PREPRINT
64EA3B4D-0874-4A9A-8192-977E811A10D1

# Hyper-runaway and hypervelocity white dwarf candidates in Gaia Data Release 3: possible remnants from Ia/Iax supernova explosions or dynamical encounters

Andrei P. Igoshev, Hagai Perets, Na'ama Hallakou

Submitted on 20 September 2022

## Abstract

Type Ia and other peculiar supernovae (SNe) are thought to originate from the thermonuclear explosions of white dwarfs (WDs). Some of the proposed channels involve the ejection of a partly exploded WD (e.g. Iax SN remnant) or the companion of an exploding WD at extremely high velocities (>400 km s${}^{-1}$). Characterisation of such hyper-runaway/hypervelocity (HVS) WDs might therefore shed light on the physics and origins of SNe. Here we analyse the Gaia DR3 data to search for HVS WDs candidates, and peculiar sub-main-sequence (sub-MS) objects. We retrieve previously identified HVS, and find tens of new HVS candidates. We identify two new unbound WD HVS, 14 new likely-unbound sub-MS objects, and a handful of WDs and sub-MS objects with velocities comparable to the Galactic escape velocity (based only on tangential velocities). We find tens of additional likely bound hyper-runaway WDs (v$>400$ km s${}^{-1}$). The numbers and properties of the HVS WD and sub-MS candidates suggest that extreme velocity ejections ($>1000$ km s${}^{-1}$) can accompany at most a small fraction of type Ia SNe, disfavouring a significant contribution of the D6-scenario to the origin of Ia SNe. The rate of HVS ejections following the hybrid WD reverse-detonation channel could be consistent with the identified HVSs. The numbers of lower-velocity HVS WDs could be consistent with type Iax SNe origin and/or contribution from dynamical encounters. We also searched for HVS WDs related to known SN remnants, but identified only one such candidate.

## Preprint

Comment: Submitted to the MNRAS

Subjects: Astrophysics - Solar and Stellar Astrophysics; Astrophysics - Astrophysics of Galaxies