Troja, E. 2012 GRB 091127的多波段观测

主要内容:
 GRB 091127和SN 2009nz是成协的。

精彩摘抄:


暴本身的光变


余辉


谱



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Title:		Broadband study of GRB 091127: a sub-energetic burst at higher redshift?
Authors:		Troja, E.; Sakamoto, T.; Guidorzi, C.; Norris, J. P.; Panaitescu, A.; Kobayashi, S.; Omodei, N.; Brown, J. C.; Burrows, D. N.;Evans, P. A.; Gehrels, N.; Marshall, F. E.; Mawson, N.; Melandri, A.; Mundell, C. G.; Oates, S. R.; Pal'shin, V.; Preece, R. D.;Racusin, J. L.; Steele, I. A.; Tanvir, N. R.; Vasileiou, V.; Wilson-Hodge, C.; Yamaoka, K.
Publication:		eprint arXiv:1201.4181
Publication Date:		01/2012
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		12 pages, 7 figures, submitted to ApJ
Bibliographic Code:		2012arXiv1201.4181T

Abstract

GRB 091127 is a bright gamma-ray burst (GRB) detected by Swift at a redshift z=0.49 and associated with SN 2009nz. We present the broadband analysis of the GRB prompt and afterglow emission and study its high-energy properties in the context of the GRB/SN association. While the high luminosity of the prompt emission and standard afterglow behavior are typical of cosmological long GRBs, its low energy release, soft spectrum and unusual spectral lag connect this GRB to the class of sub-energetic bursts. We discuss the suppression of high-energy emission in this burst, and investigate whether this behavior could be connected with the sub-energetic nature of the explosion.

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Abadie, J. 2012 GRB 051103 的LIGO的引力波观测

主要内容:
依然只是上限，不过如果是来自很近的话，M81，那么排除了双星并合的模型，而可能是SGR。

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Title:		Implications For The Origin Of GRB 051103 From LIGO Observations
Authors:		The LIGO Scientific Collaboration; Abadie, J.;
Publication:		eprint arXiv:1201.4413
Publication Date:		01/2012
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena, General Relativity and Quantum Cosmology
Comment:		8 pages, 3 figures. For a repository of data used in the publication, go to: https://dcc.ligo.org/cgi-bin/DocDB/ShowDocument?docid=15166. Also see the announcement for this paper on ligo.org at: http://www.ligo.org/science/Publication-GRB051103/index.php
Bibliographic Code:		2012arXiv1201.4413T

Abstract

We present the results of a LIGO search for gravitational waves (GWs) associated with GRB 051103, a short-duration hard-spectrum gamma-ray burst (GRB) whose electromagnetically determined sky position is coincident with the spiral galaxy M81, which is 3.6 Mpc from Earth. Possible progenitors for short-hard GRBs include compact object mergers and soft gamma repeater (SGR) giant flares. A merger progenitor would produce a characteristic GW signal that should be detectable at the distance of M81, while GW emission from an SGR is not expected to be detectable at that distance. We found no evidence of a GW signal associated with GRB 051103. Assuming weakly beamed gamma-ray emission with a jet semi-angle of 30 deg we exclude a binary neutron star merger in M81 as the progenitor with a confidence of 98%. Neutron star-black hole mergers are excluded with > 99% confidence. If the event occurred in M81 our findings support the the hypothesis that GRB 051103 was due to an SGR giant flare, making it the most distant extragalactic magnetar observed to date.

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MacLachlan, G. A. 2012 长暴和短暴的最短光变时标也不一样.

