Malesani 2007 GRB 060418 and GRB 060607A的早期余辉观测

主要内容:
给出了用REM对GRB 060418 and GRB 060607A的早期余辉观测，估算早期的Lorentz因子有400。而余辉的流量有暴本身的16%，对GRB 060418来说的话。

精彩摘抄:


文章信息:
arXiv:0706.1772 [ ps, pdf, other] : Title: The GRB afterglow onset observed by REM: fireball Lorentz factor and afterglow fluence
Authors: Daniele Malesani (DARK), Emilio Molinari (INAF/Brera), Susanna Vergani (DIAS and DCU), Stefano Covino (INAF/Brera), for the REM team
Comments: 4 pages, 1 figure, to appear in New Astronomy Reviews, proceedings of "070228: The Next Decade of Gamma-Ray Burst Afterglows", Amsterdam, 2007 March 19-23, eds. R.A.M.J. Wijers, L. Kaper, E. van Eerten

We report observations of the early light curves of GRB 060418 and GRB 060607A, carried out with the pink robotic telescope REM. A clear peak is detected for both events, which is interpreted as the onset of the afterglow, that is the time at which the fireball starts decelerating. This detection allows to directly measure the initial fireball Lorentz factor, which was found to be Gamma_0 ~ 400 for both events, fully confirming the ultrarelativistic nature of gamma-ray burst fireballs. Sampling the light curve before the peak also allows to compute the bolometric fluence of the afterglow, which is 16% of the prompt one in the case of GRB 060418.

Falcone 2007 Swift X射线耀发的大总结

主要内容:
总结了所有目前Swift暴的X射线耀发，包括每个暴的耀发的个数，光度，谱指数等。还有flares的E_pk- E_iso。


精彩摘抄:


文章信息:
arXiv:0706.1564 [ ps, pdf, other] : Title: The First Survey of X-ray Flares from Gamma Ray Bursts Observed by Swift: Spectral Properties and Energetics
Authors: A. D. Falcone (1), D. Morris (1), J. Racusin (1), G. Chincarini (2 and 3), A. Moretti (2), P. Romano (2 and 3), D. N. Burrows (1), C. Pagani (1), M. Stroh (1), D. Grupe (1), S. Campana (2), S. Covino (2), G. Tagliaferri (2), R. Willingale (4), N. Gehrels (5) ((1) Pennsylvania State University, (2)INAF-Osservatorio Astronomico di Brera, (3) Universita degli studi di Milano-Bicocca, (4) University of Leicester, (5) NASA/Goddard Space Flight Center)
Comments: submitted to ApJ; 37 pages with 14 figures

Observations of gamma ray bursts (GRBs) with Swift produced the initially surprising result that many bursts have large X-ray flares superimposed on the underlying afterglow. The flares were sometimes intense, had rapid rise and decay phases, and occurred late relative to the ``prompt'' phase. Some remarkable flares are observed with fluence comparable to the prompt GRB fluence. Many GRBs have several flares, which are sometimes overlapping. Short, intense, repetitive, and late flaring can be most easily understood within the context of the standard fireball model with the internal engine that powers the prompt GRB emission in an active state at late times. However, other models for flares have been proposed. Flare origin can be investigated by comparing the flare spectra to that of the afterglow and the initial prompt emission. In this work, we have analyzed all significant X-ray flares from the first 110 GRBs observed by Swift. From this sample 33 GRBs were found to have significant X-ray flares, with 77 flares that were detected above the 3$\sigma$ level. In addition to temporal analysis presented in a companion paper, a variety of spectral models have been fit to each flare. In some cases, we find that the spectral fits favor a Band function model, which is more akin to the prompt emission than to that of an afterglow. We find that the average fluence of the flares is 2.4e-7 erg/cm^2/s in the 0.2-10 keV energy band, which is approximately a factor of ten below the average prompt GRB fluence. These results, when combined with those presented in the companion paper on temporal properties of flares, supports the hypothesis that most X-ray flares are late-time activity of the internal engine that spawned the initial GRB; not an afterglow related effect.

X射线的平降阶段和外部介质分布

假设n \propto r^{-k}, 而且k>2. 这样喷流在往外运动的过程中基本不会被减速，自身也不会怎么被激波化，所以也不用计算辐射。只算正向激波的辐射，可能可以和早期平降阶段吻合。

然后也许进入ISM，成为标准余辉。

超新星的伽玛暴成分

如果伽玛暴和超新星成协的话（这几乎是肯定的），由于伽玛暴是极束的，那么有一些超新星虽然伴随有伽玛暴，但不朝着我们，可能看不到。可是余辉应该是可以看到的啊，特别是射电余辉。

