Rubbia 2007 用伽玛暴瞬时辐射的偏振定轴子模型

主要内容:


精彩摘抄:


文章信息:
Constraining axion by polarized prompt emission from gamma ray bursts

Authors: A. Rubbia (ETH-Zurich), A.S. Sakharov (ETH-Zurich, CERN)

(Submitted on 20 Aug 2007 (v1), last revised 21 Aug 2007 (this version, v3))

Abstract: A polarized gamma ray emission spread over a sufficiently wide energy band from a strongly magnetized astrophysical object like gamma ray bursts (GRBs) offers an opportunity to test the hypothesis of invisible axion. The axionic induced dichroism of gamma rays at different energies should cause a misalignment of the polarization plane for higher energy events relative to that one for lower energies events resulting in the loss of statistics needed to form a pattern of the polarization signal to be recognized in a detector. According to this, any evidence of polarized gamma rays coming from an object with extended magnetic field could be interpreted as a constraint on the existence of the invisible axion for a certain parameter range. Based on reports of polarized MeV emission detected in several GRBs we derive a constraint on the axion-photon coupling. This constraint $\g_{a\gamma\gamma}\le 2.2\cdot 10^{-11} {\rm GeV^{-1}}$ calculated for the axion mass $m_a=10^{-3} {\rm eV}$ is competitive with the sensitivity of CAST and becomes even stronger for lower masses.

Cite as: arXiv:0708.2646v3 [hep-ph]

Wang 2006 用Ia型超新星定暗能量和加速处的红移

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文章信息:
Constraining Dark Energy and Cosmological Transition Redshift with Type Ia Supernovae

Authors: F. Y. Wang, Z. G. Dai (NJU)

(Submitted on 30 Aug 2007)

Abstract: The property of dark energy and the physical reason for acceleration of the present universe are two of the most difficult problems in modern cosmology. The dark energy contributes about two-thirds of the critical density of the present universe from the observations of type-Ia supernova (SNe Ia) and anisotropy of cosmic microwave background (CMB).The SN Ia observations also suggest that the universe expanded from a deceleration to an acceleration phase at some redshift, implying the existence of a nearly uniform component of dark energy with negative pressure. We use the ``gold'' sample containing 157 SNe Ia and two recent well-measured additions, SNe Ia 1994ae and 1998aq to explore the properties of dark energy and the transition redshift. For a flat universe with the cosmological constant, we measure $\Omega_{M}=0.28_{-0.05}^{+0.04}$, which is consistent with Riess et al. The transition redshift is $z_{T}=0.60_{-0.08}^{+0.06}$. We also discuss several dark energy models that define the $w(z)$ of the parameterized equation of state of dark energy including one parameter and two parameters ($w(z)$ being the ratio of the pressure to energy density). Our calculations show that the accurately calculated transition redshift varies from $z_{T}=0.29_{-0.06}^{+0.07}$ to $z_{T}=0.60_{-0.08}^{+0.06}$ across these models. We also calculate the minimum redshift $z_{c}$ at which the current observations need the universe to accelerate.

Comments:	16 pages, 5 figures, 1 table
Subjects:	Astrophysics (astro-ph)
Journal reference:	Chin. J. Astron. Astrophys. Vol. 6. 2006, No. 5, 561-571
Cite as:	arXiv:0708.4062v1 [astro-ph]

Zhang 2007 伽玛暴时标再分析

主要内容:
重新统计了有红移的伽玛暴的时标，包含Swift的数据，得到和以前一样的结论：分长短暴。不过长暴的时长和中间值与之前的有别。

精彩摘抄:


文章信息:
An analysis of the durations of Swift Gamma-Ray Bursts

Authors: Zhi-Bin Zhang, Chul-Sung Choi

(Submitted on 30 Aug 2007)

Abstract: We report the systematic analysis of the durations for Swift gamma-ray bursts (GRBs) and compare the results with those of pre-Swift data. For 95 GRBs with known redshift, we show that the observed durations have two lognormal distributions that are clearly divided at $T_{90}\simeq2$ s. This is consistent with the earlier BATSE results. The intrinsic durations also show a bimodal distribution but shift systematically toward the smaller value and the distribution exhibits a narrower width compared with the observed one. We find that the intrinsic distributions of long GRBs between Swift and pre-Swift are significantly different particularly in the width and the median value. In addition, the Swift data exhibit a wider duration dynamic range. Our present study also confirms the spectra of short GRBs are in general harder than the long GRBs.

arXiv:0708.4049

Yonetoku 2007 GRB 060904A的谱演化

主要内容:
光子谱指数演化比较剧烈，最引人注目的是在prompt晚期，指数高达5，很软。

精彩摘抄:

X射线的光变
中间一项是光子谱指数

文章信息:
Spectral evolution of GRB 060904A observed with Swift and Suzaku -- Possibility of Inefficient Electron Acceleration

Authors: Daisuke Yonetoku, et al.
(Submitted on 29 Aug 2007)

Abstract: We observed an X-ray afterglow of GRB 060904A with the Swift and Suzaku satellites. We found rapid spectral softening during both the prompt tail phase and the decline phase of an X-ray flare in the BAT and XRT data. The observed spectra were fit by power-law photon indices which rapidly changed from $\Gamma = 1.51^{+0.04}_{-0.03}$ to $\Gamma = 5.30^{+0.69}_{-0.59}$ within a few hundred seconds in the prompt tail. This is one of the steepest X-ray spectra ever observed, making it quite difficult to explain by simple electron acceleration and synchrotron radiation. Then, we applied an alternative spectral fitting using a broken power-law with exponential cutoff (BPEC) model. It is valid to consider the situation that the cutoff energy is equivalent to the synchrotron frequency of the maximum energy electrons in their energy distribution. Since the spectral cutoff appears in the soft X-ray band, we conclude the electron acceleration has been inefficient in the internal shocks of GRB 060904A. These cutoff spectra suddenly disappeared at the transition time from the prompt tail phase to the shallow decay one. After that, typical afterglow spectra with the photon indices of 2.0 are continuously and preciously monitored by both XRT and Suzaku/XIS up to 1 day since the burst trigger time. We could successfully trace the temporal history of two characteristic break energies (peak energy and cutoff energy) and they show the time dependence of $\propto t^{-3} \sim t^{-4}$ while the following afterglow spectra are quite stable. This fact indicates that the emitting material of prompt tail is due to completely different dynamics from the shallow decay component. Therefore we conclude the emission sites of two distinct phenomena obviously differ from each other.
arXiv:0708.3968 [ps, pdf, other]

