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Register a new useriPTF16asu: A Luminous, Rapidly-Evolving, and High-Velocity Supernova
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Wide-field surveys are discovering a growing number of rare transients whose physical origin is not yet well understood. Here, we present optical and UV data and analysis of iPTF16asu, a luminous, rapidly-evolving, high velocity, stripped-envelope supernova. With a rest-frame rise-time of just 4 days and a peak absolute magnitude of $M_{rm g}=-20.4$ mag, the light curve of iPTF16asu is faster and more luminous than previous rapid transients. The spectra of iPTF16asu show a featureless, blue continuum near peak that develops into a Type Ic-BL spectrum on the decline. We show that while the late-time light curve could plausibly be powered by $^{56}$Ni decay, the early emission requires a different energy source. Non-detections in the X-ray and radio strongly constrain any associated gamma-ray burst to be low-luminosity. We suggest that the early emission may have been powered by either a rapidly spinning-down magnetar, or by shock breakout in an extended envelope of a very energetic explosion. In either scenario a central engine is required, making iPTF16asu an intriguing transition object between superluminous supernovae, Type Ic-BL supernovae, and low-energy gamma-ray bursts.
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Only a few cases of type Ic supernovae (SNe) with high-velocity ejecta have been discovered and studied. Here we present our analysis of radio and X-ray observations of a Type Ic SN, PTF12gzk. The radio emission rapidly declined less than 10 days after explosion, suggesting SN ejecta expanding at high velocity (~0.3c). The radio data also indicate that the density of the circumstellar material (CSM) around the supernova is lower by a factor of ~10 than the CSM around normal Type Ic SNe. Our observations of this rapidly declining radio SN at a distance of 58 Mpc demonstrates the potential to detect many additional radio SNe, given the new capabilities of the VLA (improved sensitivity and dynamic scheduling), that are currently missed, leading to a biased view of radio SNe Ic. Early optical discovery followed by rapid radio observations would provide a full description of the ejecta velocity distribution and CSM densities around stripped massive star explosions, as well as strong clues about the nature of their progenitor stars.
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We present ground-based and Swift photometric and spectroscopic observations of the tidal disruption event (TDE) ASASSN-15oi, discovered at the center of 2MASX J20390918-3045201 ($dsimeq216$ Mpc) by the All-Sky Automated Survey for SuperNovae (ASAS-SN). The source peaked at a bolometric luminosity of $Lsimeq1.3times10^{44}$ ergs s$^{-1}$ and radiated a total energy of $Esimeq6.6times10^{50}$ ergs over the first $sim3.5$ months of observations. The early optical/UV emission of the source can be fit by a blackbody with temperature increasing from $Tsim2times10^4$ K to $Tsim4times10^4$ K while the luminosity declines from $Lsimeq1.3times10^{44}$ ergs s$^{-1}$ to $Lsimeq2.3times10^{43}$ ergs s$^{-1}$, requiring the photosphere to be shrinking rapidly. The optical/UV luminosity decline during this period is most consistent with an exponential decline, $Lpropto e^{-(t-t_0)/tau}$, with $tau simeq46.5$ days for $t_0simeq57241.6$ (MJD), while a power-law decline of $Lpropto (t-t_0)^{-alpha}$ with $t_0simeq57212.3$ and $alpha=1.62$ provides a moderately worse fit. ASASSN-15oi also exhibits roughly constant soft X-ray emission that is significantly weaker than the optical/UV emission. Spectra of the source show broad helium emission lines and strong blue continuum emission in early epochs, although these features fade rapidly and are not present $sim3$ months after discovery. The early spectroscopic features and color evolution of ASASSN-15oi are consistent with a TDE, but the rapid spectral evolution is unique among optically-selected TDEs.
We present optical and near-infrared observations of the rapidly evolving supernova (SN) 2017czd that shows hydrogen features. The optical light curves exhibit a short plateau phase ($sim 13$ days in the $R$-band) followed by a rapid decline by $4.5$ mag in $sim 20 mathrm{days}$ after the plateau. The decline rate is larger than those of any standard SNe, and close to those of rapidly evolving transients. The peak absolute magnitude is $-16.8$ mag in the $V$-band, which is within the observed range for SNe IIP and rapidly evolving transients. The spectra of SN 2017czd clearly show the hydrogen features and resemble those of SNe IIP at first. The H$alpha$ line, however, does not evolve much with time and it becomes similar to those in SNe IIb at decline phase. We calculate the synthetic light curves using a SN IIb progenitor which has 16 M$_{odot}$ at the zero-age main sequence and evolves in a binary system. The model with a low explosion energy ($5times 10^{50}$ erg) and a low ${}^{56}$Ni mass ($0.003 mathrm{M}_{odot}$) can reproduce the short plateau phase as well as the sudden drop of the light curve as observed in SN 2017czd. We conclude that SN 2017czd might be the first identified weak explosion from a SN IIb progenitor. We suggest that some rapidly evolving transients can be explained by such a weak explosion of the progenitors with little hydrogen-rich envelope.
This paper describes the rapidly evolving and unusual supernova LSQ13ddu, discovered by the La Silla-QUEST survey. LSQ13ddu displayed a rapid rise of just 4.8$pm$0.9 d to reach a peak brightness of $-$19.70$pm$0.02 mag in the $mathit{LSQgr}$ band. Early spectra of LSQ13ddu showed the presence of weak and narrow He I features arising from interaction with circumstellar material (CSM). These interaction signatures weakened quickly, with broad features consistent with those seen in stripped-envelope SNe becoming dominant around two weeks after maximum. The narrow He I velocities are consistent with the wind velocities of luminous blue variables but its spectra lack the typically seen hydrogen features. The fast and bright early light curve is inconsistent with radioactive $^{56}$Ni powering but can be explained through a combination of CSM interaction and an underlying $^{56}$Ni decay component that dominates the later time behaviour of LSQ13ddu. Based on the strength of the underlying broad features, LSQ13ddu appears deficient in He compared to standard SNe Ib.
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