Possible ∼0.4 h X-ray quasi-periodicity from an ultrasoft active galactic nucleus

Abstract

RX J1301.9+2747 is an ultrasoft active galactic nucleus (AGN) with unusual X-ray variability that is characterized by a long quiescent state and a short-lived flare state. The X-ray flares are found to recur quasi-periodically on a timescale of 13-20 ks. Here, we report the analysis of the light curve in the quiescent state from two XMM-Newton observations spanning 18.5 years, along with the discovery of a possible quasi-periodic X-ray oscillation (QPO) with a period of ∼1500s. The QPO is detected at the same frequency in the two independent observations, with a combined significance of >99.89%. The QPO is in agreement with the relation between frequency and black hole mass (M BH) that has been reported in previous works for AGNs and Galactic black hole X-ray binaries (XRBs). The QPO frequency is stable over almost two decades, suggesting that it may correspond to the high-frequency type found in XRBs and originates, perhaps, from a certain disk resonance mode. In the 3:2 twin-frequency resonance model, our best estimate on the M BH range implies that a maximal black hole spin can be ruled out. We find that all ultrasoft AGNs reported so far display quasiperiodicities in the X-ray emission, suggesting a possible link on the part of the extreme variability phenomenon to the ultrasoft X-ray component. This indicates that ultrasoft AGNs could be the most promising candidates in future searches for X-ray periodicities.

Searching for Quasi-periodic Oscillations in Active Galactic Nuclei of the Chandra Deep Field South

“…A similar case is seen in RX J1301.9+274715, which exhibited high-amplitude soft-X-ray flares recurring quasi-periodically on a timescale of 13-20 ks (Giustini et al 2020). Moreover, Song et al (2020) found that this source exhibited a 0.4 hour QPO in the quiescent state, as caught by two XMM-Newton observations taken respectively in 2000 and 2019.…”

“…The advantage of the LS periodogram lies in its relatively high operation speed and adequate tolerance for observational gaps. Moreover, the LS periodogram has proved successful in the detection of a few AGN QPOs based on single X-ray observations (e.g., Zhang et al 2017;Gupta et al 2018;Song et al 2020).…”

“…This leaves the possibility that shortlived, or transient, QPOs are missed in our above search. In fact, a number of known AGN QPOs are transient QPOs, i.e., they were only detected over single X-ray observations or even over a fraction of the observation (e.g., Pan et al 2016;Zhang et al 2017;Song et al 2020), such that the duration of activity is not much longer than the period itself.…”

Stellar Revival and Repeated Flares in Deeply Plunging Tidal Disruption Events

“…Our present results, however, call this conclusion into question; it could instead be the case that this even more extreme β results in yet another reformed core post-pericenter (i.e., if β = 16 results in a reformed core, then it may well be the case that β = 47 does as well), with each successive disruption producing a reformed core with progressively less mass and having a correspondingly even more extreme β. The recurrent disruptions at each pericenter passage could lead to periodic flaring events such as those documented in the recent literature (Miniutti et al 2019;Song et al 2020;Arcodia et al 2021;Chakraborty et al 2021;Payne et al 2021a,b).…”

Using the Hills Mechanism to Generate Repeating Partial Tidal Disruption Events and ASASSN-14ko

“…Repeating optical and X-ray flares have recently been detected in the nuclei of galaxies, e.g., Miniutti et al (2019); Song et al (2020); Chakraborty et al (2021); Arcodia et al (2021); Payne et al (2021); Arcodia et al (2021); Payne et al (2022), with ASASSN-14ko in particular displaying outbursts at an extremely regular period of P = 114 days (Payne et al 2021; see Shappee et al (2014); Holoien et al (2017); Kochanek et al (2017) for specifics related to the ASAS-SN survey). The physical origin of these flares (in general) remains an open question, but if the flaring activity is related to accretion onto the supermassive black hole (SMBH) in the galactic nucleus, the high degree of regularity in the flaring rate of is strongly indicative of a binary origin.…”