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In this work, BV RI light curves of 55 Type II supernovae (SNe II) from the Lick Observatory Supernova Search program obtained with the Katzman Automatic Imaging Telescope and the 1 m Nickel telescope from 2006 to 2018 are presented. Additionally, more than 150 spectra gathered with the 3 m Shane telescope are published. We conduct an analyse of the peak absolute magnitudes, decline rates, and time durations of different phases of the light and colour curves. Typically, our light curves are sampled with a median cadence of 5.5 days for a total of 5093 photometric points. In average V-band plateau declines with a rate of 1.29 mag (100 days)-1, which is consistent with previously published samples. For each band, the plateau slope correlates with the plateau length and the absolute peak magnitude: SNe II with steeper decline have shorter plateau duration and are brighter. A time-evolution analysis of spectral lines in term of velocities and pseudoequivalent widths is also presented in this paper. Our spectroscopic sample ranges between 1 and 200 days post-explosion and has a median ejecta expansion velocity at 50 days post-explosion of 6500 km/s (Halpha line) and a standard dispersion of 2000 km/s. Nebular spectra are in good agreement with theoretical models using a progenitor star having a mass <16 Msol. All the data are available to the community and will help to understand SN II diversity better, and therefore to improve their utility as cosmological distance indicators., Comment: 24 pages, 12 figures, accepted for publication in MNRAS

We study 34 Type Ic supernovae that have broad spectral features (SNe Ic-BL). We obtained our photometric data with the Palomar Transient Factory (PTF) and its continuation, the intermediate Palomar Transient Factory (iPTF). This is the first large, homogeneous sample of SNe Ic-BL from an untargeted survey. Furthermore, given the high cadence of (i)PTF, most of these SNe were discovered soon after explosion. We present K-corrected $Bgriz$ light curves of these SNe, obtained through photometry on template-subtracted images. We analyzed the shape of the $r$-band light curves, finding a correlation between the decline parameter $\Delta m_{15}$ and the rise parameter $\Delta m_{-10}$. We studied the SN colors and, based on $g-r$, we estimated the host-galaxy extinction. Peak $r$-band absolute magnitudes have an average of $-18.6\pm0.5$ mag. We fit each $r$-band light curve with that of SN 1998bw (scaled and stretched) to derive the explosion epochs. We computed the bolometric light curves using bolometric corrections, $r$-band data, and $g-r$ colors. Expansion velocities from Fe II were obtained by fitting spectral templates of SNe Ic. Bolometric light curves and velocities at peak were fitted using the semianalytic Arnett model to estimate ejecta mass $M_{\rm ej}$, explosion energy $E_{K}$ and $^{56}$Ni mass $M(^{56}$Ni). We find average values of $M_{\rm ej} = 4\pm3~{\rm M}_{\odot}$, $E_{K} = (7\pm6) \times 10^{51}~$erg, and $M(^{56}$Ni) $= 0.31\pm0.16~{\rm M}_{\odot}$. We also estimated the degree of $^{56}$Ni mixing using scaling relations derived from hydrodynamical models and we find that all the SNe are strongly mixed. The derived explosion parameters imply that at least 21% of the progenitors of SNe Ic-BL are compatible with massive ($>28~{\rm M}_{\odot}$), possibly single stars, whereas at least 64% might come from less massive stars in close binary systems., Comment: 53 pages, 40 figures, 6 tables, accepted for publication in Astronomy and Astrophysics. Abstract abridged to fit the arXiv limit

We present a comparative study of absolute distances to a sample of very nearby, bright Type Ia supernovae (SNe) derived from high cadence, high signal-to-noise, multi-band photometric data. Our sample consists of four SNe: 2012cg, 2012ht, 2013dy and 2014J. We present new homogeneous, high-cadence photometric data in Johnson-Cousins BVRI and Sloan g'r'i'z' bands taken from two sites (Piszkesteto and Baja, Hungary), and the light curves are analyzed with publicly available light curve fitters (MLCS2k2, SNooPy2 and SALT2.4). When comparing the best-fit parameters provided by the different codes, it is found that the distance moduli of moderately-reddened SNe Ia agree within ~0.2 mag, and the agreement is even better (< 0.1 mag) for the highest signal-to-noise BVRI data. For the highly-reddened SN~2014J the dispersion of the inferred distance moduli is slightly higher. These SN-based distances are in good agreement with the Cepheid distances to their host galaxies. We conclude that the current state-of-the-art light curve fitters for Type Ia SNe can provide consistent absolute distance moduli having less than ~0.1 -- 0.2 mag uncertainty for nearby SNe. Still, there is room for future improvements to reach the desired ~0.05 mag accuracy in the absolute distance modulus., Comment: accepted for publication in PASP

We report the first results from our long-term observational survey aimed at discovering late-time interaction between the ejecta of hydrogen-poor Type I supernovae and the hydrogen-rich envelope expelled from the progenitor star several decades/centuries before explosion. The expelled envelope, moving with a velocity of ~10 -- 100 km s$^{-1}$, is expected to be caught up by the fast-moving SN ejecta several years/decades after explosion depending on the history of the mass-loss process acting in the progenitor star prior to explosion. The collision between the SN ejecta and the circumstellar envelope results in net emission in the Balmer-lines, especially in H-alpha. We look for signs of late-time H-alpha emission in older Type Ia/Ibc/IIb SNe having hydrogen-poor ejecta, via narrow-band imaging. Continuum-subtracted H-alpha emission has been detected for 13 point sources: 9 SN Ibc, 1 SN IIb and 3 SN Ia events. Thirty-eight SN sites were observed on at least two epochs, from which three objects (SN 1985F, SN 2005kl, SN 2012fh) showed significant temporal variation in the strength of their H-alpha emission in our DIAFI data. This suggests that the variable emission is probably not due to nearby H II regions unassociated with the SN, and hence is an important additional hint that ejecta-CSM interaction may take place in these systems. Moreover, we successfully detected the late-time H-alpha emission from the Type Ib SN 2014C, which was recently discovered as a strongly interacting SN in various (radio, infrared, optical and X-ray) bands., Comment: 8 pages, 7 figures, accepted in ApJ

Context: Research on supernovae (SNe) over the past decade has confirmed that there is a distinct class of events which are much more luminous (by $\sim2$ mag) than canonical core-collapse SNe (CCSNe). These events with visual peak magnitudes $\lesssim-21$ are called superluminous SNe (SLSNe). Aims: There are a few intermediate events which have luminosities between these two classes. Here we study one such object, SN 2012aa. Methods: The optical photometric and spectroscopic follow-up observations of the event were conducted over a time span of about 120 days. Results: With V_abs at peak ~-20 mag, the SN is an intermediate-luminosity transient between regular SNe Ibc and SLSNe. It also exhibits an unusual secondary bump after the maximum in its light curve. We interpret this as a manifestation of SN-shock interaction with the CSM. If we would assume a $^{56}$Ni-powered ejecta, the bolometric light curve requires roughly 1.3 M_sun of $^{56}$Ni and an ejected mass of ~14 M_sun. This would also imply a high kinetic energy of the explosion, ~5.4$\times10^{51}$ ergs. On the other hand, the unusually broad light curve along with the secondary peak indicate the possibility of interaction with CSM. The third alternative is the presence of a central engine releasing spin energy that eventually powers the light curve over a long time. The host of the SN is a star-forming Sa/Sb/Sbc galaxy. Conclusions: Although the spectral properties and velocity evolution of SN 2012aa are comparable to those of normal SNe Ibc, its broad light curve along with a large peak luminosity distinguish it from canonical CCSNe, suggesting the event to be an intermediate-luminosity transient between CCSNe and SLSNe at least in terms of peak luminosity. We argue that SN 2012aa belongs to a subclass where CSM interaction plays a significant role in powering the SN, at least during the initial stages of evolution., Comment: 21 pages, 15 figures, accepted for publication in Astronomy & Astrophysics

Type IIP supernovae (SNe IIP) have recently been proposed as metallicity ($Z$) probes. The spectral models of Dessart et al. (2014) showed that the pseudo-equivalent width of Fe II $\lambda$5018 (pEW$_{5018}$) during the plateau phase depends on the primordial $Z$, but there was a paucity of SNe IIP exhibiting pEW$_{5018}$ that were compatible with $Z < 0.4$ ${\rm Z}_{\odot}$. This lack might be due to some physical property of the SN II population or to the fact that those SNe have been discovered in luminous, metal-rich targeted galaxies. Here we use SN II observations from the untargeted (intermediate) Palomar Transient Factory [(i)PTF] survey, aiming to investigate the pEW$_{5018}$ distribution of this SN population and, in particular, to look for the presence of SNe II at lower $Z$. We perform pEW$_{5018}$ measurements on the spectra of a sample of 39 (i)PTF SNe II, selected to have well-constrained explosion epochs and light-curve properties. Based on the comparison with the pEW$_{5018}$ spectral models, we subgrouped our SNe into four $Z$ bins from $Z \approx 0.1$ $Z_{\odot}$ up to $Z \approx 2$ $Z_{\odot}$. We also independently investigated the $Z$ of the hosts by using their absolute magnitudes and colors and, in a few cases, using strong-line diagnostics from spectra. We searched for possible correlations between SN observables, such as their peak magnitudes and the $Z$ inferred from pEW$_{5018}$. We found 11 events with pEW$_{5018}$ that were small enough to indicate $Z \approx 0.1$ $Z_{\odot}$. The trend of pEW$_{5018}$ with $Z$ matches the $Z$ estimates obtained from the host-galaxy photometry, although the significance of the correlation is weak. We also found that SNe with brighter peak magnitudes have smaller pEW$_{5018}$ and occur at lower $Z$., Comment: Replaced to match the accepted version

