Exoplanets and Stellar Physics

Abstract:

We present a new analysis of the light curve of the young planet-hosting star TOI 451 in the light of new observations from TESS Cycle 3. Our joint analysis of the transits of all three planets, using all available TESS data, results in an improved ephemeris for TOI 451 b and TOI 451 c, which will help to plan follow-up observations. The updated mid-transit times are BJD–2,457,000 = ${1410.9896}_{-0.0029}^{+0.0032}$ , ${1411.7982}_{-0.0020}^{+0.0022}$, and ${1416.63407}_{-0.00100}^{+0.00096}$ for TOI 451 b, c, and d, respectively, and the periods are ${1.8587028}_{-10e-06}^{+08e-06}$, ${9.192453}_{-3.3e-05}^{+4.1e-05}$ , and ${16.364932}_{-3.5e-05}^{+3.6e-05}$ days. We also model the out-of-transit light curve using a Gaussian Process with a quasi-periodic kernel, and infer a change in the properties of the active regions on the surface of TOI 451 between TESS Cycles 1 and 3.

Abstract:

Binary supermassive black hole (SMBH) systems result from galaxy mergers, and will eventually coalesce due to gravitational wave (GW) emission if the binary separation can be reduced to . 0.1 pc by other mechanisms. Here, we explore a gravitational self-lensing binary SMBH model for the sharp (duration ⇠ 1 hr), quasi-regular X-ray flares – dubbed quasiperiodic eruptions – recently observed from two low mass active galactic nuclei: GSN 069 and RX J1301.9+2747. In our model, the binary is observed ⇠edge-on, such that each SMBH gravitationally lenses light from the accretion disc surrounding the other SMBH twice per orbital period. The model can reproduce the flare spacings if the current eccentricity of RX J1301.9+2747 is n0 & 0.16, implying a merger within ⇠ 1000 yrs. However, we cannot reproduce the observed flare profiles with our current calculations. Model flares with the correct amplitude are ⇠ 2/5 the observed duration, and model flares with the correct duration are ⇠ 2/5 the observed amplitude. Our modelling yields three distinct behaviours of self-lensing binary systems that can be searched for in current and future X-ray and optical time-domain surveys: i) periodic lensing flares, ii) partial eclipses (caused by occultation of the background mini-disc by the foreground mini-disc), and iii) partial eclipses with a very sharp in-eclipse lensing flare. Discovery of such features would constitute very strong evidence for the presence of a supermassive binary, and monitoring of the flare spacings will provide a measurement of periastron precession.