Lamon 2008 GLAST 和Lorentz violation

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· arXiv e-print (arXiv:0805.1219)

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Title:		GLAST and Lorentz violation
Authors:		Lamon, Raphael
Publication:		eprint arXiv:0805.1219
Publication Date:		05/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		11 pages, 7 figures and 2 tables
Bibliographic Code:		2008arXiv0805.1219L

Abstract

We study possible Lorentz violations by means of gamma-ray bursts (GRB) with special focus on the Large Array Telescope (LAT) of GLAST. We simulate bursts with gtobssim and introduce a Lorentz violating term in the arrival times of the photons. We further perturb these arrival times and energies with a Gaussian distribution corresponding to the time resp. energy resolution of GLAST. We then vary the photon flux in gtobssim in order to derive a relation between the photon number and the standard deviation of the Lorentz violating term. We conclude with the fact that our maximum likelihood method as first developed in [1] is able to make a statement whether Nature breaks the Lorentz symmetry if the number of bursts with known redshifts is of the order of 100.

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Malesani 2008 SN 2008D 的早期谱

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· arXiv e-print (arXiv:0805.1188)

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Title:		Early spectroscopic identification of SN 2008D
Authors:		Malesani, D.; Fynbo, J. P. U.; Hjorth, J.; Leloudas, G.; Sollerman, J.; Stritzinger, M. D.; Vreeswijk, P. M.; Watson, D. J.; Gorosabel, J.; Michałowski, M. J.; Thöne, C. C.; Augusteijn, T.; Bersier, D.; Jakobsson, P.; Jaunsen, A. O.; Ledoux, C.; Levan, A. J.; Milvang-Jensen, B.; Rol, E.; Tanvir, N. R.; Wiersema, K.; Xu, D.; Albert, L.; Bayliss, M.; Gall, C.; Grove, L. F.; Koester, B. P.; Leitet, E.; Pursimo, T.; Skillen, I.
Publication:		eprint arXiv:0805.1188
Publication Date:		05/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		6 pages, 5 figures, 4 tables; submitted to ApJ Letters
Bibliographic Code:		2008arXiv0805.1188M

Abstract

SN 2008D was discovered while following up a luminous, unusual X-ray transient in the nearby spiral galaxy NGC 2770. We present early spectra of the optical counterpart (1.77 days after the X-ray transient) which first allowed to identify the object as a supernova at redshift z = 0.007. These spectra were acquired during the initial declining phase of the light curve, likely due to the shock breakout. They show a relatively flat continuum with broad undulations, and a strong, W-shaped feature with minima at 3980 and 4190 AA (rest frame). We also present extensive spectroscopic and photometric monitoring of the supernova covering the photospheric phase. Unlike supernovae associated with gamma-ray bursts, SN 2008D displayed prominent He features and is therefore of Type Ib.

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Updike 2008 GRB 070125 observations

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· arXiv e-print (arXiv:0805.1094)

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Title:		The Rapidly Flaring Afterglow of the Very Bright and Energetic GRB 070125
Authors:		Updike, Adria C.; Haislip, Joshua B.; Nysewander, Melissa C.; Fruchter, Andrew S.; Kann, D. Alexander; Klose, Sylvio; Milne, Peter A.; Williams, G. Grant; Zheng, Weikang; Hergenrother, Carl W.; Prochaska, Jason X.; Halpern, Jules P.; Mirabal, Nestor; Thorstensen, John R.; van der Horst, Alexander J.; Starling, Rhaana L. C.; Racusin, Judith L.; Burrows, David N.; Kuin, N. P. M.; Roming, Peter W. A.; Bellm, Eric; Hurley, Kevin; Li, Weidong; Filippenko, Alexei V.; Blake, Cullen; Starr, Dan; Falco, Emilio E.; Brown, Warren R.; Dai, Xinyu; Deng, Jinsong; Xin, Liping; Qiu, Yulei; Wei, Jianyan; Urata, Yuji; Nanni, Domenico; Maiorano, Elisabetta; Palazzi, Eliana; Greco, Giuseppe; Bartolini, Corrado; Guarnieri, Adriano; Piccioni, Adalberto; Pizzichini, Graziella; Terra, Federica; Misra, Kuntal; Bhatt, B. C.; Anupama, G. C.; Fan, X.; Jiang, L.; Wijers, Ralph A. M. J.; Reichart, Dan E.; Eid, Hala A.; Bryngelson, Ginger; Puls, Jason; Goldthwaite, R. C.; Hartmann, Dieter H.
Publication:		eprint arXiv:0805.1094
Publication Date:		05/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		50 pages, 9 figures, 5 tables Accepted to the Astrophysical Journal
Bibliographic Code:		2008arXiv0805.1094U

