CDF-S XT1 and XT2: White Dwarf Tidal Disruption Events by Intermediate-Mass Black Holes?

TL;DR

This paper proposes that the fast X-ray transients XT1 and XT2 are caused by white dwarf tidal disruptions by intermediate-mass black holes, offering a new interpretation supported by theoretical modeling of their light curves.

Contribution

It introduces a novel model for these transients as accretion-driven flares from white dwarf disruptions, differing from previous neutron-star merger explanations.

Findings

Theoretical accretion rate model fits observed light curves.

Super-Eddington luminosity explained by beaming and jet formation.

Supports white dwarf disruption as origin of the transients.

Abstract

Recently two fast X-ray transients (XT1 and XT2) have been reported from the search in the Chandra Deep Field (CDF) data. Each transient shows an initial plateau lasting around hundreds to thousands seconds followed by a rapid decay in the light curve. In particular, CDF-S XT2 is found to be associated with a galaxy at redshift z= 0.738 and was explained as a counterpart of a binary neutron-star merger event. In this paper, motivated by the short duration and decay slopes of the two transients, we consider an alternative interpretation in which both events are accretion-driven flares from tidal disruption of white dwarfs by intermediate-mass black holes. We derive a theoretical model of the accretion rate history, and find that it fits the observed X-ray light curves well. The extremely super-Eddington peak luminosity of XT2 can be explained by the beaming effect of the system, likely in the form of a jet.