Supernova (SN) 1987A was a peculiar H-rich event with a long-rising (LR) light curve (LC), stemming from a compact blue supergiant star (BSG). Only a few similar events have been presented in the literature. We present new data for a sample of 6 LR Type II SNe (SNe II), 3 of which were discovered and observed by the Palomar Transient Factory (PTF) and 3 observed by the Caltech Core-Collapse Project (CCCP). Our aim is to enlarge the family of LR SNe II, characterizing their properties. Spectra, LCs, and host-galaxies (HG) of these SNe are presented. Comparisons with known SN 1987A-like events are shown, with emphasis on the absolute magnitudes, colors, expansion velocities, and HG metallicities. Bolometric properties are derived from the multiband LC. By modeling the early-time LCs with scaling relations derived from the SuperNova Explosion Code (SNEC) models of MESA progenitor stars, we estimate the progenitor radii of these SNe and other progenitor parameters. We present PTF12kso, a LR SN II with the largest amount of 56Ni mass for this class. PTF09gpn and PTF12kso are found at the lowest HG metallicities for this SN group. The variety of early LC luminosities depends on the wide range of progenitor radii, from a few tens of solar radii (SN 2005ci) up to thousands (SN 2004ek) with intermediate cases between 100 (PTF09gpn) and 300 solar radii (SN 2004em). We confirm that LR SNe II with LC shapes closely resembling that of SN 1987A generally arise from BSGs. However, some of them likely have progenitors with larger radii (~300 solar radii, typical of yellow supergiants) and can thus be regarded as intermediate cases between normal SNe IIP and SN 1987A-like SNe. Some extended red supergiant (RSG) stars such as the progenitor of SN 2004ek can also produce LR SNe II if they synthesized a large amount of 56Ni. Low HG metallicity is confirmed as a characteristic of BSG SNe., Comment: Accepted for publication, 26 pages, 16 figures. Abstract shortened by ~25% to match the ArXiv character limit

We have acquired Hubble Space Telescope (HST) and Very Large Telescope near-infrared spectra and images of supernova (SN) Refsdal after its discovery as an Einstein cross in Fall 2014. The HST light curve of SN Refsdal matches the distinctive, slowly rising light curves of SN 1987A-like supernovae (SNe), and we find strong evidence for a broad H-alpha P-Cygni profile in the HST grism spectrum at the redshift (z = 1.49) of the spiral host galaxy. SNe IIn, powered by circumstellar interaction, could provide a good match to the light curve of SN Refsdal, but the spectrum of a SN IIn would not show broad and strong H-alpha absorption. From the grism spectrum, we measure an H-alpha expansion velocity consistent with those of SN 1987A-like SNe at a similar phase. The luminosity, evolution, and Gaussian profile of the H-alpha emission of the WFC3 and X-shooter spectra, separated by ~2.5 months in the rest frame, provide additional evidence that supports the SN 1987A-like classification. In comparison with other examples of SN 1987A-like SNe, SN Refsdal has a blue B-V color and a high luminosity for the assumed range of potential magnifications. If SN Refsdal can be modeled as a scaled version of SN 1987A, we estimate it would have an ejecta mass of 20+-5 solar masses. The evolution of the light curve at late times will provide additional evidence about the potential existence of any substantial circumstellar material (CSM). Using MOSFIRE and X-shooter spectra, we estimate a subsolar host-galaxy metallicity (8.3+-0.1 dex and <8.4 dex, respectively) near the explosion site., Comment: Submitted to ApJ; 26 pages

Supernovae (SNe) embedded in dense circumstellar material (CSM) may show prominent emission lines in their early-time spectra ($\leq 10$ days after the explosion), owing to recombination of the CSM ionized by the shock-breakout flash. From such spectra ("flash spectroscopy"), we can measure various physical properties of the CSM, as well as the mass-loss rate of the progenitor during the year prior to its explosion. Searching through the Palomar Transient Factory (PTF and iPTF) SN spectroscopy databases from 2009 through 2014, we found 12 Type II SNe showing flash-ionized (FI) signatures in their first spectra. All are younger than 10 days. These events constitute 14\% of all 84 SNe in our sample having a spectrum within 10 days from explosion, and 18\% of SNe~II observed at ages $<5$ days, thereby setting lower limits on the fraction of FI events. We classified as "blue/featureless" (BF) those events having a first spectrum which is similar to that of a black body, without any emission or absorption signatures. It is possible that some BF events had FI signatures at an earlier phase than observed, or that they lack dense CSM around the progenitor. Within 2 days after explosion, 8 out of 11 SNe in our sample are either BF events or show FI signatures. Interestingly, we found that 19 out of 21 SNe brighter than an absolute magnitude $M_R=-18.2$ belong to the FI or BF groups, and that all FI events peaked above $M_R=-17.6$ mag, significantly brighter than average SNe~II., Comment: Accepted to ApJ

We present photometric and spectroscopic observations of SN 2013fc, a bright type II supernova (SN) in a circumnuclear star-forming ring in the luminous infrared galaxy ESO 154-G010, observed as part of the Public ESO Spectroscopic Survey of Transient Objects (PESSTO). SN 2013fc is both photometrically and spectroscopically similar to the well-studied type IIn SN 1998S and to the bright type II-L SN 1979C. It exhibits an initial linear decline, followed by a short plateau phase and a tail phase with a decline too fast for $^{56}$Co decay with full gamma-ray trapping. Initially the spectrum was blue and featureless. Later on, a strong broad ($\sim 8000$ km s$^{-1}$) H $\alpha$ emission profile became prominent. We apply a Starlight stellar population model fit to the SN location (observed when the SN had faded) to estimate a high extinction of $A_V = 2.9 \pm 0.2$ mag and an age of $10_{-2}^{+3}$ Myr for the underlying cluster. We compare the SN to SNe 1998S and 1979C and discuss its possible progenitor star considering the similarities to these events. With a peak brightness of $B = -20.46 \pm 0.21$ mag, SN 2013fc is 0.9 mag brighter than SN 1998S and of comparable brightness to SN 1979C. We suggest that SN 2013fc was consistent with a massive red supergiant (RSG) progenitor. Recent mass loss probably due to a strong RSG wind created the circumstellar matter illuminated through its interaction with the SN ejecta. We also observe a near-infrared excess, possibly due to newly condensed dust., Comment: 27 pages, 15 figures; accepted for publication in MNRAS

We present extensive optical ($UBVRI$, $g'r'i'z'$, and open CCD) and near-infrared ($ZYJH$) photometry for the very nearby Type IIP SN ~2013ej extending from +1 to +461 days after shock breakout, estimated to be MJD $56496.9\pm0.3$. Substantial time series ultraviolet and optical spectroscopy obtained from +8 to +135 days are also presented. Considering well-observed SNe IIP from the literature, we derive $UBVRIJHK$ bolometric calibrations from $UBVRI$ and unfiltered measurements that potentially reach 2\% precision with a $B-V$ color-dependent correction. We observe moderately strong Si II $\lambda6355$ as early as +8 days. The photospheric velocity ($v_{\rm ph}$) is determined by modeling the spectra in the vicinity of Fe II $\lambda5169$ whenever observed, and interpolating at photometric epochs based on a semianalytic method. This gives $v_{\rm ph} = 4500\pm500$ km s$^{-1}$ at +50 days. We also observe spectral homogeneity of ultraviolet spectra at +10--12 days for SNe IIP, while variations are evident a week after explosion. Using the expanding photosphere method, from combined analysis of SN 2013ej and SN 2002ap, we estimate the distance to the host galaxy to be $9.0_{-0.6}^{+0.4}$ Mpc, consistent with distance estimates from other methods. Photometric and spectroscopic analysis during the plateau phase, which we estimated to be $94\pm7$ days long, yields an explosion energy of $0.9\pm0.3\times10^{51}$ ergs, a final pre-explosion progenitor mass of $15.2\pm4.2$~M$_\odot$ and a radius of $250\pm70$~R$_\odot$. We observe a broken exponential profile beyond +120 days, with a break point at +$183\pm16$ days. Measurements beyond this break time yield a $^{56}$Ni mass of $0.013\pm0.001$~M$_\odot$., Comment: 29 pages, 23 figures, 15 tables, Published in The Astrophisical Journal

