Meliani 2007 双成分喷流的不稳定性

主要内容:
数值模拟计算了双成分喷流的不稳定性，结论是：是非线性稳定的。

精彩摘抄:


文章信息:

arXiv:0709.3838 [ps, pdf, other]

Title: Transverse stability of relativistic two-component jets

Authors: Z. Meliani, R. Keppens

Comments: Accepted in A&A 24/09/2007

Subjects: Astrophysics (astro-ph)

Context: Astrophysical jets from various sources seem to be stratified, with a fast inner jet and a slower outer jet. As it is likely that the launching mechanism for each component is different, their interface will develop differential rotation, while the outer jet radius represents a second interface where disruptions may occur. Aims: We explore the stability of stratified, rotating, relativistic two-component jets, in turn embedded in static interstellar medium. Methods: In a grid-adaptive relativistic hydrodynamic simulation with the AMRVAC code, the non-linear azimuthal stability of two-component relativistic jets is investigated. We simulate until multiple inner jet rotations have been completed. Results: We find evidence for the development of an extended shear flow layer between the two jet components, resulting from the growth of a body mode in the inner jet, Kelvin-Helmholtz surface modes at their original interface, and their nonlinear interaction. Both wave modes are excited by acoustic waves which are reflected between the symmetry axis and the interface of the two jet components. Their interaction induces the growth of near stationary, counterrotating vortices at the outer edge of the shear flow layer. The presence of a heavy external jet allows to slow down their further development, and maintain a collimated flow. At the outer jet boundary, small-scale Rayleigh-Taylor instabilities develop, without disrupting the jet configuration. Conclusion: We demonstrate that the cross-section of two-component relativistic jets, with a heavy, cold outer jet, is non-linearly stable.

Horan 2007 VERITAS和Whipple对伽玛暴的高能观测

主要内容:
VERITAS给伽玛暴有较高的权限，如果伽玛暴事件发生了，会在较短的时间里定向，观测。不过到目前位置还基本没有任何关于伽玛暴事件的高能观测。文中给出了VERITAS和Whipple在2005-2007年的观测，也只有上限。

精彩摘抄:


文章信息:

arXiv:0709.3830 [pdf, other]

Title: Observations of Gamma-ray Bursts with VERITAS and Whipple

Authors: D. Horan, for the VERITAS Collaboration

Comments: 4 pages; contribution to the 30th International Cosmic Ray Conference, Merida, Mexico, July 2007

Subjects: Astrophysics (astro-ph)

Many authors have predicted very-high-energy (VHE; E > 100 GeV) emission from gamma-ray bursts (GRBs) both during the prompt phase and during the multi-component afterglow. To date, however, there has been no definitive detection of such emission. Recently, the Swift Satellite made the exciting discovery that almost 50% of GRBs are accompanied by one or more X-ray flares, which are found to occur from several seconds to many hours after the prompt emission. The discovery of this phenomenon and the many predictions that VHE emission should accompany these flares increases the already strong motivation for making immediate follow-up VHE observations of GRBs. Observations of GRBs have high priority at VERITAS, preempting any observations that may be in progress. GRB alerts are received from the GCN via a socket connection. This is interfaced to the VERITAS Tracking Software to minimize the time between a notification arriving and the telescope being slewed to the GRB. We report here on GRB observations with VERITAS and with the Whipple Telescope from 2005 through 2007.

Kamble 2007 用wind加ISM解释GRB050319的余辉

主要内容:
GRB 050319的多波段余辉可以用wind加ISM的外部环境来解释，在0.02天的时候是转换时间。以此，也可以从侧面证实伽玛暴的大质量恒星坍缩模型。

精彩摘抄:


文章信息:

arXiv:0709.3561 [ps, pdf, other]

Title: Observations of the Optical Afterglow of GRB 050319 : Wind to ISM transition in view

Authors: Atish Kamble, L. Resmi, Kuntal Misra

Comments: 11 pages, 3 tables, 1 figures

Journal-ref: The Astrophysical Journal Letters, vol. 664, L5-L8, 2007 July 20

Subjects: Astrophysics (astro-ph)

The collapse of a massive star is believed to be the most probable progenitor of a long GRB. Such a star is expected to modify its environment by stellar wind. The effect of such a circum-stellar wind medium is expected to be seen in the evolution of a GRB afterglow, but has so far not been conclusively found. We claim that a signature of wind to constant density medium transition of circum-burst medium is visible in the afterglow of GRB 050319. Along with the optical observations of the afterglow of GRB 050319 we present a model for the multiband afterglow of GRB 050319. We show that the break seen in optical light curve at $\sim$ 0.02 day could be explained as being due to wind to constant density medium transition of circum-burst medium, in which case, to our knowledge, this could be the first ever detection of such a transition at any given frequency band. Detection of such a transition could also serve as a confirmation of massive star collapse scenario for GRB progenitors, independent of supernova signatures.

