The Search for Thermonuclear Transients from the Tidal Disruption of a White Dwarf by an Intermediate Mass Black Hole

TL;DR

This study searches for thermonuclear transients caused by white dwarf disruptions by intermediate mass black holes in dwarf galaxy nuclei, aiming to identify IMBHs and understand their role in galaxy evolution.

Contribution

First systematic search for Ia-TDE candidates in ZTF data focusing on dwarf galaxy nuclei, identifying promising candidates and establishing a method for future IMBH discovery.

Findings

Six Ia-TDE candidates identified, with SN 2020lrt being the most likely.

Host dwarf galaxies have stellar masses less than 10^9 solar masses.

No robust off-nuclear Ia-TDE candidates found, supporting nuclear origin hypothesis.

Abstract

The close encounter of a white dwarf (WD) with a black hole (BH) could result in the tidal disruption of the WD. During this encounter, the WD can undergo a thermonuclear explosion due to its tidal compression, resulting in an optical transient similar to a Type Ia supernova (SN Ia), hereafter a Ia-TDE. Nevertheless, this will only be physically observable if the BH is $\lesssim 10^5$M$_\odot$. Finding a Ia-TDE would therefore imply the discovery of an intermediate mass black hole (IMBH) $\lesssim 10^5$ M$_\odot$. Here, we search the entire Zwicky Transient Facility (ZTF) alert stream for the elusive Ia-TDEs. We restrict our search to nuclear transients in dwarf galaxies, the likely sites for IMBHs, and find a total of six possible nuclear Ia-TDE candidates. We find SN\,2020lrt to be the most likely Ia-TDE candidate, thanks to its strong resemblance to light curve and spectroscopic models of Ia-TDEs. We measure the stellar masses of the dwarf galaxies hosting these transients to be $\lesssim 10^{9}$M$_\odot$; if confirmed to harbor BHs, these would prove the existence of IMBHs in some of the lowest-mass galaxies known. Additionally, we searched for off-nuclear Ia-TDEs, but were unable to find more robust candidates in the outskirts of galaxies than in their nuclei. This supports the hypothesis that the nuclear Ia-TDEs candidates are WDs tidally compressed by IMBHs in the cores of galaxies, as opposed to a class of transient that can happen anywhere in a galaxy. We have laid the groundwork to systematically search for Ia-TDE candidates in existing and future time-domain surveys. Rapid characterization of their nature will result in not only the confirmation of a Ia-TDE, but also the unambiguous discovery of bonafide IMBHs.