Pulsars, transients and relativistic astrophysics

Abstract:

We present the first polarization measurements of the radio emission from RRAT J1819-1458. Our observations, conducted in parallel to regular timing sessions, have yielded a small number of bright and polarized pulses. The polarization characteristics and integrated profile resemble those of normal pulsars with average spin-down energy Ė: moderate to low linear polarization in the integrated profile despite relatively high polarization in the individual pulses. On average, a small degree of circular polarization is also observed. The polarization position angle (PA) executes a remarkably smooth, steep S-shaped curve, interrupted by two orthogonal jumps. Based on the shape of the PA swing, we place some constraints on the emission geometry. We compare these polarization properties to those of other radio-emitting neutron star populations, including young pulsars, pulsars with a high surface magnetic field and radio-emitting magnetars. From the polarization measurements, the Faraday rotation measure of this rotating radio transient is derived. © 2009 The Authors. Journal compilation © 2009 RAS.

Abstract:

The final fate of massive stars depends on many factors. Theory suggests that some with initial masses greater than 25 to 30 solar masses end up as Wolf-Rayet stars, which are deficient in hydrogen in their outer layers because of mass loss through strong stellar winds. The most massive of these stars have cores which may form a black hole and theory predicts that the resulting explosion of some of them produces ejecta of low kinetic energy, a faint optical luminosity and a small mass fraction of radioactive nickel. An alternative origin for low-energy supernovae is the collapse of the oxygen-neon core of a star of 7-9 solar masses. No weak, hydrogen-deficient, core-collapse supernovae have hitherto been seen. Here we report that SN 2008ha is a faint hydrogen-poor supernova. We propose that other similar events have been observed but have been misclassified as peculiar thermonuclear supernovae (sometimes labelled SN 2002cx-like events). This discovery could link these faint supernovae to some long-duration gamma-ray bursts, because extremely faint, hydrogen-stripped core-collapse supernovae have been proposed to produce such long gamma-ray bursts, the afterglows of which do not show evidence of associated supernovae.