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 high-cadence survey of the Zwicky Transient Facility (ZTF) has completely dominated the discovery of tidal disruption events (TDEs) in the past few years and resulted in the largest sample of TDEs with optical/UV light curves well sampled around their peaks, providing us an excellent opportunity to construct a peak luminosity function (LF) of tidal disruption flares (TDFs). The new construction is necessary particularly considering that the most updated LF reported in literature has been inferred from only 13 sources from five different surveys. Here we present the optical and blackbody LFs calculated by 33 TDFs discovered in the ZTF-I survey. The optical LF can be described by both a power-law profile dN / dL g ∝ L g − 2.3 ± 0.2 , and a Schechter-like function. The blackbody LF can be described by a power-law profile dN / dL bb ∝ L bb − 2.2 ± 0.2 , shallower than the LF made of the previous van Velzen (2018) sample. A possible low-luminosity turnover in the optical LF supports an Eddington-limited emission scenario. The drop of the volumetric rate at high luminosity suggests a rate suppression due to direct captures of the black hole. The total volumetric rate is 1 order of magnitude lower than the previous estimation, which is probably not simply caused by the high fraction postpeak sources (7/13) in the previous sample. Instead, the normalization step during the previous LF construction to reconcile various surveys might adversely amplify the influence of serendipitous discoveries. Therefore, TDFs selected from ongoing and upcoming uniform surveys like ZTF, Vera Rubin Observatory, and the Wide-Field Survey Telescope should yield more accurate LFs.

Emission-line galaxies (ELGs) are crucial for understanding the formation and evolution of galaxies, while little is known about their variability. Here we report on the optical variability of a sample of ELGs selected in the COSMOS field, which has narrowband observations in two epochs separated by ≳12 yr. This sample was observed with the Suprime-Cam (SC) and Hyper Suprime-Cam (HSC) on the Subaru telescope in NB816 and i ′ / i bands, respectively. After carefully removing the wing effect of a narrowband filter, we check the optical variability in a sample of 181 spectroscopically confirmed ELGs. We find that 0 (0/68) Hα emitters, 11.9% (5/42) [O iii] emitters, and 0 (0/71) [O ii] emitters show significant variability ( ∣ Δ m NB ∣ ≥ 3 σ Δ m NB , AGN = 0.20 mag ) in the two-epoch narrowband observations. We investigate the presence of active galactic nuclei (AGN) in this variable ELG (var-ELG) sample with three methods, including X-ray luminosity, mid-infrared activity, and radio excess. We find zero bright AGN in this var-ELG sample but cannot rule out the contribution from faint AGN. We find that supernovae explosions (SNe) could also dominate the variability of the var-ELG sample. The merger morphology shown in the HST/F814W images of the entire var-ELG sample is in agreement with the enhancement of star formation, i.e., the SNe activity.

We present a broadband spectrophotometric analysis of an unusual quasar, SDSS J160558.86+474300.1, at z = 0.9, found in a systematic search for reddened radio-loud narrow-line Seyfert 1 galaxies (NLS1s). J1605+4743 qualifies for the conventional definition of an NLS1 in its permitted emission line widths and Hβ/[O iii] flux ratio. It also shows strong Fe ii emissions. J1605+4743 has a steep radio spectrum. With a radio loudness of ∼150 (70) before (after) reddening correction, it is among the most radio-loud NLS1s discovered. In addition, the blueshifted emission lines are also found to be weak, suggesting that it can be an exotic “wind-dominated” Seyfert similar to weak-line quasars, especially the ones with strong reddening. As an extreme hybrid central engine, its environment and host galaxy become rather intriguing. We discover in it a proximate 2175 Å absorber with a bump strength similar to the average value of 2175 Å absorbers in the Milky Way, which we suspect can be intrinsic to the quasar. In addition, the quasar seems to have enhanced instead of suppressed star formation at a rate of ≳94 M ⊙ yr−1. The combination of these unusual properties, i.e., the unique extinction, strong Fe ii and [O ii] lines, weak [O iii], Mg ii, and Balmer lines, and large radio loudness, might hold important clues to accretion physics, the formation/destruction of dust grains in the environment of active galactic nuclei, and possibly also the coevolution of supermassive black holes and their host galaxies in general.