Upper Limit on Radio Polarization for GRB 110328A / Swift J164449.3+573451
ATel #3278; Geoffrey Bower, Joshua Bloom, Brad Cenko (UC Berkeley)
on 13 Apr 2011; 18:12 UT
Credential Certification: S. Bradley Cenko (cenko@astro.berkeley.edu)
Subjects: Radio, AGN, Black Hole, Blazar, Gamma-Ray Burst
We observed the radio source (GCN #11836) associated with GRB110328A / Swift J164449.3+573451 (GCN #11823) with the Very Long Baseline Array on 1 April 2011 beginning at 05:30 UT for 4 four hours (see also GCN #11911). We detect the radio counterpart at a frequency of 8.4 GHz with a flux density of 1.7 +/- 0.1 mJy. We place an upper limit of 17% variations in the flux density during the course of these observations. The source is point-like to a synthesized beam of 2.9 x 1.8 mas. We also set a 2-sigma upper limit on the linear polarization fraction of 4.5%. While linear polarization is an expected property of compact synchrotron sources, we note that fewer than 10% of flat spectrum quasars and Bl Lac objects have 4.8 GHz polarization > 5% (Aller, Aller, & Hughes 2003).