Gedalin 2007 相对论激波的电子加热

主要内容:
给出了在相对论激波的下电子的加速机制，既可以是磁场也可以是电场。也符合同步辐射的要求。

精彩摘抄:


文章信息:

arXiv:0709.3097 [ps, pdf, other]

Title: Efficient electron heating in relativistic shocks and gamma ray burst afterglow

Authors: M. Gedalin, M. A. Balikhin, D. Eichler

Comments: revtex4

Subjects: Astrophysics (astro-ph)

Electrons in shocks are efficiently energized due to the cross-shock potential, which develops because of differential deflection of electrons and ions by the magnetic field in the shock front. The electron energization is necessarily accompanied by scattering and thermalization. The mechanism is efficient in both magnetized and non-magnetized relativistic electron-ion shocks. It is proposed that the synchrotron emission from the heated electrons in a layer of strongly enhanced magnetic field is responsible for gamma ray burst afterglows.

Gotz 2007 ECLAIRs对伽玛暴多波段观测

ECLAIRs将在2011年上天，将是那时候唯一能准确定位伽玛暴的探测器。预期可探测80暴/年。 仪器特点如下：

• the study of the prompt X-ray emission associated to GRBs
• the detection of a large sample of soft GRBs, potentially the most distant ones,
thanks to the 4–50 keV triggering band
• the broad band spectra (from 1 keV to a few MeV)
• the prompt (and/or precursive) optical emission

arXiv:0709.2570 [ps, pdf, other]

Title: Multiwavelength Gamma-Ray Bursts Observations with ECLAIRs

Authors: Diego Gotz

Comments: 6 pages, 1 figure, proceedings of the Cefalu Astrophysical Conference, 11-24 June 2006

Journal-ref: AIPC, 924, 44, 2007

Subjects: Astrophysics (astro-ph)

ECLAIRs is the next space borne instrument that will be fully dedicated to multi-wavelength studies of Gamma-Ray Bursts (GRBs). It consists of a coded mask telescope with a wide (~2 sr) field of view, made of 6400 CdTe pixels (~1000 cm^2), which will work in the 4-300 keV energy band. It is expected to localise ~80 GRBs/yr, thanks to the on-board real time event processing. The GRBs (and other transients) coordinates will be distributed within a few seconds from the onset of the burst with a typical uncertainty of ~5-10 arcmin. The detection system will also include a soft X-ray camera (1-10 keV) allowing to study in detail the prompt soft X-ray emission and to reduce the error box for about half of the GRBs seen by ECLAIRs to ~30 arcsec. ECLAIRs is expected to be flown in late 2011 and to be the only instrument capable of providing GRB triggers with sufficient localisation accuracy for GRB follow-up observations with the powerful ground based spectroscopic telescopes available by then. We will present the current status of the ECLAIRs project and its possible developments.

Hermann 2007 契仑科夫望远镜阵

主要内容:
把几个Cherenkov望远镜联合起来，可以提高观测极高能伽玛射线的能力。

精彩摘抄:


文章信息:

arXiv:0709.2048 [pdf, other]

Title: Cherenkov Telescope Array: The next-generation ground-based gamma-ray observatory

Authors: G. Hermann, W. Hofmann, T. Schweizer, M. Teshima, for the CTA consortium

Comments: 4 pages, 3 figures, to appear in the proceedings of the 30th International Cosmic Ray Conference, Merida, July 2007

Subjects: Astrophysics (astro-ph)

High energy gamma-ray astronomy is a newly emerging and very successful branch of astronomy and astrophysics. Exciting results have been obtained by the current generation Cherenkov telescope systems such as H.E.S.S., MAGIC, VERITAS and CANGAROO. The H.E.S.S. survey of the galactic plane has revealed a large number of sources and addresses issues such as the question about the origin of cosmic rays. The detection of very high energy emission from extragalactic sources at large distances has provided insights in the star formation during the history of the universe and in the understanding of active galactic nuclei. The development of the very large Cherenkov telescope array system (CTA) with a sensitivity about an order of magnitude better than current instruments and significantly improved sensitivity is under intense discussion. This observatory will reveal an order of magnitude more sources and due to its higher sensitivity and angular resolution it will be able to detect new classes of objects and phenomena that have not been visible until now. A combination of different telescope types will provide the sensitivity needed in different energy ranges.

Ghisellini 2007 火球与静止物质的膨胀产生伽玛暴

主要内容:
提出了标准内激波模型的一些弊端：效率要求不同shell的Lorentz因子相差很大，早期余辉的变平，Amati等统计关系不能从标准模型推出。然后提出在暴源不远的外边可能存在一个静止的物质块，火球与它撞上产生了伽玛暴。

精彩摘抄:


文章信息:

arXiv:0709.1945 [ps, pdf, other]

Title: Re-born fireballs in Gamma-Ray Bursts

Authors: G. Ghisellini (1), A. Celotti (2), G. Ghirlanda (1), C. Firmani (1,3), L. Nava (1,4) ((1) INAF-Oss. Astr. di Brera, (2) SISSA, Trieste, (3) U.N.A.M., Mexico, (4) Univ. Insubria)

Comments: 5 pages, 3 Figures, accepted for publication in MNRAS (Letters)

Subjects: Astrophysics (astro-ph)

We consider the interaction between a relativistic fireball and material assumed to be still located just outside the progenitor star. Only a small fraction of the expected mass is sufficient to efficiently decelerate the fireball, leading to dissipation of most of its kinetic energy. Since the scattering optical depths are still large at distances comparable to the progenitor radius, the dissipated energy is trapped in the system, accelerating it to relativistic velocities. The process resembles the birth of another fireball at radii R~1e11 cm, not far from the transparency radius, and with a starting bulk Lorentz factors Gamma_c~10. As seen in the observer frame, this "re--generated" fireball appears collimated within an angle theta_j=1/Gamma_c. If the central engine works intermittently, the funnel can, at least partially, refill and the process can repeat itself. We discuss how this idea can help solving some open issues of the more conventional internal shock scenario for interpreting the Gamma-Ray Burst properties.

