Browsing by Subject "late-time spectra"

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The Broad-Lined Type Ic SN 2012ap And The Nature Of Relativistic Supernovae Lacking A Gamma-Ray Burst Detection
(2015-01) Milisavljevic, Dan; Margutti, R.; Parrent, Jerod T.; Soderberg, Alicia M.; Fesen, Robert A.; Mazzali, P.; Maeda, K.; Sanders, N. E.; Cenko, S. Bradley; Silverman, Jeffrey M.; Filippenko, Alexei V.; Kamble, A.; Chakraborti, S.; Drout, M. R.; Kirshner, Robert P.; Pickering, T. E.; Kawabata, K.; Hattori, T.; Hsiao, Eric Y.; Stritzinger, Maximillian D.; Marion, G. H.; Vinko, Jozsef; Wheeler, J. Craig; Silverman, Jeffrey M.; Marion, G. H.; Vinko, Jozsef; Wheeler, J. Craig
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 +/- 0.5mag. The spectra are dominated by Fe II, OI, and Ca II absorption lines at ejecta velocities of nu approximate to 20,000 km s(-1) 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 (nu greater than or similar to 27,000 km s(-1)). We use these observations to estimate explosion properties and derive a total ejecta mass of similar to 2.7 M-circle dot, a kinetic energy of similar to 1.0 x 10(52) erg, and a Ni-56 mass of 0.1-0.2 M-circle dot. Nebular spectra (t > 200 days) exhibit an asymmetric double-peaked [O I] lambda lambda 6300, 6364 emission profile that we associate with absorption in the supernova interior, although toroidal ejecta geometry is an alternative explanation. SN 2012ap joins SN2009bb 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 observed properties including environmental metallicities of Z greater than or similar to Z(circle dot), moderate to high levels of host galaxy extinction (E(B - V) > 0.4mag), 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.
Hubble Space Telescope And Ground-Based Observations Of The Type Iax Supernovae SN 2005Hk And SN 2008A
(2014-05) McCully, C.; Jha, Saurabh W.; Foley, Ryan J.; Chornock, Ryan; Holtzman, Jon A.; Balam, D. D.; Branch, D.; Filippenko, Alexei V.; Frieman, J.; Fynbo, J.; Galbany, Lluis; Ganeshalingam, Mohan; Garnavich, Peter M.; Graham, M. L.; Hsiao, Eric Y.; Leloudas, G.; Leonard, D. C.; Li, W. D.; Riess, Adam G.; Sako, Masao; Schneider, Donald P.; Silverman, Jeffrey M.; Sollerman, Jesper; Steele, Thea N.; Thomas, R. C.; Wheeler, J. Craig; Zheng, C.; Silverman, Jeffrey M.; Wheeler, J. Craig
We present Hubble Space Telescope (HST) and ground-based optical and near-infrared observations of SN 2005hk and SN 2008A, typical members of the Type Iax class of supernovae (SNe). Here we focus on late-time observations, where these objects deviate most dramatically from all other SN types. Instead of the dominant nebular emission lines that are observed in other SNe at late phases, spectra of SNe 2005hk and 2008A show lines of Fe II, Ca II, and Fe I more than a year past maximum light, along with narrow [ Fe II] and [ Ca II] emission. We use spectral features to constrain the temperature and density of the ejecta, and find high densities at late times, with n(e) greater than or similar to 10(9) cm(-3). Such high densities should yield enhanced cooling of the ejecta, making these objects good candidates to observe the expected "infrared catastrophe," a generic feature of SN Ia models. However, our HST photometry of SN 2008A does not match the predictions of an infrared catastrophe. Moreover, our HST observations rule out a "complete deflagration" that fully disrupts the white dwarf for these peculiar SNe, showing no evidence for unburned material at late times. Deflagration explosion models that leave behind a bound remnant can match some of the observed properties of SNe Iax, but no published model is consistent with all of our observations of SNe 2005hk and 2008A.
The Lick AGN Monitoring Project 2011: Spectroscopic Campaign and Emission-Line Light Curves
(2015-04) Barth, Aaron J.; Bennert, Vardha N.; Canalizo, Gabriela; Filippenko, Alexei V.; Gates, Elinor L.; Greene, Jenny E.; Li, Weidong; Malkan, Matthew A.; Pancoast, Anna; Sand, David J.; Stern, Daniel; Treu, Tommaso; Woo, Jong-Hak; Assef, Roberto J.; Bae, Hyun-Jin; Brewer, Brendon J.; Cenko, S. Bradley; Clubb, Kelsey I.; Cooper, Michael C.; Diamond-Stanic, Aleksandar M.; Hiner, Kyle D.; Hoenig, Sebastian F.; Hsiao, Eric; Kandrashoff, Michael T.; Lazarova, Mariana S.; Nierenberg, A. M.; Rex, Jacob; Silverman, Jeffrey M.; Tollerud, Erik J.; Walsh, Jonelle L.; Silverman, Jeffrey M.
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 active galactic nucleus (AGN) continuum, and measurements of the broad H beta line widths in mean and rms spectra. For the most highly variable AGNs we also measured broad Ha 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 Ha velocity centroids can undergo substantial changes in response to continuum variations; in NGC 4593, the broad H beta velocity shifted by similar to 250 km s(-1) over a 1 month period. 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.