Collaboration 2007 Very high energy emission observations by Milagro

主要内容:
Over 100 GRBs are known to have been in the field of view of Milagro since January 2000, but seems no dections of very high energy emissions.

精彩摘抄:
The Milagro gamma-ray observatory is a wide field of view (2 sr) instrument employing a water Cherenkov detector to continuously ($>$ 90% duty cycle) observe the overhead sky in the 100 GeV to 100 TeV energy range.

文章信息:
A Search for Prompt Very High Energy Emission from Satellite-detected Gamma-ray Bursts using Milagro

Authors: Milagro Collaboration: P. M. Saz Parkinson, B. L. Dingus

(Submitted on 11 Oct 2007)

Abstract: Gamma-ray bursts (GRBs) have been detected up to GeV energies and are predicted by many models to emit in the very high energy (VHE, > 100 GeV) regime too. Detection of such emission would allow us to constrain GRB models. Since its launch, in late 2004, the Swift satellite has been locating GRBs at a rate of approximately 100 per year. The rapid localization and follow-up in many wavelengths has revealed new and unexpected phenomena, such as delayed emission in the form of bright X-ray flares. The Milagro gamma-ray observatory is a wide field of view (2 sr) instrument employing a water Cherenkov detector to continuously ($>$ 90% duty cycle) observe the overhead sky in the 100 GeV to 100 TeV energy range. Over 100 GRBs are known to have been in the field of view of Milagro since January 2000, including 57 since the launch of Swift (through May 2007). We discuss the results of the searches for prompt emission from these bursts, as well as for delayed emission from the X-ray flares observed in some of the Swift bursts.

Comments:	4 pages, Proceedings of the 30th ICRC, Merida, Mexico, 3-11 July 2007
Subjects:	Astrophysics (astro-ph)
Cite as:	arXiv:0710.2350v1 [astro-ph]

Massaro 2007 $E_{iso}$ vs $E_p$ relation is not reliable

主要内容:


精彩摘抄:
Astrophysical consequences from $E_{iso}$ vs $E_p$ relation are then to be revised after a more accurate and possibly bias free analysis.

文章信息:
Functional biases in GRB's spectral parameter correlations

Authors: F. Massaro, S. Cutini, M. L. Conciatore, A. Tramacere

(Submitted on 11 Oct 2007)

Abstract: Gamma Ray Bursts (GRBs) show evidence of different spectral shapes, light curves, duration, host galaxies and they explode within a wide redshift range. However, the most of them seems to follow very tight correlations among some observed quantities relating to their energetic. If true, these correlations have significant implications on burst physics, giving constraints on theoretical models. Moreover, several suggestions have been made to use these correlations in order to calibrate GRBs as standard candles and to constrain the cosmological parameters. We investigate the cosmological relation between low energy $\alpha$ index in GRBs prompt spectra and the redshift $z$. We present a statistical analysis of the relation between the total isotropic energy $E_{iso}$ and the peak energy $E_p$ (also known as Amati relation) in GRBs spectra searching for possible functional biases. Possible implications on the $E_{iso}$ vs $E_p$ relation of the $\alpha$ vs $(1+z)$ correlation are evaluated. We used MonteCarlo simulations and the boostrap method to evaluate how large are the effects of functional biases on the $E_{iso}$ vs $E_p$. We show that high values of the linear correlation coefficent, up to about 0.8, in the $E_{iso}$ vs $E_p$ relation are obtained for random generated samples of GRBs, confirming the relevance of functional biases. Astrophysical consequences from $E_{iso}$ vs $E_p$ relation are then to be revised after a more accurate and possibly bias free analysis.

Comments:	6 pages, 6 figures, conference poster session: "070228: The Next Decade of Gamma-Ray Burst Afterglows", Amsterdam, March 2007, MNRAS submitted
Subjects:	Astrophysics (astro-ph)
Cite as:	arXiv:0710.2226v1 [astro-ph]

Amati 2007 Unveiling the hard X-ray afterglow by Simbol-X

主要内容:
Simbol-X to observe the 10-80keV X-ray afterglow. Will launched earliest in 2010.

