Two radio supernova remnants discovered in the outer Galaxy

¹ Department of Physics & AstronomyBrandon University 270-18th Street, Brandon, MB R7A 6A9, Canada
e-mail: fostert@brandonu.ca
² National Research Council of Canada, Emerging Technologies – National Science Infrastructure, Dominion Radio Astrophysical Observatory, PO Box 248, Penticton BC, V2A 6J9, Canada
³ Dept. of Physics & Astronomy, University of British Columbia Okanagan, 3333 University Way, Kelowna BC V1V 1V7, Canada
⁴ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁵ Dept. of Physics & Astronomy, University of Calgary, 2500 University Drive NW Calgary, AB T2N 1N4, Canada
⁶ Dept. of Physics & Astronomy University of Manitoba, Winnipeg, MB R3T 2N2, Canada

Received: 10 September 2012
Accepted: 16 November 2012

Abstract

Context. New and existing large-scale radio surveys of the Milky Way at centimetre wavelengths can play an important role in uncovering the hundreds of expected but missing supernova remnants in the Galaxy’s interstellar medium. We report on the discovery of two supernova remnants (SNRs) designated G152.4−2.1 and G190.9−2.2, using Canadian Galactic Plane Survey data.

Aims. The aims of this paper are, first, to present evidence that favours the classification of both sources as SNRs, and, second, to describe basic parameters (integrated flux density, spectrum, and polarization) as well as properties (morphology, line-of-sight velocity, distance and physical size) to facilitate and motivate future observations.

Methods. Spectral and polarization parameters are derived from multiwavelength data from existing radio surveys carried out at wavelengths between 6 and 92 cm. In particular for the source G152.4−2.1 we also use new observations at 11 cm done with the Effelsberg 100 m telescope. The interstellar medium around the discovered sources is analyzed using 1-arcmin line data from neutral hydrogen (H i) and 45-arcsec ¹²CO(J = 1 → 0).

Results. G152.4−2.1 is a barrel shaped SNR with two opposed radio-bright polarized flanks on the north and south. The remnant, which is elongated along the Galactic plane is evolving in a more-or-less uniform medium. G190.9−2.2 is also a shell-type remnant with east and west halves elongated perpendicular to the plane, and is evolving within a low-density region bounded by dense neutral hydrogen in the north and south, and molecular (¹²CO) clouds in the east and west. The integrated radio continuum spectral indices are −0.65 ± 0.05 and −0.66 ± 0.05 for G152.4−2.1 and G190.9−2.2 respectively. Both SNRs are approximately 1 kpc distant, with G152.4−2.1 being larger (32 × 30 pc in diameter) than G190.9−2.2 (18 × 16 pc). These two remnants are the lowest surface brightness SNRs yet catalogued at Σ_{1 GHz} ≲ 5 × 10^-23 W m^-2 Hz^-1 sr^-1.