Polarimetry of the transient relativistic jet of GRB110328/Swift J164449.3+573451

• Published in: Monthly notices of the Royal Astronomical Society 2012-04, Vol.421 (3), p.1942-1948
• Main Authors: Wiersema, K, van der Horst, AJ, Levan, A J, Tanvir, N R, Karjalainen, R, Kamble, A, Kouveliotou, C, Metzger, B D, Russell, D M, Skillen, I, Starling, RLC, Wijers, RAMJ
• Format: Article
• Language: English
• Subjects: Afterglows; Astronomy; Gamma ray bursts; Gamma rays; Imaging; Linear polarization; Polarimetry; Polarization; Radio; Red shift; Searching; Stars & galaxies
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1111/j.1365-2966.2011.20379.x

We present deep infrared (Ks-band) imaging polarimetry and radio (1.4- and 4.8-GHz) polarimetry of the enigmatic transient Swift J164449.3+573451. This source appears to be a short-lived jet phenomenon in a galaxy at redshift z= 0.354, activated by a sudden mass accretion on to the central massive black hole, possibly caused by the tidal disruption of a star. We aim to find evidence for this scenario through linear polarimetry, as linear polarization is a sensitive probe of jet physics, source geometry and the various mechanisms giving rise to the observed radiation. We find a formal Ks-band polarization measurement of Plin= 7.4 +/- 3.5 per cent (including systematic errors). Our radio observations show continuing brightening of the source, which allows sensitive searches for linear polarization as a function of time. We find no evidence of linear polarization at radio wavelengths of 1.4 and 4.8 GHz at any epoch, with the most sensitive 3 sigma limits as deep as 2.1 per cent. These upper limits are in agreement with expectations from scenarios in which the radio emission is produced by the interaction of a relativistic jet with a dense circumsource medium. We further demonstrate how polarization properties can be used to derive properties of the jet in Swift J164449.3+573451, exploiting the similarities between this source and the afterglows of gamma-ray bursts.