精彩摘抄:


文章信息:
Unveiling GRB hard X-ray afterglow emission with Simbol-X

Authors: L. Amati, E. Maiorano, E. Palazzi, R. Landi, F. Frontera, N. Masetti, L. Nicastro

(Submitted on 5 Oct 2007)

Abstract: Despite the enormous progress occurred in the last 10 years, the Gamma-Ray Bursts (GRB) phenomenon is still far to be fully understood. One of the most important open issues that have still to be settled is the afterglow emission above 10 keV, which is almost completely unexplored. This is due to the lack of sensitive enough detectors operating in this energy band. The only detection, by the BeppoSAX/PDS instrument (15-200 keV), of hard X-ray emission from a GRB (the very bright GRB 990123), combined with optical and radio observations, seriously challenged the standard scenario in which the dominant mechanism is synchrotron radiation produced in the shock of a ultra-relativistic fireball with the ISM, showing the need of a substantial revision of present models. In this respect, thanks to its unprecedented sensitivity in the 10-80 keV energy band, Simbol-X, through follow-up observations of bright GRBs detected and localized by GRB dedicated experiments that will fly in the >2010 time frame, will provide an important breakthrough in the GRB field.

Comments:	4 pages, 2 figures. Paper presented at "Simbol-X: the hard X-ray universe in focus", held in Bologna, Italy, on 14-16 May 2007. To be published in Memorie della Societa' Astronomica Italiana
Subjects:	Astrophysics (astro-ph)
Cite as:	arXiv:0710.1327v1 [astro-ph]

Bucciantini 2007 Magnetar driven bubble for GRB jets

主要内容:
Their model magnetar driven bubble can not only produce jet in GRB, but also asymmetric explosion in supernovae, X-ray flashes.

精彩摘抄:


文章信息:
Magnetar Driven Bubbles and the Origin of Collimated Outflows from GRBs

Authors: N. Bucciantini (1), E. Quataert (1), J. Arons (1), B.D. Metzger (1), Todd A. Thompson (2) ((1)Astronomy Department, UC Berkeley, (2)Department of Astrophysical Sciences, Princeton)

(Submitted on 5 Oct 2007)

Abstract: We model the interaction between the wind from a newly formed rapidly rotating magnetar and the surrounding progenitor. In the first few seconds after core collapse the magnetar inflates a bubble of plasma and magnetic fields behind the supernova shock, which expands asymmetrically because of the pinching effect of the toroidal magnetic field, as in PWNe, even if the host star is spherically symmetric. The degree of asymmetry depends on the ratio of the magnetic energy to the total energy in the bubble. We assume that the wind by newly formed magnetars inflating these bubbles is more magnetized than for PWNe. We show that for a magnetic to total power supplied by the central magnetar $\sim 0.1$ the bubble expands relatively spherically while for values greater than 0.3, most of the pressure in the bubble is exerted close to the rotation axis, driving a collimated outflow out through the host star. This can account for the collimation inferred from observations of long-duration gamma-ray bursts (GRBs). Given that the wind magnetization increases in time, we thus suggest that the magnetar-driven bubble initially expands relatively spherically (enhancing the energy of the associated supernova) while at late times it becomes progressivelymore collimated (producing the GRB). Similar processes may operate in more modestly rotating neutron stars to produce asymmetric supernovae and lower energy transients such as X-ray flashes.

Gallerani 2007 Testing Reionization with spectra

主要内容:


精彩摘抄:


文章信息:
Testing Reionization with Gamma Ray Burst Absorption Spectra

Authors: S. Gallerani, R. Salvaterra, A. Ferrara, T. Roy Choudhury

(Submitted on 5 Oct 2007)

Abstract: We propose a novel method to study cosmic reionization using absorption line spectra of high-redshift Gamma Ray Burst (GRB) afterglows. We show that the time evolution and the statistics of the dark portions (gaps) in the observed spectra taken during the first days after the GRB explosion represent exquisite tools to discriminate among different reionization models. We then compute the probability to find the largest gap in a given width range for burst afterglows of observed J-band flux F_J, and redshift z_GRB. We show that different reionization scenarios populate the (F_J,z_GRB) plane in a very different way, allowing to distinguish among different reionization histories. We provide here useful plots that allow a very simple and direct comparison between observations and model results. Finally, we apply our methods to GRB050904 detected at z=6.29 whose largest gap is found to be almost equal to 65 angstrom. We show that the observation of this burst provides strong indications of a highly ionized intergalactic medium at z=6, with an estimated mean neutral hydrogen fraction x_HI=7.0 \pm 4.0 10^-4 along the line of sight towards GRB050904.

