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.

星期一, 七月 09, 2007

Murase 2007 早期余辉阶段的高能中微子

主要内容:
考虑各种模型在早期余辉阶段的高能中微子辐射,以及探测到的可能性。认为正反激波不能产生。

精彩摘抄:


文章信息:

arXiv:0707.1140 [ps, pdf, other]
Title: High energy neutrino early afterglows gamma-ray bursts revisited
Authors: Kohta Murase
Comments: 17 pages, 11 figures
Subjects: Astrophysics (astro-ph)

High energy neutrino emission from gamma-ray bursts (GRBs) has been expected in various scenarios. In this paper, we study neutrino emission under the various models for early afterglows of GRBs, and discuss implications for neutrino signals from recent Swift observations. Future neutrino detectors such as IceCube might detect neutrino signals from early afterglows under the late prompt emission model, but it would be difficult under the reverse-forward shock model. Neutrino-detections are inviting because they could provide us with not only information on baryon acceleration but also one of the clues to the model of early afterglows. They also lead to motivating neutrino telescopes that are larger than IceCube. Finally, we compare various predictions for the neutrino background from GRBs.

De Rujula 2007 Swift观测继续验证canonball模型

主要内容:
作者认为他们的模型可以很好地解释长暴和XRFes。

精彩摘抄:


文章信息:

What SWIFT has taught us about X-ray flashes and long-duration gamma-ray bursts

Authors: A. De Rujula
Abstract: Recent data gathered and triggered by the SWIFT satellite have greatly improved our knowledge of long-duration gamma ray bursts (GRBs) and X-ray flashes (XRFs). This is particularly the case for the X-ray data at all times, and for UV and optical data at very early times. I show that the optical and X-ray observations are in excellent agreement with the predictions of the "cannonball" model of GRBs and XRFs. Elementary physics and just two mechanisms underlie these predictions: inverse Compton scattering and synchrotron radiation, generally dominant at early and late times, respectively. I put this result in its proper context and dedicate the paper to those who planed, built and operate SWIFT, a true flying jewel.

用050904的模型拟合XRFs的光变曲线

rt

中子星磁场的消失作为伽玛暴的能源

如果黑洞确实没有磁场,那么在中子星变成黑洞的时候,中子星内部和外边的磁场就应该消失,其能量可能被“挤"出来。这部分能量说不定就可以作为伽玛暴的能源机制。

两个问题:
1. 这样只有一次爆发,和伽玛暴看到的多峰结构不符(那是不是precursor?)
2. 能量比较低(或者只驱动低能量的如980425这样的暴?)下面估算一下:
假设只有中子星内部的磁场转化出去:
E=4/3 \pi R_NS^3 B^2/8\pi ~ 1.7E45 R_6^3 B_14^2 erg
只有10^45erg。

如果有磁场,磁压可以帮助抵抗一些引力,那么中子星的质量和半径是否可以更大一些呢?



新出文章:http://www.arxiv.org/abs/0707.0576

Magnetically-dominated jets inside collapsing stars as a model for gamma-ray bursts and supernova explosions

Authors: Dmitri A. Uzdensky (Princeton University), Andrew I. MacFadyen (IAS and NYU)

光变曲线的谷

现在一般都只看光变曲线的峰值,看峰值对应着什么过程。而光变的谷却没有人关心。

至少,如果光变曲线的谷不是零,就说明在那个时候源依然有辐射。

那可以从谷中挖些什么信息呢?

黑体辐射是效率最高的吗

在一个特定体积内,黑体辐射是所有辐射机制中所能辐射的功率最高的吗?(当然只指电磁辐射)因为只有黑体是辐射量达到饱和了的,其它的辐射的条件都是光深要小于1. 什么时候计算一下。

通过超新星的光变推测爆发时间

往往变换一个环境,就会产生一些新的想法。这次在黄山开会的时候 ,也有一些小的想法,有的可能可以继续做一下,有的也就是垃圾。不管怎样,把它们记下来。

根据流量F \propto \pi R^2 a T^4。
先假设T不变,则F \propto R^2,
再假设辐射区膨胀的速度v不变,则r=vt~t,于是F \propto t^2.
观测肯定只能看到辐射上升到一定程度之后的光变,那么通过把这段上升的光变向前延伸,并且保持t^2的形状,这样就可以找到时间零点,即超新星爆发的时间。

