K. Itagaki

The Type IIb SN 2008ax: spectral and light curve evolution

We present spectroscopy and photometry of the He-rich supernova (SN) 2008ax. The early-time spectra show prominent P-Cygni H lines, which decrease with time and disappear completely about 2 months after the explosion. In the same period He I lines become the most prominent spectral features. SN 2008ax displays the ordinary spectral evolution of a Type IIb supernova. A stringent pre-discovery limit constrains the time of the shock breakout of SN 2008ax to within only a few hours. Its light curve, which peaks in the B band about 20 d after the explosion, strongly resembles that of other He-rich core-collapse supernovae. The observed evolution of SN 2008ax is consistent with the explosion of a young Wolf-Rayet (of WNL type) star, which had retained a thin, low-mass shell of its original H envelope. The overall characteristics of SN 2008ax are reminiscent of those of SN 1993J, except for a likely smaller H mass. This may account for the findings that the progenitor of SN 2008ax was a WNL star and not a K supergiant as in the case of SN 1993J, that a prominent early-time peak is missing in the light curve of SN 2008ax, and that H alpha is observed at higher velocities in SN 2008ax than in SN 1993J.

Estimating the First-light Time of the Type?Ia Supernova 2014J in M82

The Type?Ia supernova (SN?Ia) 2014J in M82 (d 3.5?Mpc) was serendipitously discovered by S. Fosseys group on 2014 January 21 UT and has been confirmed to be the nearest known SN?Ia since at least SN?1986G. Although SN?2014J was not discovered until ~7?days after first light, both the Katzman Automatic Imaging Telescope at Lick Observatory and K. Itagaki obtained several prediscovery observations of SN?2014J. With these data, we are able to constrain the objects time of first light to be January 14.75 UT, only 0.82 ? 0.21?days before our first detection. Interestingly, we find that the light curve is well described by a varying power law, much like SN?2013dy, which makes SN?2014J the second example of a changing power law in early-time SN?Ia light curves. A low-resolution spectrum taken on January 23.388 UT, ~8.70?days after first light, shows that SN?2014J is a heavily reddened but otherwise spectroscopically normal SN?Ia.

Dead or Alive? Long-term evolution of SN 2015bh (SNhunt275)

Supernova (SN) 2015bh (or SNhunt275) was discovered in NGC 2770 on 2015 February with an absolute magnitude of Mr ~ −13.4 mag, and was initially classified as a SN impostor. Here we present the photometric and spectroscopic evolution of SN 2015bh from discovery to late phases (~ 1 yr after). In addition, we inspect archival images of the host galaxy up to ~ 21 yr before discovery, finding a burst ~ 1 yr before discovery, and further signatures of stellar instability until late 2014. Later on, the luminosity of the transient slowly increases, and a broad light curve peak is reached after about three months. We propose that the transient discovered in early 2015 could be a core-collapse SN explosion. The pre-SN luminosity variability history, the long-lasting rise and faintness first light curve peak suggests that the progenitor was a very massive, unstable and blue star, which exploded as a faint SN because of severe fallback of material. Later on, the object experiences a sudden brightening of 3 mag, which results from the interaction of the SN ejecta with circumstellar material formed through repeated past mass-loss events. Spectroscopic signatures of interaction are however visible at all epochs. A similar chain of events was previously proposed for the similar interacting SN 2009ip.

The Double-Peaked SN 2013ge: A Type Ib/c Sn with an Asymmetric Mass Ejection or an Extended Progenitor Envelope

We present extensive multiwavelength (radio to X-ray) observations of the Type Ib/c SN2013ge from −13 to +457 days relative to maximum light, including a series of optical spectra and Swift UV-optical photometry beginning 2 − 4 days post explosion. This makes SN2013ge one of the best observed normal Type Ib/c SN at early times, when the light curve is particularly sensitive to the progenitor configuration and mixing of radioactive elements. These early observations reveal two distinct light curve components in the UV bands. The first component rises over 4 − 5 days and is visible for the first week post-explosion. Spectra of the first component have a blue continuum and show a plethora of high velocity (~ 14,000 km s^(−1)) but narrow (~ 3500 km s^(−1)) spectroscopic features, indicating that the line forming region is restricted. The explosion parameters estimated for the bulk explosion (M_(ej) ~ 2 − 3 M_⊙; EK ~ 1 − 2 × 10^(51) ergs) are standard for Type Ib/c SN, while detailed analysis of optical and NIR spectra identify weak He features at early times (in an object which would have otherwise been classified as Type Ic), and nebular spectra show evidence for mixing and asymmetry in the bulk ejecta. In addition, SN2013ge exploded in a low metallicity environment (~ 0.5 Z_⊙) and we have obtained some of the deepest radio and X-ray limits for a Type Ib/c SN to date that constrain the progenitor mass-loss rate to be M < 4 × 10^(−6) M_⊙ yr^(−1). We are left with two distinct progenitor scenarios for SN2013ge depending on our interpretation of the early emission. If the first component is cooling envelope emission, then the progenitor of SN2013ge possessed a low-mass extended (≳ 30 R_⊙) envelope. Alternatively, if the first component is due to outwardly mixed 56Ni then our observations are consistent with the asymmetric ejection of a small amount of mass (~ 0.05 M_⊙) ahead of the bulk explosion. Current models for the collision of a SN shock with a binary companion cannot reproduce both the timescale and luminosity of the early emission in SN2013ge. Finally, we find that the spectra of the first component of SN2013ge are similar to those of the rapidly-declining SN2002bj.

The possible detection of a binary companion to a Type Ibn supernova progenitor

We present late-time observations of the site of the Type Ibn supernova (SN) 2006jc acquired with the Hubble Space Telescope Advanced Camera for Surveys. A faint blue source is recovered at the SN position with brightness

THE YOUNG AND BRIGHT TYPE IA SUPERNOVA ASASSN-14lp: DISCOVERY, EARLY-TIME OBSERVATIONS, FIRST-LIGHT TIME, DISTANCE TO NGC 4666, AND PROGENITOR CONSTRAINTS

m_{F435W}=26.76\pm0.20

iPTF15eqv: Multiwavelength Exposé of a Peculiar Calcium-rich Transient

,

Short-lived Circumstellar Interaction in the Low-luminosity Type IIP SN 2016bkv

m_{F555W}=26.60\pm0.23

Dwarf Nova in Pegasus (Pnv J21095047+1348396)

and

Supernova 2011gc = Psn J18121900+2131150 = Psn J18121913+2131136

m_{F625W} = 26.32\pm0.19