The faint supernova remnant G 116.5+1.1 and the detection of a new candidate remnant

¹ University of Crete, Physics Department, PO Box 2208, 710 03 Heraklion, Crete, Greece e-mail: fotis@physics.uoc.gr
² Institute of Astronomy & Astrophysics, National Observatory of Athens, I. Metaxa & V. Pavlou, P. Penteli, 15236 Athens, Greece
³ Foundation for Research and Technology-Hellas, PO Box 1527, 711 10 Heraklion, Crete, Greece
⁴ Astronomical Laboratory, Department of Physics, University of Patras, 26500 Rio–Patras, Greece

Received: 15 October 2004
Accepted: 13 January 2005

Abstract

The extended supernova remnant G 116.5+1.1 was observed in the optical emission lines of H], [] and []; deep long slit spectra were also obtained. The morphology of the remnant's observed emission is mainly diffuse and patchy in contrast to the known filamentary emission seen along the western limb. The bulk of the detected emission in the region appears unrelated to the remnant but there is one area of emission in the south-east which is characterized by a []/Hα ratio of ~0.5, implying a possible relation to G 116.5+1.1. If this is actually the case, it would imply a more extended remnant than previously realized. Emission in the [] 5007 Å line image is not detected, excluding moderate or fast velocity shocks running into ionized interstellar clouds. Our current estimate of the distance to G 116.5+1.1 of ~3 kpc is in agreement with earlier estimates and implies a very extended remnant ( pc). 
 Observations further to the north-east of G 116.5+1.1 revealed a network of filamentary structures prominent in H] and [] but failed to detect [] line emission. Long slit spectra in a number of positions provide strong evidence that this newly detected emission arises from shock heated gas. Typical Hα fluxes lie in the range of 9 to 17  10^-17 erg s^-1 cm^-2 arcsec^-2, while low electron densities are implied by the intensities of the sulfur lines. Weak emission from the medium ionization line at 5007 Å is detected in only one spectrum. Cool dust emission at 60 and 100 microns may be correlated with the optical emission in a limited number of positions. Surpisingly, radio emission is not detected in published surveys suggesting that the new candidate remnant may belong to the class of “radio quiet” supernova remnants.