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.

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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

主要内容:


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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;">

精彩摘抄:


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

主要内容:


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.

精彩摘抄:


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]