但实际上是伽玛暴的射电余辉（包括于超新星成协的）比超新星自己（没看到伽玛暴的超新星）的射电高4个量级。这可能说明两个问题，要么这些超新星（也就是所有没看到伽玛暴的超新星）都不和伽玛暴成协；要么偏轴的射电比正轴的低4个量级。

我相信后者。因为说只有看到伽玛暴和超新星成协的才成协，没看到的就都不成协好像不对哦。那后者怎么解释呢？

一、偏轴由于极束效应，流量会降低，不过在晚期的射电波段，喷流的Lorentz因子已经很小了，这种降低也会很弱；
二、假设辐射区是一个薄片，在标准模型里就是作薄层近似的，那边偏轴观测者所对应的光深就要大一些了，L=L_垂直／cos\theta。 光深大了流量自然较低。不过需要两方面的验证：一是具体计算看是否真能这么底；二是射电的谱此时应该是黑体，看观测到的是不是。

如果偏轴的射电确实比超新星的射电相比差不多，那么就要想办法把它区分出来。这个区分出来的成分就可以叫做超新星的伽玛暴成分。和目前动不动就说伽玛暴的超新星成分对应，呵呵。

Rol 2007 暗暴GRB 051022的观测

主要内容:
给出了射电和X射线的观测，红外和光学分布有2.8和6个星等的消光。

精彩摘抄:


文章信息:
arXiv:0706.1518 [ps, pdf, other] : Title: GRB051022: physical parameters and extinction of a prototype dark burst
Authors: Evert Rol, Alexander van der Horst, Klaas Wiersema, Sandeep K. Patel, Andrew Levan, Melissa Nysewander, Chryssa Kouveliotou, Ralph A.M.J. Wijers, Nial Tanvir, Dan Reichart, Andrew S. Fruchter, John Graham, Rhaana L.C. Starling, Paul T. O'Brien, Jens Hjorth, Johan Fynbo, Peter Jonker, Wilbert van Ham, David N. Burrows, Jan-Erik Ovaldsen, Andreas O. Jaunsen, Richard Strom
Comments: 18 pages, 1 figure. Submitted to ApJ

GRB051022 was undetected to deep limits in early optical observations, but precise astrometry from radio and X-ray showed that it most likely originated in a galaxy at z ~ 0.8. We report radio, optical, near infra-red and X-ray observations of GRB051022. Using the available X-ray and radio data, we model the afterglow and calculate the energetics of the afterglow, finding it to be an order of magnitude lower than that of the prompt emission. The broad-band modeling also allows us to precisely define various other physical parameters and the minimum required amount of extinction, to explain the absence of an optical afterglow. Our observations suggest a high extinction, at least 2.8 magnitudes in the infrared (J) and at least 6 magnitudes in the optical (U) in the host-galaxy restframe. Such high extinctions are unusual for GRBs, and likely indicate a geometry where our line of sight to the burst passes through a dusty region in the host that is not directly co-located with the burst itself.

Wiersema 2007 GRB 040924的观测

主要内容:
给出GRB 040924和宿主星系的观测。z = 0.858 ± 0.001

精彩摘抄:
晚期好平啊，说是超新星成分。

文章信息:
arXiv:0706.1345 [ps, pdf, other] : Title: Spectroscopy and multiband photometry of the afterglow of intermediate duration gamma-ray burst 040924 and its host galaxy
Authors: K. Wiersema, A.J. van der Horst, D.A. Kann, E. Rol, R.L.C. Starling, P.A. Curran, J. Gorosabel, A.J. Levan, J.P.U. Fynbo, A. de Ugarte Postigo, R.A.M.J. Wijers, A.J. Castro-Tirado, S.S. Guziy, A. Hornstrup, J. Hjorth, M. Jelinek, B.L. Jensen, M. Kidger, F. Martin-Luis, N.R. Tanvir, P. Tristram, P.M. Vreeswijk
Comments: A&A submitted. 10 pages, 4 figures

We present optical photometry and spectroscopy of the afterglow and host galaxy of gamma-ray burst 040924. This GRB had a rather short duration of T90 ~2.4s, and a well sampled optical afterglow light curve. We aim to use this dataset to find further evidence that this burst is consistent with a massive star core-collapse progenitor. We combine the afterglow data reported here with data taken from the literature and compare the host properties with survey data. We find that the global behaviour of the optical afterglow is well fit by a broken power-law, with a break at ~0.03 days. We determine the redshift z = 0.858 +/- 0.001 from the detected emission lines in our spectrum. Using the spectrum and photometry we derive global properties of the host, showing it to have similar properties to long GRB hosts. We detect the [Ne III] emission line in the spectrum, and compare the fluxes of this line of a sample of 15 long GRB host galaxies with survey data, showing the long GRB hosts to be comparable to local metal-poor emission line galaxies in their [Ne III] emission. We fit the supernova bump accompanying this burst, and find that it is similar to other long GRB supernova bumps, but fainter. All properties of GRB 040924 are consistent with an origin in the core-collapse of a massive star: the supernova, the spectrum and SED of the host and the afterglow.

