Astronomers Discover a Double Take of Exploding Stars in a Distant Galaxy
By: Stu Parker
As stories go the Supernova in NGC6984 has a really good blend of amateur and professional involvement and just goes to show the value of amateur discoveries and a quick response by professionals to get real science done.
When I first saw the new possible supernova in NGC6984 I ignored it as I knew there had been a previous SN in that galaxy (SN2012im) in the past and thought that it was just the same one that was still visible. After a few minutes of thinking it over I went back to the image and blinked it against the previous discovery and sure enough it was right on top. But this seemed strange as I looked at the date of sn2012im and it was nearly a year to the day that the last one had been found. This is not normal and it was not visible in the previous image of only a week previous. After talking it over with the BOSS guys and doing all the normal background checks I decided to send an alert out to the professional astronomers who do the spectra for us. Eric Hsiao at Carnegie Observatories was the first to contact me back. He informed me that this may be an important event and thought it may be a good idea to release an Atel to inform the wider professional community so they had the information as soon as possible. With his help we released Atel #5225.The Boss group had never released our own Atel before and this alone was a pretty big deal for us.
Here is the Atel:
ATel #5225; Stu Parker, Greg Bock, Peter Marples, Colin Drescher, Patrick Pearl, Brendan Downs, and the BOSS team
Distributed as an Instant Email Notice Supernovae
Credential Certification: Eric Hsiao
We report a new supernova candidate in NGC 6984. TOCP Designation: PSN J20575390-5152245 Observation Date: 2013 07 24.457 J2000 Position: 20 57 53.90 -51 52 24.5 Magnitude: 16.9 U Offset (arcsec): 1W 10S Locale: NGC 6984 It was detected at mag 16.9 on two 30 second imagestaken on the same night, July 24.457, 2013. Nothing was visible on the previous image taken on July 13.552, 2013 and 15 images taken during the past year down to mag 19. Another supernova, PSN J20575392-5152248 (SNhunt142), was discovered one year ago very close to this position by the Catalina Real-Time Transient Survey and Stan Howerton. It was discovered on July 25.540, 2012 at the position 20 57 53.92 -51 52 24.8 at mag 17.7. It was then typed as a SN Ic around peak on August 8, 2012 by PESSTO (ATEL 4300).
Around this time Dan Milisavljevic at the Harvard-Smithsonian Center for Astrophysics (CfA) contacted me with the great news that SALT had a spectra and it was a new SN. All this in ½ a hour!!. Dan and SALT had done a lot of spectra for us in the past.This was fantastic news and to be honest a real relief as we didn’t want to release an ATel with a false alert for the professional community.
This set off a chain of events which is explained below in Dan Milisavljevic’s release which is a great summary of events. It was fantastic to be involved with this. I was lucky enough to be one of the first to see the Hubble Space Telescope raw fits files of NGC6984 and process the image,I have attached my result to date.This was pretty cool to do.
There has been a delay in releasing this as Dan and others needed to get everything ready to present these results at the 223rd annual meeting of the American Astronomical Society taking place in Washington, D.C. between January 5-9, 2014.
I make special note here of Dan Milisavljevic who got use of Director's Discretionary time on the HST.His quick thinking along with others who saw an urgent need to interrupt regular operations with the HST and to be granted time is by itself pretty amazing credit to him and his team for this fantastic effort. I was lucky enough to spend some time with Dan and Professor Robert Fesen when he asked me to be a guest at the 4 metre telescope at Kitt Peak National Observatory in October what a fantastic guy and I had a great time so here is a little bit about Dan.
“I completed my PhD studies at Dartmouth College in June 2011 and started work at the Harvard-Smithsonian center for Astrophysics in September 2011. My interests surround observational research on supernovae and supernova remnants at optical and NIR wavelengths. I focus on understanding the progenitor stars (i.e., what were they before they blew up?) and explosion mechanisms (i.e., how did they blow up?) of core-collapse events.”
