The rebrightening of a ROSAT-selected tidal disruption event: repeated weak partial disruption flares from a quiescent galaxy?. Issue 3 (9th January 2023) - Malyali, A
ABSTRACT: The ROSAT -selected tidal disruption event (TDE) candidate RX J133157.6−324319.7 (J1331) was detected in 1993 as a bright [0.2–2 keV flux of (1.0 ± 0.1) × 10 −12 erg s −1 cm −2 ], ultra-soft ( kT = 0.11 ± 0.03 keV) X-ray flare from a quiescent galaxy ( z = 0.051 89). During its fifth all-sky survey (eRASS5) in 2022, Spectrum-Roentgen-Gamma (SRG )/ eROSITA detected the repeated flaring of J1331, where it had rebrightened to an observed 0.2–2 keV flux of (6.0 ± 0.7) × 10 −13 erg s −1 cm −2, with spectral properties ( kT = 0.115 ± 0.007 keV) consistent with the ROSAT -observed flare ∼30 yr earlier. In this work, we report on X-ray, ultraviolet, optical, and radio observations of this system. During a pointed XMM observation ∼17 d after the eRASS5 detection, J1331 was not detected in the 0.2–2 keV band, constraining the 0.2–2 keV flux to have decayed by a factor of ≳40 over this period. Given the extremely low probability (∼5 × 10 −6 ) of observing two independent full TDEs from the same galaxy over a 30 yr period, we consider the variability seen in J1331 to be likely caused by two partial TDEs involving a star on an elliptical orbit around a black hole. J1331-like flares show faster rise and decay time-scales [$\mathcal {O}(\mathrm{d})$ ] compared to standard TDE candidates, with negligible ongoing accretion at late times post-disruption between outbursts.