Abstract

We report on multi-wavelength observations, ranging from the X-ray to radio wave bands, of the IPN-localized gamma-ray burst GRB 070125. Spectroscopic observations reveal the presence of absorption lines due to O I, Si II, and C IV, implying a likely redshift of z = 1.547. The well-sampled light curves, in particular from 0.5 to 4 days after the burst, suggest a jet break at 3.7 days, corresponding to a jet opening angle of ~7.0 degrees, and implying an intrinsic GRB energy in the 1 - 10,000 keV band of around E = (6.3 - 6.9)x 10^(51) erg (based on the fluences measured by the gamma-ray detectors of the IPN network). GRB 070125 is among the brightest afterglows observed to date. The spectral energy distribution implies a host extinction of Av <> Bibtex entry for this abstract Preferred format for this abstract

Basilakos 2008 用伽玛暴做标准烛光

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统计了几种标准烛光关系$1:\epkk-E_\gamma$, $2:\epkk-L$, $3:\tlag-L$, $4:V-L$, $5:\trt-L$，结论基本上是否定结果。

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· arXiv e-print (arXiv:0805.0875)

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Title:		Testing GRBs as Standard Candles
Authors:		Basilakos, S.; Perivolaropoulos, L.
Publication:		eprint arXiv:0805.0875
Publication Date:		05/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		10 two-column pages, 3 figures. The mathematica files used in the numerical analysis of the paper may be found at http://leandros.physics.uoi.gr/grb/grb.htm
Bibliographic Code:		2008arXiv0805.0875B

Abstract

Several correlations among Gamma Ray Burst (GRB) observables with available redshifts have been recently identified. Proper evaluation and calibration of these correlations may facilitate the use of GRBs as standard candles constraining the expansion history of the universe up to redshifts of $z>6$. Here we use the 69 GRB dataset recently compiled by Schaefer (astro-ph/0612285) and we test the calibration of five of the above correlations ($1:\epkk-E_\gamma$, $2:\epkk-L$, $3:\tlag-L$, $4:V-L$, $5:\trt-L$) with respect to two potential sources of systematics: Evolution with redshift and cosmological model used in the calibration. In examining the model dependence we assume flat \lcdm and vary $\omm$. Our approach avoids the circularity problem of previous studies since we do not fix $\omm$ to find the correlation parameters. Instead we simultaneously minimize $\chi^2$ with respect to both the log-linear correlation parameters $a$, $b$ and the cosmological parameter $\omm$. We find no statistically significant evidence for redshift dependence of $a$ and $b$ in any of the correlation relations tested. We also find that one of the five correlation relations tested ($\epkk-E_\gamma$) has a significantly lower intrinsic dispersion compared to the other correlations. For this correlation relation, the maximum likelihood method favors the existence of a cosmological constant while the other four correlation favor a flat matter dominated universe $\omm \simeq 1$. Finally, a cross-correlation analysis between the GRBs and SnIa data for various values of $\omm$ has shown that the $E_{peak}-E_\gamma$ relation traces well the SnIa redshift regime. However, even the tightest correlation relation ($E_{peak}-E_\gamma$) provides much weaker constraints on $\omm$ than current SnIa data.

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Berger 2008 短暴的宿主星系

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· arXiv e-print (arXiv:0805.0306)

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Title:		The Host Galaxies of Short-Duration Gamma-Ray Bursts: Luminosities, Metallicities, and Star Formation Rates
Authors:		Berger, E.
Publication:		eprint arXiv:0805.0306
Publication Date:		05/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		Submitted to ApJ
Bibliographic Code:		2008arXiv0805.0306B

