Ambient magnetic field amplification in shock fronts of relativistic jets: an application to GRB afterglows

Autor(es)

Rocha da Silva, G. ^[1] ; Falceta-Goncalves, D. ^{[2, 3]} ; Kowal, G. ^[2] ; de Gouveia Dal Pino, E. M. ^[1]

Afiliação do(s) autor(es)

^[1] Univ Sao Paulo, Inst Astron Geofis & Ciencias Atmosfer, BR-05508090 Sao Paulo - Brazil

^[2] Univ Sao Paulo, Escola Artes Ciencias & Humanidades, BR-03828000 Sao Paulo - Brazil

^[3] Univ St Andrews, Sch Phys & Astron, SUPA, St Andrews KY16 9SS, Fife - Scotland

• Tipo de documento: Artigo Científico
• Fonte: Monthly Notices of the Royal Astronomical Society; v. 446, n. 1, p. 104-119, JAN 2015.
• Citações Web of Science: 5

Resumo

Strong downstream magnetic fields of the order of similar to 1G, with large correlation lengths, are believed to cause the large synchrotron emission at the afterglow phase of gamma-ray bursts (GRBs). Despite the recent theoretical efforts, models have failed to fully explain the amplification of the magnetic field, particularly in a matter-dominated scenario. We revisit the problem by considering the synchrotron emission to occur at the expanding shock front of a weakly magnetized relativistic jet over a magnetized surrounding medium. Analytical estimates and a number of high-resolution 2D relativistic magnetohydrodynamical (RMHD) simulations are provided. Jet opening angles of theta = 0 degrees-20 degrees, and ambient to jet density ratios of 10(-4)-10(2) were considered. We found that most of the amplification is due to compression of the ambient magnetic field at the contact discontinuity between the reverse and forward shocks at the jet head, with substantial pile-up of the magnetic field lines as the jet propagates sweeping the ambient field lines. The pile-up is maximum for theta -> 0, decreasing with theta, but larger than in the spherical blast problem. Values obtained for certain models are able to explain the observed intensities. The maximum correlation lengths found for such strong fields is of l(corr) <= 10(14) cm, 2-6 orders of magnitude larger than the found in previous works. (AU)

• Processo FAPESP: 11/12909-8 - Campos magnéticos, turbulência e efeitos de plasma no meio intergaláctico
• Beneficiário: Diego Antonio Falceta Gonçalves
• Linha de fomento: Auxílio à Pesquisa - Regular
• Processo FAPESP: 13/04073-2 - Reconexão magnética e processos relacionados em plasmas astrofísicos colisionais e acolisionais: das chamas solares para fontes extragaláticas
• Beneficiário: Grzegorz Kowal
• Linha de fomento: Auxílio à Pesquisa - Apoio a Jovens Pesquisadores
• Processo FAPESP: 09/54006-4 - Um cluster de computadores para o Departamento de Astronomia do IAG-USP e para o Núcleo de Astrofísica da UNICSUL
• Beneficiário: Elisabete Maria de Gouveia Dal Pino
• Linha de fomento: Auxílio à Pesquisa - Programa Equipamentos Multiusuários
• Processo FAPESP: 13/18815-0 - Reconexão magnética e processos relacionados em plasmas astrofísicos colisionais e acolisionais: das chamas solares para fontes extragaláticas
• Beneficiário: Grzegorz Kowal
• Linha de fomento: Bolsas no Brasil - Apoio a Jovens Pesquisadores
• Processo FAPESP: 09/50053-8 - Magnetic reconnection and particle acceleration in astrophysical sources and diffuse media
• Beneficiário: Grzegorz Kowal
• Linha de fomento: Bolsas no Brasil - Pós-Doutorado
• Processo FAPESP: 06/50654-3 - Investigação de fenômenos de altas energias e plasmas astrofísicos: teoria, observação e simulações numéricas
• Beneficiário: Elisabete Maria de Gouveia Dal Pino
• Linha de fomento: Auxílio à Pesquisa - Temático
• Processo FAPESP: 11/51275-4 - Magnetic field effects and particle acceleration in gamma-ray bursts (GRBs): theory, numerical simulations, and observational prospects
• Beneficiário: Elisabete Maria de Gouveia Dal Pino
• Linha de fomento: Auxílio à Pesquisa - Regular