Konopelko 2007 地面低能伽玛射线望远镜的设计

主要内容:
已有一些地面高能伽玛射线望远镜，大于100GeV，现在考虑设计10－100GeV的。原理也还是探测次级Cherenkov辐射。

人总是能想到办法的，以前知道伽玛射线穿不过大气层，所以要用卫星观测伽玛辐射。但是穿不过就意味着要和大气层作用，这种作用就会有次级辐射，通过观测这种次级辐射也可以反推原来的伽玛辐射的嘛。

精彩摘抄:


文章信息:
Design Study of a Low Energy IACT Array for Ground-Based Gamma-Ray Astronomy

Authors: A. Konopelko, J.P. Finley, G. Urbanski (Purdue University)

(Submitted on 28 Aug 2007)

Abstract: Recently, ground-based very high-energy (VHE) gamma-ray astronomy achieved a remarkable advancement in the development of the observational technique for the registration and study of gamma-ray emission above 100 GeV. Construction of telescopes of substantially larger sizes than the currently used 12 m class telescopes can drastically improve the sensitivity of ground-based detectors to gamma rays of energy from 10 GeV to 100 GeV. Based on Monte Carlo simulations we have studied the response of an array of three large area imaging atmospheric Cherenkov telescopes (IACT) as a prototype for a future large-scale low energy ground-based experiment. The sensitivity of a three-telescope array as a function of optical reflector size was investigated here in detail.
arXiv:0708.3865 [ps, pdf, other]

Michałowski 2007 四个宿主星系的观测

主要内容:
对GRBs 980703, 000210, 000418 and 010222四个暴的宿主星系的观测，发现这几个暗弱的星系相比一般星系：更热更年轻，更小更多尘。

这是不是就是伽玛暴宿主星系的普遍特征呢？

精彩摘抄:


文章信息:
The nature of GRB-selected submillimeter galaxies: hot and young

Authors: M. J. Michałowski, J. Hjorth, J. M. Castro Cerón, D. Watson (Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Denmark)

(Submitted on 29 Aug 2007)

Abstract: We present detailed fits of the spectral energy distributions (SEDs) of four submillimeter (submm) galaxies selected by the presence of a gamma-ray burst (GRB) event (GRBs 980703, 000210, 000418 and 010222). These faint ~3 mJy submm emitters at redshift ~1 are characterized by an unusual combination of long- and short-wavelength properties, namely enhanced submm and/or radio emission combined with optical faintness and blue colors. We exclude an active galactic nucleus as the source of long-wavelength emission. From the SED fits we conclude that the four galaxies are young (ages <2>45 K) indicate that GRB host galaxies are hotter, younger, and less massive counterparts to submm-selected galaxies detected so far. Future facilities like Herschel, JCMT/SCUBA-2 and ALMA will test this hypothesis enabling measurement of dust temperatures of fainter GRB-selected galaxies.


Spectral energy distributions of submm/radio bright gamma-ray burst host galaxies

Authors: M. J. Michałowski, J. Hjorth (Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Denmark)

(Submitted on 29 Aug 2007)

Abstract: We present optical to radio spectral energy distribution fitting of the host galaxies of four long gamma-ray bursts: 980703, 000210, 000418 and 010222, which were detected at submillimetre and/or radio wavelengths. We find that only very young starburst galaxy models are consistent with the data having both blue optical colors and a pronounced submm emission. For each host we are able to construct a model consistent with the short- and long-wavelength parts of the spectra. We find galaxy ages ranging from 0.09 to 2.0 Gyrs and star formation rates ranging from 138 to 380 MSun/yr.

Cite as:

arXiv:0708.4014v1 [astro-ph]

Stratta 2007 短暴061201的暴本身和余辉的观测

主要内容:
有X射线和光学余辉，没有宿主星系的确定候选者。X射线余辉有关着，如果是喷流拐折，张角在1－2度。

精彩摘抄:


文章信息:
A study of the prompt and afterglow emission of the Short GRB 061201

Authors: G. Stratta, et. al

(Submitted on 27 Aug 2007)

Abstract: Our knowledge of the intrinsic properties of short duration Gamma-Ray Bursts has relied, so far, only upon a few cases for which the estimate of the distance and an extended, multiwavelength monitoring of the afterglow have been obtained. We carried out multiwavelength observations of the short GRB 061201 aimed at estimating its distance and studying its properties. We performed a spectral and timing analysis of the prompt and afterglow emission and discuss the results in the context of the standard fireball model. A clear temporal break was observed in the X-ray light curve about 40 minutes after the burst trigger. We find that the spectral and timing behaviour of the X-ray afterglow is consistent with a jet origin of the observed break, although the optical data can not definitively confirm this and other scenarios are possible. No underlying host galaxy down to R~26 mag was found after fading of the optical afterglow. Thus, no secure redshift could be measured for this burst. The nearest galaxy is at z=0.111 and shows evidence of star formation activity. We discuss the association of GRB 061201 with this galaxy and with the ACO S 995 galaxy cluster, from which the source is at an angular distance of 17'' and 8.5', respectively. We also test the association with a possible undetected, positionally consistent galaxy at z~1. In all these cases, in the jet interpretation, we find a jet opening angle of 1-2 degrees.

