Supermassive black holes have powerful gravitational fields with strong gradients that can destroy stars that get too close, producing a bright flare in ultraviolet and X-ray spectral regions from stellar debris that forms an accretion disk around the black hole. The aftermath of this process may have been seen several times over the past two decades in the form of sparsely sampled, slowly fading emission from distant galaxies, but the onset of the stellar disruption event has not hitherto been observed. Here we report observations of a bright X-ray flare from the extragalactic transient Swift J164449.3+573451. This source increased in brightness in the X-ray band by a factor of at least 10,000 since 1990 and by a factor of at least 100 since early 2010. We conclude that we have captured the onset of relativistic jet activity from a supermassive black hole. A companion paper comes to similar conclusions on the basis of radio observations. This event is probably due to the tidal disruption of a star falling into a supermassive black hole, but the detailed behaviour differs from current theoretical models of such events.

Hyper Suprime-Cam (HSC) is a wide-field imaging camera on the prime focus of the 8.2m Subaru telescope on the summit of Maunakea in Hawaii. A team of scientists from Japan, Taiwan and Princeton University is using HSC to carry out a 300-night multi-band imaging survey of the high-latitude sky. The survey includes three layers: the Wide layer will cover 1400 deg 2 in five broad bands (grizy), with a 5 σ point-source depth of r ≈ 26. The Deep layer covers a total of 26 deg 2 in four fields, going roughly a magnitude fainter, while the UltraDeep layer goes almost a magnitude fainter still in two pointings of HSC (a total of 3.5 deg 2). Here we describe the instrument, the science goals of the survey, and the survey strategy and data processing. This paper serves as an introduction to a special issue of the Publications of the Astronomical Society of Japan, which includes a large number of technical and scientific papers describing results from the early phases of this survey.

The high luminosity and slow decline of their light curves ( Fig PTF12dam is not detected in z P1 images on 1 January 2012, 132 days before the peak.Although their light curves match the declining phases of SN 2007bi and the PISN models quite well, PTF12dam and PS1-11ap rise to maximum light a factor of ~2 faster than these models.The spectra of PTF12dam and PS1-11ap show them to be similar supernovae. After 50 days from the respective light curve peaks, these spectra are almost identical to that of SN 2007bi at the same epoch ( Particularly around and after maximum light, PISN colours are expected to evolve to the red owing to increasing blanketing by iron group elements 7,8 abundant in their ejecta. We see no evidence of line blanketing in our spectra, even down to 2,000 Å (rest frame) in PS1-11ap, which suggests lower iron group abundances and a higher degree of ionization than in PISN models. Such conditions are fulfilled in models of ejecta reheated by magnetars-highly magnetic, rapidly rotating nascent pulsars 13,16,17 . The pressure of the magnetar wind on the inner ejecta can form a dense shell 13,14,17 at near-constant photospheric velocity. ForPTF12dam, the velocities of spectral lines are close to 10,000 km s −1 at all times. Intriguingly, Page 4 of 26 the early spectra of our objects are very similar to those of superluminous supernovae of type I (refs 2, 11, 12) and evolve in the same way, but on longer timescales and with lower line velocities (Fig. 2).Nebular modelling of SN 2007bi spectra has been used to argue 1 for large ejected oxygen and magnesium masses of 8-15M ! and 0.07-0.13M ! , respectively (where M ! is the solar mass). Such masses are actually closer to values in massive core-collapse models 18 than in PISN models, which eject ~40M ! oxygen and ~4M ! magnesium 1,8,9 . In the work reported in ref.1, an additional 37M ! in total of Ne, Si, S, and Ar were added to the model, providing a total ejecta mass consistent with a PISN. However, this was not directly measured 1 , because these elements lack any identified lines. These constraints are important, so we investigated line formation in this phase using our own non-local thermodynamic equilibrium code We suggest here one model that can consistently explain the data. A magnetarpowered supernova can produce a light curve with the observed rise and decline rates as the neutron star spins down and reheats the ejecta 13,14,16,17 . It has been suggested that ~10% of core-collapses may form magnetars 14 . Although their initial-spin distribution is unknown, periods ≳1 ms are physically plausible. This mechanism has already been proposed for SN (Fig. 4), and found a good fit for magnetic field B ≈ 10 14 G and spin period P ≈ 2.6 ms, with an ejecta mass of ~10-16M ! . At peak, the r-band luminosities of PTF12dam and PS1-11ap are ~1.5 times that of SN 2007bi. Scaling our light curve by this factor, our model implies a similar ejected mass for SN 2007bi, with a slower-spinning magnetar (P ≈ 3.3 ms), comparable to previous models 14 . If the mag...

Recent searches by unbiased, wide-field surveys have uncovered a group of extremely luminous optical transients. The initial discoveries of SN 2005ap by the Texas Supernova Search and SCP-06F6 in a deep Hubble pencil beam survey were followed by the Palomar Transient Factory confirmation of host redshifts for other similar transients. The transients share the common properties of high optical luminosities (peak magnitudes ∼ −21 to −23), blue colors, and a lack of H or He spectral features. The physical mechanism that produces the luminosity is uncertain, with suggestions ranging from jet-driven explosion to pulsational pair-instability. Here we report the most detailed photometric and spectral coverage of an ultra-bright transient (SN 2010gx) detected in the Pan-STARRS 1 sky survey. In common with other transients in this family, early-time spectra show a blue continuum, and prominent broad absorption lines of O II. However, about 25d after discovery, the spectra developed type Ic supernova features, showing the characteristic broad Fe II and Si II absorption lines. Detailed, post-maximum follow-up may show that all SN 2005ap and SCP-06F6 type transients are linked to supernovae Ic. This poses problems in understanding the physics of the explosions: there is no indication from late-time photometry that the luminosity is powered by 56 Ni, the broad lightcurves suggest very large ejected masses, and the slow spectral evolution is quite different from typical Ic timescales. The nature of the progenitor stars and the origin of the luminosity are intriguing and open questions. Subject headings: supernovae: general -supernovae: individual(SN 2010gx, SCP-06F6, SN 2005ap)

The Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) is a three-layered imaging survey aimed at addressing some of the most important outstanding questions in astronomy today, including the nature of dark matter and dark energy. The survey has been awarded 300 nights of observing time at the Subaru Telescope, and it started in 2014 March. This paper presents the first public data release of HSC-SSP. This release includes data taken in the first 1.7 yr of observations (61.5 nights), and each of the Wide, Deep, and UltraDeep layers covers about 108, 26, and 4 square degrees down to depths of i ∼ 26.4, ∼26.5, and ∼27.0 mag, respectively (5 σ for point sources). All the layers are observed in five broad bands (grizy), and the Deep and UltraDeep layers are observed in narrow bands as well. We achieve an impressive image quality of 0${^{\prime\prime}_{.}}$6 in the i band in the Wide layer. We show that we achieve 1%–2% point spread function (PSF) photometry (root mean square) both internally and externally (against Pan-STARRS1), and ∼10 mas and 40 mas internal and external astrometric accuracy, respectively. Both the calibrated images and catalogs are made available to the community through dedicated user interfaces and database servers. In addition to the pipeline products, we also provide value-added products such as photometric redshifts and a collection of public spectroscopic redshifts. Detailed descriptions of all the data can be found online. The data release website is https://hsc-release.mtk.nao.ac.jp.