, Nanjing 210093, PR China fayinwang@nju.edu.cn ; Department of Astronomy, University of Texas at Austin, Austin, TX 78712, USA), AB(Department of Astronomy, Nanjing University, Nanjing 210093, PR China), AC(Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008, PR China ; Joint Center for Particle, Nuclear Physics and Cosmology, Nanjing University - Purple Mountain Observatory, Nanjing 210093, PR China)
Publication:
Astronomy and Astrophysics, Volume 507, Issue 1, 2009, pp.53-59 (A&A Homepage)
Publication Date:
11/2009
Origin:
EDP Sciences
Keywords:
gamma rays: bursts, cosmology: cosmological parameters, cosmology: distance scale
DOI:
10.1051/0004-6361/200911998
Bibliographic Code:
2009A&A...507...53W

Abstract

Aims: In this paper we investigate the deceleration, jerk and snap parameters to distinguish between the dark energy and modified gravity models using high redshift gamma-ray bursts (GRBs) and supernovae (SNe). 
Methods: We first derive the expressions of deceleration, jerk and snap parameters in dark energy and modified gravity models. In order to constrain the cosmographic parameters, we calibrate the GRB luminosity relations without assuming any cosmological models using SNe Ia. Then we constrain the model parameters (including dark energy and modified gravity models) using type Ia supernovae and gamma-ray bursts. Finally we calculate the cosmographic parameters. GRBs can extend the redshift-distance relation up to high redshifts, because they can be detected to high redshifts. 
Results: We find that the statefinder pair (r,s) could not be used to distinguish between some dark energy and modified gravity models, but these models could be differentiated by the snap parameter. Using the model-independent constraints on cosmographic parameters, we conclude that the ΛCDM model is consistent with current data.
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Wang, F. Y. 2010 用伽马暴来限定高红移的恒星形成率

主要内容:
并考虑不同的宇宙学模型。
说在比较高的地方有一个变陡。

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Title:
High-redshift star formation rate up to z ~ 8.3 derived from gamma-ray bursts and influence of background cosmology
Authors:
Wang, F. Y.; Dai, Z. G.
Affiliation:
AA(Department of Astronomy, Nanjing University, Nanjing 210093, P. R. China; ), AB(Department of Astronomy, Nanjing University, Nanjing 210093, P. R. China; )
Publication:
Monthly Notices of the Royal Astronomical Society: Letters, Volume 400, Issue 1, pp. L10-L14. (MNRAS Homepage)
Publication Date:
11/2009
Origin:
MNRAS
MNRAS Keywords:
stars: formation , gamma-rays: bursts
DOI:
10.1111/j.1745-3933.2009.00751.x
Bibliographic Code:
2009MNRAS.400L..10W

Abstract

The high-redshift star formation rate (SFR) is difficult to measure directly even by modern approaches. Long-duration gamma-ray bursts (GRBs) can be detected to the edge of the visible universe because of their high luminosities. The collapsar model of long GRBs indicates that they may trace the star formation history. So, long GRBs may be a useful tool of measuring the high-redshift SFR. Observations show that long GRBs prefer to form in a low-metallicity environment. We study the high-redshift SFR up to z ~ 8.3 considering the Swift GRBs tracing the star formation history and the cosmic metallicity evolution in different background cosmological models including Λ cold dark matter (ΛCDM), quintessence, quintessence with a time-varying equation of state and brane-world model. We use latest Swift GRBs including two highest-z GRBs, GRB 080913 at z = 6.7 and GRB 090423 at z = 8.3. We find that the SFR at z > 4 shows a steep decay with a slope of ~-5.0 in ΛCDM. In the other three models, the high-redshift SFR is slightly different from ΛCDM model and also shows a steep decay.
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Viganò, D. 2010 通过伽马暴的观测来校准ITEGRAL的一个仪器

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Title:
Calibration of the INTEGRAL SPI Anti Coincidence Shield with Gamma Ray Bursts observations
Authors:
Viganò, D.; Mereghetti, S.
Publication:
eprint arXiv:0912.5329
Publication Date:
12/2009
Origin:
ARXIV
Keywords:
Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - High Energy Astrophysical Phenomena
Comment:
6 pages, 3 figures, poster paper, to appear in the proceedings of The Extreme sky: Sampling the Universe above 10 keV, held in Otranto (Lecce, Italy) on 2009 October 13-17
Bibliographic Code:
2009arXiv0912.5329V