伽玛暴、X射线耀、余辉 猜测--进动的喷流

模型：伽玛暴就是一个连续比较长时间的持续喷流，但是喷流的方向有进动。

原因：假设伽玛暴是由喷流产生，喷流是有黑洞吸积盘产生。一般喷流轴应该与磁轴一致，但是黑洞吸积盘系统的自转轴与磁轴不一致（脉冲星是一个很好的佐证），特别是黑洞吸积盘刚诞生的时候，更可能不一致。

现象解释：
暴本身：高速的喷流产生，并由于集束效应，只有转到正对着观测者的时候才能看到，导致伽玛暴的多峰结构。这个雷卫华去年的AA文章有模拟其光变。（这里伽玛暴的本身的产生机制可以是：进动的喷流形成螺旋形状往外运动，最前面的可能慢一些，或者碰到外部介质慢下来了，这样螺旋形的喷流的后面部分会赶上前面的，导致发生激波碰撞，内激波，辐射）

X射线耀：同样，暴本身结束之后的X射线耀，实际上是和暴本身一样的，只不过时间较晚，发生碰撞的地方较远，导致谱线较软，持续时间较长。

早期余辉的变平：本来由于很高的洛仑兹因子，喷到别的方向的是看不到的，但是在过了几百秒之后洛仑兹因子降下来了，旁边的也可以看到，使得余辉的下降指数变平。这个有点类似于有人提出过的用很多的不同方向的小喷流解释这个现象。而且我曾经用ring jet的曲率辐射来解释变平，在这里也可以用上。 观测上在变平阶段也有X射线耀发，这也是能同时存在的。有内激波就有XRFs，没有的话也就是只有外激波，则只有变平。

正常的晚期余辉：当其它方向的都能看到之后，或者再没有新增加的喷流余辉，就到了正常的余辉阶段（只不过注意此时的总动能是进动喷流总体的动能）。由于从平降到正常仅仅是几何上的变化，因此这个拐着的地方没有谱指数的变化。

问题：进动的速度是不是会变化，减慢？如果是（应该会变慢），对结果的影响是什么？

Björnsson 2007 GRB060218的光学成分来自于同步自吸收

主要内容:
认为此暴和一般的暴差不多，只不过磁场比较强，洛仑兹因子比较低。然后同步字吸收频率比较高，使得光学和UV也在自吸收频率以下。

精彩摘抄:


文章信息:

arXiv:0709.1855 [ps, pdf, other]

Title: GRB 060218: The nature of the optical-UV component

Authors: C.-I. Björnsson (Stockholm Observatory)

Comments: 16 pages, 1 figure, accepted to ApJ

Subjects: Astrophysics (astro-ph)

The optical-UV component in GRB 060218 is assumed to be due to optically thick cyclotron emission. The key aspect of this model is the high temperature of the absorbing electrons. The heat input derives from nuclei accelerated in semi-relativistic internal shocks, like in ordinary gamma-ray bursts. Coulomb collisions transfer part of that energy to electrons. Inverse Compton cooling on the X-ray photons leads to electron temperatures around 100 keV. Such a high brightness temperature for the optical-UV emission implies an emitting area roughly equal to that of the thermal X-ray component. This suggests a model in which the radio, optical-UV and thermal X-ray emission are closely related: Although the optical-UV and thermal X-ray emission are two separate spectral components, it is argued that they both come from the photosphere of a quasi-spherical, continuous outflow, whose interaction with the circumstellar medium gives rise to the radio emission. The properties of GRB 060218, as measured in the co-moving frame, are similar to those of ordinary gamma-ray burst; i.e., the main difference is the much lower value of the bulk Lorentz factor in GRB 060218. The cyclotron absorption implies a magnetic field in rough equipartition with the matter energy density in the outflow. Hence, the magnetic field could have a dynamically important role, possibly with a magnetar as the central engine.

