A giant X-ray dust scattering ring around the black hole transient MAXI J1348-630 discovered with SRG/eROSITA

TL;DR

This paper reports the discovery of the largest X-ray dust scattering ring around the black hole transient MAXI J1348-630, enabling precise distance measurement and a revised black hole mass estimate using multi-instrument data.

Contribution

It presents the first observation of a giant dust scattering ring around MAXI J1348-630 and demonstrates a novel method for accurate distance determination of black hole transients.

Findings

Largest X-ray dust scattering ring observed to date.

Black hole distance measured with 1.1% statistical uncertainty.

Revised black hole mass estimate of 11±2 solar masses.

Abstract

We report the discovery of a giant dust scattering ring around the Black Hole transient MAXI J1348-630 with SRG/eROSITA during its first X-ray all-sky survey. During the discovery observation in February 2020 the ring had an outer diameter of 1.3 deg, growing to 1.6 deg by the time of the second all sky survey scan in August 2020. This makes the new dust ring the by far largest X-ray scattering ring observed so far. Dust scattering halos, in particular the rings found around transient sources, offer the possibility of precise distance measurements towards the original X-ray sources. We combine data from SRG/eROSITA, XMM-Newton, MAXI, and Gaia to measure the geometrical distance of MAXI J1348-630. The Gaia data place the scattering dust at a distance of 2050 pc, from the measured time lags and the geometry of the ring, we find MAXI J1348-630 at a distance of 3390 pc with a statistical uncertainty of only 1.1% and a systematic uncertainty of 10% caused mainly by the parallax offset of Gaia. This result makes MAXI J1348-630 one of the black hole transients with the best determined distances. The new distance leads to a revised mass estimate for the black hole of 11+-2 solar masses, the transition to the soft state during the outburst occurred when the bolometric luminosity of MAXI J1348-630 had reached 1.7% of its Eddington luminosity.