arXiv:0708.3553

Nysewander 2007 PROMPT对GRB 060607A的早期光学观测

主要内容:
PROMPT (Panchromatic Robotic Optical Monitoring and Polarimetry Telescopes)是专门为观测伽玛暴余辉准备的。观测GRB 060607A很早的光学余辉和谱。同样，光学和X射线的拐折没有什么时间上的联系。

精彩摘抄:


文章信息: PROMPT Observations of the Early-Time Optical Afterglow of GRB 060607A

Authors: M. Nysewander, D. E. Reichart, J. A. Crain, A. Foster, J. Haislip, K. Ivarsen, A. Lacluyze, A. Trotter

(Submitted on 27 Aug 2007)

Abstract: PROMPT (Panchromatic Robotic Optical Monitoring and Polarimetry Telescopes) observed the early-time optical afterglow of GRB 060607A and obtained a densely sampled multiwavelength light curve that begins only tens of seconds after the GRB. Located at Cerro Tololo Inter-American Observatory in Chile, PROMPT is designed to observe the afterglows of gamma-ray bursts using multiple automated 0.4-m telescopes that image simultaneously in many filters when the afterglow is bright and may be highly variable. The data span the interval from 44 seconds after the GRB trigger to 3.3 hours in the Bgri filters. We observe an initial peak in the light curve at approximately three minutes, followed by rebrightenings peaking around 40 minutes and again at 66 minutes. Although our data overlap with the early Swift gamma-ray and x-ray light curves, we do not see a correlation between the optical and high-energy flares. We do not find evidence for spectral evolution throughout the observations. We model the variations in the light curves and find that the most likely cause of the rebrightening episodes is a refreshment of the forward shock preceded by a rapidly fading reverse shock component, although other explanations are plausible.

arXiv:0708.3444 [ps, pdf, other]

Metzger 2007 富含中子成分的外流

主要内容:
如果中心是磁星的话，可以产生富中子的外流。NDAF

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文章信息:
On the Conditions for Neutron-Rich Gamma-Ray Burst Outflows

Authors: Brian D. Metzger, Todd A. Thompson, Eliot Quataert

(Submitted on 24 Aug 2007)

Abstract: We calculate the structure and neutron content of neutrino-heated MHD winds driven from the surface of newly-formed magnetars (``proto-magnetars'') and from the midplane of hyper-accreting disks, two of the possible central engines for gamma-ray bursts (GRBs) and hyper-energetic supernovae (SNe). Both the surface of proto-magnetars and the midplane of neutrino-cooled accretion flows (NDAFs) are electron degenerate and neutron-rich (neutron-to-proton ratio n/p >> 1). If this substantial free neutron excess is preserved to large radii in ultra-relativistic outflows, several important observational consequences may result. Weak interaction processes, however, can drive n/p to ~1 in the nondegenerate regions that obtain just above the surfaces of NDAFs and proto-magnetars. Our calculations show that mildly relativistic neutron-rich outflows from NDAFs are possible in the presence of a strong poloidal magnetic field. However, we find that neutron-rich winds possess a minimum mass-loss rate that likely precludes simultaneously neutron-rich and ultra-relativistic (Lorentz factor > 100) NDAF winds accompanying a substantial accretion power. In contrast, proto-magnetars are capable of producing neutron-rich long-duration GRB outflows ~10-30 seconds following core bounce for sub-millisecond rotation periods; such outflows would, however, accompany only extremely energetic events, in which the GRB + SN energy budget exceeds ~ 4e52 ergs. Neutron-rich highly relativistic outflows may also be produced during some short-duration GRBs by geometrically thick accretion disks formed from compact object mergers. The implications for r-process nucleosynthesis, optical transients due to non-relativistic neutron-rich winds, and Nickel production in proto-magnetar and NDAF winds are also briefly discussed.

arXiv:0708.3395

Tanaka 2007 数值模拟SN 1998bw的不对称爆发

主要内容:
数值模拟不对称爆发的动力学、核合成和辐射转移。

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文章信息:
Multi-Dimensional Simulations for Early Phase Spectra of Aspherical Hypernovae: SN 1998bw and Off-Axis Hypernovae

Authors: Masaomi Tanaka, Keiichi Maeda, Paolo A. Mazzali, Ken'ichi Nomoto

(Submitted on 23 Aug 2007)

Abstract: Early phase optical spectra of aspherical jet-like supernovae (SNe) are presented. We focus on energetic core-collapse SNe, or hypernovae. Based on hydrodynamic and nucleosynthetic models, radiative transfer in SN atmosphere is solved with a multi-dimensional Monte-Carlo radiative transfer code, SAMURAI. Since the luminosity is boosted in the jet direction, the temperature there is higher than in the equatorial plane by ~ 2,000 K. This causes anisotropic ionization in the ejecta. Emergent spectra are different depending on viewing angle, reflecting both aspherical abundance distribution and anisotropic ionization. Spectra computed with an aspherical explosion model with kinetic energy 20 x 10^{51} ergs are compatible with those of the Type Ic SN 1998bw if ~ 10-20% of the synthesized metals are mixed out to higher velocities. The simulations enable us to predict the properties of off-axis hypernovae. Even if an aspherical hypernova explosion is observed from the side, it should show hypernova-like spectra but with some differences in the line velocity, the width of the Fe absorptions and the strength of the Na I line.

arXiv:0708.3242 [ps, pdf, other]

Castro-Tirado 2007 GRB051022及其宿主星系

主要内容:
GRB 051022的X射线余辉辐射很强，但是一个光学暗暴。通过观测认定原因是宿主星系是一个刚发生过星暴的星系，可能在光路上有一个致密的区域对光学消光（不是尘埃散射）。

精彩摘抄:


文章信息:
The dark nature of GRB 051022 and its host galaxy

Authors: A. J. Castro-Tirado, M. Bremer, S. McBreen, J. Gorosabel, S. Guziy, R. M. Gonzalez Delgado, G. Bihain, T. Fakthullin, S. B. Pandey, M. Jelinek, A. de Ugarte Postigo, V. Sokolov, K. Misra, R. Sagar, P. Bama, A. P. Kamble, G. C. Anupama, J. Licandro, F. J. Aceituno, R. Neri

(Submitted on 22 Aug 2007)

Abstract: We present multiwavelength (X-ray/optical/near-infrared/millimetre) observations of GRB 051022 between 2.5 hours and ~1.15 yr after the event. It is the most intense gamma-ray burst (~ 10^-4 erg cm^-2) detected by HETE-2, with the exception of the nearby GRB 030329. Optical and near infrared observations did not detect the afterglow despite a strong afterglow at X-ray wavelengths. Millimetre observations at Plateau de Bure (PdB) detected a source and a flare, confirming the association of this event with a moderately bright (R = 21.5) galaxy. Spectroscopic observations of this galaxy show strong [O II], Hbeta and [O III] emission lines at a redshift of 0.809. The spectral energy distribution of the galaxy implies Av (rest frame) = 1.0 and a starburst occuring ~ 25 Myr ago, during which the star-forming-rate reached >= 25 Msun/yr. In conjunction with the spatial extent (~ 1'') it suggests a very luminous (Mv = - 21.8) blue compact galaxy, for which we also find with Z Zsun. The X-ray spectrum shows evidence of considerable absorption by neutral gas with NH, X-ray = 3.47(+0.48/-0.47) x 10^22 cm^-2 (rest frame). Absorption by dust in the host galaxy at z = 0.809 certainly cannot account for the non-detection of the optical afterglow, unless the dust-to-gas ratio is quite different than that seen in our Galaxy (i.e. large dust grains). It is likely that the afterglow of the dark GRB 051022 was extinguished along the line of sight by an obscured, dense star forming region in a molecular cloud within the parent host galaxy. This galaxy is different from most GRB hosts being brighter than L* by a factor of 3. We have also derived a SFR ~ 50 Msun/yr and predict that this host galaxy will be detected at sub-mm wavelengths.

Godet 2007 Swift/XRT的CCD

主要内容:


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文章信息:
The in-flight spectroscopic performance of the Swift XRT CCD camera during 2006-2007

Authors: O. Godet, A. P. Beardmore, A. F. Abbey, J. P. Osborne, K. L. Page, L. Tyler, D. N. Burrows, P. Evans, R. Starling, A. A. Wells, L. Angelini, S. Campana, G. Chincarini, O. Citterio, G. Cusumano, P. Giommi, J. E. Hill, J. Kennea, V. LaParola, V. Mangano, T. Mineo, A. Moretti, J. A. Nousek, C. Pagani, M. Perri, M. Capalbi, P. Romano, G. Tagliaferri, F. Tamburelli

(Submitted on 22 Aug 2007)

Abstract: The Swift X-ray Telescope focal plane camera is a front-illuminated MOS CCD, providing a spectral response kernel of 135 eV FWHM at 5.9 keV as measured before launch. We describe the CCD calibration program based on celestial and on-board calibration sources, relevant in-flight experiences, and developments in the CCD response model. We illustrate how the revised response model describes the calibration sources well. Comparison of observed spectra with models folded through the instrument response produces negative residuals around and below the Oxygen edge. We discuss several possible causes for such residuals. Traps created by proton damage on the CCD increase the charge transfer inefficiency (CTI) over time. We describe the evolution of the CTI since the launch and its effect on the CCD spectral resolution and the gain.

Liang 2007 Swift暴X射线和光学拐折的统计

主要内容:
统计了179 GRBs (from 050124 to 070129)，它们的X射线和光学的拐折。没有一个暴可以很肯定地说是喷流拐折。整体上X射线的拐折时间比光学的早。

精彩摘抄:
GRB060124的X射线和R波段的余辉光变，拐折时间不同（光学就没有）。

文章信息: A Comprehensive Analysis of the Swift/XRT Data: III. Jet Break Candidates in the X-ray and Optical Afterglow Lightcurves

Authors: En-Wei Liang, Judith L. Racusin, Bing Zhang, Bin-Bin Zhang, David N. Burrows

(Submitted on 22 Aug 2007)

Abstract: The Swift/XRT data of 179 GRBs (from 050124 to 070129) and the optical afterglow data of 57 pre- and post-Swift GRBs are analyzed, in order to systematically investigate the jet-like breaks in the X-ray and optical afterglow lightcurves. We find that not a single burst can be included in the ``Platinum'' sample, in which the data satisfy all the criteria of a jet break. By releasing one or more requirements to define a jet break, some candidates of various degrees could be identified. In the X-ray band, 42 out of the 109 well-sampled X-ray lightcurves have a decay slope of the post-break segment >1.5 (``Bronze'' sample), and 27 of them also satisfy the closure relations of the forward models (``Silver'' sample). The numbers of the ``Bronze'' and ``Silver'' candidates in the optical lightcurves are 27 and 23, respectively. Thirteen bursts have well-sampled optical and X-ray lightcurves, but only seven cases are consistent with an achromatic break, but even in these cases only one band satisfies the closure relations (``Gold'' sample). The observed break time in the XRT lightcurves is systematically earlier than that in the optical bands. All these raise great concerns in interpreting the jet-like breaks as jet breaks and further inferring GRB energetics from these breaks. By assuming that these breaks are jet breaks, we perform a similar analysis as previous work to calculate the jet opening angle (theta_j) and energetics (E_k) with the ``Silver'' and ``Gold'' jet break candidates. The derived E_K distribution reveals a much larger scatter than the pre-Swift sample. A tentative anti-correlation between theta_j and E_{K,iso} is found for both the pre-Swift and Swift GRBs, indicating that the E_K could still be quasi-universal, if the breaks in discussion are indeed jet breaks(abridge).
arXiv:0708.2942 [ps, pdf, other]

Janiuk 2007 长暴中坍缩星吸积盘的形成

主要内容:
考虑长暴的形成的时候，坍缩星要形成一个可供吸积的盘（torus），期间的角动量过程。

精彩摘抄:


文章信息:
Low angular momentum accretion in the collapsar: how long can be a long GRB?