Mizuno 2007 磁流体力学驱动相对论喷流

主要内容:
虽然伽玛暴还有很多其它现象要求极端相对论性的喷流，但是目前还没有可靠的模型来产生这种喷流。文章采用别人的程序，考虑磁流体力学，数值模拟出了极端相对论性的喷流。

精彩摘抄:


文章信息:

arXiv:0709.1839 [ps, pdf, other]

Title: A Magnetohydrodynamic Boost for Relativistic Jets

Authors: Yosuke Mizuno (NSSTC/NASA-MSFC), Philip Hardee (UA), Dieter H. Hartmann (Clemson Univ.), Ken-Ichi Nishikawa (NSSTC/UAH), Bing Zhang (UNLV)

Comments: 25 pages, 10 figures, accepted for publication in ApJ

Subjects: Astrophysics (astro-ph)

We performed relativistic magnetohydrodynamic simulations of the hydrodynamic boosting mechanism for relativistic jets explored by Aloy & Rezzolla (2006) using the RAISHIN code. Simulation results show that the presence of a magnetic field changes the properties of the shock interface between the tenuous, overpressured jet ($V^z_j$) flowing tangentially to a dense external medium. Magnetic fields can lead to more efficient acceleration of the jet, in comparison to the pure-hydrodynamic case. A ``poloidal'' magnetic field ($B^z$), tangent to the interface and parallel to the jet flow, produces both a stronger outward moving shock and a stronger inward moving rarefaction wave. This leads to a large velocity component normal to the interface in addition to acceleration tangent to the interface, and the jet is thus accelerated to larger Lorentz factors than those obtained in the pure-hydrodynamic case. Likewise, a strong ``toroidal'' magnetic field ($B^y$), tangent to the interface but perpendicular to the jet flow, also leads to stronger acceleration tangent to the shock interface relative to the pure-hydrodynamic case. Overall, the acceleration efficiency in the ``poloidal'' case is less than that of the ``toroidal'' case but both geometries still result in higher Lorentz factors than the pure-hydrodynamic case. Thus, the presence and relative orientation of a magnetic field in relativistic jets can significant modify the hydrodynamic boost mechanism studied by Aloy & Rezzolla (2006).

Hoshino 2007 Wakefield加速相对论激波的粒子为非热分布

主要内容:
文中先回顾了三类经典的加速机制（按照能量来源）：磁重联、激波加速（如费米机制）、大振幅的波的能量转化。文章模拟了大振幅的Wakefield，发现能很快将相对论激波中的粒子加速。

精彩摘抄:


文章信息:

arXiv:0709.1783 [ps, pdf, other]

Title: Wakefield Acceleration by Radiation Pressure in Relativistic Shock Waves

Authors: Masahiro Hoshino

Comments: Accepted in ApJ (5 Sept 2007)

Subjects: Astrophysics (astro-ph)

A particle acceleration mechanism by radiation pressure of precursor waves in a relativistic shock is studied. For a relativistic, perpendicular shock with the upstream bulk Lorentz factor of $\gamma_1 \gg 1$, large amplitude electromagnetic (light) waves are known to be excited in the shock front due to the synchrotron maser instability, and those waves can propagate towards upstream as precursor waves. We find that non-thermal, high energy electrons and ions can be quickly produced by an action of electrostatic wakefields generated by the ponderomotive force of the precursor waves. The particles can be quickly accelerated up to $\epsilon_{\rm max}/\gamma_1 m_e c^2 \sim \gamma_1$ in the upstream coherent wakefield region, and they can be further accelerated during the nonlinear stage of the wakefield evolution. The maximum attainable energy is estimated by $\epsilon_{\rm max}/\gamma_1 m_e c^2 \sim L_{\rm sys}/(c/\omega_{pe})$, where $L_{\rm sys}$ and $c/\omega_{pe}$ are the size of an astrophysical object and the electron inertial length, respectively.

Bastieri 2007 MAGIC对伽玛暴的高能辐射的上限限制

主要内容:
80 to 200 GeV， 对一批暴做了上限，从2005年4月到2006年3月。

精彩摘抄:
部分上限

文章信息:

arXiv:0709.1386 [ps, pdf, other]

Title: MAGIC upper limits on the high energy emission from GRBs

Authors: D. Bastieri, N. Galante, M. Garczarczyk, M. Gaug, F. Longo, S. Mizobuchi, V. Scapin

Comments: Contribution to the 30th ICRC, Merida Mexico, July 2007 on behalf of the MAGIC Collaboration

Subjects: Astrophysics (astro-ph)

During its cycle-1 observation period, between April 2005 and March 2006, the MAGIC telescope was able to observe nine Gamma Ray Burst (GRB) events since their early beginning. Other observations were performed during the following months in the cycle-2 observation period. The observations, with an energy threshold spanning from 80 to 200 GeV, did not reveal any gamma ray emission. The computed upper limits are compatible with a power law extrapolation, where intrinsic fluxes are evaluated taking into account the attenuation due to the scattering in the metagalactic radiation field.