当然,速度v可能是变化的,T也可能在变,但如果给出它们的变化规律,只不过光变的时间指数不是2了,同样可以找到时间零点。

黄山会议印象-学术版

这次会议的名字叫“International conference of astrophysics in compact objects”,也属于郭守敬会议系列之一。 根据所来的人来看,是一次致密天体的盛会。究其原因,可能在于一、黄山的魅力;二、赖东的号召力。因为这基本上不是一个常规会议,而是突然插进来的专题会议。时间四天,7.2-3, 7.5-6。

就来的大牛们,总结一下:国外的顶尖人物来了几个代表;国内在国外的少壮派和国内的少壮派几乎全到(也许孤陋寡闻,有没来而不知道的);国内老字号只有一个;国内学生和我这种虾米来了一堆。

具体的,大牛有Narayan,吸积盘方面最权威的人物,也是这次会议最重量级的人,有几次听报告的时候坐在他旁边,想想还有点儿激动;Kouveliotou,伽玛暴早期的领军人物之一,据说贡献包括余辉的发现,以前常听老板提起她的名字,具体做什么不清楚,查了一下ads,此人工作还包括SGR,GRO,这次报告是与超新星成协,98年都发表与超新星成协的文章了;Gehrels,swift的负责人,伽玛暴观测的权威;Harding,脉冲星的权威,好像不是第一天来的,来之前有人说是大美女,看到后,虽然年纪有点大,但确实是美女(这次会上美女也很多,呵呵);Mereghetti,名字常听说,报告题目是SGR;Maxim Lyutikov,名字听说过,看起来比较年轻,在上黄山路上碰到了他,嫌我们慢,不愿意和我们一起走;Matthew Baring,报告上和Harding是联合署名的,但单位不一样,记得他仅仅是因为去宏村的路上坐在他旁边;Makishima,日本人,年纪比较大了,很认真,不苟言笑,可能是负责Suzaku(朱雀)卫星,应该是一个很重量级的;Levinson,伽玛暴的能源机制里有此人出没,据说都是和van Putten一起,主要做喷流机制,会议上也是常发言的人之一,但平时不怎么说话,coffee break的时候,当他走到我的poster去看的时候我把poster的内容给他讲了一下,然后他提了一点点问题,再其他时间也就不理我了;Roni Waldman,会八国语言的以色列人,包括中文,博后,不过在这些人里不算牛;肯定至少还漏掉了一个人,因为在最后一天下午四个人在台上主持讨论的时候,除了Narayan、Kouveliotou、赖东,还有一个人。可惜的是伽玛暴方面的Meszaros和Kumar没有来。

少壮派中国人(不知道在美国的有没有不是中国人了的):赖东,有关强磁场的权威,99年就在RMP上发表了“matter in strong magnetic field”的综述文章,我念硕士的时候就要读他的文章,没想到转方向读博士的时候更常听说和在开会的时候见到他;张冰,内华达大学助理教授,目前swift组理论实际负责人,出了好多综述和类综述的文章,当然研究性的也很多;范一中,快速上升,虽然还没有建立像其他人那样的地位,但文章出的太快,在我眼里也算少壮派了;戴子高,南大,两篇Science,三篇PRL,n多astronomy三大杂志文章,太了解,不写了;乔国俊,北大,貌似这里唯二的老杆子了,带出好几个叫的响的学生,包括张冰、徐仁新(?);Qinghuan Luo(不写仅表示不了解);韩金林;余文飞,从今年还是知道此牛,刚到上海台,研究员,从华中师大出去,吃饭的时候他说还是华师一附中的,好像是马普做过博后,这次开会带着家眷,有两个小孩;张新民;崔伟,Purdue大学,只知道是牛人,很少来国内,今年才比较多了;张双男,清华大学,观测理论双面手,经常各处访问;申志强,上海台,VLBI观测;Jun-Hui Zhao;袁峰,上海台,卢炬甫的学生,好像在Narayan手下做过博后,黑洞吸积盘的理论和计算应该是国内最好的;吴学兵,北大;汪定雄,华中科大,黑洞吸积盘+广义相对论(也属于老杆子);袁业飞,中科大,会议的本地组织者;Kinwah Wu,香港人,第一次见此人,作报告像上课一样,很严肃;楼雨庆,清华,没做报告,也是在国外很多年再回来的,听到一点八卦说杨振宁给清华的上普通物理上了一学期(还是一年)不上了,然后就是他顶上的;还有没做报告的牛人,像黄永锋,还有别人,就不知道了,毕竟圈子窄,也不是很八卦。

