Mizuno 2014 相对论性激波中的磁场放大--MHD模拟

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Title:		Magnetic Field Amplification and Saturation in Turbulence Behind a Relativistic Shock
Authors:		Mizuno, Yosuke; Pohl, Martin; Niemiec, Jacek; Zhang, Bing; Nishikawa, Ken-Ichi; Hardee, Philip E.
Publication:		eprint arXiv:1401.7080
Publication Date:		01/2014
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena, General Relativity and Quantum Cosmology
Comment:		14 pages, 15 figures, accepted for publication in MNRAS
Bibliographic Code:		2014arXiv1401.7080M

Abstract

We have investigated via two-dimensional relativistic MHD simulations the long-term evolution of turbulence created by a relativistic shock propagating through an inhomogeneous medium. In the postshock region, magnetic field is strongly amplified by turbulent motions triggered by preshock density inhomogeneities. Using a long-simulation box we have followed the magnetic-field amplification until it is fully developed and saturated. The turbulent velocity is sub-relativistic even for a strong shock. Magnetic-field amplification is controled by the turbulent motion and saturation occurs when the magnetic energy is comparable to the turbulent kinetic energy. Magnetic-field amplification and saturation depend on the initial strength and direction of the magnetic field in the preshock medium, and on the shock strength. If the initial magnetic field is perpendicular to the shock normal, the magnetic field is first compressed at the shock and then can be amplified by turbulent motion in the postshock region. Saturation occurs when the magnetic energy becomes comparable to the turbulent kinetic energy in the postshock region. If the initial magnetic field in the preshock medium is strong, the postshock region becomes turbulent but significant field amplification does not occur. If the magnetic energy after shock compression is larger than the turbulent kinetic energy in the postshock region, significant field amplification does not occur. We discuss possible applications of our results to gamma-ray bursts and active galactic nuclei.

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Boylan 2014 短暴的offset

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说矮星系不太可能是宿主信息（也就是说找不到宿主信息的还是来自于kick）

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Title:		Short gamma ray bursts: formation and offsets
Authors:		Boylan, C.; Li, Y.; Fan, X. L.; Heng, I. S.
Publication:		eprint arXiv:1401.7851
Publication Date:		01/2014
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		undergrad project, 7 pages, 3 figures, MNRAS style
Bibliographic Code:		2014arXiv1401.7851B

Abstract

Short gamma ray bursts have been observed a variety of galaxies types with varying angular offsets from the centre of their host galaxies. To investigate the properties of short gamma ray burst offsets, a sample of short gamma ray bursts with host galaxies has been gathered. Two formation channels proposed to explain the observed offsets of short gamma ray bursts from their host galaxies are discussed. The classification of short gamma ray bursts into these formation channels is demonstrated for short gamma ray bursts with host galaxies. The possibility of faint dwarf galaxies as host environments for the observed short gamma ray bursts is also investigated. However, by extrapolating the distribution of dwarf galaxies around the Milky Way to redshifts corresponding to the short gamma ray bursts, we show that it is unlikely that dwarf galaxies are the hosts of short gamma ray bursts.

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Behroozi 2014 短暴的kick

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Title:		Reinterpreting Short Gamma Ray Burst Progenitor Kicks and Time Delays Using the Host Galaxy-Dark Matter Halo Connection
Authors:		Behroozi, Peter S.; Ramirez-Ruiz, Enrico; Fryer, Christopher L.
Publication:		eprint arXiv:1401.7986
Publication Date:		01/2014
Origin:		ARXIV
Keywords:		Astrophysics - Cosmology and Extragalactic Astrophysics
Comment:		18 pages, ApJ submitted
Bibliographic Code:		2014arXiv1401.7986B

Abstract

Nearly 20% of short gamma-ray bursts (sGRBs) have no observed host galaxies. Combining this finding with constraints on galaxies' dark matter halo potential wells gives strong limits on the natal kick velocity distribution for sGRB progenitors. For the best-fitting velocity distribution, one in five sGRB progenitors receives a natal kick above 150 km/s, consistent with merging neutron star models but not with merging white dwarf binary models. This progenitor model constraint is robust to a wide variety of systematic uncertainties, including the sGRB progenitor time-delay model, the Swift redshift sensitivity, and the shape of the natal kick velocity distribution. We also use constraints on the galaxy-halo connection to determine the host halo and host galaxy demographics for sGRBs, which match extremely well with available data. Most sGRBs are expected to occur in halos near 10^12 Msun and in galaxies near 5 x 10^10 Msun (~L_*); unobserved faint and high-redshift host galaxies contribute a small minority of the observed hostless sGRB fraction. We find that sGRB redshift distributions and host galaxy stellar masses weakly constrain the progenitor time-delay model; the active vs. passive fraction of sGRB host galaxies may offer a stronger constraint. Finally, we discuss how searches for gravitational wave optical counterparts in the local Universe can reduce followup times using these findings.