We present optical and near-infrared light curves and optical spectra of SN 2013dx, associated with the nearby (redshift 0.145) gamma-ray burst GRB 130702A. The prompt isotropic gamma-ray energy released from GRB 130702A is measured to be $E_{\gamma,iso}=6.4_{-1.0}^{+1.3}\times10^{50}$erg (1keV-10MeV in the rest frame), placing it intermediate between low-luminosity GRBs like GRB 980425/SN 1998bw and the broader cosmological population. We compare the observed $g'r'i'z'$ light curves of SN 2013dx to a SN 1998bw template, finding that SN 2013dx evolves ~20% faster (steeper rise time), with a comparable peak luminosity. Spectroscopically, SN 2013dx resembles other broad-lined Type Ic supernovae, both associated with (SN 2006aj and SN 1998bw) and lacking (SN 1997ef, SN 2007I, and SN 2010ah) gamma-ray emission, with photospheric velocities around peak of ~21,000km s$^{-1}$. We construct a quasi-bolometric ($g'r'i'z'yJ$) light curve for SN 2013dx, only the fifth GRB-associated SN with extensive NIR coverage and the third with a bolometric light curve extending beyond $\Delta t>40$d. Together with the measured photospheric velocity, we derive basic explosion parameters using simple analytic models. We infer a $^{56}$Ni mass of $M_{\mathrm{Ni}}=0.37\pm0.01$M$_{\odot}$, an ejecta mass of $M_{\mathrm{ej}}=3.1\pm0.1$M$_{\odot}$, and a kinetic energy of $E_{\mathrm{K}}=(8.2\pm0.43)\times10^{51}$ erg (statistical uncertainties only), consistent with previous GRB-associated SNe. When considering the ensemble population of GRB-associated SNe, we find no correlation between the mass of synthesized $^{56}$Ni and high-energy properties, despite clear predictions from numerical simulations that $M_{\mathrm{Ni}}$ should correlate with the degree of asymmetry. On the other hand, $M_{\mathrm{Ni}}$ clearly correlates with the kinetic energy of the supernova ejecta across a wide range of core-collapse events., Comment: 23 pages, 11 figures, accepted for publication in ApJ

A series of optical and one near-infrared nebular spectra covering the first year of the Type Ia supernova SN 2011fe are presented and modelled. The density profile that proved best for the early optical/ultraviolet spectra, "rho-11fe", was extended to lower velocities to include the regions that emit at nebular epochs. Model rho-11fe is intermediate between the fast deflagration model W7 and a low-energy delayed-detonation. Good fits to the nebular spectra are obtained if the innermost ejecta are dominated by neutron-rich, stable Fe-group species, which contribute to cooling but not to heating. The correct thermal balance can thus be reached for the strongest [FeII] and [FeIII] lines to be reproduced with the observed ratio. The 56Ni mass thus obtained is 0.47 +/- 0.05 Mo. The bulk of 56Ni has an outermost velocity of ~8500 km/s. The mass of stable iron is 0.23 +/- 0.03 Mo. Stable Ni has low abundance, ~10^{-2} Mo. This is sufficient to reproduce an observed emission line near 7400 A. A sub-Chandrasekhar explosion model with mass 1.02 Mo and no central stable Fe does not reproduce the observed line ratios. A mock model where neutron-rich Fe-group species are located above 56Ni following recent suggestions is also shown to yield spectra that are less compatible with the observations. The densities and abundances in the inner layers obtained from the nebular analysis, combined with those of the outer layers previously obtained, are used to compute a synthetic bolometric light curve, which compares favourably with the light curve of SN 2011fe., Comment: 14 pages, 8 figures, to appear in MNRAS

SN 2013dy is a Type Ia supernova for which we have compiled an extraordinary dataset spanning from 0.1 to ~ 500 days after explosion. We present 10 epochs of ultraviolet (UV) through near-infrared (NIR) spectra with HST/STIS, 47 epochs of optical spectra (15 of them having high resolution), and more than 500 photometric observations in the BVrRiIZYJH bands. SN 2013dy has a broad and slowly declining light curve (delta m(B) = 0.92 mag), shallow Si II 6355 absorption, and a low velocity gradient. We detect strong C II in our earliest spectra, probing unburned progenitor material in the outermost layers of the SN ejecta, but this feature fades within a few days. The UV continuum of SN 2013dy, which is strongly affected by the metal abundance of the progenitor star, suggests that SN 2013dy had a relatively high-metallicity progenitor. Examining one of the largest single set of high-resolution spectra for a SN Ia, we find no evidence of variable absorption from circumstellar material. Combining our UV spectra, NIR photometry, and high-cadence optical photometry, we construct a bolometric light curve, showing that SN 2013dy had a maximum luminosity of 10.0^{+4.8}_{-3.8} * 10^{42} erg/s. We compare the synthetic light curves and spectra of several models to SN 2013dy, finding that SN 2013dy is in good agreement with a solar-metallicity W7 model., Comment: 22 pages, 18 figures, replaced with version accecpted for publication in MNRAS

In the Spring of 2011 we carried out a 2.5 month reverberation mapping campaign using the 3 m Shane telescope at Lick Observatory, monitoring 15 low-redshift Seyfert 1 galaxies. This paper describes the observations, reductions and measurements, and data products from the spectroscopic campaign. The reduced spectra were fitted with a multicomponent model in order to isolate the contributions of various continuum and emission-line components. We present light curves of broad emission lines and the AGN continuum, and measurements of the broad H-beta line widths in mean and root-mean square (rms) spectra. For the most highly variable AGNs we also measured broad H-beta line widths and velocity centroids from the nightly spectra. In four AGNs exhibiting the highest variability amplitudes, we detect anticorrelations between broad H-beta width and luminosity, demonstrating that the broad-line region "breathes" on short timescales of days to weeks in response to continuum variations. We also find that broad H-beta velocity centroids can undergo substantial changes in response to continuum variations; in NGC 4593 the broad H-beta velocity shifted by ~250 km/s over a one-month duration. This reverberation-induced velocity shift effect is likely to contribute a significant source of confusion noise to binary black hole searches that use multi-epoch quasar spectroscopy to detect binary orbital motion. We also present results from simulations that examine biases that can occur in measurement of broad-line widths from rms spectra due to the contributions of continuum variations and photon-counting noise., Comment: 33 pages, 28 figures, accepted for publication in ApJ Supplement Series

What are Type II-Linear supernovae (SNe II-L)? This class, which has been ill defined for decades, now receives significant attention -- both theoretically, in order to understand what happens to stars in the ~15-25Mo range, and observationally, with two independent studies suggesting that they cannot be cleanly separated photometrically from the regular hydrogen-rich SNe II-P characterised by a marked plateau in their light curve. Here, we analyze the multi-band light curves and extensive spectroscopic coverage of a sample of 35 SNe II and find that 11 of them could be SNe II-L. The spectra of these SNe are hydrogen deficient, typically have shallow Halpha absorption, may show indirect signs of helium via strong OI 7774 absorption, and have faster line velocities consistent with a thin hydrogen shell. The light curves can be mostly differentiated from those of the regular, hydrogen-rich SNe II-P by their steeper decline rates and higher luminosity, and we propose as a defining photometric characteristic the decline in the V band: SNe II-L seem to decline by more than 0.5 mag from peak brightness by day 50 after explosion. Using our sample we provide template light curves for SNe II-L and II-P in 4 photometric bands., Comment: MNRAS in press

We present ultraviolet, optical, and near-infrared observations of SN 2012ap, a broad-lined Type Ic supernova in the galaxy NGC 1729 that produced a relativistic and rapidly decelerating outflow without a gamma-ray burst signature. Photometry and spectroscopy follow the flux evolution from -13 to +272 days past the B-band maximum of -17.4 +/- 0.5 mag. The spectra are dominated by Fe II, O I, and Ca II absorption lines at ejecta velocities of 20,000 km/s that change slowly over time. Other spectral absorption lines are consistent with contributions from photospheric He I, and hydrogen may also be present at higher velocities (> 27,000 km/s). We use these observations to estimate explosion properties and derive a total ejecta mass of 2.7 Msolar, a kinetic energy of 1.0x10^{52} erg, and a 56Ni mass of 0.1-0.2 Msolar. Nebular spectra (t > 200d) exhibit an asymmetric double-peaked [OI] 6300,6364 emission profile that we associate with absorption in the supernova interior, although toroidal ejecta geometry is an alternative explanation. SN 2012ap joins SN 2009bb as another exceptional supernova that shows evidence for a central engine (e.g., black-hole accretion or magnetar) capable of launching a non-negligible portion of ejecta to relativistic velocities without a coincident gamma-ray burst detection. Defining attributes of their progenitor systems may be related to notable properties including above-average environmental metallicities of Z > Zsolar, moderate to high levels of host-galaxy extinction (E(B-V) > 0.4 mag), detection of high-velocity helium at early epochs, and a high relative flux ratio of [Ca II]/[O I] > 1 at nebular epochs. These events support the notion that jet activity at various energy scales may be present in a wide range of supernovae., Comment: 16 pages, 15 figures, submitted to The Astrophysical Journal; revised references

