Abstract The Double Asteroid Redirection Test1,2 (DART) was intended to test planetary defense strategies via the reaction of the near-Earth asteroid Dimorphos, a satellite of Didymous, to a spacecraft impact. Pre-impact modeling3–7 predicted a momentum gain of the impacted asteroid in the range of 1−5 times that of the impactor. These models further suggest that the velocity distribution of the ejecta depends, for example, on the material cohesion and porosity. Therefore, detailed observations of the velocity and particle-size distribution in the ejecta can be used to calibrate the models and assess the target properties. Here we report on ultraviolet (UV), visible, and near-infrared (NIR) observations of the Dimorphos-DART impact. We show that the ejecta were composed of two main components. A slow component with high scattering efficiency expanding at a few ms−1 with a mass ≳ 2×104 kg, and a fast component moving at 1,600ms−1. Measuring the time scale on which these ejecta become optically thin, the surface brightness evolution, and multi-band Mie scattering, we detect not only the visible scattering ejecta, but also the “unseen" absorbing ejecta. The fast component is composed of ∼ 0.01 to ≈ 0.2μm sized particles, with a total mass of ∼ 103 kg. Most of the momentum gain of Dimorphos, after the impact, was due to the fast ejecta, and so the momentum gain of impacts can be estimated using such observations.

Abstract Tidal disruption events (TDEs) are bursts of electromagnetic energy released when supermassive black holes at the center of galaxies violently disrupt stars that pass too close. TDEs provide a new window to study accretion onto supermassive black holes; in some cases, this accretion leads to launching of a relativistic jet, but the necessary conditions are not fully understood. Here, we report the optical discovery of AT2022cmc, a rapidly fading source located at redshift z=1.19325. Observations of a bright counterpart at other wavelengths, including X-rays, sub-millimeter, and radio, supports the interpretation of AT2022cmc as a jetted TDE containing a synchrotron ``afterglow.'' Using 4 years of Zwicky Transient Facility survey data, we calculated a rate of 0.02 ^{+ 0.04 }_{- 0.01 } Gpc^{-3} yr^{-1} for jetted TDEs based on the luminous, fast-fading red component, thus providing a measurement complementary to the rates derived from X--ray and radio observations (Brown et al., 2015), confirming that ~1% of TDEs have on-axis jets. Forthcoming observations of AT2022cmc could resolve the jet through high-resolution imaging, while optical surveys have the potential to unveil a population of cosmological flares of the AT2022cmc class.

Corresponding author: S.R. Kulkarni srk@astro.caltech.edu ar X iv :2 11 1. 15 60 8v 1 [ as tr oph .G A ] 3 0 N ov 2 02 1

We use a sample of 27 gamma-ray bursts (GRBs) at redshift z = 2–6 to probe the outflows in their respective host galaxies (log(M */M ⊙) ∼ 9–11) and search for possible relations between the outflow properties and those of the host galaxies, such as M *, the star formation rate (SFR), and the specific SFR (sSFR). First, we consider three outflow properties: outflow column density (N out), maximum outflow velocity (V max), and normalized maximum velocity (V norm = V max/V circ,halo, where V circ,halo is the halo circular velocity). We observe clear trends of N out and V max with increasing SFR in high-ion-traced outflows, with a stronger (>3σ) V max–SFR correlation. We find that the estimated mass outflow rate and momentum flux of the high-ion outflows scale with SFR and can be supported by the momentum imparted by star formation (supernovae and stellar winds). The kinematic correlations of high-ion-traced outflows with SFR are similar to those observed for star-forming galaxies at low redshifts. The correlations with SFR are weaker in low-ion outflows. This, along with the lower detection fraction in low-ion outflows, indicates that the outflow is primarily high-ion dominated. We also observe a strong (>3σ) trend of normalized velocity (V norm) decreasing with halo mass and increasing with sSFR, suggesting that outflows from low-mass halos and high-sSFR galaxies are most likely to escape and enrich the outer circumgalactic medium (CGM) and intergalactic medium with metals. By comparing the CGM–GRB stacks with those of starbursts at z ∼ 2 and z ∼ 0.1, we find that over a broad redshift range, the outflow strength strongly depends on the main-sequence offset at the respective redshifts, rather than simply the SFR.

The Zwicky Transient Facility ( ZTF ) is a new optical time-domain survey that uses the Palomar 48 inch Schmidt telescope. A custom-built wide- fi eld camera provides a 47 deg 2 fi eld of view and 8 s readout time, yielding more than an order of magnitude improvement in survey speed relative to its predecessor survey, the Palomar Transient Factory. We describe the design and implementation of the camera and observing system. The ZTF data system at the Infrared Processing and Analysis Center provides near-real-time reduction to identify moving and varying objects. We outline the analysis pipelines, data products, and associated archive. Finally, we present on-sky performance analysis and fi rst scienti fi c results from commissioning and the early survey. ZTF ’ s public alert stream will serve as a useful precursor for that of the Large Synoptic Survey Telescope.

