Kawanaka 2013 超吸积中的一种新的不稳定性可能作为伽马暴的中心引擎

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Title:		The Discovery of a New Instability in a Hyperaccretion Flow and its Implication for Gamma-Ray Bursts
Authors:		Kawanaka, Norita; Mineshige, Shin; Piran, Tsvi
Affiliation:		AA(Department of Astronomy, Graduate School of Science, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan norita@astron.s.u-tokyo.ac.jp), AB(Department of Astronomy, Kyoto University, Kitashirakawa-Oiwakecho, Sakyo-ku, Kyoto 606-8502, Japan), AC(Racah Institute of Physics, The Hebrew University, Jerusalem 91904, Israel)
Publication:		The Astrophysical Journal Letters, Volume 777, Issue 1, article id. L15, 5 pp. (2013). (ApJL Homepage)
Publication Date:		11/2013
Origin:		IOP
Astronomy Keywords:		accretion, accretion disks, black hole physics, gamma-ray burst: general, neutrinos
DOI:		10.1088/2041-8205/777/1/L15
Bibliographic Code:		2013ApJ...777L..15K

Abstract

A hyperaccretion flow around a stellar mass black hole is thought to be the most plausible engine that powers gamma-ray bursts (GRBs). The flow efficiently cools via neutrino emission at >~ 0.003-0.01 M _☉ s^–1 (corresponding to a luminosity of ~10⁵⁰ erg s^–1), while neither neutrino nor photon emission is efficient below this rate, so the flow should be advection-dominated. We carefully solve how a transition occurs from the advection-dominated to the neutrino-dominated branches, and find that the slope of the thermal equilibrium curve is negative in the surface density-accretion rate (Σ-\dot{M}) plane, a condition for viscous instability, at radii smaller than ~12 R _g (with R _g being the gravitational radius). We also confirm that the flow is thermally stable. The consequence of this instability is the formation of a clumpy structure in the flow. This is because the larger (respectively smaller) surface density is, the smaller (respectively larger) the mass accretion rate from the region in question becomes, leading to growth of the density contrast. The timescale for clump formation is estimated to be shorter than 0.1 s. The observational implication is discussed in the context of GRBs. We suggest that this might explain the origin of the large variability observed in the prompt emission of GRBs.

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Lü, Hou-Jun 2014 磁星作为伽马暴的中心引擎

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用closure relation和磁星的预言对比，发现一致。

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Title:		A test of the millisecond magnetar central engine model of GRBs with Swift data
Authors:		Lü, Hou-Jun; Zhang, Bing
Publication:		eprint arXiv:1401.1562
Publication Date:		01/2014
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		19 pages, 35 figures, 3 Tables. comments are welcome
Bibliographic Code:		2014arXiv1401.1562L

Abstract

A rapidly spinning, strongly magnetized neutron star (magnetar) has been proposed as one possible candidate of the central engine of gamma-ray bursts (GRBs). In this paper, we systematically analyze the Swift/XRT light curves of long GRBs detected before 2013 August, and characterize them into four categories based on how likely they may harbor a magnetar central engine: "Gold", "Silver", "Aluminum" and "Non-magnetar". We also independently analyze the data of short GRBs with a putative magnetar central engine. We then perform a statistical study of various properties of the magnetar samples and the non-magnetar sample, and investigate whether the data are consistent with the hypothesis that there exist two types of central engines. By deriving the physical parameters of the putative magnetars, we find that the observations of the Gold and Silver samples are generally consistent with the predictions of the magnetar model. For a reasonable beaming factor for long GRBs, the derived magnetar surface magnetic field $B_p$ and initial spin period $P_0$ fall into the reasonable range. Magnetar winds in short GRBs, on the other hand, are consistent with being isotropic. No GRB in the magnetar sample has a beam-corrected total energy exceeding the maximum energy budget defined by the initial spin energy of the magnetar ($E_{\rm rot}\sim 2\times 10^{52}$ erg), while some non-magnetar GRBs do violate such a limit. With beaming correction, on average the non-magnetar sample (probably powered by a black hole) is more energetic and luminous than the magnetar samples. Our analysis hints that millisecond magnetars are likely operating in a good fraction, but probably not all, GRBs.

