The growth, polarization, and motion of the radio afterglow from the giant flare from SGR 1806-20 Academic Article uri icon


  • The extraordinary giant flare (GF) of 2004 December 27 from the soft gamma repeater SGR 180620 was followed by a bright radio afterglow. We present an analysis of VLA observations of this radio afterglow from SGR 180620, consisting of previously reported 8.5 GHz data covering days 7–20 after the GF, plus new observations at 8.5 and 22 GHz from day 24 to 81. We detect motion in the flux centroid of the afterglow, at an average velocity of (0.26 0.03)c (assuming a distance of 15 kpc) at a position angle of 45. This motion, in combination with the growth and polarization measurements, suggests an asymmetric outflow, mainly from one side of the magnetar. We find a deceleration in the expansion, from ∼ 9t o!5 mas day 1 . The time of deceleration is roughly coincident with the rebrightening in the radio light curve, as expected to result when the ejecta from the GF sweeps up enough of the external medium and transitions from a coasting phase to the SedovTaylor regime. The radio afterglow is elongated and maintains a 2 : 1 axis ratio with an average position angle of 40 (north through east), oriented perpendicular to the average intrinsic linear polarization angle. Subject headings: pulsars: individual (SGR 180620) — radio continuum: general — stars: flare — stars: neutron — stars: winds, outflows

publication date

  • January 1, 2005