Off-axis gamma-ray burst afterglow modeling based on a two-dimensional axisymmetric hydrodynamics simulation

Hendrik Van Eerten, Weiqun Zhang, Andrew MacFadyen

    Research output: Contribution to journalArticlepeer-review

    Abstract

    Starting as highly relativistic collimated jets, gamma-ray burst outflows gradually slow down and become nonrelativistic spherical blast waves. Although detailed analytical solutions describing the afterglow emission received by an on-axis observer during both the early and late phases of the outflow evolution exist, a calculation of the received flux during the intermediate phase and for an off-axis observer requires either a more simplified analytical model or direct numerical simulations of the outflow dynamics. In this paper, we present light curves for off-axis observers covering the long-term evolution of the blast wave, calculated from a high-resolution two-dimensional relativistic hydrodynamics simulation using a synchrotron radiation model. We compare our results to earlier analytical work and calculate the consequence of the observer angle with respect to the jet axis both for the detection of orphan afterglows and for jet break fits to the observational data. We confirm earlier results in the literature finding that only a very small number of local type Ibc supernovae can harbor an orphan afterglow. For off-axis observers, the observable jet break can be delayed up to several weeks, potentially leading to overestimation of the beaming-corrected total energy. In addition we find that, when using our off-axis light curves to create synthetic Swift X-ray data, jet breaks are likely to remain hidden in the data.

    Original languageEnglish (US)
    Pages (from-to)235-247
    Number of pages13
    JournalAstrophysical Journal
    Volume722
    Issue number1
    DOIs
    StatePublished - Oct 10 2010

    Keywords

    • Acceleration of particles
    • Gamma-ray burst: General
    • Hydrodynamics
    • Methods: Numerical
    • Relativistic processes
    • Shock waves

    ASJC Scopus subject areas

    • Astronomy and Astrophysics
    • Space and Planetary Science

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