The Search for Faint Radio Supernova Remnants in the Outer Galaxy: Five New Discoveries

Abstract

High resolution and sensitivity large-scale radio surveys of the Milky Way are critical in the discovery of very low surface brightness supernova remnants (SNRs), which may constitute a significant portion of the Galactic SNRs still unaccounted for (ostensibly the Missing SNR problem). The overall purpose here is to present the results of a systematic, deep data-mining of the Canadian Galactic Plane Survey (CGPS) for faint, extended non-thermal and polarized emission structures that are likely the shells of uncatalogued supernova remnants. We examine 5$\times$5 degree mosaics from the entire 1420 MHz continuum and polarization dataset of the CGPS after removing unresolved point sources and subsequently smoothing them. Newly revealed extended emission objects are compared to similarly-prepared CGPS 408 MHz continuum mosaics, as well as to source-removed mosaics from various existing radio surveys at 4.8 GHz, 2.7 GHz, and 327 MHz, to identify candidates with non-thermal emission characteristics. We integrate flux densities at each frequency to characterise the radio spectra behaviour of these candidates. We further look for mid- and high-frequency (1420 MHz, 4.8 GHz) ordered polarized emission from the limb brightened shell-like continuum features that the candidates sport. Finally, we use IR and optical maps to provide additional backing evidence. Here we present evidence that five new objects, identified as filling all or some of the criteria above, are strong candidates for new SNRs. These five are designated by their Galactic coordinate names G108.5+11.0, G128.5+2.6, G149.5+3.2, G150.8+3.8, and G160.1$-$1.1. These discoveries represent a significant increase in the number of SNRs known in the outer Galaxy second quadrant of longitude (90${}^{\circ }\le \ell \le$180${}^{\circ }$).

arXiv comment11 pages, 10 figures, accepted May 2014 for publication in Astronomy & Astrophysics

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• Discovery of a new supernova remnant G150.3+4.5
• G107.0+9.0: A New Large Optically Bright, Radio and X-Ray Faint Galactic Supernova Remnant in Cepheus
• Investigating Galactic supernova remnant candidates with LOFAR
• High-energy gamma-ray study of the dynamically young SNR G150.3+4.5
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• SRG/eROSITA discovery of a radio faint X-ray candidate supernova remnant SRGe J003602.3+605421=G121.1-1.9
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• G279.0+1.1: a new extended source of high-energy gamma rays
• The infrared counterpart and proper motion of magnetar SGR0501+4516
• Large-field CO (J=1-0) observations toward SNR G150.3+4.5
• Radio detection of supernova remnant G310.7-5.4 with $\gamma$-ray counterpart: Abeona SNR