Wang 2007 Amati relation and the host galaxy lumonosity

主要内容:
According to B-band luminosity of the host galaxies, Amati relation can be devided into two sub-groups.

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文章信息:
Does Amati Relation Depend on Luminosity of GRB's Host Galaxies?

Authors: Jing Wang, Jing-song Deng, Yu-lei Qiu

(Submitted on 28 Oct 2007)

Abstract: In order to test systematic of the Amati relation, the 24 long-duration GRBs with firmly determined $E_{\gamma,\mathrm{iso}}$ and $E_{\mathrm p}$ are separated into two sub-groups according to B-band luminosity of their host galaxies. The Amati relations in the two subgroups are found to be in agreement with each other within uncertainties. Taking into account of the well established luminosity - metallicity relation of galaxies, no strong evolution of the Amati relation with GRB's environment metallicity is implied in this study.

Comments:	7 pages, 3 figures and 1 table, accepted by ChJAA
Subjects:	Astrophysics (astro-ph)
Cite as:	arXiv:0710.5302v1 [astro-ph]

Curran 2007 X-ray breaks may be hidden in the light curves

主要内容:
By fitting with single power law and breaked power law, the later is good either. So, the broken power law in Swift era may be just hidden in the smooth light curves.

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文章信息:
Are the missing X-ray breaks in Gamma-ray Burst afterglow light curves merely hidden?

Authors: P.A. Curran (1), A.J. van der Horst (1,2), R.A.M.J. Wijers (1) ((1) University of Amsterdam, The Netherlands, (2)University of Alabama, Huntsville, USA)

(Submitted on 28 Oct 2007)

Abstract: Gamma-ray burst afterglow observations in the Swift era have a perceived lack of achromatic jet breaks compared to the BeppoSAX, or pre-Swift era. Specifically, relatively few breaks, consistent with jet breaks, are observed in the X-ray light curves of these bursts. If these breaks are truly missing, it has serious consequences for the interpretation of GRB jet collimation and energy requirements, and the use of GRBs as cosmological tools. Here we address the issue of X-ray breaks that are possibly `hidden' and hence the light curves are misinterpreted as being single power laws. We do so by synthesising XRT light curves and fitting both single and broken power laws, and comparing the relative goodness of each fit via Monte Carlo analysis. Even with the well sampled light curves of the Swift era, these breaks may be left misidentified, hence caution is required when making definite statements on the absence of achromatic breaks.

Comments:	6 pages including 3 figures, submitted to MNRAS
Subjects:	Astrophysics (astro-ph)
Cite as:	arXiv:0710.5285v1 [astro-ph]

Band 2007 EXIST on GRB sensitivity

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文章信息:
EXIST's Gamma-Ray Burst Sensitivity

Authors: D. L. Band, J. E. Grindlay, J. Hong, G. Fishman, D. H. Hartmann, A. Garson III, H. Krawczynski, S. Barthelmy, N. Gehrels, G. Skinner

(Submitted on 25 Oct 2007)

Abstract: We use semi-analytic techniques to evaluate the burst sensitivity of designs for the EXIST hard X-ray survey mission. Applying these techniques to the mission design proposed for the Beyond Einstein program, we find that with its very large field-of-view and faint gamma-ray burst detection threshold, EXIST will detect and localize approximately two bursts per day, a large fraction of which may be at high redshift. We estimate that EXIST's maximum sensitivity will be ~4 times greater than that of Swift's Burst Alert Telescope. Bursts will be localized to better than 40 arcsec at threshold, with a burst position as good as a few arcsec for strong bursts. EXIST's combination of three different detector systems will provide spectra from 3 keV to more than 10 MeV. Thus, EXIST will enable a major leap in the understanding of bursts, their evolution, environment, and utility as cosmological probes.