The explosive fate of massive stripped Wolf-Rayet (W-R) stars is a key open question in stellar physics. An appealing option is that hydrogen-deficient W-R stars are the progenitors of some H-poor supernova (SN) explosions of Types IIb, Ib, and Ic. A blue object, having luminosity and colors consistent with those of some W-R stars, has been recently identified at the location of a SN~Ib in pre-explosion images but has not yet been conclusively determined to have been the progenitor. Similar previous works have so far only resulted in nondetections. Comparison of early photometric observations of Type Ic supernovae with theoretical models suggests that the progenitor stars had radii <10^12 cm, as expected for some W-R stars. However, the hallmark signature of W-R stars, their emission-line spectra, cannot be probed by such studies. Here, we report the detection of strong emission lines in an early-time spectrum of SN 2013cu (iPTF13ast; Type IIb) obtained ~15.5 hr after explosion ("flash spectroscopy"). We identify W-R-like wind signatures suggesting a progenitor of the WN(h) subclass. The extent of this dense wind may indicate increased mass loss from the progenitor shortly prior to its explosion, consistent with recent theoretical predictions., Comment: Nature, Volume 509, Issue 7501, pp. 471-474 (2014). Author version prior to final editing to conform to Journal style; includes extended data figures and methods; see final official version at http://www.nature.com/nature/journal/v509/n7501/full/nature13304.html

We present optical photometry and spectroscopy of the broad-lined Type Ic supernova (SNIc-BL) PTF10qts, which was discovered as part of the Palomar Transient Factory. The supernova was located in a dwarf galaxy of magnitude $r=21.1$ at a redshift $z=0.0907$. We find that the $R$-band light curve is a poor proxy for bolometric data and use photometric and spectroscopic data to construct and constrain the bolometric light curve. The derived bolometric magnitude at maximum light is $M_{\rm bol} = -18.51\pm0.2$ mag, comparable to that of SN 1998bw ($M_{\rm bol} = -18.7$ mag) which was associated with a gamma-ray burst (GRB). PTF10qts is one of the most luminous SNIc-BL observed without an accompanying GRB. We estimate the physical parameters of the explosion using data from our programme of follow-up observations, finding that it produced a larger mass of radioactive nickel compared to other SNeIc-BL with similar inferred ejecta masses and kinetic energies. The progenitor of the event was likely a $\sim20$M$_{\odot}$ star., Comment: Accepted for publication in MNRAS

We present optical and near infrared (NIR) observations of the nearby Type Ia SN 2014J. Seventeen optical and twenty-three NIR spectra were obtained from 10 days before ($-$10d) to 10 days after (+10d) the time of maximum $B$-band brightness. The relative strengths of absorption features and their patterns of development can be compared at one day intervals throughout most of this period. Carbon is not detected in the optical spectra, but we identify CI $\lambda$ 1.0693 in the NIR spectra. We find that MgII lines with high oscillator strengths have higher initial velocities than other MgII lines. We show that the velocity differences can be explained by differences in optical depths due to oscillator strengths. The spectra of SN 2014J show it is a normal SN Ia, but many parameters are near the boundaries between normal and high-velocity subclasses. The velocities for OI, MgII, SiII, SII, CaII and FeII suggest that SN 2014J has a layered structure with little or no mixing. That result is consistent with the delayed detonation explosion models. We also report photometric observations, obtained from $-$10d to +29d, in the $UBVRIJH$ and $K_s$ bands. SN 2014J is about 3 magnitudes fainter than a normal SN Ia at the distance of M82, which we attribute to extinction in the host. The template fitting package SNooPy is used to interpret the light curves and to derive photometric parameters. Using $R_V$ = 1.46, which is consistent with previous studies, SNooPy finds that $A_V = 1.80$ for $E(B-V)_{host}=1.23 \pm 0.01$ mag. The maximum $B$-band brightness of $-19.19 \pm 0.10$ mag was reached on February 1.74 UT $ \pm 0.13$ days and the supernova had a decline parameter of $\Delta m_{15}=1.11 \pm 0.02$ mag., Comment: 6 figures, 6 tables, submitted to the ApJ

SN 2014J in M82 is the closest detected Type Ia supernova (SN Ia) in at least 28 years and perhaps in 410 years. Despite its small distance of 3.3 Mpc, SN 2014J is surprisingly faint, peaking at V = 10.6 mag, and assuming a typical SN Ia luminosity, we infer an observed visual extinction of A_V = 2.0 +/- 0.1 mag. But this picture, with R_V = 1.6 +/- 0.2, is too simple to account for all observations. We combine 10 epochs (spanning a month) of HST/STIS ultraviolet through near-infrared spectroscopy with HST/WFC3, KAIT, and FanCam photometry from the optical to the infrared and 9 epochs of high-resolution TRES spectroscopy to investigate the sources of extinction and reddening for SN 2014J. We argue that the wide range of observed properties for SN 2014J is caused by a combination of dust reddening, likely originating in the interstellar medium of M82, and scattering off circumstellar material. For this model, roughly half of the extinction is caused by reddening from typical dust (E(B-V ) = 0.45 mag and R_V = 2.6) and roughly half by scattering off LMC-like dust in the circumstellar environment of SN 2014J., Comment: 17 pages (excluding references and tables), 15 figures, accepted to MNRAS. A high-resolution HST image of SN 2014J in M82 is available upon request

The diffuse interstellar bands (DIBs) are absorption features observed in optical and near-infrared spectra that are thought to be associated with carbon-rich polyatomic molecules in interstellar gas. However, because the central wavelengths of these bands do not correspond with electronic transitions of any known atomic or molecular species, their nature has remained uncertain since their discovery almost a century ago. Here we report on unusually strong DIBs in optical spectra of the broad-lined Type Ic supernova SN 2012ap that exhibit changes in equivalent width over short (~30 days) timescales. The 4428 and 6283 Angstrom DIB features get weaker with time, whereas the 5780 Angstrom feature shows a marginal increase. These nonuniform changes suggest that the supernova is interacting with a nearby source of the DIBs and that the DIB carriers possess high ionization potentials, such as small cations or charged fullerenes. We conclude that moderate-resolution spectra of supernovae with DIB absorptions obtained within weeks of outburst could reveal unique information about the mass-loss environment of their progenitor systems and provide new constraints on the properties of DIB carriers., Comment: 6 pages, 3 figures, accepted for publication in ApJL

We present the supernova (SN) sample and Type-Ia SN (SN Ia) rates from the Cluster Lensing And Supernova survey with Hubble (CLASH). Using the Advanced Camera for Surveys and the Wide Field Camera 3 on the Hubble Space Telescope (HST), we have imaged 25 galaxy-cluster fields and parallel fields of non-cluster galaxies. We report a sample of 27 SNe discovered in the parallel fields. Of these SNe, ~13 are classified as SN Ia candidates, including four SN Ia candidates at redshifts z > 1.2. We measure volumetric SN Ia rates to redshift 1.8 and add the first upper limit on the SN Ia rate in the range 1.8 < z < 2.4. The results are consistent with the rates measured by the HST/GOODS and Subaru Deep Field SN surveys. We model these results together with previous measurements at z < 1 from the literature. The best-fitting SN Ia delay-time distribution (DTD; the distribution of times that elapse between a short burst of star formation and subsequent SN Ia explosions) is a power law with an index of -1.00 +0.06(0.09) -0.06(0.10) (statistical) +0.12 -0.08 (systematic), where the statistical uncertainty is a result of the 68% and 95% (in parentheses) statistical uncertainties reported for the various SN Ia rates (from this work and from the literature), and the systematic uncertainty reflects the range of possible cosmic star-formation histories. We also test DTD models produced by an assortment of published binary population synthesis (BPS) simulations. The shapes of all BPS double-degenerate DTDs are consistent with the volumetric SN Ia measurements, when the DTD models are scaled up by factors of 3-9. In contrast, all BPS single-degenerate DTDs are ruled out by the measurements at a >99% significance level., Comment: Accepted by ApJ. 19 pages, 14 figures, 6 tables. Minor corrections

We present extensive multi-wavelength observations of the extremely rapidly declining Type Ic supernova, SN 2005ek. Reaching a peak magnitude of M_R = -17.3 and decaying by ~3 mag in the first 15 days post-maximum, SN 2005ek is among the fastest Type I supernovae observed to date. The spectra of SN 2005ek closely resemble those of normal SN Ic, but with an accelerated evolution. There is evidence for the onset of nebular features at only nine days post-maximum. Spectroscopic modeling reveals an ejecta mass of ~0.3 Msun that is dominated by oxygen (~80%), while the pseudo-bolometric light curve is consistent with an explosion powered by ~0.03 Msun of radioactive Ni-56. Although previous rapidly evolving events (e.g., SN 1885A, SN 1939B, SN 2002bj, SN 2010X) were hypothesized to be produced by the detonation of a helium shell on a white dwarf, oxygen-dominated ejecta are difficult to reconcile with this proposed mechanism. We find that the properties of SN 2005ek are consistent with either the edge-lit double detonation of a low-mass white dwarf or the iron-core collapse of a massive star, stripped by binary interaction. However, if we assume that the strong spectroscopic similarity of SN 2005ek to other SN Ic is an indication of a similar progenitor channel, then a white-dwarf progenitor becomes very improbable. SN 2005ek may be one of the lowest mass stripped-envelope core-collapse explosions ever observed. We find that the rate of such rapidly declining Type I events is at least 1-3% of the normal SN Ia rate., Comment: Accepted for publication in ApJ. Please visit http://www.cfa.harvard.edu/~mdrout to hear a sonification of SN2005ek

