Imaging on PAPER: Centaurus A at 148 MHz

TL;DR

This paper presents low-frequency radio observations of Centaurus A using PAPER, revealing detailed spectral index maps, correlations with X-ray data, and insights into electron reacceleration and magnetic fields in the galaxy's radio lobes.

Contribution

First detailed low-frequency imaging of Centaurus A with spectral and X-ray comparison, providing new insights into electron reacceleration and magnetic field estimates.

Findings

Spectral index map shows electron reacceleration in radio lobes.

Tentative correlation between radio and X-ray features at lobe edges.

Estimated magnetic fields are around 1 microGauss, consistent with minimum pressure assumptions.

Abstract

We present observations taken with the Precision Array for Probing the Epoch of Reionization (PAPER) of the Centaurus A field in the frequency range 114 to 188 MHz. The resulting image has a 25' resolution, a dynamic range of 3500 and an r.m.s. of 0.5 Jy\beam (for a beam size of 25' x 23'). A spectral index map of Cen A is produced across the full band. The spectral index distribution is qualitatively consistent with electron reacceleration in regions of excess turbulence in the radio lobes, as previously identified morphologically. Hence, there appears to be an association of 'severe weather' in radio lobes with energy input into the relativistic electron population. We compare the PAPER large scale radio image with the X-ray image from the ROSAT All Sky Survey. There is a tentative correlation between radio and X-ray features at the end of the southern lobe, some 200 kpc from the nucleus, as might be expected from inverse Compton scattering of the CMB by the relativistic electrons also responsible for the radio synchrotron emission. The magnetic fields derived from the (possible) IC and radio emission are of similar magnitude to fields derived under the minimum pressure assumptions, ~ 1 {\mu}G. However, the X-ray field is complex, with large scale gradients and features possibly unrelated to Cen A. If these X-ray features are unrelated to Cen A, then these fields are lower limits.