Van den Heuvel and Tauris argue that if the red giant star in the system 2MASS J05215658+4359220 has a mass of 1 solar mass (M-circle dot), then its unseen companion could be a binary composed of two 0.9 M. stars, making a triple system. We contend that the existing data are most consistent with a giant of mass 3.2(-1.0)(+1.0) M-circle dot, implying a black hole companion of 3.3(-0.7)(+2.8) M-circle dot

The existence of optical-ultraviolet Tidal Disruption Events (TDEs) could be considered surprising because their electromagnetic output was originally predicted to be dominated by X-ray emission from an accretion disk. Yet over the last decade, the growth of optical transient surveys has led to the identification of a new class of optical transients occurring exclusively in galaxy centers, many of which are considered to be TDEs. Here we review the observed properties of these events, identified based on a shared set of both photometric and spectroscopic properties. We present a homogeneous analysis of 33 sources that we classify as robust TDEs, and which we divide into classes. The criteria used here to classify TDEs will possibly get updated as new samples are collected and potential additional diversity of TDEs is revealed. We also summarize current measurements of the optical-ultraviolet TDE rate, as well as the mass function and luminosity function. Many open questions exist regarding the current sample of events. We anticipate that the search for answers will unlock new insights in a variety of fields, from accretion physics to galaxy evolution.

In November 2020, the Swift team announced an update to the UltraViolet and Optical Telescope calibration to correct for the loss of sensitivity over time. This correction affects observations in the three near-ultraviolet (UV) filters, by up to 0.3 mag in some cases. As UV photometry is critical to characterizing tidal disruption events (TDEs) and other peculiar nuclear outbursts, we recomputed published Swift data for TDEs and other singular nuclear outbursts with Swift photometry in 2015 or later as a service to the community. Using archival UV, optical, and infrared photometry, we ran host SED fits for each host galaxy. From these, we computed synthetic host magnitudes and host-galaxy properties. We calculated host-subtracted magnitudes for each transient and computed blackbody fits. In addition to the nuclear outbursts, we include the ambiguous transient ATLAS18qqn (AT2018cow), which has been classified as a potential TDE on an intermediate-mass black hole. Finally, with updated bolometric light curves, we recover the relationship of Hinkle et al., where more-luminous TDEs decay more slowly than less-luminous TDEs, with decreased scatter compared to the original relationship.

Blazars are active galactic nuclei with their relativistic jets pointing toward the observer, comprising two major subclasses, flat-spectrum radio quasars (FSRQs) and BL Lac objects. We present multiwavelength photometric and spectroscopic monitoring observations of the blazar B2 1420+32, focusing on its outbursts in 2018-2020. Multiepoch spectra show that the blazar exhibited large-scale spectral variability in both its continuum and line emission, accompanied by dramatic gamma-ray and optical variability by factors of up to 40 and 15, respectively, on week to month timescales. Over the last decade, the gamma-ray and optical fluxes increased by factors of 1500 and 100, respectively. B2 1420+32 was an FSRQ with broad emission lines in 1995. Following a series of flares starting in 2018, it transitioned between BL Lac and FSRQ states multiple times, with the emergence of a strong Fe pseudocontinuum. Two spectra also contain components that can be modeled as single-temperature blackbodies of 12,000 and 5200 K. Such a collection of "changing-look" features has never been observed previously in a blazar. We measure gamma-ray-optical and interband optical lags implying emission-region separations of less than 800 and 130 gravitational radii, respectively. Since most emission-line flux variations, except the Fe continuum, are within a factor of 2-3, the transitions between FSRQ and BL Lac classifications are mainly caused by the continuum variability. The large Fe continuum flux increase suggests the occurrence of dust sublimation releasing more Fe ions in the central engine and an energy transfer from the relativistic jet to subrelativistic emission components.

We present new photometric and spectroscopic observations of SN. 2019yvq, a Type Ia supernova (SN Ia) exhibiting several peculiar properties including an excess of UV/optical flux within days of explosion, a high Si II velocity, and a low peak luminosity. Photometry near the time of first light places new constraints on the rapid rise of the UV/optical flux excess. A near-infrared spectrum at +173.days after maximum light places strict limits on the presence of H or He emission, effectively excluding the presence of a nearby nondegenerate star at the time of explosion. New optical spectra, acquired at +128 and +150 days after maximum light, confirm the presence of [Ca II]lambda 7300 and persistent Ca II NIR triplet emission as SN.2019yvq transitions into the nebular phase. The lack of [O I]lambda 6300 emission disfavors the violent merger of two C/O white dwarfs (WDs) but the merger of a C/OWD with a He WD cannot be excluded. We compare our findings with several models in the literature postulated to explain the early flux excess including double-detonation explosions, Ni-56 mixing into the outer ejecta during ignition, and interaction with H- and He-deficient circumstellar material. Each model may be able to explain both the early flux excess and the nebular [Ca II] emission, but none of the models can reconcile the high photospheric velocities with the low peak luminosity without introducing new discrepancies.