We present a broadband study of gamma-ray burst (GRB) 091024A within the context of other ultra-long-duration GRBs. An unusually long burst detected by Konus–Wind (KW), Swift, and Fermi, GRB 091024A has prompt emission episodes covering ∼1300 s, accompanied by bright and highly structured optical emission captured by various rapid-response facilities, including the 2 m autonomous robotic Faulkes North and Liverpool Telescopes, KAIT, S-LOTIS, and the Sonoita Research Observatory. We also observed the burst with 8 and 10 m class telescopes and determine the redshift to be z = 1.0924 ± 0.0004. We find no correlation between the optical and γ -ray peaks and interpret the optical light curve as being of external origin, caused by the reverse and forward shock of a highly magnetized jet (RB ≈ 100–200). Low-level emission is detected throughout the near-background quiescent period between the first two emission episodes of the KW data, suggesting continued central-engine activity; we discuss the implications of this ongoing emission and its impact on the afterglow evolution and predictions. We summarize the varied sample of historical GRBs with exceptionally long durations in gamma-rays ( 1000 s) and discuss the likelihood of these events being from a separate population; we suggest ultra-long GRBs represent the tail of the duration distribution of the long GRB population.

We present ground-based and Swift observations of iPTF16fnl, a likely tidal disruption event (TDE) discovered by the intermediate Palomar Transient Factory (iPTF) survey at 66.6 Mpc. The lightcurve of the object peaked at absolute M g = − 17 . 2 mag. The maximum bolometric luminosity (from optical and UV) was L p (cid:39) (1 . 0 ± 0 . 15) × 10 43 erg s − 1 , an order of magnitude fainter than any other optical TDE discovered so far. The luminosity in the first 60 days is consistent with an exponential decay, with L ∝ e − ( t − t 0 ) /τ , where t 0 = 57631.0 (MJD) and τ (cid:39) 15 days. The X-ray shows a marginal detection at L X = 2 . 4 1 . 9 − 1 . 1 × 10 39 erg s − 1 ( Swift X-ray Telescope). No radio counterpart was detected down to 3 σ , providing upper limits for monochromatic radio luminosity of νL ν < 2 . 3 × 10 36 erg s − 1 and νL ν < 1 . 7 × 10 37 erg s − 1 (VLA, 6.1 and 22 GHz). The blackbody temperature, obtained from combined Swift UV and optical photometry, shows a constant value of 19,000 K. The transient spectrum at peak is characterized by broad He II and H α emission lines, with an FWHM of about 14,000 km s − 1 and 10,000 km s − 1 respectively. He I lines are also detected at λλ 5875 and 6678. The spectrum of the host is dominated by strong Balmer absorption lines, which are consistent with a post-starburst (E+A) galaxy with an age of ∼ 650 Myr and solar metallicity. The characteristics of iPTF16fnl make it an outlier on both luminosity and decay timescales, as compared to other optically selected TDEs. The discovery of such a faint optical event suggests a higher rate of tidal disruptions, as low luminosity events may have gone unnoticed in previous searches. Foundation (NSF) 1313484. This work makes use of observations from the LCO network. G.H. is supported Foundation (NSF) This work makes use of observations from the LCO network. We acknowledge the use of public data from the Swift data archive. The CSS survey Observations The CRTS

The progenitors of some supernovae (SNe) exhibit outbursts with super-Eddington luminosities prior to their final explosions. This behavior is common among Type IIn SNe, but the driving mechanisms of these precursors are not yet well understood. SNHunt 275 was announced as a possible new SN during May 2015. Here we report on pre-explosion observations of the location of this event by the Palomar Transient Factory (PTF) and report the detection of a precursor about 500days prior to the 2015 May activity (PTF13efv). The observed velocities in the 2015 transient and its 2013 precursor absorption spectra are low (1000–2000km s), so it is not clear yet if the recent activity indeed marks the final disruption of the progenitor. Regardless of the nature of this event, we use the PTF photometric and spectral observations, as well as Swift-UVOT observations, to constrain the efficiency of the radiated energy relative to the total kinetic energy of the precursor. We find that, using an order-of-magnitude estimate and under the assumption of spherical symmetry, the ratio of the radiated energy to the kinetic energy is in the range of 4× 10 to 3.4× 10. Subject headings: stars: mass-loss — supernovae: general — supernovae: individual: PTF13efv, SNHunt 275