We construct spectra of supernovae interacting strongly with a circumstellar medium (CSM) by adding SN templates, a black-body continuum and an emission-line spectrum. In a Monte Carlo simulation we generate more than 800 spectra, distribute them to 10 different classifiers and study how the different simulation parameters affect the appearance of the spectra. SNe IIn showing some structure over the continuum were characterized as SNe IInS. We demonstrate that the flux ratio of the underlying SN to the continuum fv is the most important parameter determining the spectral classification. Thermonuclear SNe get progressively classified as Ia-CSM, IInS and IIn as fv decreases. The transition between Ia-CSM and IInS occurs at fv~0.2-0.3. It shown that SNe Ia-CSM are found at the magnitude range -19.5> M >-21.6, in good agreement with observations, and that the faintest SN IIn that can hide a SN Ia has M = -20.1. The sample of SNe Ia-CSM shows an association with 91T-like SNe Ia. Our experiment does not support that this association is due to a luminosity bias (91T-like being brighter than normal Ia). We therefore conclude that this association has real physical origins and we propose that 91T-like explosions result from single degenerate progenitors. Despite the similarities between SNe Ibc and SNe Ia, the number of misclassifications between these types was small and mostly at low S/N. Combined with the luminosity function needed to reproduce the observed SN Ia-CSM luminosities, it is unlikely that SNe Ibc constitute an important contaminant within this sample. We show how Type II spectra transition to IIn and how the Ha profiles vary with fv. SNe IIn fainter than M = -17.2 are unable to mask SNe IIP brighter than M = -15. A simulation including radiative transfer shows that our simplified model is a good first order approximation. The spectra obtained are in good agreement with real data., Comment: Accepted 16 November 2014, published 27 January 2015. 19 pages, 15 figures, 1 Table. Abstract abridged. The first author is responsible for the long delay. 500 more spectra were simulated and classified, including lower S/N and a new Type Ic template. All main conclusions remain unchanged; graphs and text were modified to include the new data; most changes can be found in Section 5.1

The 2012 explosion of SN2009ip raises questions about our understanding of the late stages of massive star evolution. Here we present a comprehensive study of SN2009ip during its remarkable re-brightening(s). High-cadence photometric and spectroscopic observations from the GeV to the radio band obtained from a variety of ground-based and space facilities (including the VLA, Swift, Fermi, HST and XMM) constrain SN2009ip to be a low energy (E~ 10^50 erg for an ejecta mass ~ 0.5 Msun) and likely asymmetric explosion in a complex medium shaped by multiple eruptions of the restless progenitor star. Most of the energy is radiated as a result of the shock breaking out through a dense shell of material located at 5x10^14 cm with M~0.1 Msun, ejected by the precursor outburst ~40 days before the major explosion. We interpret the NIR excess of emission as signature of dust vaporization of material located further out (R>4x 10^15 cm), the origin of which has to be connected with documented mass loss episodes in the previous years. Our modeling predicts bright neutrino emission associated with the shock break-out if the cosmic ray energy is comparable to the radiated energy. We connect this phenomenology with the explosive ejection of the outer layers of the massive progenitor star, that later interacted with material deposited in the surroundings by previous eruptions. Future observations will reveal if the luminous blue variable (LBV) progenitor star survived. Irrespective of whether the explosion was terminal, SN2009ip brought to light the existence of new channels for sustained episodic mass-loss, the physical origin of which has yet to be identified., Comment: Visit https://www.cfa.harvard.edu/~rmargutt/ for a 5-minute presentation highlighting the major results and to hear a sonification of the SN2009ip explosion

We present 65 optical spectra of the Type Ia supernova SN 2012fr, of which 33 were obtained before maximum light. At early times SN 2012fr shows clear evidence of a high-velocity feature (HVF) in the Si II 6355 line which can be cleanly decoupled from the lower velocity "photospheric" component. This Si II 6355 HVF fades by phase -5; subsequently, the photospheric component exhibits a very narrow velocity width and remains at a nearly constant velocity of v~12,000 km/s until at least 5 weeks after maximum brightness. The Ca II infrared (IR) triplet exhibits similar evidence for both a photospheric component at v~12,000 km/s with narrow line width and long velocity plateau, as well as a high-velocity component beginning at v~31,000 km/s two weeks before maximum. SN 2012fr resides on the border between the "shallow silicon" and "core-normal" subclasses in the Branch et al. (2009) classification scheme, and on the border between normal and "high-velocity" SNe Ia in the Wang et al. (2009a) system. Though it is a clear member of the "low velocity gradient" (LVG; Benetii et al., 2005) group of SNe Ia and exhibits a very slow light-curve decline, it shows key dissimilarities with the overluminous SN 1991T or SN 1999aa subclasses of SNe Ia. SN 2012fr represents a well-observed SN Ia at the luminous end of the normal SN Ia distribution, and a key transitional event between nominal spectroscopic subclasses of SNe Ia., Comment: 20 pages, 19 figures, version accepted by ApJ. Spectra now available from WISEREP or from http://www.mso.anu.edu.au/~mjc/SN2012fr/

Various lines of evidence suggest that very massive stars experience extreme mass-loss episodes shortly before they explode as a supernova. Interestingly, several models predict such pre-explosion outbursts. Establishing a causal connection between these mass-loss episodes and the final supernova explosion will provide a novel way to study pre-supernova massive-star evolution. Here we report on observations of a remarkable mass-loss event detected 40 days prior to the explosion of the Type IIn supernova SN 2010mc (PTF 10tel). Our photometric and spectroscopic data suggest that this event is a result of an energetic outburst, radiating at least 6x10^47 erg of energy, and releasing about 0.01 Solar mass at typical velocities of 2000 km/s. We show that the temporal proximity of the mass-loss outburst and the supernova explosion implies a causal connection between them. Moreover, we find that the outburst luminosity and velocity are consistent with the predictions of the wave-driven pulsation model and disfavor alternative suggestions., Comment: Nature 494, 65, including supplementary information

We present observations and analysis of the host galaxies of 23 heavily dust-obscured gamma-ray bursts (GRBs) observed by the Swift satellite during the years 2005-2009, representing all GRBs with an unambiguous host-frame extinction of A_V>1 mag from this period. Deep observations with Keck, Gemini, VLT, HST, and Spitzer successfully detect the host galaxies and establish spectroscopic or photometric redshifts for all 23 events, enabling us to provide measurements of the intrinsic host star-formation rates, stellar masses, and mean extinctions. Compared to the hosts of unobscured GRBs at similar redshifts, we find that the hosts of dust-obscured GRBs are (on average) more massive by about an order of magnitude and also more rapidly star-forming and dust-obscured. While this demonstrates that GRBs populate all types of star-forming galaxies including the most massive, luminous systems at z~2, at redshifts below 1.5 the overall GRB population continues to show a highly significant aversion away from massive galaxies and a preference for low-mass systems relative to what would be expected given a purely SFR-selected galaxy sample. This supports the notion that the GRB rate is strongly dependent on metallicity, and may suggest that the most massive galaxies in the Universe underwent a transition in their chemical properties ~9 Gyr ago. We also conclude that, based on the absence of unobscured GRBs in massive galaxies and the absence of obscured GRBs in low-mass galaxies, the dust distributions of the lowest-mass and the highest-mass galaxies are relatively homogeneous, while intermediate-mass galaxies (~10^9 M_sun) have diverse internal properties., Comment: Accepted to ApJ. Some figures compressed; full-resolution version is available at http://www.astro.caltech.edu/~dperley/papers/darkesthost/darkesthosts.pdf. Host photometry is available at http://www.astro.caltech.edu/~dperley/papers/darkesthost/hostphotometry.txt

We describe observed properties of the Type Iax class of supernovae (SNe Iax), consisting of SNe observationally similar to its prototypical member, SN 2002cx. The class currently has 25 members, and we present optical photometry and/or optical spectroscopy for most of them. SNe Iax are spectroscopically similar to SNe Ia, but have lower maximum-light velocities (2000 < |v| < 8000 km/s), typically lower peak magnitudes (-14.2 > M_V,peak > -18.9 mag), and most have hot photospheres. Relative to SNe Ia, SNe Iax have low luminosities for their light-curve shape. There is a correlation between luminosity and light-curve shape, similar to that of SNe Ia, but offset from that of SNe Ia and with larger scatter. Despite a host-galaxy morphology distribution that is highly skewed to late-type galaxies without any SNe Iax discovered in elliptical galaxies, there are several indications that the progenitor stars are white dwarfs (WDs): evidence of C/O burning in their maximum-light spectra, low ejecta masses, strong Fe lines in their late-time spectra, a lack of X-ray detections, and deep limits on massive stars and star formation at the SN sites. However, two SNe Iax show strong He lines in their spectra. The progenitor system and explosion model that best fits all of the data is a binary system of a C/O WD that accretes matter from a He star and has a significant deflagration. At least some of the time, this explosion will not disrupt the WD. We estimate that in a given volume there are 31^+17_-13 SNe Iax for every 100 SNe Ia, and for every 1 M_sun of iron generated by SNe Ia at z = 0, SNe Iax generate 0.052^+0.017_-0.014 M_sun. Being the largest class of peculiar SNe, thousands of SNe Iax will be discovered by LSST. Future detailed observations of SNe Iax should further our understanding of both their progenitor systems and explosions as well as those of SNe Ia., Comment: 31 pages, 35 figures, accepted to ApJ