Comments:	25 pages, 10 figures, accepted by ApJ
Subjects:	Astrophysics (astro-ph)
Cite as:	arXiv:0710.4602v1 [astro-ph]

Bellm 2007 GRB 070125 prompt observations

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文章信息:
Observations of the Prompt Gamma-Ray Emission of GRB 070125

Authors: Eric C. Bellm, Kevin Hurley, Valentin Pal'shin, Kazutaka Yamaoka, Mark E. Bandstra, Steven E. Boggs, Soojing Hong, Natsuki Kodaka, A. S. Kozyrev, M. L. Litvak, I. G. Mitrofanov, Yujin E. Nakagawa, Masanori Ohno, Kaori Onda, A. B. Sanin, Satoshi Sugita, Makoto Tashiro, V. I. Tretyakov, Yuji Urata, Claudia Wigger

(Submitted on 24 Oct 2007)

Abstract: The long, bright gamma-ray burst GRB 070125 was localized by the Interplanetary Network. We present light curves of the prompt gamma-ray emission as observed by Konus-WIND, RHESSI, Suzaku-WAM, and Swift-BAT. We detail the results of joint spectral fits with Konus and RHESSI data. The burst shows moderate hard-to-soft evolution in its multi-peaked emission over a period of about one minute. The total burst fluence as observed by Konus is $1.75 \times 10^{-4}$ erg/cm$^2$ (20 keV-10 MeV). Using the spectroscopic redshift z = 1.547, we find that the burst is consistent with the Amati $E_{peak,i}-E_{iso}$ and the Ghirlanda $E_{peak,i}-E_\gamma$ correlations.

Subjects:	Astrophysics (astro-ph)
Cite as:	arXiv:0710.4590v1 [astro-ph]

Cen 2007 GRB biased trace star formation

主要内容:
GRB history doesn't agree with that of Star formation in well.

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文章信息:
Gamma-Ray Bursts May Be Biased Tracers of Star Formation

Authors: Renyue Cen (Princeton), Taotao Fang (UCI)

(Submitted on 24 Oct 2007)

Abstract: Based on a simulation of galaxy formation in the standard cosmological model, we suggest that a consistent picture for Gamma-Ray Bursts and star formation may be found that is in broad agreement with observations: GRBs preferentially form in low metallicity environments and in galaxies substantially less luminous that L*. We find that the computed formation rate of stars with metallicity less than 0.1Zsun agrees remarkably well with the rate evolution of Gamma-Ray Bursts observed by Swift from z=0 to z=4, whereas the evolution of total star formation rate is weaker by a factor of about 4. Given this finding, we caution that any inference of star formation rate based on observed GRB rate may require a more involved exercise than a simple proportionality.

Comments:	submitted to ApJL, 4 pages
Subjects:	Astrophysics (astro-ph)
Cite as:	arXiv:0710.4370v1 [astro-ph]

Salvaterra 2007 instructions on design future instruments on high-z GRBs

主要内容:
requires soft band detectors with a high sensitivity and moderately large FOV.

精彩摘抄:


文章信息:
Gamma Ray Bursts from the early Universe: predictions for present-day and future instruments

Authors: R. Salvaterra, S. Campana, G. Chincarini, S. Covino, G. Tagliaferri

(Submitted on 23 Oct 2007)

Abstract: Long Gamma Ray Bursts (GRBs) constitute an important tool to study the Universe near and beyond the epoch of reionization. We delineate here the characteristics of an 'ideal' instrument for the search of GRBs at z>6-10. We find that the detection of these objects requires soft band detectors with a high sensitivity and moderately large FOV. In the light of these results, we compare available and planned GRB missions, deriving conservative predictions on the number of high-z GRBs detectable by these instruments along with the maximum accessible redshift. We show that the Swift satellite will be able to detect various GRBs at z>6, and likely at z>10 if the trigger threshold is decreased by a factor of ~2. Furthermore, we find that INTEGRAL and GLAST are not the best tool to detect bursts at z>6: the former being limited by the small FOV, and the latter by its hard energy band and relatively low sensitivity. Finally, future missions (SVOM, EDGE, but in particular EXIST) will provide a good sample of GRBs at z>6 in a few years of operation.