内容:按时间顺序,最先是伽玛暴,然后中子星、脉冲星,吸积盘,并合,黑洞和超新星,中间还有几个关于卫星的。每个报告之后有提问,然后每半个半天之后有个讨论,讨论这一节几个报告,然后coffee break或者吃饭。第一次参加这种形式的会议,不过每次讨论都有人发言。最后一天的下午的第二节,就纯粹是讨论,赖东在ppt上放上这次会议的主要内容,然后四个大牛在台上,和台下的人一起就各个专题讨论。我抄下来了那个总结:

Some topics discussed at the meeting

GRB/SNe:
afterglow, B effects, central engine (NS->BH, NS/BH, ms magnetars, etc.), SN connection, classification, application to cosmology, etc.

Many different manifestations of NSs:
thermal emitters, PWN, PRATs, gamma-ray pulsars, magnetars (flares, seismology, nonthermal emissions), magnetospheres/surface, pulsars as a tool, quark stars, accreting NSs (QPOs, field burial, etc.), magnetism, etc.

Accreting BHs:
bassics BH parameters, Fe lines/reflection, various accreting states, coronae, ULXs (intermediate mass BHs), jet (microphysics) / microquasars, TeV emissions (neutrinos), similarity/connection with AGNs, AgrA* and GCs (massive star puzzle, imaging BH), accretion flow

Gravitational waves:
LIGO/LISA etc., compact star merger (kicks), NS disruption, WP binaries, magnetic mountain on NS (what's this?), etc.

White Dwarfs:
spin and magnetism, connect to NSs, SN Ia progenitors

Future Missions:
GLAST, Con-X, HMXT, ground-based TeV & neutrios

英语: 上次去北京开cospar会议就感觉英语实在需要提高,特别是听力,不然不知道别人在说什么,非常尴尬。这次稍微好一点点,主要是方向相近一下,特别是开始的伽玛暴部分。有两种最容易听懂,一是张双南老师那样的,说的慢,吐词清楚,重点强调,不过这一类貌似只有他一个,Kouveliotou也还可以;然后就是标准的chinglish,就是基本没出国国的说的英语,和我自己说的一样,又还比较慢,能听懂。其次是标准的英语。然后是在国外呆的比较久说的比较快的以及欧洲方言。再然后是日本英语。最难懂的是印度英语,这次还好没有印度人。好像Narayan是印度人,有口音,不过坐在他旁边的时候听得还是比较清楚。这个听到的信息有关,如果隔得远,靠话筒,就基本上之后高频和说得比较响亮的音能听到,而离得近的话,一些没怎么发出来的音也听到了,就好懂一些。 中国人说英语,有个规律很明显,出国呆至少一年以上的就可以说得很溜了;没怎么出国国的,发音chinglish比较严重。看来就冲着英语,出去一下也是必要的。有了环境,语言的提高是自然而然的。

讨论:中间有一个晚上(7月3号),戴老师召集我们去他房间和张冰讨论。组里在读的研究生都介绍了一下正在做的工作:邵琅继续作尘埃的X射线散射(跟余辉相关);俞云伟作能量注入等对早期X射线余辉的解释(Swift的新观测现象)和高能辐射(将被GLAST观测);王发印做宇宙学参数拟合(熟悉整套宇宙学的做法,和陆老师的宇宙学中心靠拢);张栋做中子星的超艾丁顿吸积(伽玛暴能源机制)。虽然戴老师基本上都是让学生自主选择研究兴趣,但是整体上的分布却是相当合理。正所谓可进(能源机制)可退(转做宇宙学),又能保持和伽玛暴研究热点同步(邵琅和俞云伟)。不得不佩服啊。

咦,写了半天,我在会议上的真正收获怎么貌似没有啊?是不是真的没有?