There is a consensus that Type-Ia supernovae (SNe Ia) arise from the thermonuclear explosion of white dwarf stars that accrete matter from a binary companion. However, direct observation of SN Ia progenitors is lacking, and the precise nature of the binary companion remains uncertain. A temporal series of high-resolution optical spectra of the SN Ia PTF 11kx reveals a complex circumstellar environment that provides an unprecedentedly detailed view of the progenitor system. Multiple shells of circumsteller are detected and the SN ejecta are seen to interact with circumstellar material (CSM) starting 59 days after the explosion. These features are best described by a symbiotic nova progenitor, similar to RS Ophiuchi., Comment: 27 pages, 5 figures. In press

The nearby Type Ia supernova SN 2011fe in M101 (cz=241 km s^-1) provides a unique opportunity to study the early evolution of a "normal" Type Ia supernova, its compositional structure, and its elusive progenitor system. We present 18 high signal-to-noise spectra of SN 2011fe during its first month beginning 1.2 days post-explosion and with an average cadence of 1.8 days. This gives a clear picture of how various line-forming species are distributed within the outer layers of the ejecta, including that of unburned material (C+O). We follow the evolution of C II absorption features until they diminish near maximum light, showing overlapping regions of burned and unburned material between ejection velocities of 10,000 and 16,000 km s^-1. This supports the notion that incomplete burning, in addition to progenitor scenarios, is a relevant source of spectroscopic diversity among SNe Ia. The observed evolution of the highly Doppler-shifted O I 7774 absorption features detected within five days post-explosion indicate the presence of O I with expansion velocities from 11,500 to 21,000 km s^-1. The fact that some O I is present above C II suggests that SN 2011fe may have had an appreciable amount of unburned oxygen within the outer layers of the ejecta., Comment: Accepted by ApJL (5 pages, 4 figures, 1 table) - Spectra will be made available on WISeREP, see http://www.weizmann.ac.il/astrophysics/wiserep/home

We present the results of a machine-learning (ML) based search for new R Coronae Borealis (RCB) stars and DY Persei-like stars (DYPers) in the Galaxy using cataloged light curves from the All-Sky Automated Survey (ASAS) Catalog of Variable Stars (ACVS). RCB stars - a rare class of hydrogen-deficient carbon-rich supergiants - are of great interest owing to the insights they can provide on the late stages of stellar evolution. DYPers are possibly the low-temperature, low-luminosity analogs to the RCB phenomenon, though additional examples are needed to fully establish this connection. While RCB stars and DYPers are traditionally identified by epochs of extreme dimming that occur without regularity, the ML search framework more fully captures the richness and diversity of their photometric behavior. We demonstrate that our ML method can use newly discovered RCB stars to identify additional candidates within the same data set. Our search yields 15 candidates that we consider likely RCB stars/DYPers: new spectroscopic observations confirm that four of these candidates are RCB stars and four are DYPers. Our discovery of four new DYPers increases the number of known Galactic DYPers from two to six; noteworthy is that one of the new DYPers has a measured parallax and is m ~ 7 mag, making it the brightest known DYPer to date. Future observations of these new DYPers should prove instrumental in establishing the RCB connection. We consider these results, derived from a machine-learned probabilistic classification catalog, as an important proof-of-concept for the efficient discovery of rare sources with time-domain surveys., Comment: 18 pages, 2 new figures, accepted for publication in ApJ

The Lick AGN Monitoring Project 2011 observing campaign was carried out over the course of 11 weeks in Spring 2011. Here we present the first results from this program, a measurement of the broad-line reverberation lag in the Seyfert 1 galaxy Mrk 50. Combining our data with supplemental observations obtained prior to the start of the main observing campaign, our dataset covers a total duration of 4.5 months. During this time, Mrk 50 was highly variable, exhibiting a maximum variability amplitude of a factor of 4 in the U-band continuum and a factor of 2 in the H-beta line. Using standard cross-correlation techniques, we find that H-beta and H-gamma lag the V-band continuum by tau_cen = 10.64(-0.93,+0.82) and 8.43(-1.28,+1.30) days, respectively, while the lag of He II 4686 is unresolved. The H-beta line exhibits a symmetric velocity-resolved reverberation signature with shorter lags in the high-velocity wings than in the line core, consistent with an origin in a broad-line region dominated by orbital motion rather than infall or outflow. Assuming a virial normalization factor of f=5.25, the virial estimate of the black hole mass is (3.2+-0.5)*10^7 solar masses. These observations demonstrate that Mrk 50 is among the most promising nearby active galaxies for detailed investigations of broad-line region structure and dynamics., Comment: Accepted for publication in ApJ Letters. 6 pages, 4 figures

We present the discovery of PTF 10vgv, a Type Ic supernova detected by the Palomar Transient Factory, using the Palomar 48-inch telescope (P48). R-band observations of the PTF 10vgv field with P48 probe the supernova emission from its very early phases (about two weeks before R-band maximum), and set limits on its flux in the week prior to the discovery. Our sensitive upper limits and early detections constrain the post-shock-breakout luminosity of this event. Via comparison to numerical (analytical) models, we derive an upper-limit of R \lesssim 4.5 Rsun (R \lesssim 1 Rsun) on the radius of the progenitor star, a direct indication in favor of a compact Wolf-Rayet star. Applying a similar analysis to the historical observations of SN 1994I, yields R \lesssim 1/4 Rsun for the progenitor radius of this supernova., Comment: 16 pages; 3 figures; accepted for publication in ApJ Letters; minor changes to match published version (results unchanged)

Supernova (SN) 2009ig was discovered 17 hours after explosion by the Lick Observatory Supernova Search, promptly classified as a normal Type Ia SN (SN Ia), peaked at V = 13.5 mag, and was equatorial, making it one of the foremost supernovae for intensive study in the last decade. Here, we present ultraviolet (UV) and optical observations of SN 2009ig, starting about 1 day after explosion until around maximum brightness. Our data include excellent UV and optical light curves, 25 premaximum optical spectra, and 8 UV spectra, including the earliest UV spectrum ever obtained of a SN Ia. SN 2009ig is a relatively normal SN Ia, but does display high-velocity ejecta - the ejecta velocity measured in our earliest spectra (v ~ -23,000 km/s for Si II 6355) is the highest yet measured in a SN Ia. The spectral evolution is very dramatic at times earlier than 12 days before maximum brightness, but slows after that time. The early-time data provide a precise measurement of 17.13 +/- 0.07 days for the SN rise time. The optical color curves and early-time spectra are significantly different from template light curves and spectra used for light-curve fitting and K-corrections, indicating that the template light curves and spectra do not properly represent all Type Ia supernovae at very early times. In the age of wide-angle sky surveys, SNe like SN 2009ig that are nearby, bright, well positioned, and promptly discovered will still be rare. As shown with SN 2009ig, detailed studies of single events can provide significantly more information for testing systematic uncertainties related to SN Ia distance estimates and constraining progenitor and explosion models than large samples of more distant SNe., Comment: 16 pages, 14 figures, ApJ, in press

Variable X-ray and gamma-ray emission is characteristic of the most extreme physical processes in the Universe, and studying the sources of these energetic photons has been a major driver in astronomy for the past 50 years. Here we present multiwavelength observations of a unique gamma-ray selected transient, discovered by Swift, which was accompanied by bright emission across the electromagnetic spectrum, and whose properties are unlike any previously observed source. We pinpoint the event to the center of a small, star-forming galaxy at redshift z=0.3534. Its high-energy emission has lasted much longer than any gamma-ray burst, while its peak luminosity was about 100 times higher than the brightest active galactic nuclei. The association of the outburst with the center of its host galaxy suggests that this phenomenon has its origin in a new, rare mechanism associated with a massive black hole in the nucleus of a galaxy.