Bastieri 2007 MAGIC还没有观测到伽玛暴的高能事件

主要内容:
MAGIC是一个Cherenkov望远镜。不过它只能是在GCN报道了暴的存在之后，所以应该是余辉阶段的高能辐射没有被观测到。

（它为什么不自己观测伽玛暴呢？可能暴本身阶段超高能的辐射也还是很弱。）

精彩摘抄:


文章信息:

arXiv:0709.1380 [ps, pdf, other]

Title: Observation of GRBs by the MAGIC Telescope, Status and Outlook

Authors: D. Bastieri, N. Galante, M. Garczarczyk, M. Gaug, F. Longo, S. Mizobuchi, V. Scapin

Comments: Contribution to the 30th ICRC, Merida Mexico, July 2007 on behalf of the MAGIC Collaboration

Subjects: Astrophysics (astro-ph)

Observation of Gamma Ray Bursts (GRBs) in the Very High Energy (VHE) domain will provide important information on the physical conditions in GRB outflows. The MAGIC telescope is the best suited Imaging Atmospheric Cherenkov Telescope (IACT) for these observations. Thanks to its fast repositioning time and low energy threshold, MAGIC is able to start quickly the follow-up observation, triggered by an alert from the GRB Coordinates Network (GCN), and observe the prompt emission and early afterglow phase from GRBs. In the last two years of operation several GRB follow-up observations were performed by MAGIC, however, until now without successful detection of VHE gamma rays above threshold energies >100 GeV. In this paper we revise the expectations for the GRB observations with MAGIC, based on the experience from the last years of operation.

Levinson 2007 伽玛射线喷流的高能辐射

主要内容:
从光球和pi介子球出发，讨论在极高能段的辐射，用于限制多普勒效应、高能中微子的辐射等。

精彩摘抄:


文章信息:

arXiv:0709.1337 [ps, pdf, other]

Title: Phenomenology of Gamma-Ray Jets

Authors: Amir Levinson

Comments: Proceedings, Huangshan meeting on "Astrophysics of Compact Objects"

Subjects: Astrophysics (astro-ph)

We discuss some phenomenological aspects of $\gamma$-ray emitting jets. In particular, we present calculations of the $\gamma$-sphere and $\pi$-sphere for various target photon fields, and employ them to demonstrate how $\gamma$-ray observations at very high energies can be used to constraint the Doppler factor of the emitting plasma and the production of VHE neutrinos. We also consider the implications of the rapid TeV variability observed in M87 and the TeV blazars, and propose a model for the very rapid TeV flares observed with HESS and MAGIC in some blazars,that accommodates the relatively small Doppler factors inferred from radio observations. Finally, we briefly discuss the prospects for detecting VHE neutrinos from relativistic jets.

Kamae 2007 PoGOLite: 软伽玛射线偏振计

主要内容:
用于观测25－50keV的偏振，计划2010年上天。气球搭载。重约800kg。

精彩摘抄:


文章信息:

arXiv:0709.1278 [pdf, other]

Title: PoGOLite - A High Sensitivity Balloon-Borne Soft Gamma-ray Polarimeter

Authors: Tuneyoshi Kamae, Viktor Andersson, Makoto Arimoto, Magnus Axelsson, Cecilia Marini Bettolo, Claes-Ingvar Björnsson, Gilles Bogaert, Per Carlson, William Craig, Tomas Ekeberg, Olle Engdegård, Yasushi Fukazawa, Shuichi Gunji, Linnea Hjalmarsdotter, Bianca Iwan, Yoshikazu Kanai, Jun Kataoka, Nobuyuki Kawai, Jaroslav Kazejev, Mózsi Kiss, Wlodzimierz Klamra, Stefan Larsson, Grzegorz Madejski, Tsunefumi Mizuno, Johnny Ng, Mark Pearce, Felix Ryde, Markus Suhonen, Hiroyasu Tajima, Hiromitsu Takahashi, Tadayuki Takahashi, Takuya Tanaka, Timothy Thurston, Masaru Ueno, Gary Varner, Kazuhide Yamamoto, Yuichiro Yamashita, Tomi Ylinen, Hiroaki Yoshida

Comments: 11 pages, 11 figures, 2 tables

Subjects: Astrophysics (astro-ph)

We describe a new balloon-borne instrument (PoGOLite) capable of detecting 10% polarisation from 200mCrab point-like sources between 25 and 80keV in one 6 hour flight. Polarisation measurements in the soft gamma-ray band are expected to provide a powerful probe into high-energy emission mechanisms as well as the distribution of magnetic fields, radiation fields and interstellar matter. At present, only exploratory polarisation measurements have been carried out in the soft gamma-ray band. Reduction of the large background produced by cosmic-ray particles has been the biggest challenge. PoGOLite uses Compton scattering and photo-absorption in an array of 217 well-type phoswich detector cells made of plastic and BGO scintillators surrounded by a BGO anticoincidence shield and a thick polyethylene neutron shield. The narrow FOV (1.25msr) obtained with well-type phoswich detector technology and the use of thick background shields enhance the detected S/N ratio. Event selections based on recorded phototube waveforms and Compton kinematics reduce the background to that expected for a 40-100mCrab source between 25 and 50keV. A 6 hour observation on the Crab will differentiate between the Polar Cap/Slot Gap, Outer Gap, and Caustic models with greater than 5 sigma; and also cleanly identify the Compton reflection component in the Cygnus X-1 hard state. The first flight is planned for 2010 and long-duration flights from Sweden to Northern Canada are foreseen thereafter.