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Eichler 2014 解决光球层热辐射的效率太低的问题

主要内容:
说如果在内部的热辐射往外走的时候，是基本不会被外层的shell挡住的，因为当光子追上外层的shell的时候，是在很远的地方，已经光学薄了。

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下面是示意图：

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Title:		Cloaked Gamma Ray Bursts
Authors:		Eichler, David
Publication:		eprint arXiv:1402.0245
Publication Date:		02/2014
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		accepted for publication in the Astrophysical Journal
Bibliographic Code:		2014arXiv1402.0245E

Abstract

It is suggested that many $\gamma$-ray bursts (GRBs) are cloaked by an ultra-relativistic baryonic shell that has high optical depth when the photons are manufactured. Such a shell would not fully block photons reflected or emitted from its inner surface, because the radial velocity of the photons can be less than that of the shell. This avoids the standard problem associated with GRBs that the thermal component should be produced where the flow is still obscured by high optical depth. The radiation that escapes high optical depth obeys the Amati relation. Observational implications may include a) anomalously high ratios of afterglow to prompt emission, such as may have been the case in the recently discovered PTF 11agg, and b) ultrahigh-energy neutrino pulses that are non-coincident with detectable GRB. It is suggested that GRB 090510, a short, very hard GRB with very little afterglow, was an {\it exposed} GRB, in contrast to those cloaked by baryonic shells. \end{abstract}

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Tunnicliffe 2014 无宿主星系的短暴

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认为有一部分是双致密星被kick到星系外边去了。

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Title:		On the nature of the `hostless' short GRBs
Authors:		Tunnicliffe, R. L.; Levan, A. J.; Tanvir, N. R.; Rowlinson, A.; Perley, D. A.; Bloom, J. S.; Cenko, S. B.; O'Brien, P. T.;Cobb, B. E.; Wiersema, K.; Malesani, D.; de Ugarte Postigo, A.; Hjorth, J.; Fynbo, J. P. U.; Jakobsson, P.
Affiliation:		AA(Department of Physics, University of Warwick, Coventry CV4 7AL, UK; R.L.Tunnicliffe@warwick.ac.uk), AB(Department of Physics, University of Warwick, Coventry CV4 7AL, UK), AC(Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK), AD(Astronomical Institute, University of Amsterdam, Science Park 904, NL-1098 XH Amsterdam, the Netherlands), AE(Department of Astronomy, University of California, Berkeley, CA 94720-3411, USA), AF(Department of Astronomy, University of California, Berkeley, CA 94720-3411, USA), AG(Department of Astronomy, University of California, Berkeley, CA 94720-3411, USA), AH(Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK), AI(Department of Astronomy, University of California, Berkeley, CA 94720-3411, USA), AJ(Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK), AK(Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen, Denmark), AL(Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen, Denmark), AM(Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen, Denmark), AN(Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, DK-2100 Copenhagen, Denmark), AO(Centre for Astrophysics and Cosmology, Science Institute, University of Iceland, Dunhaga 5, IS-107 Reykjavik, Iceland)
Publication:		Monthly Notices of the Royal Astronomical Society, Volume 437, Issue 2, p.1495-1510 (MNRAS Homepage)
Publication Date:		01/2014
Origin:		OUP
Astronomy Keywords:		techniques: photometric, gamma-ray burst: individual: 090305A, gamma-ray burst: individual: 091109B, gamma-ray burst: individual: 110112A, gamma-ray burst: individual: 111020A, stars: neutron
Abstract Copyright:		2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
DOI:		10.1093/mnras/stt1975
Bibliographic Code:		2014MNRAS.437.1495T

Abstract

A significant proportion (˜30 per cent) of the short-duration gamma-ray bursts (SGRBs) localized by Swift have no detected host galaxy coincident with the burst location to deep limits, and also no high-likelihood association with proximate galaxies on the sky. These SGRBs may represent a population at moderately high redshifts (z ≳ 1), for which the hosts are faint, or a population where the progenitor has been kicked far from its host or is sited in an outlying globular cluster. We consider the afterglow and host observations of three `hostless' bursts (GRBs 090305A, 091109B and 111020A), coupled with a new observational diagnostic to aid the association of SGRBs with putative host galaxies to investigate this issue. Considering the well localized SGRB sample, 7/25 SGRBs can be classified as `hostless' by our diagnostic. Statistically, however, the proximity of these seven SGRBs to nearby galaxies is higher than is seen for random positions on the sky. This suggests that the majority of `hostless' SGRBs have likely been kicked from proximate galaxies at moderate redshift. Though this result still suggests only a small proportion of SGRBs will be within the Advanced Laser Interferometer Gravitational Wave Observatory horizon for neutron star-neutron star (NS) or neutron star-black hole (BH) inspiral detection (z ˜ 0.1), in the particular case of GRB 111020A a plausible host candidate is at z = 0.02.