Comments:	6 pages, 2 figures, MNRAS in press
Subjects:	Astrophysics (astro-ph)
Cite as:	arXiv:0710.4280v1 [astro-ph]

Jarvis 2007 STACEE observations on GRB high energy

主要内容:
The Solar Tower Atmospheric Cherenkov Effect Experiment (STACEE) , gave upper limits on the high energy emissions of GRB during 2003-2007

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文章信息:
Gamma-Ray Burst Follow-up Observations with STACEE During 2003-2007

Authors: STACEE Collaboration: A. Jarvis, J. Ball, J. E. Carson, C. E. Covault, D. D. Driscoll, P. Fortin, D. M. Gingrich, D. S. Hanna, J. Kildea, T. Lindner, R. Mukherjee, C. Mueller, R. A. Ong, K. Ragan, D. A. Williams, J. Zweerink

(Submitted on 22 Oct 2007)

Abstract: The Solar Tower Atmospheric Cherenkov Effect Experiment (STACEE) is an atmospheric Cherenkov telescope (ACT) that uses a large mirror array to achieve a relatively low energy threshold. For sources with Crab-like spectra, at high elevations, the detector response peaks near 100 GeV. Gamma-ray burst (GRB) observations have been a high priority for the STACEE collaboration since the inception of the experiment. We present the results of 20 GRB follow-up observations at times ranging from 3 minutes to 15 hours after the burst triggers. Where redshift measurements are available, we place constraints on the intrinsic high-energy spectra of the bursts.

Comments:	4 pages, 1 table, 2 figures, presented at the 30th International Cosmic Ray Conference, Merida, Mexico, 2007
Subjects:	Astrophysics (astro-ph)
Cite as:	arXiv:0710.4149v1 [astro-ph]

Lugones 2007 Quark matter conversion as origin of giant flare of SGRs

主要内容:
Fall back disc offer the meterial for NS to transit some into quark matter.

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文章信息:
A model for giant flares in soft gamma repeaters

Authors: G. Lugones, E. M. de Gouveia Dal Pino, J. E. Horvath

(Submitted on 22 Oct 2007)

Abstract: We argue that giant flares in SGRs can be associated to the core conversion of an isolated neutron star having a subcritical magnetic field $\sim 10^{12}$ G and a fallback disk around it. We show that, in a timescale of $\lesssim 10^5$ yrs, accretion from the fallback disk can increase the mass of the central object up to the critical mass for the conversion of the core of the star into quark matter. A small fraction of the neutrino-antineutrino emission from the just-converted quark-matter hot core annihilates into $e^+e^-$ pairs above the neutron star surface originating the gamma emission of the spike while the further cooling of the heated neutron star envelope originates the tail of the burst. We show that several characteristics of the giant flare of the SGR 1806-20 of 27 December 2004 (spike and tail energies, timescales, and spectra) can be explained by this mechanism.

Comments:	4 pages, submitted to Phys. Rev. Lett
Subjects:	Astrophysics (astro-ph)
Cite as:	arXiv:0710.3984v1 [astro-ph]

Willingale 2007 a new relation E_pw-L_iso

主要内容:
Ewz keV vs. the peak isotropic luminosity seems better than the Amati relation.

Many data contained in the tables, including beta_X, beta_gamma, E_p, F_tot, T_90, etc.

精彩摘抄:
Amati relation

Ewz keV vs. the peak isotropic luminosity, Liso = EwzQpz/TLz ergs s−1.

文章信息:
A universal GRB photon energy-peak luminosity relation

Authors: R. Willingale, P.T. O'Brien, M.R. Goad, J.P. Osborne, K.L. Page, N.R. Tanvir

(Submitted on 19 Oct 2007)

Abstract: The energetics and emission mechanism of GRBs are not well understood. Here we demonstrate that the instantaneous peak flux or equivalent isotropic peak luminosity, L_iso ergs s^-1, rather than the integrated fluence or equivalent isotropic energy, E_iso ergs, underpins the known high-energy correlations. Using new spectral/temporal parameters calculated for 101 bursts with redshifts from BATSE, BeppoSAX, HETE-II and Swift we describe a parameter space which characterises the apparently diverse properties of the prompt emission. We show that a source frame characteristic-photon-energy/peak luminosity ratio, K_z, can be constructed which is constant within a factor of 2 for all bursts whatever their duration, spectrum, luminosity and the instrumentation used to detect them. The new parameterization embodies the Amati relation but indicates that some correlation between E_peak and E_iso follows as a direct mathematical inference from the Band function and that a simple transformation of E_iso to L_iso yields a universal high energy correlation for GRBs. The existence of K_z indicates that the mechanism responsible for the prompt emission from all GRBs is probably predominantly thermal.

