Eichler 2014 解决光球层热辐射的效率太低的问题

主要内容:
说如果在内部的热辐射往外走的时候，是基本不会被外层的shell挡住的，因为当光子追上外层的shell的时候，是在很远的地方，已经光学薄了。

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Title:		Cloaked Gamma Ray Bursts
Authors:		Eichler, David
Publication:		eprint arXiv:1402.0245
Publication Date:		02/2014
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		accepted for publication in the Astrophysical Journal
Bibliographic Code:		2014arXiv1402.0245E

Abstract

It is suggested that many $\gamma$-ray bursts (GRBs) are cloaked by an ultra-relativistic baryonic shell that has high optical depth when the photons are manufactured. Such a shell would not fully block photons reflected or emitted from its inner surface, because the radial velocity of the photons can be less than that of the shell. This avoids the standard problem associated with GRBs that the thermal component should be produced where the flow is still obscured by high optical depth. The radiation that escapes high optical depth obeys the Amati relation. Observational implications may include a) anomalously high ratios of afterglow to prompt emission, such as may have been the case in the recently discovered PTF 11agg, and b) ultrahigh-energy neutrino pulses that are non-coincident with detectable GRB. It is suggested that GRB 090510, a short, very hard GRB with very little afterglow, was an {\it exposed} GRB, in contrast to those cloaked by baryonic shells. \end{abstract}

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Zalamea 2010 黑洞超吸积下的中微子碰撞

主要内容:
在Kerr度规下计算中微子流量和散射，看是否能产生伽马暴所需的能量。公式（22）给出了所能产生的能量，（23）给出了效率(中微子转换为喷流的效率)，都在可行范围内。

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Title:		Neutrino heating near hyper-accreting black holes
Authors:		Zalamea, Ivan; Beloborodov, Andrei M.
Publication:		eprint arXiv:1003.0710
Publication Date:		03/2010
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		8 pages, submitted to MNRAS
Bibliographic Code:		2010arXiv1003.0710Z

Abstract

Hyper-accretion discs around black holes emit copious neutrinos and anti-neutrinos. A fraction of the emitted neutrinos convert to electron-positron plasma above the disc through the annihilation reaction $\nu\bar\nu\to e^+e^-$. This process may drive relativistic jets associated with GRB explosions. We calculate the efficiency of energy deposition by neutrinos. Our calculation is fully relativistic and based on a geodesic-tracing method. We find that the efficiency of neutrino heating is a well-defined function of (i) accretion rate and (ii) spin of the black hole. It is practically independent of the details of neutrino transport in the opaque zone of the disc. The results help identify accretion discs whose neutrino emission can power GRBs.

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Mimica 2009 磁化内激波的效率可以很高

主要内容:
而且不怎么依赖于相对罗仑兹因子和状态方程.

(当然, 因为能量主要靠释放磁场的能量.)

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Title:		On the dynamic efficiency of internal shocks in magnetized relativistic outflows
Authors:		Mimica, P.; Aloy, M. A.
Publication:		eprint arXiv:0909.1328
Publication Date:		09/2009
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		Accepted for publication in MNRAS. 8 pages, 6 figures. The definitive version is available at http://www.blackwell-synergy.com
Bibliographic Code:		2009arXiv0909.1328M

Abstract

We study the dynamic efficiency of conversion of kinetic-to-thermal/magnetic energy of internal shocks in relativistic magnetized outflows. We model internal shocks as being caused by collisions of shells of plasma with the same energy flux and a non-zero relative velocity. The contact surface, where the interaction between the shells takes place, can break up either into two oppositely moving shocks (in the frame where the contact surface is at rest), or into a reverse shock and a forward rarefaction. We find that for moderately magnetized shocks (magnetization $\sigma\simeq 0.1$), the dynamic efficiency in a single two-shell interaction can be as large as 40%. Thus, the dynamic efficiency of moderately magnetized shocks is larger than in the corresponding unmagnetized two-shell interaction. If the slower shell propagates with a sufficiently large velocity, the efficiency is only weakly dependent on its Lorentz factor. Consequently, the dynamic efficiency of shell interactions in the magnetized flow of blazars and gamma-ray bursts is effectively the same. These results are quantitatively rather independent on the equation of state of the plasma. The radiative efficiency of the process is expected to be a fraction $f_r<1$>

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Lazzati 2009 光球辐射可以效率很高

主要内容:
数值模拟, 不过这个结论是容易理解的, 主要光学薄半径和coasting半径相当, 就可以辐射效率很高了.

但是有个问题是光球辐射是黑体谱, 怎么转换成观测到的非热谱呢? 文中给了点儿定性的解释, 说是康普顿散射.

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Title:		Very high efficiency photospheric emission in long duration gamma-ray bursts
Authors:		Lazzati, Davide; Morsony, Brian J.; Begelman, Mitch
Publication:		eprint arXiv:0904.2779
Publication Date:		04/2009
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		4 pages, uses emulateapj and apjfonts (both included). 4 color figures. Submitted to ApJL
Bibliographic Code:		2009arXiv0904.2779L

Abstract

We numerically analyze the evolution of a long-duration gamma-ray burst jet as it leaves the progenitor star and propagates to the photospheric radius, where radiation can be released. We find that the interaction of the relativistic material with the progenitor star has influences well beyond the stellar surface. Tangential collimation shocks are observed throughout the jet evolution, out to about 100 stellar radii, which is the whole range of our simulation. We find that the jet is internally hot at the photospheric radius and we compute the photospheric emission. The photosphere is a very efficient radiator, capable of converting more than half of the total energy of the jet into radiation. We show that bright photospheres are a common feature of jets born inside massive progenitor stars and that this effect can explain the high radiative efficiency observed in long-duration bursts.