Authors: Agnieszka Janiuk, Daniel Proga (UNLV)

(Submitted on 20 Aug 2007)

Abstract: The collapsar model is the most promising scenario to explain the huge release of energy associated with long duration gamma-ray-bursts (GRBs). Within this scenario GRBs are believed to be powered by accretion through a rotationally support torus or by fast rotation of a compact object. In both cases then, rotation of the progenitor star is one of the key properties because it must be high enough for the torus to form, the compact object to rotate very fast, or both. Here, we check what rotational properties a progenitor star must have in order to sustain torus accretion over relatively long activity periods as observed in most GRBs. We show that simple, often cited, estimates of the total mass available for torus formation and consequently the duration of a GRB are only upper limits. We revise these estimates by taking into account the long term effect that as the compact object accretes the minimum specific angular momentum needed for torus formation increases. This in turn leads to a smaller fraction of the stellar envelope that can form a torus. We demostrate that this effect can lead to a significant, an order of magnidute, reduction of the total energy and overall duration of a GRB event. This of course can be mitigated by assuming that the progenitor star rotates faster then we assumed. However, our assumed rotation is already high compared to observational and theoretical constraints. We also discuss implications of our result.

Chary 2007 Spitzer对3个高红移伽玛暴宿主星系的观测

主要内容:
三个z～5的宿主星系的观测，表明这三个星系的光度比那里的平均光度要低三倍，说明在GOODS的深度巡天中并没有包括所有的恒星形成中的星系。这对恒星形成率的估计很有帮助。

精彩摘抄:


文章信息:
Spitzer Observations of Gamma-Ray Burst Host Galaxies: A Unique Window into High Redshift Chemical Evolution and Star-formation

Authors: Ranga-Ram Chary, Edo Berger, Len Cowie

(Submitted on 17 Aug 2007)

Abstract: We present deep Spitzer 3.6 micron observations of three z~5 GRB host galaxies. Our observations reveal that z~5 GRB hosts are a factor of 3 less luminous than the median rest-frame V-band luminosity of spectroscopically confirmed z~5 galaxies in the GOODS fields and the UDF. The strong connection between GRBs and massive star formation implies that not all star-forming galaxies at these redshifts are currently being accounted for in deep surveys and GRBs provide a unique way to measure the contribution to the star-formation rate density from galaxies at the faint end of the galaxy luminosity function. By correlating the co-moving star-formation rate density with co-moving GRB rates at lower redshifts, we estimate a lower limit to the star-formation rate density of 0.12+/-0.09 and 0.09+/-0.05 M_sun/yr/Mpc^3 at z~4.5 and z~6, respectively. Finally, we provide evidence that the average metallicity of star-forming galaxies evolves as (stellar mass density)^(0.69+/-0.17) between $z\sim5$ and $z\sim0$, probably indicative of the loss of a significant fraction of metals to the intergalactic medium, particularly in low-mass galaxies.

arXiv:0708.2440 [ps, pdf, other]

Manchester 2007 搜寻SN1987A的脉冲星

主要内容:
只给出了流量的上限。

也就是说这个著名的超新星有没有遗留一颗中子星还不是定论。

精彩摘抄:


文章信息:
Searching for a Pulsar in SN1987A

Authors: R. N. Manchester

(Submitted on 17 Aug 2007)

Abstract: SN 1987A offered a unique opportunity to detect a pulsar at the very beginning of its life and to study its early evolution. Despite many searches at radio and optical wavelengths, no pulsar has yet been detected. Details of a recent search using the Parkes radio telescope are given. Limits on the X-ray, optical and radio luminosity of a point source at the centre of SN 1987A place limits on the properties of a central neutron star. However, neither these nor the pulsar limits preclude the presence of a relatively slowly rotating neutron star (P >~ 100 ms) with a moderate surface dipole magnetic field in SN 1987A. Galactic studies suggest that a significant fraction of pulsars are born with parameters in this range. In view of this, continued searches for a pulsar in SN 1987A are certainly justified.

Middleditch 2007 SN1987A可能也是伽玛暴

主要内容:
认为SN1987A和其他很多超新星产生于双简并星的并合，也能产生长暴。

那就是认为现在的普遍模型不对咯

精彩摘抄:


文章信息:
The SN 1987A Link to Others and Gamma-Ray Bursts

Authors: John Middleditch

(Submitted on 16 Aug 2007 (v1), last revised 26 Aug 2007 (this version, v2))

Abstract: Early measurements of SN 1987A can be interpreted in light of the beam/jet (BJ) which had to hit polar ejecta (PE) to produce the "Mystery Spot" (MS), some 22 light-days distant. Other details of SN 1987A strongly suggest that it resulted from a merger of two stellar cores of a common envelope (CE) binary, i.e. a "double degenerate" (DD)-initiated SN. Without having to blast through the CE of Sk -69 202, it is likely that the BJ would have caused a full, long-soft gamma-ray burst (lGRB) upon hitting the PE, thus DD can produce lGRBs (and, of course, MSPs). Because DD must be the overwhelmingly dominant merger/SN mechanism in elliptical galaxies, where only short, hard GRBs (sGRBs) have been observed, DD without CE or PE must also produce sGRBs, and thus the pre-CE/PE impact photon spectrum of 99% of all GRBs is known, and neutron star (NS)-NS mergers may not make GRBs as we know them, and/or be as common as previously thought. The many details of Ia's strongly suggest that these are also DD formed, and the single degenerate total thermonuclear disruption paradigm is now in serious doubt as well. This is a cause for concern in Ia Cosmology, because Type Ia SNe will appear to be Ic's when viewed from their DD merger poles, given sufficient matter above that lost to core-collapse. As a DD-initiated SN, 1987A appears to be the Rosetta Stone for 99% of SNe, GRBs and MSPs, including all recent nearby SNe except SN 1986J, and the more distant SN 2006gy. There is no for exotica, such as "collapsars," to account for GRBs.

