RADIATIVE COOLING IN RELATIVISTIC COLLISIONLESS SHOCKS: CAN SIMULATIONS AND EXPERIMENTS PROBE RELEVANT GAMMA-RAY BURST PHYSICS? / Medvedev Mikhail V.,Spitkovsky Anatoly // ASTROPHYSICAL JOURNAL. - 2009. - V. 700, l. 2. - P. 956-964.

ISSN/EISSN:

0004-637X / 1538-4357

Type:

Article

Abstract:

We address the question of whether numerical particle-in-cell (PIC) simulations and laboratory laser-plasma experiments can (or will be able to, in the near future) model realistic gamma-ray burst (GRB) shocks. For this, we compare the radiative cooling time, t(cool), of relativistic electrons in the shock magnetic fields to the microscopic dynamical time of collisionless relativistic shocks-the inverse plasma frequency of protons, omega(-1)(pp). We obtain that for t(cool)omega(-1)(pp) less than or similar to few hundred, the electrons cool efficiently at or near the shock jump and are capable of emitting away a large fraction of the shock energy. Such shocks are well resolved in existing PIC simulations; therefore, the microscopic structure can be studied in detail. Since most of the emission in such shocks would be coming from the vicinity of the shock, the spectral power of the emitted radiation can be directly obtained from finite-length simulations and compared with observational data. Such shocks have very high radiative efficiency and correspond to the internal baryon-dominated GRB shocks for the conventional range of ejecta parameters. Fermi acceleration of electrons in such shocks is limited by electron cooling, hence the emitted spectrum should be lacking a nonthermal tail, whereas its peak likely falls in the multi-MeV range. For lower radiative efficiency shocks, these constraints are relaxed: the peak energy is smaller and the nonthermal tail can be expected to form. Incidentally, the conditions in internal shocks are almost identical to those in laser-produced plasmas; thus, such GRB-like plasmas can be created and studied in laboratory experiments using the presently available Petawatt-scale laser facilities. An analysis of the external shocks shows that only the highly relativistic shocks, corresponding to the extremely early afterglow phase, can have efficient electron cooling in the shock transition. We emphasize the importance of radiative PIC simulations for further studies.

Author keywords:

gamma rays: bursts; magnetic fields; shock waves JITTER RADIATION; MAGNETIC-FIELDS; SELF-ABSORPTION; PROMPT EMISSION; AFTERGLOWS; SPECTRA; TURBULENCE; EVOLUTION; PLASMAS; ENERGY

DOI:

10.1088/0004-637X/700/2/956

Web of Science ID:

ISI:000268098100008

Соавторы в МНС:

—

Другие поля

Поле	Значение
Month	AUG 1
Publisher	IOP PUBLISHING LTD
Address	TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND
Language	English
EISSN	1538-4357
Keywords-Plus	JITTER RADIATION; MAGNETIC-FIELDS; SELF-ABSORPTION; PROMPT EMISSION; AFTERGLOWS; SPECTRA; TURBULENCE; EVOLUTION; PLASMAS; ENERGY
Research-Areas	Astronomy \& Astrophysics
Web-of-Science-Categories	Astronomy \& Astrophysics
Author-Email	medvedev@ku.edu
Funding-Acknowledgement	NSF {[}AST-0708213, AST-0807381]; NASA ATFP {[}NNX-08AL39G]; Swift Guest Investigator {[}NNX-07AJ50G]; DOE {[}DE-FG02-07ER54940]; Alfred P. Sloan Foundation fellowship
Funding-Text	This work has been supported by NSF grants AST-0708213 and AST-0807381, NASA ATFP grant NNX-08AL39G, Swift Guest Investigator grant NNX-07AJ50G, and DOE grant DE-FG02-07ER54940. A. S. acknowledges the support from Alfred P. Sloan Foundation fellowship.
Number-of-Cited-References	32
Usage-Count-Since-2013	8
Journal-ISO	Astrophys. J.
Doc-Delivery-Number	471ZU