e-VLBI observations of SN2001em - an off-axis GRB candidate

TL;DR

This paper introduces the e-VLBI technique for rapid data transfer and presents observational results of SN2001em, a supernova candidate for an off-axis gamma-ray burst, highlighting its potential for timely transient studies.

Contribution

The paper demonstrates the application of e-VLBI for real-time observations of transient phenomena, showcasing its advantages over traditional VLBI methods.

Findings

SN2001em is marginally detected in e-VLBI observations.

Data suggest SN2001em may be fading or have an inverted spectrum at low frequencies.

The study highlights the potential of e-VLBI for rapid transient source analysis.

Abstract

Studying transient phenomena with the Very Long Baseline Interferometry (VLBI) technique faces severe difficulties because the turnaround time of the experiments from the observations to the scientific result is rather long. The e-VLBI technique has made it possible to transfer the data from a number of European VLBI Network (EVN) telescopes to the central data processor at JIVE through optical fibres, and correlate them in real time. The main goal of this paper is to introduce this rapidly developing new technique, by presenting observational results from a recent experiment. We observed SN2001em, a Type Ib/c supernova with an e-VLBI array and the Multi-Element Radio Linked Interferometer Network (MERLIN) in the UK. The source is marginally detected in our observations. We cannot make definite conclusions whether it is resolved at 1.6 GHz or not. Our data show that SN2001em either started fading in the last couple of months, or its radio spectrum is inverted at low frequencies,indicating free-free or synchrotron self-absorption. This is quite unusual, but not unprecedented in radio SNe.