Abstract

The Anti Coincidence Shield (ACS) of the INTEGRAL SPI instrument provides an excellent sensitivity for the detection of Gamma Ray Bursts (GRBs) above ~ 75keV, but no directional and energy information is available. We studied the ACS response by using GRBs with known localizations and good spectral information derived by other satellites. We derived a count rate to flux conversion factor for different energy ranges and studied its dependence on the GRB direction and spectral hardness. For a typical GRB spectrum, we found that 1 ACS count corresponds on average to ~ 1E-10 erg/cm^2 in the 75keV-1MeV range, for directions orthogonal to the satellite pointing axis. This is broadly consistent with the ACS effective area derived from the Monte Carlo simulations, but there is some indication that the latter slightly overestimates the ACS sensitivity, especially for directions close to the instrument axis.
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Qin, Shu-Fu 2010 模拟高红移伽马暴的诞生率

主要内容:
说现在观测到的暴15%的红移大于4,还有大于14的被观测了。

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Title:
Simulations on high-z long gamma-ray burst rate
Authors:
Qin, Shu-Fu; Liang, En-Wei; Lu, Rui-Jing; Wei, Jian-Yan; Zhang, Shuang-Nan
Affiliation:
AA(Department of Physics, Guangxi University, Nanning 530004, China), AB(Department of Physics, Guangxi University, Nanning 530004, China), AC(Department of Physics, Guangxi University, Nanning 530004, China), AD(National Astronomical Observatories, Chinese Academy of Sciences, 100012 Beijing, China), AE(Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China; Physics Department, University of Alabama in Huntsville, Huntsville, AL 35899, USA)
Publication:
Monthly Notices of the Royal Astronomical Society, Volume 406, Issue 1, pp. 558-565. (MNRAS Homepage)
Publication Date:
07/2010
Origin:
WILEY
MNRAS Keywords:
instrumentation: detectors, stars: evolution, stars: formation, gamma-ray burst: general, stars: luminosity function, mass function, galaxies: high-redshift
Abstract Copyright:
(c) Journal compilation © 2010 RAS
DOI:
10.1111/j.1365-2966.2010.16691.x
Bibliographic Code:
2010MNRAS.406..558Q

Abstract

Since the launch of Swift satellite, the detections of high-z (z > 4) long gamma-ray bursts (LGRBs) have been rapidly growing, even approaching the very early Universe (the record holder currently is z = 8.3). The observed high-z LGRB rate shows significant excess over that estimated from the star formation history. We investigate what may be responsible for this high productivity of GRBs at high-z through Monte Carlo simulations, with effective Swift/Burst Alert Telescope (BAT) trigger and redshift detection probabilities based on current Swift/BAT sample and Compton Gamma-ray Observatory/Burst and Transient Source Experiment LGRB sample. We compare our simulations to the Swift observations via log N - log P, peak luminosity (L) and redshift distributions. In the case that LGRB rate is purely proportional to the star formation rate, our simulations poorly reproduce the LGRB rate at z > 4, although the simulated log N - log P distribution is in good agreement with the observed one. Assuming that the excess of high-z GRB rate is due to the cosmic metallicity evolution or unknown LGRB rate increase parametrized as (1 + z)δ, we find that although the two scenarios alone can improve the consistency between our simulations and observations, incorporation of them gives much better consistency. We get 0.2 < ɛ < 0.6 and δ < 0.6, where ɛ is the metallicity threshold for the production of LGRBs. The best consistency is obtained with a parameter set (ɛ, δ) = (~ 0.4, ~ 0.4), and BAT might trigger a few LGRBs at z ~= 14. With increasing detections of GRBs at z > 4 (~15 per cent of GRBs in current Swift LGRB sample based on our simulations), a window for very early Universe is opening by Swift and up-coming space-based multiband astronomical variable object monitor missions.
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