Comments:	5 pages, 3 figures, submitted to MNRAS
Subjects:	Astrophysics (astro-ph)
Cite as:	arXiv:0710.1303v1 [astro-ph]

Galli 2007 内激波的逆康普顿高能辐射的探测限度

主要内容:
文中计算了内激波包括暴本身和X射线耀的逆康普顿散射的高能辐射谱，看在将上天的AGILE和GLAST的探测情况。高的洛仑兹因子和时间variability会有更高的高能辐射。

精彩摘抄:


文章信息:
Gamma-Ray Burst high energy emission from Internal Shocks

Authors: A. Galli (1,2,3), D. Guetta (4) ((1) IASF-Roma/INAF, (2) Univerisita' di Roma "La Sapienza", (3) INFN-Trieste, (4) OAR/INAF)

(Submitted on 28 Sep 2007)

Abstract: In this paper we study synchrotron and Self Compton (SSC) emission from internal shocks (IS) during the prompt and X-ray flare phases of Gamma-Ray Bursts (GRBs). The aim is to test the IS model for the flare emission and if GRBs can be GeV sources. We determine the parameters for which the IS model can account for the observed prompt and X-ray flares emission, and study the detectability of the high energy SSC emission by the AGILE and GLAST satellites. We find that the detectability of the SSC emission during the prompt phase of GRBs improves for higher values of the fireball Lorentz factor and of the temporal variability. If IS is the mechanism responsible of the flare emission, the flares light curves must present some substructures with temporal variability of 100 ms much smaller than the average duration of flares, and similar to those observed during the prompt phase of GRBs. An investigation on the substructures of the X-ray flares light curves will allow to corroborate the hypothesis that late IS are responsible of the X-ray flares. We find that higher values of Lorentz factor and variability time favor the detection by AGILE and GLAST of the X-ray flare high energy counterpart.

Comments:	9 pages, 11 figures, submitted to Astronomy & Astrophysics
Subjects:	Astrophysics (astro-ph)
Cite as:	arXiv:0709.4568v1 [astro-ph]

ChapmanChapman 2007 短暴两个来源更符合观测

主要内容:
考虑到SGR如果放到河外星系，可能被当做短暴。如果考虑短暴来自SGR或者NS-NS并合，与观测到的形成率更符合：短暴的诞生率=NS-NS形成率(理论)+SGR形成率（银河系外推）。

精彩摘抄:


文章信息:
Two populations are better than one: Short gamma-ray bursts from SGR giant flares and NS-NS mergers

Authors: Robert Chapman (1), Robert S. Priddey (1), Nial R. Tanvir (2) ((1) University of Hertfordshire, UK. (2) University of Leicester, UK.)

(Submitted on 28 Sep 2007)

Abstract: With a peak luminosity of ~10^47 erg/s, the December 27th 2004 giant flare from SGR1806-20 would have been visible by BATSE (the Burst and Transient Source Experiment) out to ~50 Mpc. It is thus plausible that some fraction of the short duration Gamma-Ray Bursts (sGRBs) in the BATSE catalogue were due to extragalactic magnetar giant flares. According to the most widely accepted current models, the remaining BATSE sGRBs were most likely produced by compact object (neutron star-neutron star or neutron star-black hole) mergers with intrinsically higher luminosities. Previously, by examining correlations on the sky between BATSE sGRBs and galaxies within 155 Mpc, we placed limits on the proportion of nearby sGRBs. Here, we examine the redshift distribution of sGRBs produced by assuming both one and two populations of progenitor with separate Luminosity Functions (LFs). Using the local Galactic SGR giant flare rate and theoretical NS-NS merger rates evolved according to well-known Star Formation Rate parameterisations, we constrain the predicted distributions by BATSE sGRB overall number counts. We show that only a dual population consisting of both SGR giant flares and NS-NS mergers can reproduce the likely local distribution of sGRBs as well as the overall number counts. In addition, the best fit LF parameters of both sub-populations are in good agreement with observed luminosities.

Comments:	3 pages, 7 figures. To be included in the proceedings of "40 Years of Pulsars" held at McGill University, Montreal, 2007. Proceedings to be published by American Institute of Physics
Subjects:	Astrophysics (astro-ph)
Cite as:	arXiv:0709.4640v1 [astro-ph]

Grebenev 2007 INTEGRAL 对 GRB 060428C的观测

主要内容:
此暴没有被INTEGRAL Burst Alert System (IBAS)发现，而是被IBIS/ISGRI and SPI telescopes看到，所以当时并没有触发其他望远镜跟进观测，而是从档案里找到的一个暴。这个暴duration 12秒，E_p 95keV。有prompt阶段和早期余辉阶段的数据。

精彩摘抄:


文章信息:
Cosmic gamma-ray burst 060428C detected in the fields of view of the IBIS and SPI telescopes of the INTEGRAL observatory and its early afterglow