Abstract

The association of some short-duration gamma-ray bursts (GRBs) with elliptical galaxies established that their progenitors, unlike those of long GRBs, belong to an old stellar population. However, the majority of short GRBs appear to occur in star forming galaxies, raising the possibility that some progenitors are related to recent star formation activity. Here we present optical spectroscopy of these hosts and measure their luminosities, star formation rates, and metallicities. We find luminosities of L_B~0.1-1.5 L*, star formation rates of SFR~0.2-6 M_sun/yr, and metallicities of 12+log(O/H)~8.5-8.9 (Z~0.6-1.6 Z_sun). A detailed comparison to the hosts of long GRBs reveals systematically higher luminosities, lower specific star formation rates (SFR/L_B) by about an order of magnitude, and higher metallicities by about 0.6 dex. The K-S probability that the short and long GRB hosts are drawn from the same underlying galaxy distribution is only 10^-3. On the other hand, short GRB hosts exhibit excellent agreement with the specific star formation rates and the luminosity-metallicity relation of field galaxies at z~0.1-1. We thus conclude that short GRB hosts are not dominated by young stellar populations like long GRBs hosts. Instead, short GRB hosts appear to be drawn uniformly from the underlying galaxy distribution, indicating that the progenitors have a wide age distribution of several Gyr.

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Amati 2008 Ep,i-Eiso关系用于宇宙学

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Ep,i ~ Eiso^0.5，是两个观测量。

同时文章还包含了从970218到080411的暴的Ep,i，Eiso，和fluence。

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· arXiv e-print (arXiv:0805.0377)

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Title:		Measuring the cosmological parameters with the Ep,i-Eiso correlation of Gamma-Ray Bursts
Authors:		Amati, L.; Guidorzi, C.; Frontera, F.; Della Valle, M.; Finelli, F.; Landi, R.; Montanari, E.
Publication:		eprint arXiv:0805.0377
Publication Date:		05/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		9 pages, 12 figures, submitted to MNRAS
Bibliographic Code:		2008arXiv0805.0377A

Abstract

We have used the Ep,i-Eiso correlation of GRBs to measure the cosmological parameter Omega_M. By adopting a maximum likelihood approach which allows us to correctly quantify the extrinsic (i.e. non--Poissonian) scatter of the correlation, we constrain (for a flat universe) Omega_M to 0.04-0.40 (68% confidence level), with a best fit value of Omega_M ~ 0.15, and exclude Omega_M = 1 at 99.9% confidence level. If we release the assumption of a flat universe, we still find evidence for a low value of \Omega_M (0.04-0.50 at 68% confidence level) and a weak dependence of the dispersion of the Ep,i-Eiso correlation on Omega_Lambda (with an upper limit of Omega_Lambda ~ 1.15 at 90% confidence level). Our approach makes no assumptions on the Ep,i-Eiso correlation and it does not use other calibrators to set the ``zero' point of the relation, therefore our treatment of the data is not affected by circularity and the results are independent of those derived via type Ia SNe (or other cosmological probes). Unlike other multi-parameters correlations, our analysis grounds on only two parameters, then including a larger number (a factor ~3) of GRBs and being less affected by systematics. Simulations based on realistic extrapolations of ongoing (and future) GRB experiments (e.g., Swift, Konus-Wind, GLAST) show that: i) the uncertainties on cosmological parameters can be significantly decreased; ii) future data will allow us to get clues on the ``dark energy'' evolution.

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Barkov 2008 伽玛暴的吸积盘模拟

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· arXiv e-print (arXiv:0805.0414)

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Title:		Hyper-accreting tori of Gamma Ray Bursters
Authors:		Barkov, M. V.
Publication:		eprint arXiv:0805.0414
Publication Date:		05/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		6 pages, 2 figures, conference "Cool discs, hot flows", Funasdalen, Sweden, 2008
Bibliographic Code:		2008arXiv0805.0414B

Abstract

We present numerical simulations of axisymmetric magnetised massive tori around rotating black holes taking into account the energy losses due to emission of neutrinos. A realistic equation of state is used which takes into account the energy losses due to dissociation of nuclei. The heating due to neutrino-antineutrino annihilation is not included. We study the cases of optically thick, semi-transparent, and optically thin to neutrino discs. We show that neutrino cooling does not change significantly the structure of accretion flow and the total energy release. The time scale of accretion is set by the torus angular momentum. Due to the lack of magnetic dynamo in our calculations, it is the initial strength of magnetic field and its topology that determine the process of jet formation and its energetics. Extrapolation of our results gives the total energy released in the jet $\sim 10^{52}$ erg. This is sufficient to explain the hypernovae explosions associated with GRB 980425 and GRB 030329.