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Lazzati 2013 长暴的中心引擎时间可能就20秒

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而看起来的T90的多样性来自1.穿出包层的时间；2.不同观测角；3.不同红移所导致的修正。

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Title:		On the observed duration distribution of gamma-ray bursts from collapsars
Authors:		Lazzati, D.; Villeneuve, M.; López-Cámara, D.; Morsony, B. J.; Perna, R.
Affiliation:		AA(Department of Physics, NC State University, 2401 Stinson Drive, Raleigh, NC 27695-8202, USA; davide_lazzati@ncsu.edu), AB(Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO 80309-0391, USA), AC(Department of Physics, NC State University, 2401 Stinson Drive, Raleigh, NC 27695-8202, USA), AD(Department of Astronomy, University of Wisconsin-Madison, 3321 Sterling Hall, 475 N. Charter Street, Madison, WI 53706-1582, USA), AE(Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO 80309-0391, USA; JILA, University of Colorado and National Institute of Standards and Technology, Boulder, CO 80309-0440, USA)
Publication:		Monthly Notices of the Royal Astronomical Society, Volume 436, Issue 2, p.1867-1872 (MNRAS Homepage)
Publication Date:		12/2013
Origin:		OUP
Astronomy Keywords:		hydrodynamics, methods: numerical, gamma-ray burst: general
Abstract Copyright:		2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
DOI:		10.1093/mnras/stt1705
Bibliographic Code:		2013MNRAS.436.1867L

Abstract

The duration of the prompt emission of long gamma-ray bursts is generally considered to be fairly similar to the duration of the activity of the engine in the centre of the progenitor star. Here, we investigate the relation between the duration of the engine activity and that of the observed light curve, using inputs from both numerical simulations and observations. We find that the observed burst duration is a good proxy for the engine duration after the time necessary for the jet to break out the star's surface is subtracted. However, the observed duration is a function of the viewing angle and can be significantly shorter than the duration of the engine activity. We also show that the observed, redshift-corrected burst duration evolves only moderately with redshift for both observations and synthetic light curves. We conclude that the broad distribution of the observed duration of long Burst And Transient Sources Experiment (BATSE) gamma-ray bursts is mostly accounted for by an engine lasting ˜20 s, the dispersion being due to viewing and redshift effects. Our results do not rule out the existence of engines with very long duration. However, we find that they are constrained to be a small minority of the BATSE detected bursts.

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Bromberg, Omer 2011 伽马暴坍缩星模型的一个证据

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下图的平台是证据。考虑到喷流冲出包层需要时间，只有冲出后的时间才被当做T90.这就相当于X射线shellow decay的时间零点移动模型一样。那么在时间短的那些暴满足的power law的分布应该是(T90+tau)^-alpha，换成T90^-beta就有一个平台。
更短的地方的突起就不应该是坍缩星的，而是另一类，短暴。


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Title:		An observational imprint of the Collapsar model of long Gamma Ray Bursts
Authors:		Bromberg, Omer; Nakar, Ehud; Piran, Tsvi; Sari, Re'em
Publication:		eprint arXiv:1111.2990
Publication Date:		11/2011
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		12 pages, 1 figure
Bibliographic Code:		2011arXiv1111.2990B

Abstract

The Collapsar model provides a theoretical framework for the well known association between long gamma-ray bursts (GRBs) and collapsing massive stars. A bipolar relativistic jet, launched at the core of a collapsing star, drills its way through the stellar envelope and breaks out of the surface before producing the observed gamma-rays. While a wealth of observations associate GRBs with the death of massive stars, as yet there is no direct evidence for the Collapsar model itself. Here we show that a distinct signature of the Collapsar model is the appearance of a plateau in the duration distribution of the prompt GRB emission at times much shorter than the typical breakout time of the jet. This plateau is evident in the data of all three major satellites. These findings provide an evidence that directly supports the Collapsar model. Additionally, it suggests the existence of a large population of choked (failed) GRBs and that the 2 s duration commonly used to separate Collapsars and non-Collapasars is inconsistent with the duration distributions of {\it Swift} and Fermi GRBs and only holds for BATSE GRBs.

