VLBA19A-303

Measuring the Size and Speed of AT2018cow's Outflow

Abstract

AT2018cow is an exciting new very energetic and relatively nearby (60 Mpc) supernova (SN). It is very unusual: in optical, it displayed a very short rise time (3.5 d), and, for the first 25 d an almost featureless blue spectrum although high photospheric velocities (40,000 km) were suggested. The X-ray luminosity was very high, ~1.4 x 10^43 erg/s, larger than those of ordinary SNe, and more consistent with those of SNe associated with gamma-ray bursts. Variable hard X-ray emission hints at a long-lived "central engine." The high luminosity suggests either a non-relativistic SN where the shock is interacting with a very dense medium, or an SN which harbours a GRB-like relativistic outflow. AT2018cow is strong in the radio, and in our first epoch of VLBI observations at 22 GHz we found a flux density of ~5 mJy at 22 GHz. We propose two further epochs of HSA observations in 2019 to continue monitoring the size, expansion velocity and possibly shock-geometry of AT2018cow. Our request is conditional upon the flux density remaining sufficiently high (>1 mJy). AT2018cow is a rare chance to capitalize on such a nearby SN with a possibly relativistic outflow, and we should exploit it to the fullest.

Investigators

Name	Institution
Megan Argo	Netherlands Institute for Radio Astronomy; Manchester, University of; Lancashire, University of Central
Giacomo Terreran	Northwestern University
Danny Milisavljevic	Purdue University; Center for Astrophysics | Harvard & Smithsonian
Cristiano Guidorzi	Ferrara, Università degli Studi di
Tarraneh Eftekhari	Northwestern University
Maria Drout	Carnegie Institute of Washington; Harvard University; Toronto, University of
Ryan Chornock	California at Berkeley, University of; Northwestern University; Ohio University; Center for Astrophysics | Harvard & Smithsonian
Norbert Bartel	York University
Kate Alexander	Arizona, University of
Deanne Coppejans	Warwick, University of
Raffaella Margutti	California at Berkeley, University of; Northwestern University; Harvard University; New York University
Michael Bietenholz *	York University; Hartebeesthoek Radio Astronomy Observatory
GBT Operator	Green Bank Observatory

* indicates the PI