Searching the non-accreting white dwarf population in eROSITA data

TL;DR

This study leverages eROSITA's deep X-ray surveys to identify non-accreting white dwarf candidates, significantly increasing known white dwarf detections and demonstrating improved sensitivity through a pilot detection threshold extension.

Contribution

The paper introduces a method to enhance eROSITA's sensitivity to soft X-ray sources, leading to a higher detection rate of non-accreting white dwarfs compared to previous surveys.

Findings

Detected 38,000 soft X-ray sources with hardness ratio below -0.94.

Identified 264 probable white dwarfs, surpassing ROSAT's total of 175.

Extending detection to 0.1 keV shows promising results in pilot tests.

Abstract

eROSITA is the soft X-ray instrument aboard the Spectrum Roentgen Gamma (SRG) satellite that is most sensitive in the energy range between 0.2 and 2.3 keV. Between December 2019 and December 2021, eROSITA completed four all-sky surveys producing all-sky X-ray source lists and sky maps of unprecedented depth. In the energy range between 0.2 keV and 1 keV, we detected about 38,000 sources with a hardness ratio below -0.94, covering a small sample of known white dwarfs found with eROSITA in the dataset to which the German eROSITA consortium has rights (half sky). 264 of these soft sources have a probability of more than 90 % to be a white dwarf. This is more than the 175 white dwarfs ROSAT found in the whole sky. Here we present the results of a pilot study to increase the sensitivity of eROSITA for soft sources by extending the detection threshold down to 0.1 keV. First tests with dedicated sky regions are promising.