Circumstellar interaction in supernovae in dense environments - an observational perspective

In a supernova explosion, the ejecta interacting with the surrounding circumstellar medium (CSM) give rise to variety of radiation. Since CSM is created from the mass lost from the progenitor star, it carries footprints of the late time evolution of the star. This is one of the unique ways to get a handle on the nature of the progenitor star system. Here, I will focus mainly on the supernovae (SNe) exploding in dense environments, a.k.a. Type IIn SNe. Radio and X-ray emission from this class of SNe have revealed important modifications in their radiation properties, due to the presence of high density CSM. Forward shock dominance of the X-ray emission, internal free-free absorption of the radio emission, episodic or non-steady mass loss rate, asymmetry in the explosion seem to be common properties of this class of SNe.Comment: Fixed minor typos. 31 pages, 9 figures, accepted for publication in Space Science Reviews. Chapter in International Space Science Institute (ISSI) Book on "Supernovae" to be published in Space Science Reviews by Springe

SN 2009ip: Constraints on the Progenitor Mass-loss Rate

Some supernovae (SNe) show evidence for mass-loss events taking place prior to their explosions. Measuring their pre-outburst mass-loss rates provides essential information regarding the mechanisms that are responsible for these events. Here we present XMM-Newton and Swift X-ray observations taken after the latest, and presumably the final, outburst of SN 2009ip. We use these observations as well as new near-infrared and visible-light spectra and published radio and visible-light observations to put six independent order-of-magnitude constraints on the mass-loss rate of the SN progenitor prior to the explosion. Our methods utilize the X-ray luminosity, the bound-free absorption, the Hα luminosity, the SN rise time, free-free absorption, and the bolometric luminosity of the outburst detected prior to the explosion. Assuming spherical mass loss with a wind-density profile, we estimate that the effective mass-loss rate from the progenitor was between 10^(–3) and 10^(–2) M_☉ yr^(–1), over a few years prior to the explosion, with a velocity of ~10^3 km s^(–1). This mass-loss rate corresponds to a total circumstellar matter (CSM) mass of ~0.04 M_☉, within 6 × 10^(15) cm of the SN. We note that the mass-loss rate estimate based on the Hα luminosity is higher by an order of magnitude. This can be explained if the narrow-line Hα component is generated at radii larger than the shock radius, or if the CSM has an aspherical geometry. We discuss simple geometries which are consistent with our results

Rapidly Rising Transients in the Supernova - Superluminous Supernova Gap

The American Astronomical Society. All rights reserved..We present observations of four rapidly rising (trise ≈ 10 days) transients with peak luminosities between those of supernovae (SNe) and superluminous SNe (Mpeak ap; -20) - one discovered and followed by the Palomar Transient Factory (PTF) and three by the Supernova Legacy Survey. The light curves resemble those of SN 2011kl, recently shown to be associated with an ultra-long-duration gamma-ray burst (GRB), though no GRB was seen to accompany our SNe. The rapid rise to a luminous peak places these events in a unique part of SN phase space, challenging standard SN emission mechanisms. Spectra of the PTF event formally classify it as an SN II due to broad Hα emission, but an unusual absorption feature, which can be interpreted as either high velocity Hα (though deeper than in previously known cases) or Si ii (as seen in SNe Ia), is also observed. We find that existing models of white dwarf detonations, CSM interaction, shock breakout in a wind (or steeper CSM), and magnetar spin down cannot readily explain the observations. We consider the possibility that a "Type 1.5 SN" scenario could be the origin of our events. More detailed models for these kinds of transients and more constraining observations of future such events should help to better determine their nature. © 2016

PTF13efv - An Outburst 500 Days Prior to the SNHUNT 275 Explosion and Its Radiative Efficiency

The American Astronomical Society. All rights reserved..The progenitors of some supernovae (SNe) exhibit outbursts with super-Eddington luminosities prior to their final explosions. This behavior is common among SNe IIn, but the driving mechanisms of these precursors are not yet well-understood. SNHunt 275 was announced as a possible new SN during 2015 May. Here we report on pre-explosion observations of the location of this event by the Palomar Transient Factory (PTF) and report the detection of a precursor about 500 days prior to the 2015 May activity (PTF 13efv). The observed velocities in the 2015 transient and its 2013 precursor absorption spectra are low (1000-2000 km s-1), so it is not clear yet if the recent activity indeed marks the final disruption of the progenitor. Regardless of the nature of this event, we use the PTF photometric and spectral observations, as well as Swift-UVOT observations, to constrain the efficiency of the radiated energy relative to the total kinetic energy of the precursor. We find that, using an order-of-magnitude estimate and under the assumption of spherical symmetry, the ratio of the radiated energy to the kinetic energy is in the range of 4 x 10-2 to 3.4 x 103. © 2016

THE NEEDLE in the 100 deg² HAYSTACK: UNCOVERING AFTERGLOWS of FERMI GRB<inf>s</inf> with the PALOMAR TRANSIENT FACTORY

The Fermi Gamma-ray Space Telescope has greatly expanded the number and energy window of observations of gamma-ray bursts (GRBs). However, the coarse localizations of tens to a hundred square degrees provided by the Fermi GRB Monitor instrument have posed a formidable obstacle to locating the bursts' host galaxies, measuring their redshifts, and tracking their panchromatic afterglows. We have built a target-of-opportunity mode for the intermediate Palomar Transient Factory in order to perform targeted searches for Fermi afterglows. Here, we present the results of one year of this program: 8 afterglow discoveries out of 35 searches. Two of the bursts with detected afterglows (GRBs 130702A and 140606B) were at low redshift (z = 0.145 and 0.384, respectively) and had spectroscopically confirmed broad-line Type Ic supernovae. We present our broadband follow-up including spectroscopy as well as X-ray, UV, optical, millimeter, and radio observations. We study possible selection effects in the context of the total Fermi and Swift GRB samples. We identify one new outlier on the Amati relation. We find that two bursts are consistent with a mildly relativistic shock breaking out from the progenitor star rather than the ultra-relativistic internal shock mechanism that powers standard cosmological bursts. Finally, in the context of the Zwicky Transient Facility, we discuss how we will continue to expand this effort to find optical counterparts of binary neutron star mergers that may soon be detected by Advanced LIGO and Virgo. © 2015. The American Astronomical Society. All rights reserved