Kuin 2007 Swift-UVOT and XMM-OM的观测误差

主要内容:


精彩摘抄:


文章信息:

arXiv:0709.1208 [ps, pdf, other]

Title: The measurement errors in the Swift-UVOT and XMM-OM

Authors: N.P.M. Kuin, S.R. Rosen

Comments: 4 pages, 2 postscript figures, submitted to MNRAS

Subjects: Astrophysics (astro-ph)

The probability of photon measurement in some photon counting instrumentation, such as the Optical Monitor on the XMM-Newton satellite, and the UVOT on the Swift satellite, does not follow a Poisson distribution due to the detector characteristics, but a Binomial distribution. For a single-pixel approximation, an expression was derived for the incident countrate as a function of the measured count rate by Fordham, Moorhead and Galbraith (2000). We show that the measured countrate error is binomial, and extend their formalism to derive the error in the incident count rate. The error on the incident count rate at large count rates is larger than the Poisson-error of the incident count rate.

Bolmont 2007 HETE-2的暴定量子引力模型

主要内容:
还是测算time lag，用波包分析的方法。 取了15个有红移的暴，得到的能量下限是：2.9 \times 10^14 GeV.

精彩摘抄:


文章信息:

arXiv:0709.1132 [ps, pdf, other]

Title: Study of time lags in HETE-2 Gamma-Ray Bursts with redshift: search for astrophysical effects and Quantum Gravity signature

Authors: J. Bolmont, A. Jacholkowska, J.-L. Atteia, F. Piron, the HETE-2 collaboration

Subjects: Astrophysics (astro-ph)

The study of time lags between spikes in Gamma-Ray Bursts light curves in different energy bands as a function of redshift may lead to the detection of effects due to Quantum Gravity. We present an analysis of 15 Gamma-Ray Bursts with measured redshift, detected by the HETE-2 mission between 2001 and 2006 in order to measure time lags related to astrophysical effects and search for Quantum Gravity signature in the framework of an extra-dimension string model. The use of photon-tagged data allows us to consider various energy ranges. Systematic effects due to selection and cuts are evaluated. No significant Quantum Gravity effect is detected from the study of the maxima of the light curves and a lower limit at 95% Confidence Level on the Quantum Gravity scale parameter of 2.9x10^14 GeV is set.

Akerlof 2007 余辉光度的分布

主要内容:
统计发现在1000秒的时候，71%的光学余辉星等亮于22.1等，最多的出现在19.5等。

精彩摘抄:
在1000秒时伽玛暴余辉的光度分布。

文章信息:

arXiv:0709.0962 [ps, pdf, other]

Title: An Estimation of the Gamma-Ray Burst Afterglow Apparent Optical Brightness Distribution Function

Authors: Carl W. Akerlof, Heather F. Swan

Comments: 15 pages including 2 tables and 7 figures, accepted for publication in ApJ

Subjects: Astrophysics (astro-ph)

By using recent publicly available observational data obtained in conjunction with the NASA Swift gamma-ray burst mission and a novel data analysis technique, we have been able to make some rough estimates of the GRB afterglow apparent optical brightness distribution function. The results suggest that 71% of all burst afterglows have optical magnitudes with mR <>

Tanvir 2007 伽玛暴的宿主星系

主要内容:
不同于一般星系研究的方法，要依靠星系本身的亮度。从而伽玛暴的宿主星系为星系研究给出了新的角度。

精彩摘抄:


文章信息:

arXiv:0709.0861 [ps, pdf, other]

Title: The population of GRB hosts

Authors: N. R. Tanvir, A. J. Levan

Comments: 10 pages, 4 figures, to appear in proceedings of 070228: The next decade of GRB afterglows, Amsterdam March 2007

Subjects: Astrophysics (astro-ph)

The properties of their hosts provide important clues to the progenitors of different classes of gamma-ray bursts (GRBs). The hosts themselves also constitute a sample of high-redshift star-forming galaxies which, unlike most other methods, is not selected on the luminosities of the galaxies themselves. We discuss what we have learnt from and about GRB host galaxies to date.

Cantiello 2007 双星作为伽玛暴长暴的起源

主要内容:
作为伽玛暴的前身星，要求有很高的自旋。如果是双星的话，可以比较容易地满足。

精彩摘抄:


文章信息:

arXiv:0709.0829 [ps, pdf, other]

Title: Long GRBs from binary stars: runaway, Wolf-Rayet progenitors

Authors: M.Cantiello, S.-C.Yoon, N.Langer, M.Livio

Comments: To appear in the proceedings of the conference "Unsolved problems in stellar physics" - Cambridge, July 2007

Subjects: Astrophysics (astro-ph)

The collapsar model for long gamma-ray bursts requires a rapidly rotating Wolf-Rayet star as progenitor. We test the idea of producing rapidly rotating Wolf-Rayet stars in massive close binaries through mass accretion and consecutive quasi-chemically homogeneous evolution; the latter had previously been shown to provide collapsars below a certain metallicity threshold for single stars. The binary channel presented here may provide a means for massive stars to obtain the high rotation rates required to evolve quasi-chemically homogeneous and fulfill the collapsar scenario. Moreover, it suggests that a possibly large fraction of long gamma-ray bursts occurs in runaway stars.