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Barkov 2011 用BZ机制解释短暴的延展辐射

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NDAF产生暴本身，BZ产生更长但更窄的喷流产生延展辐射。

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Title:		Model of extended emission of short Gamma-ray Bursts
Authors:		Barkov, Maxim V.; Pozanenko, Alexei S.
Publication:		eprint arXiv:1103.4246
Publication Date:		03/2011
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		6 pages, 4 figures
Bibliographic Code:		2011arXiv1103.4246B

Abstract

Until now the existence of extended emission is an intriguing property of short bursts. It is not clear what is the nature of the extended emission. It might be a rising x-ray afterglow, or it could be a manifestation of the prolonged activity of a central engine. We consider short duration gamma-ray bursts, emphasizing the common properties of short bursts and short burst with extended emission. Assuming that the extended emission with broad dynamic range is a common property of short bursts, we propose a two jet model which can describe both short main episode of hard spectra emission, specific for short bursts, and softer spectra extended emission by different off axis position of observer. The toy model involves a short duration jet powered by heating due to $\nu\tilde{\nu}$ annihilation and long-lived Blandford-Znajek jet with significantly narrow opening angle. Our proposed model is a plausible mechanism for short duration burst energization, and can explain both short burst with and without extended emission within a single class of progenitor.

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Cannizzo 2011 伽马暴的回落盘

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Title:		Fall-back Disks in Long and Short Gamma-Ray Bursts
Authors:		Cannizzo, J. K.; Troja, E.; Gehrels, N.
Affiliation:		AA(CRESST and Astroparticle Physics Laboratory NASA/GSFC, Greenbelt, MD 20771, USA ; Department of Physics, University of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA ;John.K.Cannizzo@nasa.gov), AB(Astroparticle Physics Laboratory NASA/GSFC, Greenbelt, MD 20771,USA ; NASA Postdoctoral Program Fellow.), AC(Astroparticle Physics Laboratory NASA/GSFC, Greenbelt, MD 20771,USA )
Publication:		The Astrophysical Journal, Volume 734, Issue 1, article id. 35 (2011). (ApJ Homepage)
Publication Date:		06/2011
Origin:		IOP
ApJ Keywords:		accretion, accretion disks, gamma-ray burst: general, gamma-ray burst: individual: GRB 060729 GRB 051221A, stars: interiors, X-rays: general
DOI:		10.1088/0004-637X/734/1/35
Bibliographic Code:		2011ApJ...734...35C

Abstract

We present time-dependent numerical calculations for fall-back disks relevant to gamma-ray bursts (GRBs) in which the disk of material surrounding the black hole powering the GRB jet modulates the mass flow and hence the strength of the jet. Given the initial existence of a small mass <~ 10^-4 M _sun near the progenitor with a circularization radius ~10¹⁰-10¹¹ cm, an unavoidable consequence will be the formation of an "external disk" whose outer edge continually moves to larger radii due to angular momentum transport and lack of a confining torque. For long GRBs, if the mass distribution in the initial fall-back disk traces the progenitor envelope, then a radius ~10¹¹ cm gives a timescale ~10⁴ s for the X-ray plateau. For late times t > 10⁷ s a steepening due to a cooling front in the disk may have observational support in GRB 060729. For short GRBs, one expects most of the mass initially to lie at small radii <10⁸ cm however, the presence of even a trace amount ~10^-9 M _sun of high angular material can give a brief plateau in the light curve. By studying the plateaus in the X-ray decay of GRBs, which can last up to ~10⁴ s after the prompt emission, Dainotti et al. find an apparent inverse relation between the X-ray luminosity at the end of the plateau and the duration of the plateau. We show that this relation may simply represent the fact that one is biased against detecting faint plateaus and therefore preferentially sampling the more energetic GRBs. If, however, there were a standard reservoir in fall-back mass, our model could reproduce the inverse X-ray luminosity-duration relation. We emphasize that we do not address the very steep, initial decays immediately following the prompt emission, which have been modeled by Lindner et al. as fall back of the progenitor core, and may entail the accretion of >~ 1 M _sun.

