The Unusual Interacting Supernova LSQ13ddu" and "The Search for AT2017gfo-like Transients with ATLAS

Thursday, 17 May 2018 8 a.m. — 8:50 a.m. MST

AURA Lecture Hall

NOIRLab South Colloquia
PETER CLARK; OWEN McBRIEN (PhD Student at Queens University Belfast Invited by NOAO South)

First Talk (25 minutes)

"The Unusual Interacting Supernova LSQ13ddu"

Transient surveys have discovered a wide range of new objects that do not fit the standard behaviour of known classes of astronomical phenomena.

In particular, large footprint high cadence surveys such as Pan-STARRS1 and ATLAS are uncovering and constraining the behaviour of so called ‘fast’ transients – objects that show significant change on the timescale of a few days that have up to now been missed by lower cadence surveys.

I present new analysis of the photometric and spectroscopic behaviour of the unusual supernova LSQ13ddu, including modelling of its photometric behaviour and underlying power source. The object displayed a rapid rise to a peak magnitude of – 19.6 in five days. This was followed by a similarly fast post maximum decline. The rapid rise triggered an active spectroscopic and photometric follow-up campaign primarily via the Public ESO Spectroscopic Survey of Transient Objects (PESSTO) revealing LSQ13ddu to share spectral features with several types of interacting stripped-envelope supernovae – narrow He features associated with Type Ibn SNe accompanied at later times by broader emission features similar to those seen in broad line Ic SNe, a subset of which have been directly linked to gamma ray bursts. The next generation of transient surveys such as the LSST may reveal a range of objects with similar hybrid properties with LSQ13ddu providing a glimpse into the potential zoo of odd objects awaiting discovery.


Second Talk (25 minutes)

"The Search for AT2017gfo-like Transients with ATLAS"

The Asteroid Terrestrial-Impact Last Alert System (ATLAS) is comprised of two wide field telescopes in Hawaii that survey the sky twice per night finding hundreds of transient objects via difference imaging. These include various transient phenomena such as supernovae, AGN and nuclear transients, cataclysmic variables and variable stars. The recent observations of a binary neutron star collision (AT2017gfo) coincident with a gravitational wave event (GW170817) has drawn the scientific world’s attention to KILONOVAE – the resulting EM signal emanating from the collision of two neutron stars - and the exciting prospects these objects hold. 

Simulations of these events can predict the volumetric rate at which kilonovae occur, as well as how many of these events survey telescopes, like ATLAS, are expected to detect. What is missing, however, is observational evidence that might be used to measure these rates quantitatively. I present an ATLAS search for kilonovae, similar to AT2017gfo, associated with galaxies within 60 Mpc.

Our methods to achieve this involve collating the nightly survey data and processing it with a machine learning code to identify and classify the multitude of objects detected. We attempted to identify hitherto unidentified kilonovae through their unique lightcurves, as exemplified by AT2017gfo. The ATLAS database contains object detections dating back to MJD 57392 (2016-01-05 UTC), and updates daily. This provides ample opportunity to identify kilonova candidates going forward and to address whether these are objects we have already observed and detected, but that have gone unrecognised. Even in the era of multi-messenger astronomy, it is important to search for kilonova-like transients without a gravitational wave trigger as the independent identification of kilonovae could enable a lower threshold search for gravitational waves in LIGO - Virgo data. I will provide information on this, as well as on recent kilonova candidates and discuss estimates of the upper limits on the volumetric rate of kilonova occurrence from the ATLAS survey alone.