Subjects:	Astrophysics (astro-ph)
Cite as:	arXiv:0708.2263v2 [astro-ph]

Shen 2007 喷流散射在伽玛暴中的应用

主要内容:
认为shell的散射可以作为shellow decay, x-ray flares， 甚至是暴本身的辐射基础。

精彩摘抄:


文章信息:
Scattered Emission from A Relativistic Outflow and Its Application to Gamma-Ray Bursts

Authors: R.-F. Shen, R. Barniol Duran, P. Kumar

(Submitted on 13 Aug 2007)

Abstract: We investigate a scenario of photons scattering by electrons within a relativistic outflow. The outflow is composed of discrete shells with different speeds. One shell emits radiation for a short duration. Some of this radiation is scattered by the shell(s) behind. We calculate in a simple two-shell model the observed scattered flux density as a function of: the observed primary flux density, the normalized arrival time delay between the two emission components, the Lorentz factor ratio of the two shells and the scattering shell's optical depth. Thomson scattering in a cold shell and Inverse Compton scattering in a hot shell are both considered. The results of our calculations are applied to the Gamma-Ray Bursts and the afterglows. We find that the scattered flux from a cold slower shell is small and likely to be detected only for those bursts with very weak afterglows. A hot scattering shell could give rise to a scattered emission as bright as the X-ray shallow decay component detected in many bursts, on a condition that the isotropically equivalent total energy carried by the hot electrons is large, $\sim 10^{52-56}$ erg. The scattered emission from a faster shell could appear as a late short $\gamma$/X-ray flash or become part of the prompt emission depending on the delay of the ejection of the shell.

Panaitescu 2007 晚期喷流的散射解释X射线耀发、慢下降和拐折

主要内容:
用晚期的喷流逆康普顿散射正向激波的光子来同时解释这三样东西。chromatic breaks好像是指不同颜色并不同时拐折。

精彩摘抄:


文章信息:

arXiv:0708.1509 [ps, pdf, other]

Title: X-ray flares, plateaus, and chromatic breaks of GRB afterglows from up-scattered forward-shock emission

Authors: A. Panaitescu

Comments: 11 pages, 7 figures, 59 easy equations. Submitted to MNRAS

Subjects: Astrophysics (astro-ph)

Scattering of the forward-shock synchrotron emission by a relativistic outflow ejected up to 10 ks after the leading blast-wave, may produce a brighter emission than that coming directly from the forward-shock and may explain three novel features discovered by Swift in the X-ray emission of GRB afterglows: flares, plateaus (slow decays), and chromatic light-curve breaks. For a cold scattering outflow, the reflected flux overshines the primary one if the scattering outflow is nearly baryon-free and highly relativistic. These two requirements can be relaxed if the scattering outflow is energized by weak internal shocks, so that the incident forward-shock photons are also inverse-Compton scattered. This sweeping-up of the photons left behind by the forward shock naturally yields X-ray flares that are (much) shorter than the time when they occur. Because of the boost in photon energy produced by bulk-scattering (and inverse-Compton, if present), the reflected emission is more likely to overshine the forward shock's at higher photon energies, yielding light-curve plateaus and breaks that appear only in the X-ray (energy injection in the forward-shock can hardly account for the latter feature). The brightness, shape, and decay of the X-ray light-curve plateau depend on the spectrum of the primary emission, as well as on the radial distribution of the scatterer's Lorentz factor and mass-flux. Thus, the various durations and decay rates displayed by X-ray afterglow plateaus reflect the diversity in the radial structure of the late outflows produced by long-lived GRB engines.

Guidorzi 2007 GRB 070311的多波段观测

主要内容:
给出了GRB 070311的多波段观测结果

精彩摘抄:

对数图上的多波段光变

光学波段的peak和伽玛射线的位置不同，有延后。

文章信息:

arXiv:0708.1383 [ps, pdf, other]

Title: GRB 070311: a direct link between the prompt emission and the afterglow

Authors: C. Guidorzi, S.D. Vergani, S. Sazonov, S. Covino, D. Malesani, S. Molkov, E. Palazzi, P. Romano, S. Campana, G. Chincarini, D. Fugazza, A. Moretti, G. Tagliaferri, A. Llorente, J. Gorosabel, L.A. Antonelli, M. Capalbi, G. Cusumano, P. D'Avanzo, V. Mangano, N. Masetti, E. Meurs, T. Mineo, E. Molinari, D.C. Morris, L. Nicastro, K.L. Page, M. Perri, B. Sbarufatti, G. Stratta, R. Sunyaev, E. Troja, F.M. Zerbi

Comments: 14 pages, 11 figures, 4 tables, accepted to A&A

Subjects: Astrophysics (astro-ph)

We present prompt gamma-ray, early NIR/optical, late optical and X-ray observations of the peculiar GRB 070311 discovered by INTEGRAL, in order to gain clues on the mechanisms responsible for the prompt gamma-ray pulse as well as for the early and late multi-band afterglow of GRB 070311. We fitted with empirical functions the gamma-ray and optical light curves and scaled the result to the late time X-rays. The H-band light curve taken by REM shows two pulses peaking 80 and 140 s after the peak of the gamma-ray burst and possibly accompanied by a faint gamma-ray tail. Remarkably, the late optical and X-ray afterglow underwent a major rebrightening between 3x10^4 and 2x10^5 s after the burst with an X-ray fluence comparable with that of the prompt emission extrapolated in the same band. Notably, the time profile of the late rebrightening can be described as the combination of a time-rescaled version of the prompt gamma-ray pulse and an underlying power law. This result supports a common origin for both prompt and late X-ray/optical afterglow rebrightening of GRB 070311 within the external shock scenario. The main fireball would be responsible for the prompt emission, while a second shell would produce the rebrightening when impacting the leading blastwave in a refreshed shock (abridged).

