VLBI Observations of SN 2011dh
ATel #3641; Michael F. Bietenholz (HartRAO/York University), Andreas Brunthaler (MPIfR/NRAO), Norbert Bartel (York University), Laura Chomiuk (Harvard-Smithsonian CfA), Michael P. Rupen (NRAO), Alicia Soderberg (CfA) and Bevin Zauderer (CfA)
on 9 Sep 2011; 04:20 UT
Credential Certification: Michael Bietenholz (mbieten@yorku.ca)
Subjects: Radio, Supernovae
We report on 22-GHz VLBI observations of SN 2011dh (ATEL #3398,
#3399, #3400, #3401, #3402, #3405, #3406, #3411, #3413, #3414, #3420,
#3428, #3431, #3432, #3433) in M51, using the NRAO VLBA and GBT, as
well as the Effelsberg telescopes. The observations were carried out
on 2011 Aug. 21, and were of 13 hours total length. The weather was
poor at several stations, resulting in relatively high noise.
Nonetheless, SN 2011dh was clearly detected, at a position
coincident with those determined from earlier VLA and EVN
observations. The peak brightness was 630 micro-Jy/beam, and the
image background rms was 92 micro-Jy/beam, where the beam was 0.66 x
0.35 mas (FWHM) at p.a. -12 degs. The true peak brightness was
likely somewhat higher, as some loss of phase coherence is
probable.
Fitting a spherical-shell model (see e.g., Bietenholz et al. 2010,
ApJ, v725, p4) directly to the visibility measurements we find an
outer angular radius of 0.11 (-0.11,+0.09) mas, corresponding to a
3-sigma upper limit of 0.38 mas. At an age of 82.3 days, this implies
an average expansion velocity of 19,000 (-19,000,+16000) km/s (for
distance = 8.4 Mpc). It is expected that the outer angular radius of
the radio emission traces the forward shock front, therefore our
expansion velocity represents an estimate of that of SN 2011dh's
forward shock. As such it is consistent with the expectations of the
forward shock velocity obtained from broadband lightcurve fitting by
Soderberg et al. 2011, ArXiv, 1107.1876.
Further VLBI observations are planned.
