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Free keywords:
STAR-DISK COLLISIONS; SUPERMASSIVE BLACK-HOLE; UNSTABLE MASS-TRANSFER;
LUMINOSITY FUNCTION; EVOLUTION; NUCLEUS; FLARES; GALAXYAstronomy & Astrophysics; accretion; accretion disks; galaxies: active; galaxies: dwarf; galaxies:
nuclei; X-rays: bursts; X-rays: galaxies;
Abstract:
Multiwavelength extragalactic nuclear transients, particularly those detectable as multi-messengers, are among the primary driversfor the next-generation observatories. X-ray quasi-periodic eruptions (QPEs) are the most recent and perhaps most peculiar additionto this group. Here, we report a first estimate of the volumetric rate of QPEs based on the first four discoveries with the eROSITAX-ray telescope onboard the Spectrum Roentgen Gamma observatory. Under the assumption, supported by a suite of simulated lightcurves, that these four sources sample the intrinsic population somewhat homogeneously, we correct for their detection efficiencyand compute a QPE abundance ofRvol=0.60(-0.43)(+4.73)x10(-6)Mpc(-3)above an intrinsic average logL(0.5)(peak)-(2.0 keV)>41.7. Since the exactlifetime of QPEs (tau(life)) is currently not better defined than between a few years or few decades, we convert this to a formation rate ofR(vol)/tau(life)approximate to 0.6x10(-7)(tau(life)/10 yr)(-1)Mpc(-3)yr(-1). As a comparison, this value is a factor similar to 10 tau lifetimes smaller than the formation rateof tidal disruption events. The origin of QPEs is still debated, although lately most models suggest that they are the electromagneticcounterpart of extreme mass ratio inspirals (EMRIs). In this scenario, the QPE rate would thus be the first ever constraint (i.e. alower limit) to the EMRI rate from observations alone. Future discoveries of QPEs and advances in their theoretical modeling willconsolidate or rule out their use for constraining the number of EMRIs detectable by the LISA mission