Scranton 2007 Google Earth的Sky功能

主要内容:
现在的Google Earth加入了Sky功能，可以看到天体的照片，包括Hubble的。

精彩摘抄:


文章信息:

arXiv:0709.0752 [pdf, other]

Title: Sky in Google Earth: The Next Frontier in Astronomical Data Discovery and Visualization

Authors: Ryan Scranton, Andrew Connolly, Simon Krughoff, Jeremy Brewer, Alberto Conti, Carol Christian, Craig Sosin, Greg Coombe, Paul Heckbert

Comments: 10 pages, 3 figures, to be submitted to PASP

Subjects: Astrophysics (astro-ph)

Astronomy began as a visual science, first through careful observations of the sky using either an eyepiece or the naked eye, then on to the preservation of those images with photographic media and finally the digital encoding of that information via CCDs. This last step has enabled astronomy to move into a fully automated era -- where data is recorded, analyzed and interpreted often without any direct visual inspection. Sky in Google Earth completes that circle by providing an intuitive visual interface to some of the largest astronomical imaging surveys covering the full sky. By streaming imagery, catalogs, time domain data, and ancillary information directly to a user, Sky can provide the general public as well as professional and amateur astronomers alike with a wealth of information for use in education and research. We provide here a brief introduction to Sky in Google Earth, focusing on its extensible environment, how it may be integrated into the research process and how it can bring astronomical research to a broader community. With an open interface available on Linux, Mac OS X and Windows, applications developed within Sky are accessible not just within the Google framework but through any visual browser that supports the Keyhole Markup Language. We present Sky as the embodiment of a virtual telescope.

Bernardini 2007 GRB970228是一类新的暴

主要内容:
这类暴开始有一个spike，较大的baryon loading，然后与外部不均匀介质作用产生余辉的峰。

精彩摘抄:


文章信息:

arXiv:0709.0651 [ps, pdf, other]

Title: GRB970228 and a class of GRBs with an initial spikelike emission

Authors: Maria Grazia Bernardini, Carlo Luciano Bianco, Letizia Caito, Maria Giovanna Dainotti, Roberto Guida, Remo Ruffini

Comments: 4 pages, 4 figures, to appear on A&A Letters

Subjects: Astrophysics (astro-ph)

(Shortened) The Swift and HETE-2 discovery of an afterglow associated possibly with short GRBs opened the new problematic of their nature and classification. This has been further enhanced by the GRB060614 observation and by a re-analysis of the BATSE catalog leading to the identification of a new GRB class with "an occasional softer extended emission lasting tenths of seconds after an initial spikelike emission". We plan: a) to fit this new class of "hybrid" sources within our "canonical GRB" scenario, where all GRBs are generated by a "common engine" (i.e. the gravitational collapse to a black hole); b) to propose GRB970228 as the prototype of the such a class. We analyze BeppoSAX data on GRB970228 in the 40-700 keV and 2-26 keV energy bands within the "fireshell" model. We find that GRB970228 is a "canonical GRB", like e.g. GRB050315, with the main peculiarity of a particularly low CircumBurst Medium (CBM) average density n_{cbm}~10^{-3} #/cm^3. We also simulate the light curve corresponding to a rescaled CBM density profile with n_{cbm}=1 #/cm^3. From such a comparison it follows that the total time-integrated luminosity is a faithful indicator of the GRB nature, contrary to the peak luminosity which is merely a function of the CBM density. We call attention on discriminating the short GRBs between the "genuine" and the "fake" ones. The "genuine" ones are intrinsically short, with baryon loading B \la 10^{-5}, as stated in our original classification. The "fake" ones, characterized by an initial spikelike emission followed by an extended emission lasting tenths of seconds, have a baryon loading 10^{-4} \la B \leq 10^{-2}. They are observed as such only due to an underdense CBM consistent with a galactic halo environment which deflates the afterglow intensity.

星际闪电

既然地球上可以有通过摩擦产生了带电体，然后放电产生闪电。那星际空间是不是也可以呢？也许也有什么分子云带了很多负电或者正电，堆积到一定程度，或者是碰到了另一块分子云（没有物质是不能击穿和发生闪电的），向周围放电。能不能看到呢？

Kistler 2007 伽玛暴的诞生率和恒星形成率的表现不一致

主要内容:
对有红移的伽玛暴的分析发现红移分布与恒星形成历史不一致，说明可能有一些伽玛暴来源不是大质量恒星坍缩。

精彩摘抄:
上图是恒星形成率，下图是伽玛暴诞生率，后者演化更大一些。

文章信息:

arXiv:0709.0381 [ps, pdf, other]

Title: An Unexpectedly Swift Rise in the Gamma-ray Burst Rate

Authors: Matthew D. Kistler, Hasan Yuksel, John F. Beacom, Krzysztof Z. Stanek (Ohio State University)

Comments: 4 pages, 4 figures

Subjects: Astrophysics (astro-ph)

The association of long gamma-ray bursts with the deaths of massive stars naturally suggests that the cosmic GRB rate should trace the star formation history. Finding otherwise would provide important clues for the further development of our views concerning these rare, curious phenomena. Making use of a sample of 44 luminous Swift GRBs with redshifts in the range z=0-4, we find evidence of enhanced evolution in the GRB rate, with ~4 times as many GRBs being observed at z~4 than expected from star formation measurements. We discuss the origins of this observed trend, including several progenitor populations that the GRBs may actually be tracing.

