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On 17 August 2017, the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo interferometer detected gravitational waves (GWs) emanating from a binary neutron star merger, GW170817. Nearly simultaneously, the Fermi and INTEGRAL (INTErnational Gamma-Ray Astrophysics Laboratory) telescopes detected a gamma-ray transient, GRB 170817A. At 10.9 hours after the GW trigger, we discovered a transient and fading optical source, Swope Supernova Survey 2017a (SSS17a), coincident with GW170817. SSS17a is located in NGC 4993, an S0 galaxy at a distance of 40 megaparsecs. The precise location of GW170817 provides an opportunity to probe the nature of these cataclysmic events by combining electromagnetic and GW observations.

The Asteroid Terrestrial impact Last Alert System (ATLAS) system consists of two 0.5 m Schmidt telescopes with cameras covering 29 square degrees at plate scale of 1.86 arcsec per pixel. Working in tandem, the telescopes routinely survey the whole sky visible from Hawaii (above δ > − 50 ° ) every two nights, exposing four times per night, typically reaching o < 19 magnitude per exposure when the moon is illuminated and c < 19.5 magnitude per exposure in dark skies. Construction is underway of two further units to be sited in Chile and South Africa which will result in an all-sky daily cadence from 2021. Initially designed for detecting potentially hazardous near earth objects, the ATLAS data enable a range of astrophysical time domain science. To extract transients from the data stream requires a computing system to process the data, assimilate detections in time and space and associate them with known astrophysical sources. Here we describe the hardware and software infrastructure to produce a stream of clean, real, astrophysical transients in real time. This involves machine learning and boosted decision tree algorithms to identify extragalactic and Galactic transients. Typically we detect 10-15 supernova candidates per night which we immediately announce publicly. The ATLAS discoveries not only enable rapid follow-up of interesting sources but will provide complete statistical samples within the local volume of 100 Mpc. A simple comparison of the detected supernova rate within 100 Mpc, with no corrections for completeness, is already significantly higher (factor 1.5 to 2) than the current accepted rates.

Technology has advanced to the point that it is possible to image the entire sky every night and process the data in real time. The sky is hardly static: many interesting phenomena occur, including variable stationary objects such as stars or QSOs, transient stationary objects such as supernovae or M dwarf flares, and moving objects such as asteroids and the stars themselves. Funded by NASA, we have designed and built a sky survey system for the purpose of finding dangerous near-Earth asteroids (NEAs). This system, the \"Asteroid Terrestrial-impact Last Alert System\" (ATLAS), has been optimized to produce the best survey capability per unit cost, and therefore is an efficient and competitive system for finding potentially hazardous asteroids (PHAs) but also for tracking variables and finding transients. While carrying out its NASA mission, ATLAS now discovers more bright (m < 19) supernovae candidates than any ground based survey, frequently detecting very young explosions due to its 2 day cadence. ATLAS discovered the afterglow of a gamma-ray burst independent of the high energy trigger and has released a variable star catalog of 5 × 106 sources. This is the first of a series of articles describing ATLAS, devoted to the design and performance of the ATLAS system. Subsequent articles will describe in more detail the software, the survey strategy, ATLAS-derived NEA population statistics, transient detections, and the first data release of variable stars and transient light curves.

Eleven hours after the detection of gravitational wave source GW170817 by the Laser Interferometer Gravitational-Wave Observatory and Virgo Interferometers, an associated optical transient, SSS17a, was identified in the galaxy NGC 4993. Although the gravitational wave data indicate that GW170817 is consistent with the merger of two compact objects, the electromagnetic observations provide independent constraints on the nature of that system. We synthesize the optical to near-infrared photometry and spectroscopy of SSS17a collected by the One-Meter Two-Hemisphere collaboration, finding that SSS17a is unlike other known transients. The source is best described by theoretical models of a kilonova consisting of radioactive elements produced by rapid neutron capture (the r-process). We conclude that SSS17a was the result of a binary neutron star merger, reinforcing the gravitational wave result.

Massive black holes (BHs) at the centres of massive galaxies are ubiquitous. The population of BHs within dwarf galaxies, on the other hand, is not yet known. Dwarf galaxies are thought to harbour BHs with proportionally small masses, including intermediate-mass BHs, with masses 10 2  <  M BH  < 10 6  solar masses ( M ⊙ ). Identification of these systems has historically relied on the detection of light emitted from accreting gaseous disks close to the BHs. Without this light, they are difficult to detect. Tidal disruption events, the luminous flares produced when a star strays close to a BH and is shredded, are a direct way to probe massive BHs. The rise times of these flares theoretically correlate with the BH mass. Here we present AT 2020neh, a fast-rising tidal disruption event candidate, hosted by a dwarf galaxy. AT 2020neh can be described by the tidal disruption of a main sequence star by a 10 4.7 –10 5.9   M ⊙ BH. We find the observable rate of fast-rising nuclear transients like AT 2020neh to be low, at ≲2 × 10 −8 events Mpc −3  yr −1 . Finding non-accreting BHs in dwarf galaxies is important to determine how prevalent BHs are within these galaxies, and to constrain models of BH formation. AT 2020neh-like events may provide a galaxy-independent method of measuring the masses of intermediate-mass BHs. The rapid rise in brightness of a tidal disruption event is attributed to the destruction of a main sequence star by a black hole of intermediate mass in a dwarf galaxy. Such events are rare, and non-accreting intermediate-mass black holes are challenging to find.