主要内容:
把费米暴拿过来，用小波分析的方法看它们的最短光变时标。

精彩摘抄:

短暴和长暴的最短光变时标\tau_beta的分布。
貌似把长暴和短暴放在一起的话，就是一个lognormal的分布嘛。



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Title:		Minimum Variability Time Scales of Long and Short GRBs
Authors:		MacLachlan, G. A.; Shenoy, A.; Sonbas, E.; Dhuga, K. S.; Cobb, B.; Ukwatta, T. N.; Morris, D. C.; Eskandarian, A.; Maximon, L. C.;Parke, W. C.
Publication:		eprint arXiv:1201.4431
Publication Date:		01/2012
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Bibliographic Code:		2012arXiv1201.4431M

Abstract

We have investigated the variability of a sample of long and short Fermi/GBM Gamma ray bursts (GRBs) using a fast wavelet technique to determine the smallest time scales. The results indicate different variability time scales for long and short bursts in the source frame and that variabilities on the order of a few milliseconds are not uncommon. The data also indicate an intriguing relation between the variability scale and the burst duration.

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Kaur, Ramanpreet 2012 VLT/X-shooter 观测的X射线双星中爆发的谱

主要内容:
MAXI J1659-152，可能是黑洞吸积盘的谱。

精彩摘抄:

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Title:		VLT/X-shooter spectroscopy of the candidate black-hole X-ray binary MAXI J1659-152 in outburst
Authors:		Kaur, Ramanpreet; Kaper, Lex; Ellerbroek, Lucas E.; Russell, David M.; Altamirano, Diego; Wijnands, Rudy; Yang, Yi-Jung;D'Avanzo, Paolo; de Ugarte Postigo, Antonio; Flores, Hector; Fynbo, Johan P. U.; Goldoni, Paolo; Thone, Christina C.;van der Horst, Alexander; van der Klis, Michiel; Kouveliotou, Chryssa; Wiersema, Klaas; Kuulkers, Erik
Publication:		eprint arXiv:1201.4883
Publication Date:		01/2012
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		Accepted for publication in ApJ Letters
Bibliographic Code:		2012arXiv1201.4883K

Abstract

We present the optical to near-infrared spectrum of MAXI J1659-152, during the onset of its 2010 X-ray outburst. The spectrum was obtained with X-shooter on the ESO - Very Large Telescope (VLT) early in the outburst simultaneous with high quality observations at both shorter and longer wavelengths. At the time of the observations, the source was in the low-hard state. The X-shooter spectrum includes many broad (~2000 km/s), double-peaked emission profiles of H, HeI, HeII, characteristic signatures of a low-mass X-ray binary during outburst. We detect no spectral signatures of the low-mass companion star. The strength of the diffuse interstellar bands results in a lower limit to the total interstellar extinction of Av ~ 0.4 mag. Using the neutral hydrogen column density obtained from the X-ray spectrum we estimate Av ~1 mag. The radial-velocity structure of the interstellar NaI D and CaII H & K lines results in a lower limit to the distance of ~ 4 +/- 1 kpc, consistent with previous estimates. With this distance and Av, the dereddened spectral energy distribution represents a flat disk spectrum. The two subsequent 10 minute X-shooter spectra show significant variability in the red wing of the emission-line profiles, indicating a global change in the density structure of the disk, though on a timescale much shorter than the typical viscous timescale of the disk.

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Hatsukade, Bunyo 2012 几个暴的射电观测

主要内容:
(GRBs) 990705, 021211, 041006, and 051022，都没有射电辐射。同时也没有光学辐射，即所谓的光学暗暴（051022除外，有很高的尘埃柱密度）。所以有些暴可能是本质上就是暗暴，而有些如051022可能是由于尘埃导致的。

精彩摘抄:


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Title:		Constraints on Obscured Star Formation in Host Galaxies of Gamma-ray Bursts
Authors:		Hatsukade, Bunyo; Hashimoto, Tetsuya; Ohta, Kouji; Nakanishi, Kouichiro; Tamura, Yoichi; Kohno, Kotaro
Publication:		eprint arXiv:1201.4947
Publication Date:		01/2012
Origin:		ARXIV
Keywords:		Astrophysics - Cosmology and Extragalactic Astrophysics
Comment:		4 pages, 1 figure, Accepted for publication in Astrophysical Journal
Bibliographic Code:		2012arXiv1201.4947H

