Optical flashes from internal pairs formed in gamma-ray burst afterglows

Panaitescu, A.

doi:10.1088/0004-637X/806/1/64

Title: Optical flashes from internal pairs formed in gamma-ray burst afterglows

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Abstract

We develop a numerical formalism for calculating the distribution with energy of the (internal) pairs formed in a relativistic source from unscattered MeV–TeV photons. For gamma-ray burst (GRB) afterglows, this formalism is more suitable if the relativistic reverse shock that energizes the ejecta is the source of the GeV photons. The number of pairs formed is set by the source GeV output (calculated from the Fermi-LAT fluence), the unknown source Lorentz factor, and the unmeasured peak energy of the LAT spectral component. We show synchrotron and inverse-Compton light curves expected from pairs formed in the shocked medium and identify some criteria for testing a pair origin of GRB optical counterparts. Pairs formed in bright LAT afterglows with a Lorentz factor in the few hundreds may produce bright optical counterparts ($$R\lt 10$$) lasting for up to one hundred seconds. As a result, the number of internal pairs formed from unscattered seed photons decreases very strongly with the source Lorentz factor, thus bright GRB optical counterparts cannot arise from internal pairs if the afterglow Lorentz factor is above several hundreds.

Authors:

Panaitescu, A. ^[1]

Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

Publication Date:: Tue Jun 09 00:00:00 EDT 2015

Research Org.:: Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

Sponsoring Org.:: USDOE

OSTI Identifier:: 1228759

Report Number(s):: LA-UR-14-29092
Journal ID: ISSN 1538-4357

Grant/Contract Number:: AC52-06NA25396

Resource Type:: Accepted Manuscript

Journal Name:: The Astrophysical Journal

Additional Journal Information:: Journal Volume: 806; Journal Issue: 1; Journal ID: ISSN 1538-4357

Publisher:: Institute of Physics (IOP)

Country of Publication:: United States

Language:: English

Subject:: 79 ASTRONOMY AND ASTROPHYSICS; numerical - radiation mechanisms; non-thermal - relativistic processes; shock waves; stars; gamma-ray burst

Citation Formats


                    Panaitescu, A. Optical flashes from internal pairs formed in gamma-ray burst afterglows.  United States: N. p., 2015. 
Web.  doi:10.1088/0004-637X/806/1/64.

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                    Panaitescu, A. Optical flashes from internal pairs formed in gamma-ray burst afterglows.  United States.  https://doi.org/10.1088/0004-637X/806/1/64

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                    Panaitescu, A. Tue .  
"Optical flashes from internal pairs formed in gamma-ray burst afterglows".  United States.  https://doi.org/10.1088/0004-637X/806/1/64.  https://www.osti.gov/servlets/purl/1228759.

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@article{osti_1228759,

  title        = {Optical flashes from internal pairs formed in gamma-ray burst afterglows},

  author       = {Panaitescu, A.},

  abstractNote = {We develop a numerical formalism for calculating the distribution with energy of the (internal) pairs formed in a relativistic source from unscattered MeV–TeV photons. For gamma-ray burst (GRB) afterglows, this formalism is more suitable if the relativistic reverse shock that energizes the ejecta is the source of the GeV photons. The number of pairs formed is set by the source GeV output (calculated from the Fermi-LAT fluence), the unknown source Lorentz factor, and the unmeasured peak energy of the LAT spectral component. We show synchrotron and inverse-Compton light curves expected from pairs formed in the shocked medium and identify some criteria for testing a pair origin of GRB optical counterparts. Pairs formed in bright LAT afterglows with a Lorentz factor in the few hundreds may produce bright optical counterparts ($R\lt 10$) lasting for up to one hundred seconds. As a result, the number of internal pairs formed from unscattered seed photons decreases very strongly with the source Lorentz factor, thus bright GRB optical counterparts cannot arise from internal pairs if the afterglow Lorentz factor is above several hundreds.},

  doi          = {10.1088/0004-637X/806/1/64},

  journal      = {The Astrophysical Journal},

  number       = 1,

  volume       = 806,

  place        = {United States},

  year         = {Tue Jun 09 00:00:00 EDT 2015},

  month        = {Tue Jun 09 00:00:00 EDT 2015}

}

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