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Fan 2011 限制短暴吸积盘的质量和外流的半径

主要内容:
假设中微子-中微子湮灭的模型下，估算盘质量和外流的launch半径。

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Title:		Short Gamma-ray Bursts: the mass of the accretion disk and the initial radius of the outflow
Authors:		Fan, Yi-Zhong; Wei, Da-Ming
Publication:		eprint arXiv:1107.2656
Publication Date:		07/2011
Origin:		ARXIV
Keywords:		Astrophysics - Cosmology and Extragalactic Astrophysics, Astrophysics - High Energy Astrophysical Phenomena
Comment:		8 pages including 1 table, to appear in ApJ
Bibliographic Code:		2011arXiv1107.2656F

Abstract

In this work we estimate the accretion-disk mass in the specific scenario of binary-neutron-star-merger with current observational data. Assuming that the outflows of short Gamma-ray Bursts (GRBs) are driven via neutrino-antineutrino annihilation we estimate the disk mass of about half of short bursts in the sample to be $\sim 0.01-0.1 M_\odot$, in agreement with that obtained in the numerical simulations. Massive disks ($\sim {\rm several} 0.1 M_\odot$) found in some other short GRBs may point to the more efficient magnetic process of energy extraction or the neutron star and black hole binary progenitor. Our results suggest that some short bursts may be really due to the coalescence of double neutron stars and are promising gravitational wave radiation sources. For future short GRBs with simultaneous gravitational-wave detections, the disk mass may be reliably inferred and the validity of our approach will be tested. We also propose a method to constrain the initial radius of a baryonic outflow where it is launched ($R_0$) without the need of identifying an ideal thermal spectrum. We then apply it to GRB 090510 and get that $R_0 \lesssim 6.5\times 10^{6}(\Gamma_{\rm ph}/2000)^{-4}$ cm, suggesting that the central engine is a black hole with a mass $< 22 M_\odot(\Gamma_{\rm ph}/2000)^{-4}$, where $\Gamma_{\rm ph}$ is the bulk Lorentz factor of the outflow at the photospheric radius.

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Narayan 2011 冷的磁场加速的喷流不能产生伽马暴，效率太低

主要内容:
所以，要么磁能在激波前就很大部分转化为了热能，要么就是传统的火球模型。

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Title:		Constraints on Cold Magnetized Shocks in Gamma-Ray Bursts
Authors:		Narayan, Ramesh; Kumar, Pawan; Tchekhovskoy, Alexander
Publication:		eprint arXiv:1105.0003
Publication Date:		04/2011
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Extragalactic Astrophysics
Comment:		Submitted to MNRAS. 9 pages, 4 figures, uses mn2e.cls
Bibliographic Code:		2011arXiv1105.0003N

Abstract

We consider a model in which the ultra-relativistic jet in a gamma-ray burst (GRB) is cold and magnetically accelerated. We assume that the energy flux in the outflowing material is partially thermalized via internal shocks or a reverse shock, and we estimate the maximum amount of radiation that could be produced in such magnetized shocks. We compare this estimate with the available observational data on prompt gamma-ray emission in GRBs. We find that, even with highly optimistic assumptions, the magnetized jet model is radiatively too inefficient to be consistent with observations. One way out is to assume that much of the magnetic energy in the post-shock, or even pre-shock, jet material is converted to particle thermal energy by some unspecified process, and then radiated. This can increase the radiative efficiency sufficiently to fit observations. Alternatively, jet acceleration may be driven by thermal pressure rather than magnetic fields. In this case, which corresponds to the traditional fireball model, sufficient prompt GRB emission could be produced either from shocks at a large radius or from the jet photosphere closer to the center.