Acute myeloid leukemia (AML) involves a block in terminal differentiation of the myeloid lineage and uncontrolled proliferation of a progenitor state. Using phorbol myristate acetate (PMA), it is possible to overcome this block in THP-1 cells (an M5-AML containing the MLL-MLLT3 fusion), resulting in differentiation to an adherent monocytic phenotype. As part of FANTOM4, we used microarrays to identify 23 microRNAs that are regulated by PMA. We identify four PMA-induced microRNAs (mir-155, mir-222, mir-424 and mir-503) that when overexpressed cause cell-cycle arrest and partial differentiation and when used in combination induce additional changes not seen by any individual microRNA. We further characterize these pro-differentiative microRNAs and show that mir-155 and mir-222 induce G2 arrest and apoptosis, respectively. We find mir-424 and mir-503 are derived from a polycistronic precursor mir-424-503 that is under repression by the MLL-MLLT3 leukemogenic fusion. Both of these microRNAs directly target cell-cycle regulators and induce G1 cell-cycle arrest when overexpressed in THP-1. We also find that the pro-differentiative mir-424 and mir-503 downregulate the anti-differentiative mir-9 by targeting a site in its primary transcript. Our study highlights the combinatorial effects of multiple microRNAs within cellular systems.

For decades, optical time-domain searches have been tuned to find ordinary supernovae, which rise and fall in brightness over a period of weeks. Recently, supernova searches have improved their cadences and a handful of fast-evolving luminous transients have been identified 1 – 5 . These have peak luminosities comparable to type Ia supernovae, but rise to maximum in less than ten days and fade from view in less than one month. Here we present the most extreme example of this class of object thus far: KSN 2015K, with a rise time of only 2.2 days and a time above half-maximum of only 6.8 days. We show that, unlike type Ia supernovae, the light curve of KSN 2015K was not powered by the decay of radioactive elements. We further argue that it is unlikely that it was powered by continuing energy deposition from a central remnant (a magnetar or black hole). Using numerical radiation hydrodynamical models, we show that the light curve of KSN 2015K is well fitted by a model where the supernova runs into external material presumably expelled in a pre-supernova mass-loss episode. The rapid rise of KSN 2015K therefore probes the venting of photons when a hypersonic shock wave breaks out of a dense extended medium. A fast-evolving luminous transient (FELT) has been detected with a rise time to peak luminosity of only 2.2 days. This implies that the light-curve of this FELT cannot be powered by the decay of radioactive elements, as with type Ia supernovae.

In Smith et al. we published estimates of the volumetric rate of supernovae within 100 Mpc. These were incorrect and we present the correct values in this corrigendum.

The Edinburgh randomised trial of breast-cancer screening recruited women aged 45-64 years from 1978 to 1981 (cohort 1), and those aged 45-49 years during 1982-85 (cohorts 2 and 3). Results based on 14 years of follow-up and 270,000 woman-years of observation are reported. Breast-cancer mortality rates in the intervention group (28,628 women offered screening) were compared with those in the control group (26,026) with adjustment for socioeconomic status (SES) of general medical practices. Rate ratios were derived by means of logistic regression for the total trial population and for women first offered screening while younger than 50 years. Analyses were by intention to treat. Initial unadjusted results showed a difference of just 13% in breast-cancer mortality rates between the intervention and control groups (156 deaths [5.18 per 10,000] vs 167 [6.04 per 10,000]; rate ratio 0.87 [95% CI 0.70-1.06]), but the results were influenced by differences in SES by trial group. After adjustment for SES, the rate ratio was 0.79 (95% CI 0.60-1.02). When deaths after diagnosis more than 3 years after the end of the study were censored the rate ratio became 0.71 (0.53-0.95). There was no evidence of heterogeneity by age at entry and no evidence that younger entrants had smaller or delayed benefit (rate ratio 0.70 [0.41-1.20]). No breast-cancer mortality benefit was observed for women whose breast cancers were diagnosed when they were younger than 50 years. Other-cause mortality rates did not differ by trial group when adjusted for SES. Our findings confirm results from randomised trials in Sweden and the USA that screening for breast cancer lowers breast-cancer mortality. Similar results are reported by the UK geographical comparison, UK Trial of Early Detection of Breast Cancer. The results for younger women suggest benefit from introduction of screening before 50 years of age.