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2013之重要事件

（仅包括我关心的）
1. GRB 130427A

2. GRB 130603B

3. FRB

4. AMS2公布初步数据了

5. IceCube的两个高能中微子

2014一开始就热闹啦

SN 2014J是距离地球第二近的超新星，除了1987A。是Ia型超新星中最近的，南极（貌似还放在国内试用着的？）望远镜又看到了“precursor”。看样子要被好好研究一番的。

银河系的旋转方向

是顺着旋臂还是逆着？

等离子云、原子云、分子云

from：http://www.cnbeta.com/articles/251244.htm
研究人员解释说，根据温度和密度，宇宙气体可以分为三类：等离子云（粒子数密度：0.01/立方厘米，几百万摄氏度）、原子云（10/立方厘米，-160摄氏度）和分子云（10000/立方厘米，-260摄氏度）。原子云密度增加会变成分子云，分子云密度增加会变成恒星“温床”。反过来，如果受到高强度紫外线照射，构成分子云的分子也会分散变成原子。

Basak, Rupal 2013 高能GeV和MeV的幂律成分相关

主要内容:
他们把MeV的分成两种成分：黑体（双温）+幂律；然后发现幂律成分的光变和GeV瞬时阶段的光变一致（注意不是晚期的，他们还是同意晚期的还是外激波的同步辐射）(另外注意，这一点不是他们文章的主要内容，而是进一步的目标，他们发现的仅仅是：对于有很多GeV光子的暴，幂律的MeV光子和LAT的GeV光子一样，也有延迟，见下图)，以此说明瞬时阶段的辐射和瞬时阶段的幂律的MeV是同源的。

那么这么说的话，一共就有如下这些成分：瞬时的两个黑体成分，可能是来自光球辐射（为什么是两个呢？） ；瞬时幂律成分，来自内激波，这个延伸到了GeV；外激波余辉，延伸到了GeV。

于是紧接着可以做的一件事情：分析幂律MeV光子和瞬时阶段的GeV光子的光变曲线的关联程度（但是估计很难，因为不知道怎么在光变上区分幂律和非幂律的光子）。

嗯，也许把MeV的分出几个不同的成分是解释GeV以及MeV自身的一个办法。

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幂律部分的MeV光子应该和GeV的track

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Title:		A lingering non-thermal component in the GRB prompt emission: predicting GeV emission from the MeV spectrum
Authors:		Basak, Rupal; Rao, A. R.
Publication:		eprint arXiv:1308.2819
Publication Date:		08/2013
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		9 Pages, 2 Figures, ApJ Accepted
Bibliographic Code:		2013arXiv1308.2819B

Abstract

The high energy GeV emission of gamma-ray bursts (GRBs), detected by \emph{Fermi}/LAT, has a significantly different morphology compared to the lower energy MeV emission, detected by \emph{Fermi}/GBM. Though the late time GeV emission is believed to be synchrotron radiation produced via an external shock, this emission as early as the prompt phase is puzzling. Meaningful connection between these two emissions can be drawn only by an accurate description of the prompt MeV spectrum. We perform a time-resolved spectroscopy of the GBM data of long GRBs having significant GeV emission, using a model consisting of 2 blackbodies and a power-law. We examine in detail the evolution of the spectral components and found that GRBs having high GeV emission (GRB 090902B and GRB 090926A) have a delayed onset of the power-law component, in the GBM spectrum, which lingers at the later part of the prompt emission. This behaviour mimics the flux evolution in LAT. In contrast, bright GBM GRBs with an order of magnitude lower GeV emission (GRB 100724B and GRB 091003) show a coupled variability of the total and the power-law flux. Further, by analyzing the data for a set of 17 GRBs, we find a strong correlation between the power-law fluence in the MeV and the LAT fluence (Pearson correlation: r=0.88 and Spearman correlation: $\rho=0.81$). We demonstrate that this correlation is not influenced by the correlation between the total and the power-law fluences at a confidence level of 2.3$\sigma$. We speculate the possible radiation mechanisms responsible for the correlation.

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