Authors: S. A. Grebenev, I. V. Chelovekov (Space Research Institute, Moscow)

(Submitted on 2 Oct 2007)

Abstract: Analyzing archival data of the INTEGRAL observatory we discovered and localized a cosmic gamma-ray burst detected within fields of view of the IBIS/ISGRI and SPI telescopes on April 28, 2006. The burst has not been revealed by the INTEGRAL Burst Alert System (IBAS), so the information on its coordinates has not been distributed in time and search for the afterglow has not been carried out. The burst has been also detected by the KONUS/WIND and RHESSI spacecrafts. Its fluence was 2.3x10^{-6} erg/cm^2 in the 20-200 keV energy band, the maximum flux was 3.6x10^{-7} erg/cm^2/s (3.9 phot/cm^2/s). The burst had a complicated multi-peak profile and was outstanding of the typical bursts by increasing its spectral hardness with time. The emission spectrum near the flux maximum was characterized by the photon index alpha ~ -1.5 and the peak energy Ep ~ 95 keV. The burst lasted ~12 s, then we observed its afterglow at energies 15-45 keV decaying according to a power law with the index ~ -4.5. The spectral hardness decreased substantially during the afterglow.

Comments:	13 pages, 7 figures
Subjects:	Astrophysics (astro-ph)
Cite as:	arXiv:0710.0598v1 [astro-ph]

Covino 2007 GRB060418 and GRB060607A余辉的开始时间

主要内容:
余辉的开始时间影响对初始洛仑兹\gamma_0的估计。这两个暴的\Gamma_0约为400

精彩摘抄:


文章信息:
The afterglow onset for GRB060418 and GRB060607A

Authors: S. Covino, S.D. Vergani,et.al

(Submitted on 3 Oct 2007)

Abstract: Gamma-ray burst are thought to be produced by highly relativistic outflows. Although upper and lower limits for the outflow initial Lorentz factor $\Gamma_0$ are available, observational efforts to derive a direct determination of $\Gamma_0$ have so far failed or provided ambiguous results. As a matter of fact, the shape of the early-time afterglow light curve is strongly sensitive on $\Gamma_0$ which determines the time of the afterglow peak, i.e. when the outflow and the shocked circumburst material share a comparable amount of energy. We now comment early-time observations of the near-infrared afterglows of GRB 060418 and GRB 060607A performed by the REM robotic telescope. For both events, the afterglow peak was singled out and allowed us to determine the initial fireball Lorentz, $\Gamma_0\sim 400$.

Comments:	This contribution is part of the proceedings of the Frascati Workshop 2007, edited by F. Giovannelli and L. Sabau-Graziati, published in a special volume of the Chinese Journal of Astronomy and Astrophysics (ChJAA)
Subjects:	Astrophysics (astro-ph)
Cite as:	arXiv:0710.0727v1 [astro-ph]

McQuinn 2007 用伽玛暴探测再电离时期的IGM

主要内容:
不过要把IGM的吸收和DLA（damped laymann-alfa absorber）区分开来。

精彩摘抄:


文章信息:

arXiv:0710.1018 [ps, pdf, other]

Title: Probing the Neutral Fraction of the IGM with GRBs during the Epoch of Reionization

Authors: Matthew McQuinn, Adam Lidz, Matias Zaldarriaga, Lars Hernquist, Suvendra Dutta

Comments: 10 pages, 8 figures, submitted to MNRAS

Subjects: Astrophysics (astro-ph)

We show that near-infrared observations of the red side of the Ly-alpha line from a single gamma ray burst (GRB) afterglow cannot be used to constrain the global neutral fraction of the intergalactic medium (IGM), x_H, at the GRB's redshift to better than ~0.3, because some GRB sight-lines will encounter more neutral hydrogen than others owing to the patchiness of reionization. Consequently, GRBs during the epoch of reionization will often bear no discernible signature of a neutral IGM in their afterglow spectra. We discuss the constraints on x_H from the z = 6.3 burst, GRB050904, and quantify the probability of detecting a neutral IGM using future spectroscopic observations of high-redshift, near-infrared GRB afterglows. Assuming an observation with signal-to-noise similar to the Subaru FOCAS spectrum of GRB050904, that the column density distribution of damped Ly-alpha absorbers is the same as measured at lower redshifts, and that the redshift of the GRB is known, a GRB from an epoch when x_H = 0.5 can be used to detect a partly neutral IGM at 98% confidence level 5 - 10% of the time (and, for an observation with three times the sensitivity, 25-30% of the time).