Repeating nuclear transients as candidate electromagnetic counterparts of LISA extreme mass ratio inspirals
Abstract
Extreme mass ratio inspirals (EMRIs) are one of the primary targets for the recently adopted millihertz gravitationalwave observatory LISA. Some previous studies have argued that a fraction of all EMRIs form in matterrich environments, and can potentially explain the dozens of soft Xray band ($\sim 10^{1}\,\rm keV$), lowfrequency ($\sim 0.1$ mHz) periodic phenomena known as quasiperiodic eruptions (QPEs) and quasiperiodic oscillations (QPOs). Here, using a representative EMRI population retrofitted with cutoffs on LISAband SNRs and luminosity distances to account for the sensitivity of current instruments, we estimate the mean frequency band in which QPEs and QPOs originating from detectable LISA EMRIs may be emitting an Xray signal 'today' (i.e. in 2024) to be $0.46 \pm 0.22$ mHz. We also model the wellknown QPO source, RE J1034+396, which falls in this frequency band, as an EMRI assuming its primary black hole mass to be $10^6{}10^7 \,{\rm M}_\odot$. Through a priorpredictive analysis, we estimate the orbiting compact object's mass to be $46^{+ 10}_{40} \,{\rm M}_\odot$ and the source's LISAband SNR as $\approx 14$, highlighting it as a candidate multimessenger EMRI target. We also highlight the role of current and nearfuture Xray and UV observatories in enabling multimessenger observations of EMRIs in conjunction with LISA, and conclude with a discussion of caveats of the current analysis, such as the exclusion of eccentricity and inclination from the model, and the measurability of subsolar mass compact object EMRIs.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 August 2024
 DOI:
 10.1093/mnras/stae1599
 arXiv:
 arXiv:2404.00941
 Bibcode:
 2024MNRAS.532.2143K
 Keywords:

 Astrophysics  High Energy Astrophysical Phenomena;
 General Relativity and Quantum Cosmology
 EPrint:
 (Beforeproofsaccepted) 15 + 1 pages, 10 + 1 figures