K. Wiersema, A. J. van der Horst, A. J. Levan, N. R. Tanvir, R. Karjalainen, A. Kamble, C. Kouveliotou, B. D. Metzger, D. M. Russell, I. Skillen, R. L. C. Starling, R. A. M. J. Wijers
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 onto 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 polarisation 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 polarisation measurement of
P_lin = 7.4 +/- 3.5 % (including systematic errors). Our radio observations
show continuing brightening of the source, which allows sensitive searches for
linear polarisation as a function of time. We find no evidence of linear
polarisation at radio wavelengths of 1.4 GHz and 4.8 GHz at any epoch, with the
most sensitive 3 sigma limits as deep as 2.1%. 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 the polarisation 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.
View original:
http://arxiv.org/abs/1112.3042
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