Polarimetry of the transient relativistic jet of GRB 110328/Swift J164449.3+573451

Abstract

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 3σ 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.

The radio afterglow of Swift J1644+57 reveals a powerful jet with fast core and slow sheath

“…However, for the fiducial parameters adopted in the present paper (including those of the CNM), the emission of the reverse shock is strongly absorbed below ∼ 10 GHz and, hence, the reverse shock contribution alone cannot account for the flux deficit of our models at early times 4 . The lack of a dominant reverse shock component at early times is potentially supported by the upper limits of 2 − 10% on the 4.8 GHz linear polarization on timescales of weeks after the BAT trigger (Wiersema et al 2012). We note, however, that if we consider a smaller value of the ζ e parameter, the synchrotron self-absorption at both the forward and reverse shocks is substantially reduced, and even counting only the forward shock emission, the flux deficit at early times can be ameliorated (see Appendix B for details).…”

Relativistic tidal disruption events

“…Observations of Swift J1644+57 are described in detail in numerous papers [7,[11][12][13][14][15][16]. To Briefly summarize, it exhibits an extremely luminous X-ray and γ−ray counterpart, which has was detected at luminous flux levels, with a peak of ∼3 × 10 48 ergs s −1 , and persisted at >10 45 ergs s −1 for in excess of a year.…”

Core-Collapse Supernovae and Gamma-Ray Bursts in TMT Era

“…For the observed afterglows in optical-NIR, lack of strong variability in the position angle of linear polarization indicate that magnetic field of the jet to be ordered rather than a random one. Even with the help of existing 8-10m class telescopes like Keck and VLT, spectropolarimetric observations of GRB afterglows have been covered sparsely with no concluding results (Wiersema et al 2012b). Some of the Type Ib/c SNe associated with GRBs have also shown polarization indicating towards asymmetry of the ejecta (photosphere/chemical inhomogeneity) for early photospheric phase of SNe (Kawabata et al 2002(Kawabata et al , 2003Tanaka et al 2009).…”