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Woosley 2011 伽马暴前身星综述

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也提到中心引擎，还有超长的低能暴（没观测到）。

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Title:		Models for Gamma-Ray Burst Progenitors and Central Engines
Authors:		Woosley, S. E.
Publication:		eprint arXiv:1105.4193
Publication Date:		05/2011
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		31 pages, 1 figure, to be published by Cambridge University Press in the volume "Gamma-Ray Bursts". Final version accepted for publication June 23, 2010
Bibliographic Code:		2011arXiv1105.4193W

Abstract

Most gamma-ray bursts are made during the deaths of massive stars. Here the environmental circumstances, stellar evolutionary paths, and explosion physics that might produce the bursts are reviewed. Neither of the two leading models - collapsar and millisecond magnetar - can be excluded, and both may operate in progenitor stars of different masses, metallicities, and rotation rates. Potential diagnostics are discussed and uncertainties highlighted. Both models are capable of producing a wide variety of transients whose properties vary with both stellar properties and viewing angle. Some of these are reviewed including the possibility of very long (days) low luminosity bursts, so far undiscovered, short hard bursts from massive stellar progenitors, and bursts from very massive Population III stars.

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Metzger 2010 伽马暴的原磁星模型

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Title:		The Proto-Magnetar Model for Gamma-Ray Bursts
Authors:		Metzger, B. D.; Giannios, D.; Thompson, T. A.; Bucciantini, N.; Quataert, E.
Publication:		eprint arXiv:1012.0001
Publication Date:		11/2010
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		21 pages (plus 2 appendices), 21 figures, 1 table, submitted to MNRAS
Bibliographic Code:		2010arXiv1012.0001M

Abstract

Long duration Gamma-Ray Bursts (GRBs) originate from the core collapse of massive stars, but the identity of the central engine remains elusive. Previous work has shown that rapidly spinning, strongly magnetized proto-neutron stars (`millisecond proto-magnetars') produce outflows with energies, timescales, and magnetizations sigma_0 (maximum Lorentz factor) that are consistent with those required to produce long GRBs. Here we extend this work in order to construct a self-consistent model that directly connects the properties of the central engine to the observed prompt emission. Just after the launch of the supernova shock, a wind heated by neutrinos is driven from the proto-magnetar. The outflow is collimated into a bipolar jet by its interaction with the star. As the magnetar cools, the wind becomes ultra-relativistic and Poynting-flux dominated (sigma_0 >> 1) on a timescale comparable to that required for the jet to clear a cavity through the star. Although the site and mechanism of the prompt emission are debated, we calculate the emission predicted by two models: magnetic dissipation and internal shocks. Our results favor the magnetic dissipation model because it (1) predicts a relatively constant `Band' spectral peak energy E_peak with time during the GRB and (2) reproduces the observed Amati/Yonetoku correlations between E_peak and the GRB energy/luminosity. The jet baryon loading decreases abruptly when the neutron star becomes transparent to neutrinos at t ~ 10-100 seconds. Jets with ultra-high magnetization cannot effectively accelerate and dissipate their energy, suggesting this transition ends the prompt emission and may explain the steep decay phase that follows. We assess several phenomena potentially related to magnetar birth, including low luminosity GRBs, thermal-rich GRBs/X-ray Flashes, very luminous supernovae, and short duration GRBs with extended emission.

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Carballido 2010 磁化的中微子冷却盘可能是伽马暴的能源机制

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Title:		Characterizing the time variability in magnetized neutrino--cooled accretion disks: signatures of the gamma-ray burst central engine
Authors:		Carballido, Augusto; Lee, William H.
Publication:		eprint arXiv:1011.5515
Publication Date:		11/2010
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		Accepted for publication in ApJ Letters
Bibliographic Code:		2010arXiv1011.5515C

Abstract

The central engine of Gamma Ray Bursts is hidden from direct probing with photons mainly due to the high densities involved. Inferences on their properties are thus made from their cosmological setting, energetics, low-energy counterparts and variability. If GRBs are powered by hypercritical accretion onto compact objects, on small spatial scales the flow will exhibit fluctuations, which could in principle be reflected in the power output of the central engine and ultimately in the high energy prompt emission. Here we address this issue by characterizing the variability in neutrino cooled accretion flows through local shearing box simulations with magnetic fields, and then convolving them on a global scale with large scale dynamical simulations of accretion disks. The resulting signature is characteristic, and sensitive to the details of the cooling mechanism, providing in principle a discriminant for GRB central engine properties.

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