Letter to the Editor

An extremely prolific supernova factory in the buried nucleus of the starburst galaxy IC 694^*

¹ Instituto de Astrofísica de Andalucía – CSIC, PO Box 3004, 18008 Granada, Spain e-mail: torres@iaa.es
² Joint Institute for VLBI in Europe (JIVE), Dwingeloo, The Netherlands
³ ASTRON, Dwingeloo, The Netherlands

Received: 23 July 2009
Accepted: 17 October 2009

Abstract

Context. The central kiloparsec of many local uminous infrared galaxies are known to host intense bursts of massive star formation, leading to numerous explosions of core-collapse supernovae (CCSNe). However, the dust-enshrouded regions where those supernovae explode hamper their detection at optical and near-infrared wavelengths.

Aims. We investigate the nuclear region of the starburst galaxy IC 694 (=Arp 299-A) at radio wavelengths, aimed at discovering recently exploded CCSNe, as well as determining their rate of explosion, which carries crucial information about star formation rates, the initial mass function, and the starburst processes in action.

Methods. We use the electronic European VLBI Network to image with milliarcsecond resolution the 5.0 GHz compact radio emission of the innermost nuclear region of IC 694.

Results. Our observations detect a rich cluster of 26 compact radio emitting sources in the central 150 pc of the nuclear starburst in IC 694. The high brightness temperatures observed for the compact sources are indicative of a non-thermal origin for the observed radio emission, implying that most, if not all, of those sources are young radio supernovae (RSNe) and supernova remnants (SNRs). We find evidence of at least three relatively young, slowly evolving, long-lasting RSNe (A0, A12, and A15) that appear to have unusual properties, suggesting that the conditions in the local circumstellar medium (CSM) play a significant role in determining the radio behaviour of expanding SNe. Their radio luminosities are typical of normal RSNe, which result from the explosion of type IIP/b and type IIL SNe. All of these results provide support for a recent (less than 10-15 Myr) instantaneous starburst in the innermost regions of IC 694.