Abstract

We present the results of the 16-cm-waveband continuum observations of four host galaxies of gamma-ray bursts (GRBs) 990705, 021211, 041006, and 051022 using the Australia Telescope Compact Array. Radio emission was not detected in any of the host galaxies. The 2sigma upper limits on star-formation rates derived from the radio observations of the host galaxies are 23, 45, 27, and 26 Msun/yr, respectively, which are less than about 10 times those derived from UV/optical observations, suggesting that they have no significant dust-obscured star formation. GRBs 021211 and 051022 are known as the so-called "dark GRBs" and our results imply that dark GRBs do not always occur in galaxies enshrouded by dust. Because large dust extinction was not observed in the afterglow of GRB021211, our result {\bf suggests the possibility} that the cause of the dark GRB is the intrinsic faintness of the optical afterglow. On the other hand, by considering the high column density observed in the afterglow of GRB051022, the likely cause of the dark GRB is the dust extinction in the line of sight of the GRB.

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伽马暴作为高能辐射的来源

记得Tsvi他们曾经做过超新星作为超高能辐射的来源的，它们只能来自于银河系，或者较近的其它星系。但是为什么不能是伽马暴呢？

不过很可能不行，不然他们更自然地应该认为是伽马暴而不是超新星。（可能是爆发率的问题，银河系一百万年才有一次伽马暴，而超新星的频率更高。）

Wellons, Sarah 2012 三个Ibc型超新星的射电观测，来揭示周围的环境

主要内容:
可能是有反常的密度跳变。

精彩摘抄:

三个彩色的都有跳变。

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Title:		Radio Observations Reveal Unusual Circumstellar Environments for Some Type Ibc Supernova Progenitors
Authors:		Wellons, Sarah; Soderberg, Alicia M.; Chevalier, Roger A.
Publication:		eprint arXiv:1201.5120
Publication Date:		01/2012
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		23 pages, 8 figures, 5 tables, submitted to ApJ
Bibliographic Code:		2012arXiv1201.5120W

Abstract

We present extensive radio observations of the nearby Type Ibc supernovae 2004cc, 2004dk, and 2004gq spanning 8-1900 days after explosion. Using a dynamical model developed for synchrotron emission from a slightly decelerated shockwave, we estimate the velocity and energy of the fastest ejecta and the density profile of the circumstellar medium. The shockwaves of all three supernovae are characterized by non-relativistic velocities of v ~ (0.1-25)c and associated energies of E ~ (2-10) * 1e47 erg, in line with the expectations for a typical homologous explosion. Smooth circumstellar density profiles are indicated by the early radio data and we estimate the progenitor mass loss rates to be ~ (0.6-13) * 1e-5 M_sun/yr (wind velocity 10^3 km/s). These estimates approach the saturation limit (~1e-4 M_sun/yr) for line-driven winds from Wolf-Rayet stars, the favored progenitors of SNe Ibc including those associated with long-duration GRBs. Intriguingly, at later epochs all three supernovae show evidence for abrupt radio variability that we attribute to large density modulations (factor of ~3-6) at circumstellar radii of r ~ (1-50) * 1e16 cm. If due to variable mass loss, these modulations are associated with progenitor activity on a timescale of ~ 10-100 years before explosion. We consider these results in the context of variable mass loss mechanisms including wind clumping, metallicity-independent continuum-driven ejections, and binary-induced modulations. It may also be possible that the SN shockwaves are dynamically interacting with wind termination shocks, however, this requires the environment to be highly pressurized and/or the progenitor to be rapidly rotating prior to explosion. The proximity of the density modulations to the explosion sites may suggest a synchronization between unusual progenitor mass loss and the SN explosion, reminiscent of Type IIn supernovae. [ABRIDGED]

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Sagi, Eran 2012 伽马暴余辉中的粒子应该是快速加速的

主要内容:
通过GRB 060729的晚期快速的衰减来限制粒子加速的机制。

精彩摘抄:


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Title:		On particle acceleration rate in GRB afterglows
Authors:		Sagi, Eran; Nakar, Ehud
Publication:		eprint arXiv:1201.5124
Publication Date:		01/2012
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		ApJ in press
Bibliographic Code:		2012arXiv1201.5124S

