The Origem Loop

TL;DR

The paper clarifies that the Origem Loop is a large supernova remnant arc in the north with associated magnetic fields, distinguished from unrelated thermal H II regions in the south, based on multi-frequency radio observations.

Contribution

It provides detailed radio spectral and polarization analysis confirming the non-thermal supernova remnant nature of the Origem Arc and estimates its distance at about 1.7 kpc.

Findings

The Origem Loop spans over 6 degrees in diameter.

The northern arc shows non-thermal emission with a spectral index of -2.70.

Polarized emission indicates tangential magnetic fields in the arc.

Abstract

The Origem Loop in the Galactic anticentre was discovered in 1970s and suggested to be a large supernova remnant. It was argued later to be a chance superposition of unrelated radio sources. We attempt to understand the properties of the Origem Loop. Available multi-frequency radio data were used for the determination of radio spectra of different parts of the Origem Loop and the polarization properties of the loop. Newly available sensitive observations show that the Origem Loop is a loop of more than 6 deg 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 6 cm, revealing tangential magnetic fields. The arc has a brightness temperature spectral index of \beta = -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. 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.