From DES- “From the DArchive: A Newly Discovered Superluminous Supernova”

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The Dark Energy Survey

April 29, 2016
Mathew Smith
Edited by R.C. Wolf & R. Cawthon

Science paper:
DES14X3taz: A Type I Superluminous Supernova Showing a Luminous, Rapidly Cooling Initial Pre-Peak Bump

In this paper we present DES14X3taz, a newly discovered superluminous supernova (SLSN). This particular SLSN is very unusual – if you look at the evolution of its brightness over time, or its light curve, there are two peaks (most only have one)! In our analysis, we attempt to explain what physical process might cause such an occurrence and determine if this is truly a unique event or common to all SLSNe.

Although the initial DECam data was fairly indicative that this was a particularly interesting object, we had to use additional information to confirm our discovery. By combining optical light-curve data from DES and its sister survey, the Survey Using Decam for Superluminous Supernovae (SUDSS), we were able to plot the evolution of brightness over time (light-curve) of DES14X3taz and find its brightest point. We then used spectra obtained on the Gran Telescopino Canarias (GTC) in La Palma, Spain to estimate the distance to this event, and thus its peak brightness, and unambiguously confirmed that it is a SLSNe.

Gran Telescopino Canarias exterior
Gran Telescopino de Canaries interior
Gran Telescopino de Canaries

What really distinguishes DES14X3taz from previously discovered SLSNe is the presence of an early “bump” in the light curve prior to the main light-curve. The figure below shows these features for DES14X3taz.

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In addition to detecting this bump, we were lucky to have observed this SLSN before explosion and to have observed it at many points during its lifetime; most other observed SLSNe have been discovered post-explosion or do not have such a large a sample of measurements.

Our observations with DECam allowed us to obtain colour information, from observations in several filters, of the bump. This enabled us to probe the physical processes driving these super-luminous events by comparing our data to pre-existing theoretical models. In the figure below, the colored-circle points are real data, and the dashed lines represent theoretical observations for different physical processes that we think might be motivating this behavior.

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Fitting models to the main curve show that the physical mechanism driving the explosion is consistent with a magnetar, a rapidly rotating neutron star (as seen in the match to the Extended Material Around the Star). In the figure, this is consistent with the solid lines. Fitting black-body curves to the DES data of DES14X3taz, we show that the initial peak cools rapidly, before a period of reheating, which drives the main part of the light-curve. Using chi-squared statistics, we compare photometric data of the initial peak with various models of shock-cooling and find that shock from material at an extended radius is consistent with observations. We also find a sample of previously discovered SLSNe that also exhibit this early bump in their light curves; therefore, we believe our findings suggest a unified physical interpretation for all SLSNe.

SLSNe are a new class of transient event, with potentially exciting consequences for cosmology. Recent work (Inserra & Smartt 2014) has suggested that these events may even be “standardisable candles”, and thus useful to measure distances to the high redshift Universe. As these events are more luminous than traditional Type Ia supernovae they have the potential to extend SN cosmology to larger distances than currently possible. However, little is well-understood about the explosion mechanism driving these events and we will need to understand more about the origin of SLSNe as we explore utilizing them as cosmological probes.

See the full article here .

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DECam, built at FNAL
DECam, built at FNAL
CTIO Victor M Blanco 4m Telescope
CTIO Victor M Blanco 4m Telescope interior
CTIO Victor M Blanco Telescope at Cerro Tololo which houses the DECAm

The Dark Energy Survey (DES) is designed to probe the origin of the accelerating universe and help uncover the nature of dark energy by measuring the 14-billion-year history of cosmic expansion with high precision. More than 120 scientists from 23 institutions in the United States, Spain, the United Kingdom, Brazil, and Germany are working on the project. This collaboration [has built] an extremely sensitive 570-Megapixel digital camera, DECam, and [has mounted] it on the Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory high in the Chilean Andes. Started in Sept. 2012 and continuing for five years, DES will survey a large swath of the southern sky out to vast distances in order to provide new clues to this most fundamental of questions.