Optical and X-ray observations of candidate isolated neutron stars in the G315.4-2.3 SNR

TL;DR

This study investigates two X-ray sources in the supernova remnant G315.4-2.3 to determine if they are isolated neutron stars, using optical and X-ray observations, and concludes they are likely associated with bright stars instead.

Contribution

The paper provides optical and X-ray follow-up observations that clarify the nature of candidate neutron stars in G315.4-2.3, ruling out their identification as isolated neutron stars.

Findings

Both X-ray sources are associated with bright stars.

Neither source is consistent with being an isolated neutron star.

The supernova remnant likely does not host a compact stellar remnant.

Abstract

G315.4-2.3 is a young Galactic supernova remnant (SNR), whose identification as the remains of a Type-II supernova (SN) explosion has been debated for a long time. In particular, recent multi-wavelength observations suggest that it is the result of a Type Ia SN, based on spectroscopy of the SNR shell and the lack of a compact stellar remnant.However, two X-ray sources, one detected by Einstein and ROSAT (Source V) and the other by Chandra (Source N) have been proposed as possible isolated neutron star candidates. In both cases, no clear optical identification was available and, therefore, we performed an optical and X-ray study to determine the nature of these two sources. Based on Chandra astrometry, Source V is associated with a bright V~14 star, which had been suggested based on the less accurate ROSAT position. Similarly, from VLT archival observations, we found that Source N is associated with a relatively bright star ($V=20.14 $). These likely identifications suggest that both X-ray sources cannot be isolated neutron stars.