GMRT Observations of the 2006 outburst of the Nova RS Ophiuchi: First detection of emission at radio frequencies < 1.4 GHz

TL;DR

This paper reports the first detection of low-frequency radio emission (<1.4 GHz) from the 2006 outburst of RS Ophiuchi, revealing non-thermal synchrotron emission affected by foreground absorption, and compares it with the 1985 event.

Contribution

It presents the first low-frequency radio detection of RS Ophiuchi's outburst and analyzes the absorption effects, highlighting differences from the 1985 event.

Findings

Detected radio emission at 0.61 GHz and 0.325 GHz during the 2006 outburst.

Identified non-thermal synchrotron emission with a spectral index of ~ -0.8.

Attributed differences from 1985 to lower foreground absorption and wind density in 2006.

Abstract

The first low radio frequency (<1.4 GHz) detection of the outburst of the recurrent nova RS Ophiuchi is presented in this letter. Radio emission was detected at 0.61 GHz on day 20 with a flux density of ~48 mJy and at 0.325 GHz on day 38 with a flux density of ~ 44 mJy. This is in contrast with the 1985 outburst when it was not detected at 0.327 GHz even on day 66. The emission at low radio frequencies is clearly non-thermal and is well-explained by a synchrotron spectrum of index alpha ~ -0.8 (S propto nu^alpha) suffering foreground absorption due to the pre-existing, ionized, warm, clumpy red giant wind. The absence of low frequency radio emission in 1985 and the earlier turn-on of the radio flux in the current outburst are interpreted as being due to higher foreground absorption in 1985 compared to that in 2006, suggesting that the overlying wind densities in 2006 are only ~30% of those in 1985.