The Seyfert 1 galaxy Zw 229-015 is among the brightest active galaxies being monitored by the Kepler mission. In order to determine the black hole mass in Zw 229-015 from H-beta reverberation mapping, we have carried out nightly observations with the Kast Spectrograph at the Lick 3m telescope during the dark runs from June through December 2010, obtaining 54 spectroscopic observations in total. We have also obtained nightly V-band imaging with the Katzman Automatic Imaging Telescope at Lick Observatory and with the 0.9m telescope at the Brigham Young University West Mountain Observatory over the same period. We detect strong variability in the source, which exhibited more than a factor of 2 change in broad H-beta flux. From cross-correlation measurements, we find that the H-beta light curve has a rest-frame lag of 3.86(+0.69,-0.90) days with respect to the V-band continuum variations. We also measure reverberation lags for H-alpha and H-gamma and find an upper limit to the H-delta lag. Combining the H-beta lag measurement with a broad H-beta width of sigma = 1590+/-47 km/s measured from the root-mean-square variability spectrum, we obtain a virial estimate of M_BH = 1.00(-0.24,+0.19)*10^7 solar masses for the black hole in Zw 229-015. As a Kepler target, Zw 229-015 will eventually have one of the highest-quality optical light curves ever measured for any active galaxy, and the black hole mass determined from reverberation mapping will serve as a benchmark for testing relationships between black hole mass and continuum variability characteristics in active galactic nuclei., Comment: 13 pages, 8 figures. Accepted for publication in ApJ

Metallicity is expected to influence not only the lives of massive stars but also the outcome of their deaths as supernovae (SNe) and as gamma-ray bursts (GRBs). However, there are surprisingly few direct measurements of the local metallicities of different flavors of core-collapse SNe. Here we present the largest existing set of host-galaxy spectra with H II region emission lines at the sites of 35 stripped-envelope core-collapse SNe. We derive local oxygen abundances in a robust manner in order to constrain the SN Ib/c progenitor population. We obtain spectra at the SN sites, include SNe from targeted and untargeted surveys, and perform the abundance determinatinos using three different oxygen-abundance calibrations. The sites of SNe Ic (the demise of the most heavily stripped stars having lost both the H and He layers) are systematically more metal rich than those of SNe Ib (arising from stars that retained their He layer) in all calibrations. A Kolmogorov-Smirnov test yields the very low probability of 1% that SN Ib and SN Ic environment abundances, which are different on average by ~0.2 dex (in the Pettini & Pagel scale), are drawn from the same parent population. Broad-lined SNe Ic (without GRBs) occur at metallicities between those of SNe Ib and SNe Ic. Lastly, we find that the host-galaxy central oxygen abundance is not a good indicator of the local SN metallicity; hence, large-scale SN surveys need to obtain local abundance measurements in order to quantify the impact of metallicity on stellar death., Comment: Accepted to ApJ Letters, v2 matches published version. Monte-Carlo simulations and more data than v1, conclusions strenghtened. 6 pages in emulateapj, 2 figures, 1 Table

Supernova (SN) 2008ax in NGC 4490 was discovered within hours after shock breakout, presenting the rare opportunity to study a core-collapse SN beginning with the initial envelope-cooling phase immediately following shock breakout. We present an extensive sequence of optical and near-infrared spectra, as well as three epochs of optical spectropolarimetry. Our initial spectra, taken two days after shock breakout, are dominated by hydrogen Balmer lines at high velocity. However, by maximum light, He I lines dominated the optical and near-infrared spectra, which closely resembled those of normal Type Ib supernovae (SNe Ib) such as SN 1999ex. This spectroscopic transition defines Type IIb supernovae, but the strong similarity of SN 2008ax to normal SNe Ib beginning near maximum light, including an absorption feature near 6270A due to H-alpha at high velocities, suggests that many objects classified as SNe Ib in the literature may have ejected similar amounts of hydrogen as SN 2008ax, roughly a few x 0.01 M_sun. Early-time spectropolarimetry (6 and 9 days after shock breakout) revealed strong line polarization modulations of 3.4% across H-alpha, indicating the presence of large asphericities in the outer ejecta. The continuum shares a common polarization angle with the hydrogen, helium, and oxygen lines, while the calcium and iron absorptions are oriented at different angles. This is clear evidence of deviations from axisymmetry even in the outer ejecta. Intrinsic continuum polarization of 0.64% only nine days after shock breakout shows that the outer layers of the ejecta were quite aspherical. A single epoch of late-time spectropolarimetry, as well as the shapes of the nebular line profiles, demonstrate that asphericities extended from the outermost layers all the way down to the center of this SN. [Abridged], Comment: 24 pages, 21 figures, 4 tables, appendix, minor revisions to match version accepted by ApJ

Stars with initial masses 10 M_{solar} < M_{initial} < 100 M_{solar} fuse progressively heavier elements in their centres, up to inert iron. The core then gravitationally collapses to a neutron star or a black hole, leading to an explosion -- an iron-core-collapse supernova (SN). In contrast, extremely massive stars (M_{initial} > 140 M_{solar}), if such exist, have oxygen cores which exceed M_{core} = 50 M_{solar}. There, high temperatures are reached at relatively low densities. Conversion of energetic, pressure-supporting photons into electron-positron pairs occurs prior to oxygen ignition, and leads to a violent contraction that triggers a catastrophic nuclear explosion. Tremendous energies (>~ 10^{52} erg) are released, completely unbinding the star in a pair-instability SN (PISN), with no compact remnant. Transitional objects with 100 M_{solar} < M_{initial} < 140 M_{solar}, which end up as iron-core-collapse supernovae following violent mass ejections, perhaps due to short instances of the pair instability, may have been identified. However, genuine PISNe, perhaps common in the early Universe, have not been observed to date. Here, we present our discovery of SN 2007bi, a luminous, slowly evolving supernova located within a dwarf galaxy (~1% the size of the Milky Way). We measure the exploding core mass to be likely ~100 M_{solar}, in which case theory unambiguously predicts a PISN outcome. We show that >3 M_{solar} of radioactive 56Ni were synthesized, and that our observations are well fit by PISN models. A PISN explosion in the local Universe indicates that nearby dwarf galaxies probably host extremely massive stars, above the apparent Galactic limit, perhaps resulting from star formation processes similar to those that created the first stars in the Universe., Comment: Accepted version of the paper appearing in Nature, 462, 624 (2009), including all supplementary information

We present early-time photometric and spectroscopic observations of supernova (SN) 2009kr in NGC 1832. We find that its properties to date support its classification as Type II-linear (SN II-L), a relatively rare subclass of core-collapse supernovae (SNe). We have also identified a candidate for the SN progenitor star through comparison of pre-explosion, archival images taken with WFPC2 onboard the Hubble Space Telescope (HST) with SN images obtained using adaptive optics (AO) plus NIRC2 on the 10-m Keck-II telescope. Although the host galaxy's substantial distance (~26 Mpc) results in large uncertainties in the relative astrometry, we find that if this candidate is indeed the progenitor, it is a highly luminous (M_V = -7.8 mag) yellow supergiant with initial mass ~18-24 M_sun. This would be the first time that a SN II-L progenitor has been directly identified. Its mass may be a bridge between the upper initial mass limit for the more common Type II-plateau SNe (SNe II-P) and the inferred initial mass estimate for one Type II-narrow SN (SN IIn)., Comment: Accepted for publication in The Astrophysical Journal Letters

We present spectroscopic and photometric observations of the Type IIn supernova (SN) 2008iy. SN 2008iy showed an unprecedentedly long rise time of ~400 days, making it the first SN to take significantly longer than 100 days to reach peak optical luminosity. The peak absolute magnitude of SN 2008iy was M_r ~ -19.1 mag, and the total radiated energy over the first ~700 days was ~2 x 10^50 erg. Spectroscopically, SN 2008iy is very similar to the Type IIn SN 1988Z at late times, and, like SN 1988Z, it is a luminous X-ray source (both supernovae had an X-ray luminosity L_ X > 10^41 erg/s). The Halpha emission profile of SN 2008iy shows a narrow P Cygni absorption component, implying a pre-SN wind speed of ~100 km/s. We argue that the luminosity of SN 2008iy is powered via the interaction of the SN ejecta with a dense, clumpy circumstellar medium. The ~400 day rise time can be understood if the number density of clumps increases with distance over a radius ~1.7 x 10^16 cm from the progenitor. This scenario is possible if the progenitor experienced an episodic phase of enhanced mass-loss < 1 century prior to explosion or the progenitor wind speed increased during the decades before core collapse. We favour the former scenario, which is reminiscent of the eruptive mass-loss episodes observed for luminous blue variable (LBV) stars. The progenitor wind speed and increased mass-loss rates serve as further evidence that at least some, and perhaps all, Type IIn supernovae experience LBV-like eruptions shortly before core collapse. We also discuss the host galaxy of SN 2008iy, a subluminous dwarf galaxy, and offer a few reasons why the recent suggestion that unusual, luminous supernovae preferentially occur in dwarf galaxies may be the result of observational biases., Comment: 15 pages, 5 figures, MNRAS accepted

