Discovery of ATLAS17jrp as an Optical-, X-Ray-, and Infrared-bright Tidal Disruption Event in a Star-forming Galaxy

Abstract

We hereby report the discovery of ATLAS17jrp as an extraordinary tidal disruption event (TDE) in the star-forming galaxy SDSS J162034.99+240726.5 in our recent sample of mid-infrared outbursts in nearby galaxies. Its optical/UV light curves rise to a peak luminosity of ∼1.06 × 1044 erg s−1 in about a month and then decay as t −5/3 with a roughly constant temperature around 19,000 K, and the optical spectra show a blue continuum and very broad Balmer lines with FWHM ∼ 15,000 km s−1, which gradually narrowed to 1400 km s−1 within 4 yr, all agreeing well with other optical TDEs. A delayed and rapidly rising X-ray flare with a peak luminosity of ∼1.27 × 1043 erg s−1 was detected ∼170 days after the optical peak. The high MIR luminosity of ATLAS17jrp (∼2 × 1043 erg s−1) has revealed a distinctive dusty environment with a covering factor as high as ∼0.2, which is comparable to that of a torus in active galactic nuclei but at least one order of magnitude higher than normal optical TDEs. Therefore, ATLAS17jrp turns out to be one of the rare unambiguous TDEs found in star-forming galaxies, and its high dust-covering factor implies that dust extinction could play an important role in the absence of optical TDEs in star-forming galaxies.

The nuclear transient AT 2017gge: a tidal disruption event in a dusty and gas-rich environment and the awakening of a dormant SMBH

“…The results of the spectral analysis are reported in Table 5 and are shown if Figure 7. These results are all consistent with the X-ray analysis already presented in the recent discovery paper of AT 2017gge (Wang et al 2022). Additionally, in order to investigate the origin of the delayed X-ray flare as produced by a newly formed accretion disk, we have modelled the data with the TBABS*ZASHIFT*DISKBB model (right panel of Figure 7, red solid line).…”

“…The detected X-ray emission has a transient nature, with only upper limits (grey triangles in the Figure ) for the first 170 days from the discovery of AT 2017gge and showing the peak around 200 days. Furthermore, no X-rays have been detected in the recent XRT observations taken at ∼1684 days (see Wang et al 2022). Such a delayed X-ray brightening with respect to the optical/UV peak has already been observed in some TDEs, specifically, ASASSN-14li (Pasham et al 2017;Gezari et al 2017), ASASSN-15oi (Holoien et al 2018), AT 2019azh (Liu et al 2022) and OGLE16aaa (Kajava et al 2020;Shu et al 2020), which have shown ∼30 days, 1 year, 200 and 140 days of delay in the X-ray emission, respectively.…”

“…The total energy radiated (𝐸 rad ) is derived by integrating the bolometric luminosity over time and it results 𝐸 rad = (3.2±0.5)×10 51 erg. In their recent letter on AT 2017gge, Wang et al (2022) independently derived the bolometric lightcurve, together with the black body temperature and radius by using all the UVOT data but V filter and only the ATLAS 𝑜 band data. Although their values are consistent with our results, they found a declining trend for the bolometric lightcurve luminosity compatible with the 𝑡 −5/3 powerlaw.…”

“…We however note that the pre-transient SDSS values placed the host galaxy on the (theoretical) extreme starburst line and this may indicate the presence of a weak AGN contribution, see Section 8.1 for a detailed discussion). Wang et al (2022) estimated the total radiated energy of AT 2017gge in the IR (until July 2021) of 1.3×10 51 erg. Combined with our estimated radiated energy in the optical the total radiated energy detected is ∼4×10 51 erg and this is a lower limit for the total radiated energy from the TDE.…”

“…Fraser et al (2017) suggest the possibility of a TDE nature for AT 2017gge, as the smooth evolution of the lightcurve is atypical for AGN variability. Recently, based on the X-ray and optical analysis, Wang et al (2022) claimed a TDE nature for this transient.…”