Proposal #19

In September 2013 the supernova impostor 2009ip had a bright outburst that had a spectrum fitting the classification of a Type II-n supernova. I put out a call for help on the AAVSO Forum and collaborated with Josch Hambsch, Ivan Curtis, and TG Tan to track the rise and decline of that event (see https://edocs.uis.edu/jmart5/www/barber/SN2009ip.html). We were able to track the decline in brightness better than any other Type-IIn light curve. This detailed tracking revealed bumps and fluctuations in the decline that are detailed in a manuscript submitted to the Astronomical Journal (http://arxiv.org/abs/1308.3682). Other well-sampled Type II-n light curves are smooth without any structure of this magnitude (see Kiewe et a l. 2012 and Taddia et al. 2013).

Type-IIn supernovae are defined by the narrow Balmer emission lines their spectra. It is theorized that these narrow emission lines are produced when the shockwave from the supernovae interacts with material in the circumstellar environment around the progenitor. But there is also accumulating evidence that events with this type of spectra may not all be of the same type. Some suspect that a subset, if not all Type-IIn are actually supernova impostors, meaning that they are not terminal core-collapse explosions of massive stars but violent shell ejection events of unknown origin that may be a short evolutionary phase in the supermassive stars on their way to becoming core-collapse supernovae. The physics of supernova impostors is not understood mainly due to insufficient observational data.

I have been tracking a number of Type-IIn supernovae as part of an NSF collaborative grant (http://www.nsf.gov/awardsearch/showAward.do?AwardNumber=1108890) designed to dramatically increase the sample of identified and observed supernova impostors. SN 2013cj has shown some variability of the type observed in the outburst of 2009ip which many believe was an impostor event, and NOT a terminal core-collaspe. Over the last 40 days, the V light curve of 2013cj has declined from 17.2 to 17.4 with at least one “bump” of about 0.1 magnitude over several days in that decline. Working on my own, I have not been able to observe it with enough detail to tell for certain. The accumulated SWIFT data shows some indication of these bumps also (http://people.physics.tamu.edu/pbrown/SwiftSN/SN2013cj_lightcurve.jpg). The number of observations for this object on VS-Net has been low and not useful for confirming what I have observed. I need more data to confirm this discovery.

I propose to use the SRO 0.5m to take V and R images of SN 2013cj with a cadence of at least once every three days. (Other AAVSO-net telescopes are probably too small to ensure good throughput.) SRO is comparable in size to the 20-inch I am currently using. I am unclear from the SRO webpage if the throughput on the CCD camera is sufficient to do between 17th and 18th magnitude. I am assuming that this will take exposures of at least 600 seconds to get good S/N. The field on SRO should be wide enough to include all of the eight comparison stars I have identified in the field. I can provide a finding chart and recent images of the field if needed. SN 2013 cj is currently transiting at about the time of dusk and I would like to follow it until SRO is unable to observe it due to small sun angle.

I intend to use this data to supplement the data I will gather with the 20-inch at the UIS Barber Observatory. If SRO confirms the fluctuations in the decline of SN 2013cj, this could be the second Type-IIn with this type of light curve. That could represent the discovery of a sub-class for this type of supernova that may be related to supernova impostors.

Please let me know if you would like any additional information or graphs showing the data I have gathered on SN 2013ch so far.