Radio Observations of Supernova Remnant G1.9+0.3

Kieran J. Luken, Miroslav D. Filipović, Nigel I. Maxted, Roland Kothes, Ray P. Norris, James R. Allison, Rebecca Blackwell, Catherine Braiding, Robert Brose, Michael Burton, Ain Y. De Horta, Tim J. Galvin, Lisa Harvey-Smith, Natasha Hurley-Walker, Denis Leahy, Nicholas O. Ralph, Quentin Roper, Gavin Rowell, Iurii Sushch, Dejan Urošević, Graeme F. Wong

Published 2019-12-04Version 1

We present 1 to 10GHz radio continuum flux density, spectral index, polarisation and Rotation Measure (RM) images of the youngest known Galactic Supernova Remnant (SNR) G1.9+0.3, using observations from the Australia Telescope Compact Array (ATCA). We have conducted an expansion study spanning 8 epochs between 1984 and 2017, yielding results consistent with previous expansion studies of G1.9+0.3. We find a mean radio continuum expansion rate of ($0.78 \pm 0.09$) per cent year$^{-1}$ (or $\sim8900$ km s$^{-1}$ at an assumed distance of 8.5 kpc), although the expansion rate varies across the SNR perimeter. In the case of the most recent epoch between 2016 and 2017, we observe faster-than-expected expansion of the northern region. We find a global spectral index for G1.9+0.3 of $-0.81\pm0.02$ (76 MHz$-$10 GHz). Towards the northern region, however, the radio spectrum is observed to steepen significantly ($\sim -$1). Towards the two so called (east & west) "ears" of G1.9+0.3, we find very different RM values of 400-600 rad m$^{2}$ and 100-200 rad m$^{2}$ respectively. The fractional polarisation of the radio continuum emission reaches (19 $\pm$ 2)~per~cent, consistent with other, slightly older, SNRs such as Cas~A.