Murase 2007 伽玛暴中的正负电子对信号

主要内容:
认为GLAST可以检验正负电子对产生以及由于超过产生的能量的光子都可以产生电子对而导致的cutoff信号。

精彩摘抄:


文章信息:

arXiv:0708.1370 [ps, pdf, other]

Title: Closure Relations for Electron-Positron Pair-Signatures in Gamma-Ray Bursts

Authors: Kohta Murase, Kunihito Ioka

Comments: 4 pages, 1 figure

Subjects: Astrophysics (astro-ph)

We present recipes to diagnose the fireball of gamma-ray bursts (GRBs) by combining observations of electron-positron pair-signatures (the pair-annihilation line and the cutoff energy due to the pair-creation process). Our recipes are largely model-independent and extract information even from the non-detection of either pair-signature. We evaluate physical quantities such as the Lorentz factor, optical depth and pair-to-baryon ratio, only from the observable quantities. In particular, we can test whether prompt emission of GRBs comes from the pair/baryonic photosphere or not. The future-coming Gamma-Ray Large Area Space Telescope (GLAST) satellite will provide us with good chances to use our recipes by detecting pair-signatures.

Cuesta 2007 伽玛暴作为Cardassian宇宙学的工具

主要内容:
于SNIa的结果一致。认为伽玛暴可以作为高精度宇宙学的工具之一。

精彩摘抄:


文章信息:

arXiv:0708.1355 [ps, pdf, other]

Title: Confronting the Hubble Diagram of Gamma-Ray Bursts with Cardassian Cosmology

Authors: Herman J. Mosquera Cuesta, Habib Dumet M., Cristina Furlanetto

Comments: Revtex4 format, 17 pages, 13 figures, 5 tables

Subjects: Astrophysics (astro-ph)

We construct the Hubble diagram (HD) of Gamma-Ray Bursts (GRBs) with redshifts reaching up to $z \sim 6$, by using five luminosity vs. luminosity indicator relations calibrated with the Cardassian cosmology. This model has a major interesting feature: despite of being matter-dominated and flat, it can explain the present accelerate expansion of the universe. This is the first study of this class of models using high redshift GRBs. We have performed a $\chi$-square statistical analysis of the GRBs calibrated with the Cardassian model, and also combined them with both the current Cosmic Microwave Background and Baryonic Acoustic Oscillation data. Our results show consistency between the current observational data and the model predictions. In particular, the best-fit parameters obtained from the $\chi^2$-analysis are in agreement with those obtained from the Concordance Cosmology ($\Lambda$-CDM). We determine the redshift at which the universe would start to follow the Cardassian expansion, i. e., \zc, and both the redshift at which the universe had started to accelerate, i. e., \zac, and the age-redshift relation $H_0t_0$. Our results also show that the universe, from the point of view of GRBs, had undergo a transition to acceleration at a redshift $z \approx 0.2-0.7$, which agrees with the SNIa results. Hence, after confronting the Cardassian scenario with the GRBs HD and proving its consistency with it, we conclude that GRBs should indeed be considered a complementary tool to several other astronomical observations for studies of high accuracy in cosmology.

Ashcraft 2007 BATSE没有z大于8的暴

主要内容:
用了好几个统计关系算BATSE暴的光度，进而计算红移z。但在几十个样本里没有发现超过8的暴（除了一个疑似）。

精彩摘抄:


文章信息:

arXiv:0708.1331 [ps, pdf, other]

Title: Are There Any Redshift >8 Gamma-Ray Bursts in the BATSE Catalog?

Authors: Teresa Ashcraft, Bradley E. Schaefer

Comments: ApJ in press, 18 pages

Subjects: Astrophysics (astro-ph)

Several luminosity indicators have been found for Gamma-Ray Bursts (GRBs) wherein measurable light curve and spectral properties are well-correlated with the peak luminosity. Several papers have each applied one different luminosity relation to find redshifts for BATSE GRBs and claim to identify specific bursts with z>8. The existence of such high redshift events is not surprising, as BATSE has enough sensitivity to see them and GRBs are expected out to the redshift of the first star formation. To improve results we used five luminosity relations with updated calibrations to determine redshifts with error bars. Combining these relations, we calculated the redshifts of 36 BATSE GRBs with claimed z>8. Our results include 13 bursts with our derived best redshift z_best>8, which looks promising at first. But the calculated redshift uncertainties are significantly large in these selected cases. With only one exception, all of our bursts have z_1siglow<9.>~4. Our best case for a very high redshift event is BATSE trigger 3142 with z_best>20 and z_1siglow=8.9, however we can only say z>4.1 at the two-sigma confidence level. In all, we cannot point toward any one BATSE burst as confidently having z>8. One implication is to greatly weaken prior claims that GRBs have a steeply rising rate-density out to high redshifts.

