Gamma-ray bursts are observed off-axis

Geoffrey Ryan, Hendrik Van Eerten, Andrew Macfadyen, Bin Bin Zhang

    Research output: Contribution to journalArticle

    Abstract

    We constrain the jet opening angle and, for the first time, the off-axis observer angle for gamma-ray bursts in the Swift-XRT catalog by using the ScaleFit package to fit afterglow light curves directly to hydrodynamic simulations. The ScaleFit model uses scaling relations in the hydrodynamic and radiation equations to compute synthetic light curves directly from a set of high-resolution two-dimensional relativistic blast wave simulations. The data sample consists of all Swift-XRT afterglows from 2005 to 2012 with sufficient coverage and a known redshift, 226 bursts in total. We find that the jet half-opening angle varies widely but is commonly less than 0.1 rad. The distribution of the electron spectral index is also broad, with a median at 2.30. We find the observer angle to have a median value of 0.57 of the jet opening angle over our sample, which has profound consequences for the predicted rate of observed jet breaks and affects the beaming-corrected total energies of gamma-ray bursts.

    Original languageEnglish (US)
    Article number3 (15pp)
    JournalAstrophysical Journal
    Volume799
    Issue number1
    DOIs
    StatePublished - Jan 20 2015

    Fingerprint

    gamma ray bursts
    afterglows
    hydrodynamics
    light curve
    hydrodynamic equations
    simulation
    blasts
    catalogs
    bursts
    electron
    scaling
    high resolution
    energy
    radiation
    electrons

    Keywords

    • gamma-ray burst: general
    • hydrodynamics
    • methods: data analysis
    • shock waves

    ASJC Scopus subject areas

    • Space and Planetary Science
    • Astronomy and Astrophysics

    Cite this

    Ryan, G., Van Eerten, H., Macfadyen, A., & Zhang, B. B. (2015). Gamma-ray bursts are observed off-axis. Astrophysical Journal, 799(1), [3 (15pp)]. https://doi.org/10.1088/0004-637X/799/1/3

    Gamma-ray bursts are observed off-axis. / Ryan, Geoffrey; Van Eerten, Hendrik; Macfadyen, Andrew; Zhang, Bin Bin.

    In: Astrophysical Journal, Vol. 799, No. 1, 3 (15pp), 20.01.2015.

    Research output: Contribution to journalArticle

    Ryan, G, Van Eerten, H, Macfadyen, A & Zhang, BB 2015, 'Gamma-ray bursts are observed off-axis', Astrophysical Journal, vol. 799, no. 1, 3 (15pp). https://doi.org/10.1088/0004-637X/799/1/3
    Ryan G, Van Eerten H, Macfadyen A, Zhang BB. Gamma-ray bursts are observed off-axis. Astrophysical Journal. 2015 Jan 20;799(1). 3 (15pp). https://doi.org/10.1088/0004-637X/799/1/3
    Ryan, Geoffrey ; Van Eerten, Hendrik ; Macfadyen, Andrew ; Zhang, Bin Bin. / Gamma-ray bursts are observed off-axis. In: Astrophysical Journal. 2015 ; Vol. 799, No. 1.
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