We present optical photometry and spectra for the Type Ia supernova (SN Ia) 2007gi in the nearby galaxy NGC 4036. SN 2007gi is characterized by extremely high-velocity (HV) features of the intermediate-mass elements (Si, Ca, and S), with expansion velocities ($v_{\rm exp}$) approaching $\sim$15,500 km s$^{-1}$ near maximum brightness (compared to $\sim$10,600 km s$^{-1}$ for SNe Ia with normal $v_{\rm exp}$). SN 2007gi reached a $B$-band peak magnitude of 13.25$\pm$0.04 mag with a decline rate of $\Delta m_{15}(B)$(true) = 1.33$\pm$0.09 mag. The $B$-band light curve of SN 2007gi demonstrated an interesting two-stage evolution during the nebular phase, with a decay rate of 1.16$\pm$0.05 mag (100 days)$^{-1}$ during $t = 60$--90 days and 1.61$\pm0.04$ mag (100 days)$^{-1}$ thereafter. Such a behavior was also observed in the HV SN Ia 2006X, and might be caused by the interaction between supernova ejecta and circumstellar material (CSM) around HV SNe Ia. Based on a sample of a dozen well-observed $R$-band (or unfiltered) light curves of SNe Ia, we confirm that the HV events may have a faster rise time to maximum than the ones with normal $v_{\rm exp}$., Comment: 30 pages, 10 figures

We study the observables of 158 relatively normal Type Ia supernovae (SNe Ia) by dividing them into two groups in terms of the expansion velocity inferred from the absorption minimum of the Si II 6355 line in their spectra near B-band maximum brightness. One group ("Normal") consists of normal SNe Ia populating a narrow strip in the Si II velocity distribution, with an average expansion velocity v=10,600+/-400 km/s near B maximum; the other group ("HV") consists of objects with higher velocities, v > 11,800 km/s. Compared with the Normal group, the HV one shows a narrower distribution in both the peak luminosity and the luminosity decline rate dm_{15}. In particular, their B-V colors at maximum brightness are found to be on average redder by ~0.1, suggesting that they either are associated with dusty environments or have intrinsically red B-V colors. The HV SNe Ia are also found to prefer a lower extinction ratio Rv~1.6 (versus ~2.4 for the Normal ones). Applying such an absorption-correction dichotomy to SNe Ia of these two groups remarkably reduces the dispersion in their peak luminosity from 0.178 mag to only 0.125 mag., Comment: Accepted for publication in ApJ Letters, 8 pages, 4 figures, 1 table

The quasar SDSS J153636.22+044127.0, exhibiting peculiar broad emission-line profiles with multiple components, was proposed as a candidate sub-parsec binary supermassive black hole system. More recently, imaging revealed two spatially distinct sources, leading some to suggest the system to be a quasar pair separated by ~5 kpc. We present Palomar and Keck optical spectra of this system from which we identify a third velocity component to the emission lines. We argue that the system is more likely an unusual member of the class of active galactic nuclei (AGNs) known as "double-peaked emitters" than a sub-parsec black hole binary or quasar pair. We find no significant velocity evolution of the two main peaks over the course of 0.95 yr, with a 3-sigma upper limit on any secular change of 70 km/s/yr. We also find that the three velocity components of the emission lines are spatially coincident to within 0.015" along the slit, apparently ruling out the double-quasar hypothesis., Comment: ApJL, 5 pages, 3 figures, revised to match accepted version

We present the results of spectroscopic observations from the ESSENCE high-redshift supernova (SN) survey during its first four years of operation. This sample includes spectra of all SNe Ia whose light curves were presented by Miknaitis et al. (2007) and used in the cosmological analyses of Davis et al. (2007) and Wood-Vasey et al. (2007). The sample represents 273 hours of spectroscopic observations with 6.5 - 10-m-class telescopes of objects detected and selected for spectroscopy by the ESSENCE team. We present 174 spectra of 156 objects. Combining this sample with that of Matheson et al. (2005), we have a total sample of 329 spectra of 274 objects. From this, we are able to spectroscopically classify 118 Type Ia SNe. As the survey has matured, the efficiency of classifying SNe Ia has remained constant while we have observed both higher-redshift SNe Ia and SNe Ia farther from maximum brightness. Examining the subsample of SNe Ia with host-galaxy redshifts shows that redshifts derived from only the SN Ia spectra are consistent with redshifts found from host-galaxy spectra. Moreover, the phases derived from only the SN Ia spectra are consistent with those derived from light-curve fits. By comparing our spectra to local templates, we find that the rate of objects similar to the overluminous SN 1991T and the underluminous SN 1991bg in our sample are consistent with that of the local sample. We do note, however, that we detect no object spectroscopically or photometrically similar to SN 1991bg. Although systematic effects could reduce the high-redshift rate we expect based on the low-redshift surveys, it is possible that SN 1991bg-like SNe Ia are less prevalent at high redshift., Comment: 21 pages, 17 figures, accepted to AJ

We present extensive photometry at ultraviolet (UV), optical, and near-infrared (NIR) wavelengths, as well as dense sampling of optical spectra, for the normal type Ia supernova (SN Ia) 2005cf. From the well-sampled light curves, we find that SN 2005cf reached a B-band maximum at 13.63+/-0.02 mag, with an observed luminosity decline rate dm_15(B) = 1.05+/-0.03 mag. The correlations between the decline rate and various color indexes, recalibrated on the basis of an expanded SN Ia sample, yielded E(B-V)_host=0.09+/-0.03 mag for SN2005cf. The UV photometry was obtained with the HST and the Swift Ultraviolet/Optical Telescope, and the results match each other to within 0.1-0.2 mag. The UV light curves show similar evolution to the broadband U, with an exception in the 2000-2500 Angstrom spectral range (corresponding to the F220W/uvm2 filters), where the light curve appears broader and much fainter than that on either side (likely owing to the intrinsic spectral evolution). Combining the UV data with the ground-based optical and NIR data, we establish the generic UV-optical-NIR bolometric light curve for SN 2005cf and derive the bolometric corrections in the absence of UV and/or NIR data. The overall spectral evolution of SN 2005cf is similar to that of a normal SN Ia, but with variety in the strength and profile of the main feature lines. The spectra at early times displayed strong, detached high-velocity (HV) features in the Ca II H&K doublet and NIR triplet. Similar HV features may exist in the SiII 6355 absorption line which evolved rapidly from a flat-bottomed feature in the earliest phase to a triangular shape one week before maximum, and may be common in other normal SNe Ia. The possible origin of the HV absorption features is briefly discussed (abridged)., Comment: 31 pages, 24 figures, 13 tables, emulateapj; submitted to ApJ

We report on our early photometric and spectroscopic observations of the extremely luminous Type II supernova (SN) 2008es. With an observed peak optical magnitude of m_V = 17.8 and at a redshift z = 0.213, SN 2008es had a peak absolute magnitude of M_V = -22.3, making it the second most luminous SN ever observed. The photometric evolution of SN 2008es exhibits a fast decline rate (~0.042 mag d^-1), similar to the extremely luminous Type II-L SN 2005ap. We show that SN 2008es spectroscopically resembles the luminous Type II-L SN 1979C. Although the spectra of SN 2008es lack the narrow and intermediate-width line emission typically associated with the interaction of a SN with the circumstellar medium of its progenitor star, we argue that the extreme luminosity of SN 2008es is powered via strong interaction with a dense, optically thick circumstellar medium. The integrated bolometric luminosity of SN 2008es yields a total radiated energy at ultraviolet and optical wavelengths of >10^51 ergs. Finally, we examine the apparently anomalous rate at which the Texas Supernova Search has discovered rare kinds of supernovae, including the five most luminous supernovae observed to date, and find that their results are consistent with those of other modern SN searches., Comment: accepted to ApJ, 10 pages, 7 figures, 6 tables. Minor revisions, conclusions remain unchanged

We present extensive early photometric (ultraviolet through near-infrared) and spectroscopic (optical and near-infrared) data on supernova (SN) 2008D as well as X-ray data analysis on the associated Swift/X-ray transient (XRT) 080109. Our data span a time range of 5 hours before the detection of the X-ray transient to 150 days after its detection, and detailed analysis allowed us to derive constraints on the nature of the SN and its progenitor; throughout we draw comparisons with results presented in the literature and find several key aspects that differ. We show that the X-ray spectrum of XRT 080109 can be fit equally well by an absorbed power law or a superposition of about equal parts of both power law and blackbody. Our data first established that SN 2008D is a spectroscopically normal SN Ib (i.e., showing conspicuous He lines), and show that SN 2008D had a relatively long rise time of 18 days and a modest optical peak luminosity. The early-time light curves of the SN are dominated by a cooling stellar envelope (for \Delta t~0.1- 4 day, most pronounced in the blue bands) followed by 56^Ni decay. We construct a reliable measurement of the bolometric output for this stripped-envelope SN, and, combined with estimates of E_K and M_ej from the literature, estimate the stellar radius R_star of its probable Wolf-Rayet progenitor. According to the model of Waxman et al. and of Chevalier & Fransson, we derive R_star^{W07}= 1.2+/-0.7 R_sun and R_star^{CF08}= 12+/-7 R_sun, respectively; the latter being more in line with typical WN stars. Spectra obtained at 3 and 4 months after maximum light show double-peaked oxygen lines that we associate with departures from spherical symmetry, as has been suggested for the inner ejecta of a number of SN Ib cores., Comment: Accepted to ApJ, v3 contains more data than v2 and more references, conclusions not significantly changed, 28 pages in emulateapj, 17 figures