Mansi M. Kasliwal

An outburst from a massive star 40 days before a supernova explosion

Some observations suggest that very massive stars experience extreme mass-loss episodes shortly before they explode as supernovae, as do several models. Establishing a causal connection between these mass-loss episodes and the final explosion would provide a novel way to study pre-supernova massive-star evolution. Here we report observations of a mass-loss event detected 40 days before the explosion of the type IIn supernova SN 2010mc (also known as PTF 10tel). Our photometric and spectroscopic data suggest that this event is a result of an energetic outburst, radiating at least 6 × 1047 erg of energy and releasing about 10−2 solar masses of material at typical velocities of 2,000 km s−1. 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 disfavour alternative suggestions.

Optical follow-up observations of PTF10qts, a luminous broad-lined Type Ic supernova found by the Palomar Transient Factory

We present optical photometry and spectroscopy of the broad-lined Type Ic supernova (SN Ic-BL) PTF10qts, which was discovered as part of the Palomar Transient Factory. The SN 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_bol = −18.51 ± 0.2 mag, comparable to that of SN 1998bw (M_bol = −18.7 mag) which was associated with a gamma-ray burst (GRB). PTF10qts is one of the most luminous SNe Ic-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 SNe Ic-BL with similar inferred ejecta masses and kinetic energies. The progenitor of the event was likely an ∼20 M_⊙ star.

Early Observations of the Type Ia Supernova iPTF 16abc: A Case of Interaction with Nearby, Unbound Material and/or Strong Ejecta Mixing

Early observations of Type Ia supernovae (SNe Ia) provide a unique probe of their progenitor systems and explosion physics. Here we report the intermediate Palomar Transient Factory (iPTF) discovery of an extraordinarily young SN Ia, iPTF 16abc. By fitting a power law to our early light curve, we infer that first light for the SN, that is, when the SN could have first been detected by our survey, occurred only 0.15 ±_(0.07)^(0.15) days before our first detection. In the ~24 hr after discovery, iPTF 16abc rose by ~2 mag, featuring a near-linear rise in flux for ≳3 days. Early spectra show strong C ii absorption, which disappears after ~7 days. Unlike the extensively observed Type Ia SN 2011fe, the (B-V)_0 colors of iPTF 16abc are blue and nearly constant in the days after explosion. We show that our early observations of iPTF 16abc cannot be explained by either SN shock breakout and the associated, subsequent cooling or the SN ejecta colliding with a stellar companion. Instead, we argue that the early characteristics of iPTF 16abc, including (i) the rapid, near-linear rise, (ii) the nonevolving blue colors, and (iii) the strong C ii absorption, are the result of either ejecta interaction with nearby, unbound material or vigorous mixing of radioactive ^(56)Ni in the SN ejecta, or a combination of the two. In the next few years, dozens of very young normal SNe Ia will be discovered, and observations similar to those presented here will constrain the white dwarf explosion mechanism.

Opening the dynamic infrared sky

While optical and radio transient surveys have enjoyed a renaissance over the past decade, the dynamic infrared sky remains virtually unexplored from the ground. The infrared is a powerful tool for probing transient events in dusty regions that have high optical extinction, and for detecting the coolest of stars that are bright only at these wavelengths. The fundamental roadblocks in studying the infrared time-domain have been the overwhelmingly bright sky background (250 times brighter than optical) and the narrow field-of-view of infrared cameras (largest is VISTA at 0.6 sq deg). To address these challenges, Palomar Gattini-IR is currently under construction at Palomar Observatory and we propose a further low risk, economical, and agile instrument to be located at Siding Spring Observatory, as well as further instruments which will be located at the high polar regions to take advantage of the low thermal sky emission, particularly in the 2.5 micron region.

Oxygen and helium in stripped-envelope supernovae

We present an analysis of 507 spectra of 173 stripped-envelope (SE) supernovae (SNe) discovered by the untargeted Palomar Transient Factory (PTF) and intermediate PTF (iPTF) surveys. Our sample contains 55 Type IIb SNe (SNe IIb), 45 Type Ib SNe (SNe Ib), 56 Type Ic SNe (SNe Ic), and 17 Type Ib/c SNe (SNe Ib/c). We have compared the SE SN subtypes via measurements of the pseudo-equivalent widths (pEWs) and velocities of the He I λλ5876, 7065 and O I λ7774 absorption lines. Consistent with previous work, we find that SNe Ic show higher pEWs and velocities in O I λ7774 compared to SNe IIb and Ib. The pEWs of the He I λλ5876, 7065 lines are similar in SNe Ib and IIb after maximum light. The He I λλ5876, 7065 velocities at maximum light are higher in SNe Ib compared to SNe IIb. We identify an anticorrelation between the He I λ7065 pEW and O I λ7774 velocity among SNe IIb and Ib. This can be interpreted as a continuum in the amount of He present at the time of explosion. It has been suggested that SNe Ib and Ic have similar amounts of He, and that lower mixing could be responsible for hiding He in SNe Ic. However, our data contradict this mixing hypothesis. The observed difference in the expansion rate of the ejecta around maximum light of SNe Ic (V_m = √2E_k/M_(ej) ≈ 15 000 km s^(−1)) and SNe Ib (V_m ≈ 9000 km s^(−1)) would imply an average He mass difference of ∼1.4 M⊙, if the other explosion parameters are assumed to be unchanged between the SE SN subtypes. We conclude that SNe Ic do not hide He but lose He due to envelope stripping.