Kavli Affiliate: Dheeraj R. Pasham
| First 5 Authors: Ananya Bandopadhyay, Eric R. Coughlin, C. J. Nixon, Dheeraj R. Pasham,
| Summary:
Some electromagnetic outbursts from the nuclei of distant galaxies have been
found to repeat on months-to-years timescales, and each of these sources can
putatively arise from the accretion flares generated through the repeated tidal
stripping of a star on a bound orbit about a supermassive black hole (SMBH),
i.e., a repeating partial tidal disruption event (rpTDE). Here we test the
rpTDE model through analytical estimates and hydrodynamical simulations of the
interaction between a range of stars, which differ from one another in mass and
age, and an SMBH. We show that higher-mass ($gtrsim 1 M_{odot}$), evolved
stars can survive many ($gtrsim 10-100$) encounters with an SMBH while
simultaneously losing $few times 0.01 M_{odot}$, resulting in accretion
flares that are approximately evenly spaced in time with nearly the same
amplitude, quantitatively reproducing ASASSN-14ko. We also show that the energy
imparted to the star via tides can lead to a change in its orbital period that
is comparable to the observed decay in the recurrence time of ASASSN-14ko’s
flares, $dot{P}simeq-0.0026$. Contrarily, lower-mass and less-evolved stars
lose progressively more mass and produce brighter accretion flares on
subsequent encounters for the same pericenter distances, leading to the rapid
destruction of the star and cessation of flares. Such systems cannot reproduce
ASASSN-14ko-like transients, but are promising candidates for recreating events
such as AT2020vdq, which displayed a second and much brighter outburst compared
to the first. Our results imply that the lightcurves of repeating transients
are tightly coupled with stellar type.
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