We present V-band photometry of the 20 000 brightest asteroids using data from the All-Sky Automated Survey for Supernovae (ASAS-SN) between 2012 and 2018. We were able to apply the convex inversion method to more than 5000 asteroids with more than 60 good measurements in order to derive their sidereal rotation periods, spin axis orientations, and shape models. We derive unique spin state and shape solutions for 760 asteroids, including 163 new determinations. This corresponds to a success rate of about 15%, which is significantly higher than the success rate previously achieved using photometry from surveys. We derive the first sidereal rotation periods for additional 69 asteroids. We find good agreement in spin periods and pole orientations for objects with prior solutions. We obtain a statistical sample of asteroid physical properties that is sufficient for the detection of several previously known trends, such as the underrepresentation of slow rotators in current databases, and the anisotropic distribution of spin orientations driven by the nongravitational forces. We also investigate the dependence of spin orientations on the rotation period. Since 2018, ASAS-SN has been observing the sky with higher cadence and a deeper limiting magnitude, which will lead to many more new solutions in just a few years.

We report on the search for electromagnetic counterparts to the nine gravitational-wave events with a >60 per cent probability of containing a neutron star during the third observing run (O3) of the Laser Interferometer Gravitational-Wave Observatory (LIGO)-Virgo Collaboration (LVC) with the All-Sky Automated Survey for SuperNovae (ASAS-SN). No optical counterparts associated with a gravitational-wave event were found. However, thanks to its network of telescopes, the average area visible to at least one ASAS-SN site during the first 10 h after the trigger contained similar to 30 per cent of the integrated source location probability. Through a combination of normal operations and target-of-opportunity observations, ASAS-SN observations of the highest probability fields began within 1 h of the trigger for four of the events. After 24 h, ASAS-SN observed >60 per cent of total probability for three events and >40 per cent for all but one of the events. This is the largest area coverage to a depth of g = 18.5 mag from any survey with published coverage statistics for seven of the nine events. With its observing strategy, five sites around the world, and a large field of view, ASAS-SN will be one of the leading surveys to optically search for nearby neutron star mergers during LVC fourth observation run (O4).

SN 2017jgh is a type IIb supernova discovered by Pan-STARRS during the C16/C17 campaigns of the Kepler/K2 mission. Here, we present the Kepler/K2 and ground based observations of SN 2017jgh, which captured the shock cooling of the progenitor shock breakout with an unprecedented cadence. This event presents a unique opportunity to investigate the progenitors of stripped envelope supernovae. By fitting analytical models to the SN 2017jgh light curve, we find that the progenitor of SN 2017jgh was likely a yellow supergiant with an envelope radius of similar to 50-290 R-circle dot, and an envelope mass of similar to 0-1.7 M-circle dot. SN 2017jgh likely had a shock velocity of similar to 7500-10 300 km s(-1). Additionally, we use the light curve of SN 2017jgh to investigate how early observations of the rise contribute to constraints on progenitor models. Fitting just the ground based observations, we find an envelope radius of similar to 50-330 R-circle dot, an envelope mass of similar to 0.3-1.7 M-circle dot and a shock velocity of similar to 9000-15 000 km s(-1). Without the rise, the explosion time cannot be well constrained that leads to a systematic offset in the velocity parameter and larger uncertainties in the mass and radius. Therefore, it is likely that progenitor property estimates through these models may have larger systematic uncertainties than previously calculated.

We report the results of ultraviolet (UV) and optical photometric and spectroscopic analysis of the tidal disruption event (TDE) AT 2019qiz. Our follow-up observations started <10 days after the source began to brighten in the optical and lasted for a period of six months. Our late-time host-dominated spectrum indicates that the host galaxy likely harbors a weak active galactic nucleus. The initial Hubble Space Telescope (HST) spectrum of AT 2019qiz exhibits an iron and low-ionization broad absorption line (FeLoBAL) system that is seen for the first time in a TDE. This spectrum also bears a striking resemblance to that of Gaia16apd, a superluminous supernova. Our observations provide insights into the outflow properties in TDEs and show evidence for a connection between TDEs and engine-powered supernovae at early phases, as originally suggested by Metzger & Stone. In a time frame of 50 days, the UV spectra of AT 2019qiz started to resemble those of previous TDEs with only high-ionization broad absorption lines. The change in UV spectral signatures is accompanied by a decrease in the outflow velocity, which began at 15,000 km s(-1) and decelerated to similar to 10,000 km s(-1). A similar evolution in the H alpha emission-line width further supports the speculation that the broad Balmer emission lines are formed in TDE outflows. In addition, we detect narrow absorption features on top of the FeLoBAL signatures in the early HST UV spectrum of AT 2019qiz. The measured H i column density corresponds to a Lyman-limit system, whereas the metal absorption lines (such as N v, C iv, Fe ii, and Mg ii) are likely probing the circumnuclear gas and interstellar medium in the host galaxy.