van der Horst 2007 GRB 030329的三年射电观测

主要内容:
两篇会议文章，是arXiv:0706.1321的补充吧。

精彩摘抄:


文章信息:

arXiv:0706.1323 [ps, pdf, other] :

Title: GRB 030329: 3 years of radio afterglow monitoring
Authors: A.J. van der Horst, A. Kamble, R.A.M.J. Wijers, L. Resmi, D. Bhattacharya, E. Rol, R. Strom, C. Kouveliotou, T. Oosterloo, C.H. Ishwara-Chandra
Comments: 5 pages, 2 figures, Phil. Trans. R. Soc. A, vol.365, p.1241, proceedings of the Royal Society Scientific Discussion Meeting, London, September 2006

Radio observations of gamma-ray burst (GRB) afterglows are essential for our understanding of the physics of relativistic blast waves, as they enable us to follow the evolution of GRB explosions much longer than the afterglows in any other wave band. We have performed a three-year monitoring campaign of GRB 030329 with the Westerbork Synthesis Radio Telescopes (WSRT) and the Giant Metrewave Radio Telescope (GMRT). Our observations, combined with observations at other wavelengths, have allowed us to determine the GRB blast wave physical parameters, such as the total burst energy and the ambient medium density, as well as investigate the jet nature of the relativistic outflow. Further, by modeling the late-time radio light curve of GRB 030329, we predict that the Low-Frequency Array (LOFAR, 30-240 MHz) will be able to observe afterglows of similar GRBs, and constrain the physics of the blast wave during its non-relativistic phase.

arXiv:0706.1324 [ps, pdf, other] :

Title: GRB 030329: three years of radio afterglow monitoring
Authors: A.J. van der Horst, A. Kamble, R.A.M.J. Wijers, L. Resmi, D. Bhattacharya, E. Rol, R. Strom, C. Kouveliotou, T. Oosterloo, C.H. Ishwara-Chandra
Comments: 2 pages, to appear in Nuovo Cimento B, proceedings of the Congress "Swift and GRBs: Unveiling the Relativistic Universe", Venice, June 2006

Radio observations of gamma-ray burst (GRB) afterglows are essential for our understanding of the physics of relativistic blast waves, as they enable us to follow the evolution of GRB explosions much longer than the afterglows in any other wave band. We have performed a three-year monitoring campaign of GRB 030329 with the Westerbork Synthesis Radio Telescopes (WSRT) and the Giant Metrewave Radio Telescope (GMRT). Our observations, combined with observations at other wavelengths, have allowed us to determine the GRB blast wave physical parameters, such as the total burst energy and the ambient medium density, as well as investigate the jet nature of the relativistic outflow. Further, by modeling the late-time radio light curve of GRB 030329, we predict that the Low Frequency Array (LOFAR, 30-240 MHz) will be able to observe afterglows of similar GRBs, and constrain the physics of the blast wave during its non-relativistic phase.

van der Horst 2007 GRB 030329深度非相对论的射电辐射观测

主要内容:
给出了一直到1128天的射电观测。用一般模型限制了一些参数。

精彩摘抄:


文章信息:
arXiv:0706.1321 [ps, pdf, other] : Title: Detailed study of the GRB 030329 radio afterglow deep into the non-relativistic phase
Authors: A.J. van der Horst, A. Kamble, L. Resmi, R.A.M.J. Wijers, D. Bhattacharya, B. Scheers, E. Rol, R. Strom, C. Kouveliotou, T. Oosterloo, C.H. Ishwara-Chandra
Comments: 9 pages, 2 figures, submitted to Astronomy & Astrophysics

We explore the physics behind one of the brightest radio afterglows ever, GRB 030329, at late times when the jet is non-relativistic. We determine the physical parameters of the blast wave and its surroundings, in particular the index of the electron energy distribution, the energy of the blast wave and the density (structure) of the circumburst medium; and compare our results with results from image size measurements. We observed the GRB 030329 radio afterglow with the Westerbork Synthesis Radio Telescope and the Giant Metrewave Radio Telescope at frequencies from 325 MHz to 8.4 GHz, spanning a time range of 268-1128 days after the burst. We modeled all the available radio data and derived the physical parameters. The index of the electron energy distribution is p=2.1, the circumburst medium is homogeneous, and the transition to the non-relativistic phase happens at t_NR ~ 80 days. The energy of the blast wave and density of the surrounding medium are comparable to previous findings. Our findings indicate that the blast wave is roughly spherical at t_NR, and they are in agreement with the implications from the VLBI studies of the image size evolution. It is not clear from the presented dataset whether we have seen emission from the counter jet or not. We predict that the Low Frequency Array will be able to observe the afterglow of GRB 030329 and many other radio afterglows, constraining the physics of the blast wave during its non-relativistic phase even further.