Comments:	Submitted to ApJ
Subjects:	Astrophysics (astro-ph)
Cite as:	arXiv:0710.3727v1 [astro-ph]

Li 2007 Probe the cosmic metallicity

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文章信息:
Probing the Cosmic Metallicity Evolution with Gamma-Ray Bursts

Authors: Li-Xin Li

(Submitted on 18 Oct 2007)

Abstract: The current Swift sample of gamma-ray bursts (GRBs) with measured redshifts allows to test the assumption that GRBs trace the star formation in the Universe. Some authors have claimed that the rate of GRBs increases with cosmic redshift faster than the star formation rate, whose cause is not known yet. In this paper, I investigate the possibility for interpreting the observed discrepancy between the GRB rate history and the star formation rate history by the cosmic metallicity evolution, motivated by the observation that the cosmic metallicity evolves strongly with redshift and GRBs prefer to occur in low metallicity galaxies. Adopting a simple model for the relation between the GRB production and the cosmic metallicity history as proposed by Langer & Norman, and a star formation rate determined by Hopkins & Beacom from current observations, I show that the observed redshift distribution of the Swift GRBs can be reproduced with a fairly good accuracy. Although the results are limited by the small size of the GRB sample and the poorly understood selection biases in detection and localization of GRBs and in redshift determination, the results suggest that GRBs trace both the star formation and the metallicity evolution. If the star formation history can be accurately measured with other approaches, which is presumably achievable in the near future, it will be possible to determine the cosmic metallicity evolution with the study on the redshift distribution of GRBs.

Comments:	9 pages, 7 figures, submitted to MNRAS on 16 October 2007. Comments are welcome
Subjects:	Astrophysics (astro-ph)
Cite as:	arXiv:0710.3587v1 [astro-ph]

Salvaterra 2007 bimodal origin of short burst

主要内容:
For lower redshift bursts (z<0.3), style="color: rgb(255, 102, 102); font-weight: bold;">

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文章信息:
Short Gamma Ray Bursts: a bimodal origin?

Authors: R. Salvaterra, A. Cerutti, G. Chincarini, M. Colpi, C. Guidorzi, P. Romano

(Submitted on 16 Oct 2007)

Abstract: Short-hard Gamma Ray Bursts (SGRBs) are currently thought to arise from gravitational wave driven coalescences of double neutron star systems forming either in the field or dynamically in globular clusters. For both channels we fit the peak flux distribution of BATSE SGRBs to derive the local burst formation rate and luminosity function. We then compare the resulting redshift distribution with the Swift data, showing that both formation channels are needed in order to reproduce the observations. Double neutron stars forming in globular clusters are found to dominate the distribution at z<0.3,>

Comments:	5 pages, 2 figures, submitted to MNRAS
Subjects:	Astrophysics (astro-ph)
Cite as:	arXiv:0710.3099v1 [astro-ph]

Esposito 2007 SGR 1806-20 two years observations

主要内容:
Return to the pre-era of the giant flare, and is still active.

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文章信息:
SGR 1806-20 about two years after the giant flare: Suzaku, XMM-Newton and INTEGRAL observations

Authors: P. Esposito, S. Mereghetti, A. Tiengo, S. Zane, R. Turolla, D. Gotz, N. Rea, N. Kawai, M. Ueno, G.L. Israel, L. Stella, M. Feroci

(Submitted on 15 Oct 2007)

Abstract: In December 2004, the soft gamma-ray repeater SGR 1806-20 emitted the most powerful giant flare ever observed. This probably involved a large-scale rearrangement of the magnetosphere leading to observable variations in the properties of its X-ray emission. Here we present the results of the first Suzaku observation of SGR 1806-20, together with almost simultaneous observations with XMM-Newton and INTEGRAL. The source seems to have reached a state characterized by a flux close to the pre-flare level and by a relatively soft spectrum. Despite this, SGR 1806-20 remained quite active also after the giant flare, allowing us to study several short bursts observed by Suzaku in the 1-100 keV range. We discuss the broad-band spectral properties of SGR 1806-20, covering both persistent and bursting emission, in the context of the magnetar model, and consider its recent theoretical developments.