Abstract

It is well known that collisionless shocks are major sites of particle acceleration in the Universe, but the details of the acceleration process are still not well understood. The particle acceleration rate, which can shed light on the acceleration process, is rarely measured in astrophysical environments. Here we use observations of gamma-ray burst afterglows, which are weakly magnetized relativistic collisionless shocks in ion-electron plasma, to constrain the rate of particle acceleration in such shocks. We find, based on X-ray and GeV afterglows, an acceleration rate that is most likely very fast, approaching the Bohm limit, when the shock Lorentz factor is in the range of 10-100. In that case X-ray observations may be consistent with no amplification of the magnetic field in the shock upstream region. We examine the X-ray afterglow of GRB 060729, which is observed for 642 days showing a sharp decay in the flux starting about 400 days after the burst, when the shock Lorentz factor is about 5. We find that inability to accelerate X-ray emitting electrons at late time provides a natural explanation for the sharp decay, and that also in that case acceleration must be rather fast, and cannot be more than a 100 times slower than the Bohm limit. We conclude that particle acceleration is most likely fast in GRB afterglows, at least as long as the blast wave is ultra-relativistic.

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Tanvir, N. R. 2012 用高红移伽马暴探测早期宇宙的恒星形成率

主要内容:
通过仔细看高红移暴的宿主星系，给出星系的极限光度，从而推测出早期宇宙的恒星形成率的上限。

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Title:		Star formation in the early universe: beyond the tip of the iceberg
Authors:		Tanvir, N. R.; Levan, A. J.; Fruchter, A. S.; Fynbo, J. P. U.; Hjorth, J.; Wiersema, K.; Bremer, M. N.; Rhoads, J.; Jakobsson, P.;O'Brien, P. T.; Stanway, E. R.; Bersier, D.; Natarajan, P.; Greiner, J.; Watson, D.; Castro-Tirado, A. J.; Wijers, R. A. M. J.;Starling, R. L. C.; Misra, K.; Graham, J. F.
Publication:		eprint arXiv:1201.6074
Publication Date:		01/2012
Origin:		ARXIV
Keywords:		Astrophysics - Cosmology and Extragalactic Astrophysics
Comment:		Submitted to ApJ. 13 pages, 6 figures
Bibliographic Code:		2012arXiv1201.6074T

Abstract

We present late-time Hubble Space Telescope imaging of the fields of six Swift GRBs lying at 5.0<z<9.5. Our data includes very deep observations of the field of the most distant spectroscopically confirmed burst, GRB 090423, at z=8.2. Using the precise positions afforded by their afterglows we can place stringent limits on the luminosities of their host galaxies. In one case, that of GRB 060522 at z=5.11, there is a marginal excess of flux close to the GRB position which may be a detection of a host at a magnitude J(AB)=28.5. None of the others are significantly detected meaning that all the hosts lie below L\star at their respective redshifts, with star formation rates SFR<4Mo/yr in all cases. Indeed, stacking the five fields with WFC3-IR data we conclude a mean SFR<0.17Mo/yr per galaxy. These results support the proposition that the bulk of star formation, and hence integrated UV luminosity, at high redshifts arises in galaxies below the detection limits of deep-field observations. Making the reasonable assumption that GRB rate is proportional to UV luminosity at early times allows us to compare our limits with expectations based on galaxy luminosity functions derived from the Hubble Ultra-Deep Field (HUDF) and other deep fields. We infer that a luminosity function which is evolving rapidly towards steeper faint-end slope (alpha) and decreasing characteristic luminosity (L\star), as suggested by some other studies, is consistent with our observations, whereas a non-evolving LF shape is ruled out at >90% confidence. Although it is not yet possible to make stronger statements, in the future, with larger samples and a fuller understanding of the conditions required for GRB production, studies like this hold great potential for probing the nature of star formation, the shape of the galaxy luminosity function, and the supply of ionizing photons in the early universe.

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