Ioka 2007 伽玛暴瞬时辐射的机制－－质子加速

主要内容:
在光球层内，热的正负电子对被质子加速成幂律分布，产生非热的辐射谱。

精彩摘抄:


文章信息:

arXiv:0708.1249 [ps, pdf, other]

Title: Unstable GRB photospheres and electron-positron annihilation lines

Authors: Kunihito Ioka, Kohta Murase, Kenji Toma, Shigehiro Nagataki, Takashi Nakamura

Comments: 4 pages, 2 figures

Subjects: Astrophysics (astro-ph)

We propose an emission mechanism of prompt gamma-ray bursts (GRBs) that can reproduce the observed non-thermal spectra with high radiative efficiencies, >50%. Internal dissipation below a photosphere can create a radiation-dominated thermal fireball. If electron-positron pairs outnumber protons, radiative acceleration of pairs drives the two-stream instabilities between pairs and protons, leading to the ``proton sedimentation'' in the accelerating pair frame. Pairs are continuously shock heated by proton clumps, scattering the thermal photons into the broken power-law shape, with the non-thermal energy that is comparable to the proton kinetic energy, consistent with observations. Pair photospheres become unstable around the radius of the progenitor star where strong thermalization occurs, if parameters satisfy the observed spectral (Yonetoku) relation. Pair annihilation lines are predicted above continua, which could be verified by GLAST.

Maeda 2007 超新星喷流的观测证据

主要内容:
认为超新星的爆发也是喷流的，并拟合了一下980425.

精彩摘抄:


文章信息:
Supernovae in Three-Dimension: A Link to Gamma-Ray Bursts

Authors: Keiichi Maeda

(Submitted on 7 Aug 2007)

Abstract: Observational consequences of a jet-driven supernova (SN) explosion model are presented. The results are compared in detail with optical observations of SN 1998bw associated with a Gamma-Ray Burst. It is shown that the jet model is able to reproduce virtually all the optical observations available for this SN, although a spherical model fails to explain some of observed features. Because of the viewing angle effect, the required kinetic energy of the SN ejecta is reduced to ~ 2 x 10^{52} erg as compared to that obtained by the previous spherical model (~ 5 x 10^{52} erg), but this is still much larger than that of a canonical SN (~10^{51} erg).

Comments:	6 pages, 3 figures. Invited talk at "Frascati Workshop 2007: Multifrequency Behaviour of High Energy Cosmic Sources", 28 May - 2 June, 2007, Vulcano, Italy. To apper in the Chinese Journal of Astronomy and Astrophysics (ChJAA)
Subjects:	Astrophysics (astro-ph)
Cite as:	arXiv:0708.0970v1 [astro-ph]

Goad 2007 用UVOT精确定位暴的位置

主要内容:
提出了一中方法，在早期用UVOT精确定位暴的位置。

精彩摘抄:


文章信息:
Accurate early positions for Swift GRBS: enhancing X-ray positions with UVOT astrometry

Authors: M.R. Goad (1) et al

Abstract: Here we describe an autonomous way of producing more accurate prompt XRT positions for Swift-detected GRBs and their afterglows, based on UVOT astrometry and a detailed mapping between the XRT and UVOT detectors. The latter significantly reduces the dominant systematic error -- the star-tracker solution to the World Coordinate System. This technique, which is limited to times when there is significant overlap between UVOT and XRT PC-mode data, provides a factor of 2 improvement in the localisation of XRT refined positions on timescales of less than a few hours. Furthermore, the accuracy achieved is superior to astrometrically corrected XRT PC mode images at early times (for up to 24 hours), for the majority of bursts, and is comparable to the accuracy achieved by astrometrically corrected X-ray positions based on deep XRT PC-mode imaging at later times (abridged).

Comments:	12 pages, 8 figures, 1 table, submitted to Astronomy and Astrophysics, August 7th 2007
Subjects:	Astrophysics (astro-ph)
Cite as:	arXiv:0708.0986v1 [astro-ph]

Kasliwal GRB070610可能是银河系内的一个暴

主要内容:
先看到了这个暴，5s。然后在相同的位置看到了X射线和光学瞬变体Swift J195509.6+261406，如果它们是同一个源，那么GRB 070610就是一个银河系内的暴，而且是一类新的 长暴（它的能量不像一般长暴那么大嘛）。

精彩摘抄:
X 射线，黑色的。
光学波段。

文章信息:

arXiv:0708.0226 [ps, pdf, other]

Title: GRB070610 : A Curious Galactic Transient

Authors: M. M. Kasliwal, S. B. Cenko, S. R. Kulkarni, P. B. Cameron, E. Nakar, E. O. Ofek, A. Rau, A. M. Soderberg, S. Campana, J. S. Bloom, D. A. Perley, L. Pollack, S. Barthelmy, J. Cummings, N. Gehrels, H. A. Krimm, C. B. Markwardt, G. Sato, P. Chandra, D. Frail, D. B. Fox, P. Price, E. Berger, S. A. Grebenev, R. A. Krivonos, R. A. Sunyaev

Comments: Submitted to ApJ, 17 pages, 11 figures, 5 tables ; Full resolution figures at this http URL

Subjects: Astrophysics (astro-ph)

GRB070610 is a typical high-energy event with a duration of 5s. Yet within the burst localization we detect a highly unusual X-ray and optical transient, Swift J195509.6+261406. We see high amplitude X-ray and optical variability on very short time scales even at late times. Using near-infrared imaging assisted by a laser guide star and adaptive optics, we have identified a quiescent counterpart to Swift J195509.6+261406. Our spectroscopic observations show that the spectral type of the counterpart is likely a K dwarf/sub-giant. It is possible that GRB070610 and Swift J195509.6+261406 are unrelated sources. However, the absence of a typical X-ray afterglow from GRB070610 in conjunction with the spatial and temporal coincidence of GRB070610 and Swift J195509.6+261406 motivate us to suggest that the sources are related. The closest analog to Swift J195509.6+261406 is V4641 Sgr, an unusual black hole binary. We suggest that Swift J195509.6+261406 along with V4641 Sgr define a sub-class of stellar black holes -- the fast X-ray novae. We further suggest that fast X-ray novae are associated with bursts of gamma-rays. If so, GRB070610 defines a new class of gamma-ray bursts and these bursts dominate the long-duration GRB demographics.