Genet 2007 对GRB 050820a的拟合

主要内容:
此暴有早期的光学余辉。作者用类似于内激波+正反激波的模型解释暴本身和早期的光学余辉。

精彩摘抄:


文章信息:
arXiv:0707.0952 [ps, pdf, other]

Title: The rise of the afterglow in GRB 050820a
Comments: 6 pages, 9 figures, accepted for publication in A&A
Subjects: Astrophysics (astro-ph)
The early optical afterglow of GRB 050820a recorded by the RAPTOR telescope shows both a contribution from the prompt emission and the initial rise of the afterglow. It is therefore well-suited for the study of the dynamical evolution of the GRB ejecta when it first undergoes the decelerating effect of the environment. This is a complex phase where the internal, reverse, and forward shocks can all be present simultaneously. We have developed a simplified model that can follow these different shocks in an approximate, but self-consistent way. It is applied to the case of GRB 050820a to obtain the prompt and afterglow light curves. We show that the rise of the afterglow during the course of the prompt emission has some important consequences. The reverse shock propagates back into the ejecta before internal shocks are completed, which affects the shape of the gamma-ray profile. We get the best results when the external medium has a uniform density, but obtaining a simultaneous fit of the prompt and afterglow emission is not easy. We discuss a few possibilities that could help to improve this situation

Daigne 2007 低光度GRB980425的两种可能解释

主要内容:
分析了低光度的来源的两个原因:或者是偏轴,或者暴本身的高度低。前者要求很强的余辉观测,但没有看到,所以作者倾向于后者。

精彩摘抄:


文章信息:

arXiv:0707.0931 [ps, pdf, other]
Title: The low-luminosity tail of the GRB distribution: the case of GRB 980425
Authors: F. Daigne (1), R. Mochkovitch (1) ((1) Institut d'Astrophysique de Paris and Universite Pierre et Marie Curie, Paris)
Comments: 10 pages, 7 figures
Journal-ref: A&A 465, 1-8 (2007)
Subjects: Astrophysics (astro-ph)

(abridged) The association of GRB 980425 with SN 1998bw at z=0.0085 implies the existence of a population of GRBs with an isotropic-equivalent luminosity which is about 10^4 times smaller than in the standard cosmological case. We investigate two scenarios to explain a weak GRB : a normal (intrinsically bright) GRB seen off-axis or an intrinsically weak GRB seen on-axis. For each of these two scenarios, we first derive the conditions to produce a GRB 980425-like event and we then discuss the consequences for the event rate. If we exclude the possibility that GRB 980425 is an occurence of an extremely rare event observed by chance during the first eight years of the 'afterglow era', the first scenario implies that (i) the local rate of standard bright GRBs is much higher than what is usually expected; (ii) the typical opening angle is much narrower than what is derived from observations of a break in the afterglow lightcurve. In addition, we show that the afterglow of GRB 980425 in this scenario should have been very bright and easily detected. For these reasons the second scenario appears more realistic. We show that the parameter space of the internal shock model indeed allows GRB 980425-like events, in cases where the outflow is only mildly-relativistic and mildly-energetic. The rate of such weak events in the Universe has to be much higher than the rate of standard bright GRBs to allow the discovery of GRB 980425 during a short period of a few years. However it is still compatible with the observations as the intrinsic weakness of these GRB 980425-like bursts does not allow detection at cosmological redshift. We finally briefly discuss the consequences of such a high local rate of GRB 980425-like events for the future prospects of detecting non-electromagnetic radiation, especially gravitational waves.