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.

We present spectra of 1796 sources selected in the AKARI North Ecliptic Pole Wide Survey field, obtained with MMT/Hectospec and WIYN/Hydra, for which we measure 1645 redshifts. We complemented the generic fluxlimited spectroscopic surveys at 11 μm and 15 μm, with additional sources selected based on the MIR and optical colors. In MMT/Hectospec observations, the redshift identification rates are ∼80% for objects with R < 21.5 mag. On the other hand, in WIYN/Hydra observations, the redshift identification rates are ∼80% at R magnitudes brighter than 19 mag. The observed spectra were classified through the visual inspection or from the line diagnostics. We identified 1128 star-forming or absorption-line-dominated galaxies, 198 Type-1 active galactic nuclei (AGNs), 8 Type-2 AGNs, 121 Galactic stars, and 190 spectra in unknown category due to low signal-to-noise ratio. The spectra were flux-calibrated but to an accuracy of 0.1-0.18 dex for most of the targets and worse for the remainder. We derive star formation rates (SFRs) from the mid-infrared fluxes or from the optical emission lines, showing that our sample spans an SFR range of 0.1 to a few hundred M yr −1 . We find that the extinction inferred from the difference between the IR and optical SFR increases as the IR luminosity increases but with a large scatter.

We present the source catalog and the properties of the B−, R−, and I−band images obtained to support the AKARI North Ecliptic Pole Wide (NEP-Wide) survey. The NEP-Wide is an AKARI infrared imaging survey of the north ecliptic pole covering a 5.8 deg 2 area over 2.5 -6 µm wavelengths. The optical imaging data were obtained at the Maidanak Observatory in Uzbekistan using the Seoul National University 4k × 4k Camera on the 1.5m telescope. These images cover 4.9 deg 2 where no deep optical imaging data are available. Our B−, R−, and I−band data reach the depths of ∼23.4, ∼23.1, and ∼22.3 mag (AB) at 5σ, respectively. The source catalog contains 96,460 objects in the R−band, and the astrometric accuracy is about 0.15 ′′ at 1σ in each RA and Dec direction. These photometric data will be useful for many studies including identification of optical counterparts of the infrared sources detected by AKARI, analysis of their spectral energy distributions from optical through infrared, and the selection of interesting objects to understand the obscured galaxy evolution. 1.the contiguous MIR wavelength coverage, and the low extinction value of E(B − V ) = 0.047 at the center of NEP (Schlegel et al. 1998), the NEP-Wide field is unique for the studies of the extragalactic objects like infrared luminous galaxies and AGNs. For further information about NEP surveys, the readers can refer to Matsuhara et al. (2006), Wada et al. (2007), and Lee et al. (2007Lee et al. ( , 2009).Optical imaging data can enhance the value of the unique AKARI NEP survey. Since AKARI has a low spatial resolution (the full width at half maximum (FWHM) of the point spread function (PSF) is about 6 ′′ at 15µm), the optical imaging with a higher resolution can help improving the astrometric accuracy and help deblending confused objects. Also, the optical bands are important to construct multi-wavelength spectral energy distributions (SEDs) of infrared sources such as galaxies and AGNs to understand their properties. There already exist deep optical data covering 2 deg 2 of the central region of the NEP-Wide field, obtained by the Canada-France-Hawaii Telescope (CFHT) with u * , g ′ , r ′ , i ′ , and z ′ filters (Hwang et al. 2007). However, there is no deep optical data for the remaining NEP-Wide area. The Digitized Sky Survey images are available, but neither their depths nor spatial resolutions are sufficient (the depth is about 20 mag at R and the seeing is about 3 ′′ with pixel scale of 1.0 ′′ at the NEP area) for identifying optical counterparts of many infrared sources. Hence, we observed this remaining NEP-Wide area in optical B, R, and I filters. The BRI filters were chosen because we needed a multiple color set at least three colors to construct the optical part of the SED of galaxy; one blue part, one red part, and a middle part between red and infrared bands. Also, those Bessell filters are wider than the Sloan Digital Sky Survey (SDSS) filters, enabling us to achieve a higher signal to noise ratio (S/N) per unit exposure time than the SDSS filters...

We present ten medium-resolution, high signal-to-noise ratio near-infrared (NIR) spectra of SN 2011fe from SpeX on the NASA Infrared Telescope Facility (IRTF) and Gemini Near-Infrared Spectrograph (GNIRS) on Gemini North, obtained as part of the Carnegie Supernova Project. This data set constitutes the earliest time-series NIR spectroscopy of a Type Ia supernova (SN Ia), with the first spectrum obtained at 2.58 days past the explosion and covering −14.6 to +17.3 days relative to B-band maximum. C I λ1.0693 µm is detected in SN 2011fe with increasing strength up to maximum light. The delay in the onset of the NIR C I line demonstrates its potential to be an effective tracer of unprocessed material. For the first time in a SN Ia, the early rapid decline of the Mg II λ1.0927 µm velocity was observed, and the subsequent velocity is remarkably constant. The Mg II velocity during this constant phase locates the inner edge of carbon burning and probes the conditions under which the transition from deflagration to detonation occurs. We show that the Mg II velocity does not correlate with the optical light-curve decline rate ∆m 15 (B). The prominent break at ∼ 1.5 µm is the main source of concern for NIR k-correction calculations. We demonstrate here that the feature has a uniform time evolution among SNe Ia, with the flux ratio across the break strongly correlated with ∆m 15 (B). The predictability of the strength and the onset of this feature suggests that the associated k-correction uncertainties can be minimized with improved spectral templates.

Recent studies suggest that faint active galactic nuclei may be responsible for the reionization of the universe. Confirmation of this scenario requires spectroscopic identification of faint quasars (M 1450 > −24 mag) at z 6, but only a very small number of such quasars have been spectroscopically identified so far. Here, we report the discovery of a faint quasar IMS J220417.92+011144.8 at z ∼ 6 in a 12.5 deg 2 region of the SA22 field of the Infrared Medium-deep Survey (IMS). The spectrum of the quasar shows a sharp break at ∼ 8443Å, with emission lines redshifted to z = 5.944 ± 0.002 and rest-frame ultraviolet continuum magnitude M 1450 = −23.59 ± 0.10 AB mag. The discovery of IMS J220417.92+011144.8 is consistent with the expected number of quasars at z ∼ 6 estimated from quasar luminosity functions based on previous observations of spectroscopically identified lowluminosity quasars . This suggests that the number of M 1450 ∼ −23 mag quasars at z ∼ 6 may not be high enough to fully account for the reionization of the universe. In addition, our study demonstrates that faint quasars in the early universe can be identified effectively with a moderately wide and deep near-infrared survey such as the IMS.