Margutti 2007 GRB 031203的宿主星系

主要内容:
GRB 031203的宿主星系就叫HG031203。分析了它的光谱，作为WR星系的可能性等。

精彩摘抄:


文章信息:

arXiv:0709.0198 [ps, pdf, other]

Title: The host galaxy of GRB031203: a new spectroscopic study

Authors: R. Margutti, G. Chincarini, S. Covino, G. Tagliaferri, S. Campana, M. Della Valle, A. V. Filippenko, F. Fiore, R. Foley, D. Fugazza, P. Giommi, D. Malesani, A. Moretti, L. Stella

Comments: 12 pages, 10 figures. Accepted by A&A

Subjects: Astrophysics (astro-ph)

The host galaxy of the long-duration gamma-ray burst (GRB) 031203 (HG031203) offers a precious opportunity to study in detail the environment of a nearby GRB. The aim is to better characterize this galaxy and analyse the possible evolution with time of the spectroscopic quantities we derive. We analyse HG031203 using a set of optical spectra acquired with the ESO-VLT and Keck telescope. We compare the metallicity, luminosity and star formation properties of this galaxy and of the other supernova-long gamma-ray burst hosts in the local universe (z<0.2) z="0.1055.">

Wijnands 2007 GRB060602B可能是一个X射线暴

主要内容:
GRB060602B可能是一个距离地球6.7kpc的X射线暴. 是一个X射线中子双星。

不过如果这样的话，以后应该还可以看到。

精彩摘抄:


文章信息:

arXiv:0709.0061 [ps, pdf, other]

Title: GRB060602B = Swift J1749.4-2807: an unusual transiently accreting neutron-star X-ray binary

Authors: Rudy Wijnands, Evert Rol, Ed M. Cackett, Rhaana L.C. Starling, Ron A. Remillard

Comments: Submitted to MNRAS

Subjects: Astrophysics (astro-ph)

We present an analysis of the Swift BAT and XRT data of GRB060602B, which is most likely an accreting neutron star in a binary system and not a gamma-ray burst. Our analysis shows that the BAT burst spectrum is consistent with a thermonuclear flash (type-I X-ray burst) from the surface of an accreting neutron star in a binary system. The X-ray binary nature is further confirmed by the report of a detection of a faint point source at the position of the XRT counterpart of the burst in archival XMM-Newton data approximately 6 years before the burst and in more recent XMM-Newton data obtained at the end of September 2006 (nearly 4 months after the burst). Since the source is very likely not a gamma-ray burst, we rename the source Swift J1749.4-2807, based on the Swift/BAT discovery coordinates. Using the BAT data of the type-I X-ray burst we determined that the source is at most at a distance of 6.7+-1.3 kpc. For a transiently accreting X-ray binary its soft X-ray behaviour is atypical: its 2-10 keV X-ray luminosity (as measured using the Swift/XRT data) decreased by nearly 3 orders of magnitude in about 1 day, much faster than what is usually seen for X-ray transients. If the earlier phases of the outburst also evolved this rapidly, then many similar systems might remain undiscovered because the X-rays are difficult to detect and the type-I X-ray bursts might be missed by all sky surveying instruments. This source might be part of a class of very-fast transient low-mass X-ray binary systems of which there may be a significant population in our Galaxy.

Mastichiadis 2007 瞬时辐射的质子超堆积模型

主要内容:
认为瞬时辐射可能来自：相空间超堆积的质子能量瞬时释放，产生正负电子对的辐射。

精彩摘抄:


文章信息:

arXiv:0708.4364 [ps, pdf, other]

Title: Compton dragged supercritical piles: The GRB prompt and afterglow scenario

Authors: A. Mastichiadis, D. Kazanas

Comments: 8 pages, 2 figures, to appear in the proceedings of 30th International Cosmic Ray Conference, Merida, Yucatan, Mexico

Subjects: Astrophysics (astro-ph)

We examine the prompt and afterglow emission within the context of the Supercritical Pile model for GRBs. For this we have performed self-consistent calculations, by solving three time-dependent kinetic equations for protons, electrons and photons in addition to the usual mass and energy conservation equations. We follow the evolution of the RBW as it sweeps up circumstellar matter and assume that the swept-up electrons and protons have energies equal to the Lorentz factor of the flow. While the electrons radiate their energies through synchrotron and inverse Compton radiation on short timescales, the protons, at least initially, start accumulating without any dissipation. As the accumulated mass of relativistic protons increases, however, they can become supercritical to the `proton-photon pair-production - synchrotron radiation' network, and, as a consequence, they transfer explosively their stored energy to secondary electron-positron pairs and radiation. This results in a burst which has many features similar to the ones observed in GRB prompt emission. We have included in our calculations the radiation drag force exerted on the flow from the scattered radiation of the prompt emission on the circumstellar material. We find that this can decelerate the flow on timescales which are much faster than the ones related to the usual adiabatic/radiative ones. As a result the emission exhibits a steep drop just after the prompt phase, in agreement with the Swift afterglow observations.