Butler 2007 Swift暴的catalog

主要内容:
从GRB 041220 到 070509一共218个暴， 其中76个有红移，给出了它们的T90,T50,T0.45,E_pk,E_iso,\alpha,\beta,等等

精彩摘抄:


Swift时代的Amati关系，灰色的小点是在一定置信度上某个暴所可能的位置。
这是什么关系？看起来蛮致密的嘛

文章信息:
arXiv:0706.1275 [ps, pdf, other] : Title: A Complete Catalog of Swift GRB Spectra and Durations: Demise of a Physical Origin for Pre-Swift High-Energy Correlations
Authors: Nathaniel R. Butler, Daniel Kocevski, Joshua S. Bloom, Jason L. Curtis
Comments: 25 pages, 7 figures, 2 tables

We calculate durations and spectral paramaters for 218 Swift bursts detected by the BAT instrument between and including GRBs 041220 and 070509, including 76 events with measured redshifts. Incorporating prior knowledge into the spectral fits, we are able to measure the characteristic $\nu F_{\nu}$ spectral peak energy $E_{\rm pk,obs}$ and the isotropic equivalent energy $E_{\rm iso}$ (1--$10^4$ keV) for all events. This complete and rather extensive catalog, analyzed with a unified methodology, allows us to address the persistence and origin of high-energy correlations suggested in pre-Swift observations. We find that the $E_{\rm pk,obs}$-$E_{\rm iso}$ correlation is present in the Swift sample, however the best-fit powerlaw relation is inconsistent from the best-fit pre-Swift relation at >5 sigma significance. Moreover, it has a factor >~ 2 larger intrinsic scatter, after accounting for large errors on $E_{\rm pk,obs}$. A large fraction of the Swift events are hard and subluminous relative to (and inconsistent with) the pre-Swift relation, in agreement with indications from BATSE GRBs without redshift. Moreover, we determine an experimental threshold for the BAT detector and show how the $E_{\rm pk,obs}$--$E_{\rm iso}$ correlation arises artificially due to partial correlation with the threshold. We show that pre-Swift correlations found by Amati et al.(2002), Yonetoku et al. (2004), Firmani et al.(2006) (and independently by others) are likely unrelated to the physical properties of GRBs and are likely useless for tests of cosmology. Also, an explanation of these correlations in terms of a detector threshold provides a natural and quantitative explanation for why short-duration GRBs and events at low redshift tend to be outliers to the correlations.

Malesani 2007 短暴GRB 050724的多波段余辉观测

主要内容:
宿主星系、光谱和多波段光变曲线

精彩摘抄:
position

light curves

文章信息:
arXiv:0706.1273 [ps, pdf, other] : Title: Multicolor observations of the afterglow of the short/hard GRB 050724
Authors: D. Malesani, S. Covino, P. D'Avanzo, V. D'Elia, D. Fugazza, S. Piranomonte, L. Ballo, S. Campana, L. Stella, G. Tagliaferri, L.A. Antonelli, G. Chincarini, M. Della Valle, P. Goldoni, C. Guidorzi, G.L. Israel, D. Lazzati, A. Melandri, P. Romano, G. Stratta, S.D. Vergani
Comments: 8 pages, 5 figures, 4 tables, submitted to A&A following referee comments

New information on short/hard gamma-ray bursts (GRBs) is being gathered thanks to the discovery of their optical and X-ray afterglows. However, some key aspects are still poorly understood, including the collimation level of the outflow, the duration of the central engine activity, and the properties of the progenitor systems. We want to constrain the physical properties of the short GRB 050724 and of its host galaxy, in turn drawing some inferences on the global short GRB population. We present optical observations of the afterglow of GRB 050724 and of its host galaxy, significantly expanding the existing dataset for this event. We compare our results with models, complementing them with available measurements in the literature. Including X-ray data, we study the afterglow light curve and spectrum. We also present observations of the host galaxy. The observed optical emission was likely related to the large flare observed in the X-ray light curve. The apparent steep decay was therefore not due to the jet effect. Available data are indeed consistent with low collimation, in turn implying a large energy release, comparable to that of long GRBs. The flare properties also constrain the internal shock mechanism, requiring a large Lorentz factor contrast between the colliding shells. This implies that the central engine was active at late times, rather than ejecting all shells simultaneously. The host galaxy has red colors and no ongoing star formation, consistent with previous findings on this GRB. However, it is not a pure elliptical, and has some faint spiral structure. GRB 050724 provides the most compelling case for association between a short burst and a galaxy with old stellar population. It thus plays a pivotal role in constraining progenitors models, which must allow long delays between birth and explosion.