Deep optical observations of the central X-ray source in the Puppis A supernova remnant

TL;DR

This study conducted deep optical observations of the central X-ray source RX J0822.0-4300 in the Puppis A supernova remnant using VLT, setting new limits on its optical counterpart and informing models of neutron star emission.

Contribution

First deep optical imaging of RX J0822.0-4300 with VLT, providing the deepest limits to date and constraining possible optical counterparts and emission mechanisms.

Findings

No optical counterpart detected within the X-ray position limits.

Limits rule out a companion brighter than an M5 dwarf.

Optical emission from the neutron star surface remains unconstrained.

Abstract

X-ray observations reveiled a group of radio-silent isolated neutron stars (INSs) at the centre of young supernova remnants (SNRs), dubbed central compact objects or CCOs, with properties different from those of classical rotation-powered pulsars. In at least three cases, evidence points towards CCOs being low-magnetized INSs, born with slow rotation periods, and possibly accreting from a debris disc of material formed out of the supernova event. Understanding the origin of the diversity of the CCOs can shed light on supernova explosion and neutron star formation models. Optical/infrared (IR) observations are crucial to test different CCO interpretations. The aim of our work is to perform a deep optical investigation of the CCO RX J0822.0-4300 in the Puppis A SNR, one of the most poorly understood in the CCO family. By using as a reference the Chandra X-ray coordinates of RX J0822.0-4300, we performed deep optical observations in the B, V and I bands with the Very Large Telescope (VLT). We found no candidate optical counterpart within 3 sigma of the computed Chandra X-ray position down to 5 sigma limits of B~27.2, V~26.9, and I~25.6, the deepest obtained in the optical band for this source. These limits confirm the non-detection of a companion brighter than an M5 dwarf. At the same time, they do not constrain optical emission from the neutron star surface, while emission from the magnetosphere would require a spectral break in the optical/IR.