Comments:	Accepted for publication in Astronomy & Astrophysics
Subjects:	Astrophysics (astro-ph)
Cite as:	arXiv:0710.2789v1 [astro-ph]

von Benda-Beckmann 2007 Void statistics

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精彩摘抄:
100 largest voids in 2dF-GRS S3 sample for BJ < −20.

文章信息: Void Statistics and Void Galaxies in the 2dFGRS

Authors: Alexander M. von Benda-Beckmann, Volker Mueller

(Submitted on 15 Oct 2007)

Abstract: For the 2dFGRS we study the properties of voids and of fainter galaxies within voids that are defined by brighter galaxies. Our results are compared with simulated galaxy catalogues from the Millenium simulation coupled with a semianalytical galaxy formation recipe. We derive the void size distribution and discuss its dependence on the faint magnitude limit of the galaxies defining the voids. While voids among faint galaxies are typically smaller than those among bright galaxies, the ratio of the void sizes to the mean galaxy separation reaches larger values. This is well reproduced in the mock galaxy samples studied. We provide analytic fitting functions for the void size distribution. Furthermore, we study the galaxy population inside voids defined by objects with $B_J -5\log{h}< -20$ and diameter larger than 10 \hMpc. We find a clear bimodality of the void galaxies similar to the average comparison sample. We confirm the enhanced abundance of galaxies in the blue cloud and a depression of the number of red sequence galaxies. There is an indication of a slight blue shift of the blue cloud. Furthermore, we find that galaxies in void centers have higher specific star formation rates as measured by the $\eta$ parameter. We determine the radial distribution of the ratio of early and late type galaxies through the voids. We find and discuss some differences between observations and the Millenium catalogues.

Comments:	12 pages, 13 figures, submitted to MNRAS with comments by referee included. A version with high resolution plots can be downloaded at this http URL
Subjects:	Astrophysics (astro-ph)
Cite as:	arXiv:0710.2783v1 [astro-ph]

Marco 2007 Optical afterglow bimodal distribution

主要内容:
About dark burst. It is significant that the bimodal distribution of the optical afterglows. Casue: intirinsical, or exist a grey extincton.

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文章信息:
Optical afterglows of gamma-ray bursts: a bimodal distribution?"

Authors: Nardini Marco, Ghisellini Gabriele, Ghirlanda Giancarlo

(Submitted on 12 Oct 2007)

Abstract: The luminosities of the optical afterglows of Gamma Ray Bursts, 12 hours (rest frame time) after the trigger, show a surprising clustering, with a minority of events being at a significant smaller luminosity. If real, this dichotomy would be a crucial clue to understand the nature of optically dark afterglows, i.e. bursts that are detected in the X-ray band, but not in the optical. We investigate this issue by studying bursts of the pre-Swift era, both detected and undetected in the optical. The limiting magnitudes of the undetected ones are used to construct the probability that a generic bursts is observed down to a given magnitude limit. Then, by simulating a large number of bursts with pre-assigned characteristics, we can compare the properties of the observed optical luminosity distribution with the simulated one. Our results suggest that the hints of bimodality present in the observed distribution reflects a real bimodality: either the optical luminosity distributions of bursts is intrinsically bimodal, or there exists a population of bursts with a quite significant grey absorption, i.e. wavelength independent extinction. This population of intrinsically weak or grey-absorbed events can be associated to dark bursts.

Comments:	10 pages, 5 figures, accepted for publication in MNRAS
Subjects:	Astrophysics (astro-ph)
Cite as:	arXiv:0710.2436v1 [astro-ph]

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

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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.

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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

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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）。

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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。

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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

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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。

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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).