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Ghisellini 2007 火球与静止物质的膨胀产生伽玛暴

主要内容:
提出了标准内激波模型的一些弊端：效率要求不同shell的Lorentz因子相差很大，早期余辉的变平，Amati等统计关系不能从标准模型推出。然后提出在暴源不远的外边可能存在一个静止的物质块，火球与它撞上产生了伽玛暴。

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文章信息:

arXiv:0709.1945 [ps, pdf, other]

Title: Re-born fireballs in Gamma-Ray Bursts

Authors: G. Ghisellini (1), A. Celotti (2), G. Ghirlanda (1), C. Firmani (1,3), L. Nava (1,4) ((1) INAF-Oss. Astr. di Brera, (2) SISSA, Trieste, (3) U.N.A.M., Mexico, (4) Univ. Insubria)

Comments: 5 pages, 3 Figures, accepted for publication in MNRAS (Letters)

Subjects: Astrophysics (astro-ph)

We consider the interaction between a relativistic fireball and material assumed to be still located just outside the progenitor star. Only a small fraction of the expected mass is sufficient to efficiently decelerate the fireball, leading to dissipation of most of its kinetic energy. Since the scattering optical depths are still large at distances comparable to the progenitor radius, the dissipated energy is trapped in the system, accelerating it to relativistic velocities. The process resembles the birth of another fireball at radii R~1e11 cm, not far from the transparency radius, and with a starting bulk Lorentz factors Gamma_c~10. As seen in the observer frame, this "re--generated" fireball appears collimated within an angle theta_j=1/Gamma_c. If the central engine works intermittently, the funnel can, at least partially, refill and the process can repeat itself. We discuss how this idea can help solving some open issues of the more conventional internal shock scenario for interpreting the Gamma-Ray Burst properties.

Zou 2007 伽玛暴的高辐射效率

主要内容:
用ApJ上050904相同的模型，假设后面喷出的所有sub－shell都相同，可以计算辐射效率，得到的效率可以很高。

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文章信息:
High Efficiency of Gamma-Ray Bursts Revisited

Authors: Y. C. Zou, Z. G. Dai

(Submitted on 7 Mar 2007)

Abstract: Using the conservation of energy and momentum during collisions of any two shells, we consider the efficiency of gamma-ray bursts by assuming that the ejecta from the central engine are equally massive and have the same Lorentz factors. We calculate the efficiency and the final Lorentz factor of the merged whole shell for different initial diversities of Lorentz factors and for different microscopic radiative efficiency. As a result, a common high efficiency in the range of 0.1 to 0.9 is considerable, and a very high value near 100% is also reachable if the diversity of the Lorentz factors is large enough.

Comments:

12 pages, 6 figures, accepted by JASR

Subjects:

Astrophysics (astro-ph)

Cite as:

arXiv:astro-ph/0703136v1

Mimica 2006 1D数值模拟伽玛暴内激波的碰撞 2

主要内容:
对于两个shell之间的碰撞， 考虑到辐射效率不能直接把两个shell当作整体，然后利用能量和动量守恒计算产生的内能，而应该是一个积分形式。计算了辐射效率，伽玛暴在6%-10%之间。

类似的还有：Mimica et al. 2005, A&A 441, 103

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astro-ph/0611765 [abs, ps, pdf, other] :

Title: Internal shocks in relativistic outflows: collisions of magnetized shells
Authors: Petar Mimica (1), Miguel-Angel Aloy (1, 2), Ewald Mueller (2) ((1) Departamento de Astronomia y Astrofisica, Universidad de Valencia, (2) MPA Garching)
Comments: 17 pages, 18 figures. 2 new references have been added. Accepted for publication in Astronomy and Astrophysics

(Abridged): We study the collision of magnetized irregularities (shells) in relativistic outflows in order to explain the origin of the generic phenomenology observed in the non-thermal emission of both blazars and gamma-ray bursts. We focus on the influence of the magnetic field on the collision dynamics, and we further investigate how the properties of the observed radiation depend on the strength of the initial magnetic field and on the initial internal energy density of the flow. The collisions of magnetized shells and the radiation resulting from these collisions are calculated using the 1D relativistic magnetohydrodynamics code MRGENESIS. The interaction of the shells with the external medium prior to their collision is also determined using an exact solver for the corresponding 1D relativistic magnetohydrodynamic Riemann problem. Our simulations show that two magnetization parameters - the ratio of magnetic energy density and thermal energy density, \alpha_B, and the ratio of magnetic energy density and mass-energy density, \sigma - play an important role in the pre-collision phase, while the dynamics of the collision and the properties of the light curves depend mostly on the magnetization parameter \sigma. The interaction of the shells with the external medium changes the flow properties at their edges prior to the collision. For sufficiently dense shells moving at large Lorentz factors (\simgt 25) these properties depend only on the magnetization parameter \sigma. Internal shocks in GRBs may reach maximum efficiencies of conversion of kinetic into thermal energy between 6% and 10%, while in case of blazars, the maximum efficiencies are \sim 2%.