After the All-Sky Automated Survey for SuperNovae (ASAS-SN) discovered a significant brightening of the inner region of NGC 2617, we began a ∼ 70 day photometric and spectroscopic monitoring campaign from the X-ray through near-infrared (NIR) wavelengths. We report that NGC 2617 went through a dramatic outburst, during which its X-ray flux increased by over an order of magnitude followed by an increase of its optical/ultraviolet (UV) continuum flux by almost an order of magnitude. NGC 2617, classified as a Seyfert 1.8 galaxy in 2003, is now a Seyfert 1 due to the appearance of broad optical emission lines and a continuum blue bump. Such "changing look Active Galactic Nuclei (AGN)" are rare and provide us with important insights about AGN physics. Based on the Hβ line width and the radius-luminosity relation, we estimate the mass of central black hole to be (4 ± 1) × 10 7 M ⊙ . When we crosscorrelate the light curves, we find that the disk emission lags the X-rays, with the lag becoming longer as we move from the UV (2 − 3 days) to the NIR (6 − 9 days). Also, the NIR is more heavily temporally smoothed than the UV. This can largely be explained by a simple model of a thermally emitting thin disk around a black hole of the estimated mass that is illuminated by the observed, variable X-ray fluxes.

Spectral analysis of Swift/XRT dataWe use the xspec v11.3.2 X-ray spectral fitting package to fit both a power law and a blackbody model to the XRT outburst data. In both models we allow for excess neutral hydrogen absorption (N H ) above the Galactic value along the line of sight to NGC 2770, N H,Gal = 1.7 × 10 20 cm −2 . The best-fit power law model (χ 2 = 7.5 for 17 degrees of freedom; probability, P = 0.98) has a photon index, Γ = 2.3 ± 0.3 (or, F ν ∝ ν −1.3±0.3 ) and N H = 6.9 +1.8 −1.5 × 10 21 cm −2 . The best-fit blackbody model is described by kT = 0.71 ± 0.08 keV and N H = 1.3 +1.0 −0.9 × 10 21 cm −2 . However, this model provides a much poorer fit to the data (χ 2 = 26.0 for 17 degrees of freedom; probability, P = 0.074). We therefore adopt the power law model as the best description of the data. The resulting count rate to flux conversion is 1 counts s −1 = 5 × 10 −11 erg cm −2 s −1 . The outburst undergoes a significant hard-to-soft spectral evolution as indicated by the ratio of counts in the 0.3 − 2 keV band and 2 − 10 keV band. The hardness ratio decreases from 1.35 ± 0.15 during the peak of the flare to 0.25 ± 0.10 about 400 s later. In the context of the power law model this spectral softening corresponds to a change from Γ = 1.70 ± 0.25 to 3.20 ± 0.35 during the same time interval. High resolution optical spectroscopyWe obtained the spectrum with the High Resolution Echelle Spectrometer (HIRES) mounted on the Keck I 10-m telescope beginning at Jan 17.46 UT. A total of four 1800-s exposures were obtained with a spectral resolution, R = 48, 000, and a slit width of 0.86 arcsec. The data reach a signal-to-noise ratio of 18 per pixel. We reduced the data with the MAKEE reduction package. We are interested in the Na I D and K I absorption features since they are sensitive to the gas column density, and hence extinction, along the line of the sight to the SN. Rejecting a Relativistic Origin for XRO 080109We investigate the possibility that XRO 080109 is the result of a relativistic outflow similar to that in GRBs. In this context the emission is non-thermal synchrotron radiation. The outburst flux density is 7.5 × 10 2 µJy at 0.3 keV. Simultaneously, we find 3σ limits on the flux density in the UBV bands (∼ 3 eV) of F ν < 9.0 × 10 2 µJy, indicating that the peak of the synchrotron spectrum must be located between the UV and X-ray bands. In the standard synchrotron model this requires the frequencies corresponding to electrons with the minimum and cooling Lorentz factors to obey ν m ≈ ν c ≈ 3 × 10 16 Hz, while the peak of the spectrum is F ν,p ≈ 3 mJy.The inferred values of ν m and ν c allow us to constrain 47 the outflow parameters and thus to check for consistency with the hypothesis of relativistic expansion. The relevant parameters are the bulk Lorentz factor (γ), the magnetic field (B), and the shock radius (R sh ). From the value of ν c we find γB 3 ≈ 8.3 × 10 3 , and since γ > 1 we conclude that B < 20 G. In addition, using ν m we find ǫ 2 e γ 3 B ≈ 3 × 10 4 ; here ǫ e is the fraction of posts...

Type Ia supernovae have been used empirically as 'standard candles' to demonstrate the acceleration of the expansion of the Universe even though fundamental details, such as the nature of their progenitor systems and how the stars explode, remain a mystery. There is consensus that a white dwarf star explodes after accreting matter in a binary system, but the secondary body could be anything from a main-sequence star to a red giant, or even another white dwarf. This uncertainty stems from the fact that no recent type Ia supernova has been discovered close enough to Earth to detect the stars before explosion. Here we report early observations of supernova SN 2011fe in the galaxy M101 at a distance from Earth of 6.4 megaparsecs. We find that the exploding star was probably a carbon-oxygen white dwarf, and from the lack of an early shock we conclude that the companion was probably a main-sequence star. Early spectroscopy shows high-velocity oxygen that slows rapidly, on a timescale of hours, and extensive mixing of newly synthesized intermediate-mass elements in the outermost layers of the supernova. A companion paper uses pre-explosion images to rule out luminous red giants and most helium stars as companions to the progenitor.

Las Cumbres Observatory Global Telescope (LCOGT) is a young organization dedicated to time-domain observations at optical and (potentially) near-IR wavelengths. To this end, LCOGT is constructing a world-wide network of telescopes, including the two 2m Faulkes telescopes, as many as 17 x 1m telescopes, and as many as 23 x 40cm telescopes. These telescopes initially will be outfitted for imaging and (excepting the 40cm telescopes) spectroscopy at wavelengths between the atmospheric UV cutoff and the roughly 1-micron limit of silicon detectors. Since the first of LCOGT's 1m telescopes are now being deployed, we lay out here LCOGT's scientific goals and the requirements that these goals place on network architecture and performance, we summarize the network's present and projected level of development, and we describe our expected schedule for completing it. In the bulk of the paper, we describe in detail the technical approaches that we have adopted to attain the desired performance. In particular, we discuss our choices for the number and location of network sites, for the number and sizes of telescopes, for the specifications of the first generation of instruments, for the software that will schedule and control the network's telescopes and reduce and archive its data, and for the structure of the scientific and educational programs for which the network will provide observations.Comment: 59 pages, 9 figures, 4 tables. AAS Latex v5.2. Accepted for publication in Pub. Astr. Soc. Pacifi