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Kumar 2008 GRB080319B的逆康普顿解释

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同步辐射产生光学，逆康普顿散射产生伽玛射线。不过假定了光学就是nu_m.
同时解释了余辉。

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· arXiv e-print (arXiv:0805.0144)

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Title:		What did we learn from gamma-ray burst 080319B ?
Authors:		Kumar, P.; Panaitescu, A.
Publication:		eprint arXiv:0805.0144
Publication Date:		05/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		5 pages, submitted to MNRAS
Bibliographic Code:		2008arXiv0805.0144K

Abstract

The optical and gamma-ray observations of GRB 080319B allow us to determine a fairly complete physical picture for this remarkable burst. The data indicate that the prompt optical and gamma-ray photons were produced at the same location but by different radiation processes: synchrotron and synchrotron self-Compton, respectively. The burst emission was produced at a distance of 10^{16.5} cm from the center of explosion by an ultra-relativistic source moving at Lorentz factor of ~500. A straightforward inference is that about 10 times more energy must have been radiated at tens of GeV than that released at ~1 MeV. Assuming that the GRB outflow was baryonic and that the gamma-ray source was shock-heated plasma, the collimation-corrected kinetic energy of the jet powering GRB 080319B was larger than 10^{52.3} erg. The decay of the early afterglow optical emission (up to 1 ks) is too fast to be attributed to the reverse shock crossing the GRB ejecta but is consistent with the expectations for the "large-angle emission" released during the burst. The pure power-law decay of the optical afterglow flux from 1 ks to 10 day is most naturally identified with the (synchrotron) emission from the shock propagating into a wind-like medium. However, the X-ray afterglow requires a departure from the standard blast-wave model.

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Lazzati 2008 中微子冷却盘的晚期吸积作为XRFs的中心能源

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· arXiv e-print (arXiv:0805.0138)

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Title:		X-ray flares, neutrino cooled disks, and the dynamics of late accretion in GRB engines
Authors:		Lazzati, Davide; Perna, Rosalba; Begelman, Mitchell C.
Publication:		eprint arXiv:0805.0138
Publication Date:		05/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		5 pages, MNRAS in press
Bibliographic Code:		2008arXiv0805.0138L

Abstract

We compute the average luminosity of X-ray flares as a function of time, for a sample of 10 long-duration gamma-ray burst afterglows. The mean luminosity, averaged over a timescale longer than the duration of the individual flares, declines as a power-law in time with index ~-1.5. We elaborate on the properties of the central engine that can produce such a decline. Assuming that the engine is an accreting compact object, and for a standard conversion factor between accretion rate and jet luminosity, the switch between a neutrino-cooled thin disk and a non-cooled thick disk takes place at the transition from the prompt to the flaring phase. We discuss the implications of this coincidence under different scenarios for the powering of the GRB outflow. We also show that the interaction of the outflow with the envelope of the progenitor star cannot produce flares out of a continuous relativistic flow, and conclude that it is the dynamics of the disk or the jet-launching mechanism that generates an intrinsically unsteady outflow on timescales much longer than the dynamical timescale of the system. This is consistent with the fact that X-ray flares are observed in short-duration GRBs as well as in long-duration ones.

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Giannios 2008 恒星光子作为种子光子的高能辐射

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让恒星的光子作为背景光子， 激波电子对这些光子进行逆康普顿散射，得到高能辐射。

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· arXiv e-print (arXiv:0805.0258)

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Title:		Powerful GeV emission from a gamma-ray-burst shock wave scattering stellar photons
Authors:		Giannios, Dimitrios
Publication:		eprint arXiv:0805.0258
Publication Date:		05/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		4 pages, 3 figures, submitted to A&A Letters
Bibliographic Code:		2008arXiv0805.0258G

Abstract

The gamma-ray bursts of long duration are likely connected to the death of massive stars. The gamma-ray emission is believed to come from energy released internally in a flow that moves at ultrarelativistic speed. The fast flow drives a shock wave into the external medium leading to the afterglow emission. Most massive stars form in dense clusters, their high luminosity producing a very dense radiation field. Here, I explore the observational consequences of the interaction of the shocked external medium of the burst with the photon field of a nearby O star. I show that inverse Compton scattering of the stellar photons by electrons heated by the shock leads to powerful gamma-ray emission in the ~1-100 GeV range. This emission appears minutes to hours after the burst and can be easily detected by Cherenkov telescopes and likely with the GLAST satellite. This signal may have already been observed in GRB 940217 and can yield important information about the circumburst environment.

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