Here is the release by Dan
Astronomers Discover a Double Take of Exploding Stars in a Distant Galaxy
By Dan Milisavljevic
Every couple of seconds a star explodes somewhere in the universe.These tremendously energetic events called supernovae shape the galaxies they live in and seed the cosmos with the raw materials of life. Telescopes located everywhere around the world - from remote,high altitude professional observatories to the backyards of amateur enthusiasts - find and study as many supernovae as possible. Sometimes it's possible to find two or more supernovae in random locations of the same galaxy over the course of years or decades. This past year,however, astronomers were surprised to learn that sometimes supernovae can even be found right on top of one another!
Excitement started in July 2013 when dairy farmer and amateur astronomer Stuart Parker in New Zealand discovered a new bright source in the galaxy NGC 6984. A seasoned supernova hunter with 50 discoveries under his belt who operates as part of the Backyard Observatory Supernova Search group, Parker quickly realized that his discovery was located at virtually the same position as another supernova named SN 2012im that had been found the year before.Parker immediately shared his peculiar result with postdoctoral fellow Dan Milisavljevic at the Harvard-Smithsonian Center for Astrophysics(CfA) who initiated a cascade of follow-up observations spanning the entire electromagnetic spectrum. First to respond within an hour of Parker's original dispatch was the new Southern African LargeTelescope (SALT) in South Africa. These data confirmed the reality of the supernova and it was given the name SN 2013ek by the International Astronomical Union.
Following the confirmation by SALT, the Swift satellite in space that has a suite of instruments sensitive to X-ray, optical and ultraviolet wavelengths was triggered into action by Raffaella Margutti (CfA).Eric Hsiao and Nidia Morrell of the Carnegie Supernova Project thencoordinated near-infrared and optical observations at Las Campanas Observatory, and supporting observations at radio wavelengths were arranged by Atish Kamble (CfA) with the Giant Metrewave Radio Telescope in India.
While these observations were taking place, emails zipped back and forth between inboxes around the globe as astronomers attempted to understand the nature of this "double supernova." Were the two explosions related? Or was this a chance alignment of two completely independent supernovae? Contributing to the analysis were Harvard University Professors Edo Berger, Robert Kirshner, and Alicia Soderberg, Harvard graduate students Maria Drout and Nathan Sanders, Professor Robert Fesen of Dartmouth College, and Caltech research scientist Andrew Drake who is co-PI of the Catalina Real-Time Sky Survey that enabled the discovery of the first supernova SN 2012im.Archival data on SN 2012im was easily retrieved from the "Bright Supernova" website that computer-programmer-by-day and supernova-enthusiast-by-night David Bishop manages in his free time.The website hosted many of the images of SN 2012im taken and investigated by Joseph Brimacombe and Stan Howerton that helped to pinpoint the locations of the two supernovae.
Milisavljevic believed that the rare discovery of two supernovae located so close to one another warranted a closer look with the razor sharp resolution of the Hubble Space Telescope (HST). He and collaborators applied for use of Director's Discretionary time, which meant justifying an urgent need to interrupt regular operations with HST. Their request was successful and the resulting images obtained August 2013 showed two sources in the region of Parker's discovery.One source is easily identifiable as SN 2013ek, but the other is something unknown and possibly the previous supernova SN 2012im.Though the offset between the two sources is very small, at the distance of the host galaxy NGC 6984 (approximately 200 million light years) it implies a large physical distance that makes an association between the two events nearly impossible.
Milisavljevic, who is presenting these results at the 223rd annual meeting of the American Astronomical Society taking place in Washington, D.C. between January 5-9, 2014, stresses that the nature of the second source is not certain and could easily be an unrelated nearby cluster of stars. A return visit with the Hubble Space Telescope could firmly resolve whether the second source is actuallySN 2012im. "By waiting a year to take another set of images with the Hubble Space Telescope," says Milisavljevic, "we can do a nose count to see what is left behind." If both sources fade, then this would be proof positive that the two events are unrelated and that Parker had uncovered a curious case of two closely neighboring supernovae occurring within a year of each other: Strange but not impossible. Alternatively, if both sources don’t fade, then the jury would still be out and it would remain possible that the two events SN 2012im and SN 2013ek could be related in some unknown and potentially very exciting way.
Hubble Space Telescope image of SN2013ek in NGC6984.Note the small galaxies at the bottom of the image these must be a vast distance away
Poster submitted to the annual meeting of the American Astronomical Society