The Origem Loop

National Astronomical Observatories, Chinese Academy of Sciences, Jia-20 Datun Road, Chaoyang District, 100012 Beijing, PR China
e-mail: bearwards@gmail.com

Received: 13 June 2012
Accepted: 6 December 2012

Abstract

Context. The Origem Loop in the Galactic anticentre was discovered in 1970s. It has been suggested that it is a large supernova remnant. One later argument is that it is a chance superposition of unrelated radio sources.

Aims. We attempt to understand the properties of the Origem Loop.

Methods. Available multi-frequency radio data were used to determine the radio spectra of different parts of the Origem Loop and the polarization properties of the loop.

Results. Newly available sensitive observations show that the Origem Loop is a loop of more than 6° in diameter. It consists of a large non-thermal arc in the north, which we call the Origem Arc, and several known thermal H II regions in the south. Polarized radio emission associated with the arc was detected at λ6 cm, revealing tangential magnetic fields. The arc has a brightness-temperature spectral index of β = −2.70, indicating its non-thermal nature as a supernova remnant. We estimate the distance to the Origem Arc to be about 1.7 kpc, similar to those of some H II regions in the southern part of the loop.

Conclusions. The Origem Loop is a visible loop in the sky, which consists of a supernova remnant arc in the north and H II regions in the south.