Cosmic ray electron acceleration in the remnant of nova GK Persei?

Abstract

Radio observations of the nova remnant of GK Per around 1985 (epoch 1) have shown it to have a spectral index of -0.4 (S propto nu^alpha) at frequencies <1.4 GHz and a spectral index of -0.7 at frequencies >1.4 GHz (Seaquist et al 1989, Biermann et al 1995). This spectrum is either due to secondary electrons from p-p interactions (Biermann et al 1995) or due to the presence of at least two electron populations which dominate the emission at different frequencies. Our radio observations (Anupama & Kantharia 2005) of the remnant of GK Persei using the Giant Metrewave Radio Telescope (GMRT) and archival Very Large Array (VLA) data show that the nova remnant has a low frequency (<1.3 GHz) spectral index alpha ~ -0.85 (in 2003; epoch 3) and a high frequency spectral index of alpha ~ -0.7 (1997; epoch 2). Moreover the higher frequencies show an annual secular decrease of ~ 2.1 % between epochs 1 and 2 whereas there is no change at 0.33 GHz. This suggests a significant evolution of the spectrum over 20 years. In this paper, we discuss a possible physical basis for this spectral evolution based on a comparison of the synchrotron loss and electron acceleration timescales.