Scientists Observe Year-long Plateaus in Decline of Type Ia Supernova Light Curves
Quote:
Originally Posted by Harvard & Smithsonian Center for Astrophysics, Monday, October 7, 2019
Cambridge, MA -
Scientists at the Center for Astrophysics | Harvard & Smithsonian have announced the discovery that, contrary to previously accepted knowledge, Type Ia supernovae experience light curve decline plateaus, and lengthy ones at that, lasting up to a year.
CfA scientist Or Graur first noticed strange light curve behaviors while studying late-time Type Ia supernovae in 2015, and this year confirmed light curve plateaus in Type Ia supernovae. "Most supernova research is conducted in the weeks or months immediately following an explosion, but we wanted to see how light curves behave at late times, around 500 to 1000 days after explosion," said Graur. "Optical observations of SN2012gc in 2015 revealed a slowdown in the light curve as expected, but as we studied additional supernovae over time, it became apparent that other mechanisms were at play, so we started looking for patterns to explain what was going on."
To better understand the strange behavior, Graur teamed up with Adam Riess of The Johns Hopkins University and the Space Telescope Science Institute, and 2011 winner of the Nobel Prize in Physics, to study nearby supernovae using Riess's already-set HST programs. "Even though these were all nearby supernovae, at these late times they were very faint. We needed Hubble's resolving power to be able to tell them apart from other stars in their respective galaxies," said Graur. "But what made the difference to our observations was that Adam's programs on Hubble also had near-infrared data in the H-band. What started as a fishing expedition revealed a portion of time where the light curve is flat, and that period lasts for up to a year. That was a surprise. I didn't expect to see that."
The idea of supernova light curve plateaus is not new to cosmology. Type IIP supernovae, which are born of the collapse and explosion of hydrogen-rich red super giants, commonly experience light curve plateaus roughly 100 days in length. Until the discovery of the Type Ia supernova light curve plateau, 100 days was considered a long-period plateau. Type Ia supernova light curve plateaus begin at between 150 and 500 days after explosion, and last approximately 350 days, or nearly a year.
"Up until this moment, the only plateaus seen in any type of supernova were in Type IIP, and they were relatively short compared to what we're seeing in our observations. This is only the second time we've ever seen a plateau like this in a supernova," said Graur. "What we’re seeing is in stark contrast to what we’ve always believed about Type Ia supernovae and it's going to impact the way we apply Type Ia light curves to cosmological models in the future."
The results of the study are published in Nature Astronomy. In addition to Graur—who also serves as a Research Associate at the American Museum of Natural History—and Riess, the study involved CfA scientist Arturo Avelino along with scientists Kate Maguire, Trinity College Dublin; Russell Ryan, Space Telescope Science Institute; Matt Nicholl, University of Edinburgh; Luke Shingles, Queens University Belfast; Ivo R. Seitenzahl, University of New South Wales Canberra; and, Robert Fisher, University of Massachusetts Dartmouth.
The supernova mentioned in the article (SN2012gc) was discovered by Greg Bock and was the 47th discovery for the BOSS team, discovery image below. The initial classification was a type II so something has changed along the way.
Goes to show (yet again) that amateurs like you and I can and do have an impact on the science of Astronomy and this may indeed come many years after the initial discovery.
Kudos indeed to Greg Bock!
Thanks for the follow-up which is very much appreciated.
In fact when I first read the press release I had you and the BOSS team
in mind with the decision of re-posting it.
So it is absolutely wonderful to hear that the cited object was one that
Greg had discovered! That's fantastic!
Having said that, between you all having done such a splendid job
in discovering so many, perhaps statistically it shouldn't come as a
surprise at all.
It was the second last paragraph in the press release that really caught
my attention when they said, "What we’re seeing is in stark contrast to
what we’ve always believed about Type Ia supernovae and it's going to
impact the way we apply Type Ia light curves to cosmological models in
the future."
I am not sure if this is implying the discovery has slightly ruffled how
Type Ia's were being used as standard candles? As I understand it,
their peak luminosity was used for that metric, so perhaps you understand
better what the implications of the plateauing is in that regard?
Thanks for the follow-up which is very much appreciated.
In fact when I first read the press release I had you and the BOSS team
in mind with the decision of re-posting it.
So it is absolutely wonderful to hear that the cited object was one that
Greg had discovered! That's fantastic!
Having said that, between you all having done such a splendid job
in discovering so many, perhaps statistically it shouldn't come as a
surprise at all.
It was the second last paragraph in the press release that really caught
my attention when they said, "What we’re seeing is in stark contrast to
what we’ve always believed about Type Ia supernovae and it's going to
impact the way we apply Type Ia light curves to cosmological models in
the future."
I am not sure if this is implying the discovery has slightly ruffled how
Type Ia's were being used as standard candles? As I understand it,
their peak luminosity was used for that metric, so perhaps you understand
better what the implications of the plateauing is in that regard?
Hi Gary,I just mentioned the same thing to Greg on FB what it might mean to the cosmological distance model.
Well done to Greg and all the team,just shows that amateurs can and do contribute to Science and Astronomy.
Cheers
Hmmm, a bit of detective work from Greg and I found that the actual science paper that refers to this research notes that the Supernova was infact SN2012cg discovered by LOSS ([Discoverer=Kandrashoff, Cenko et al. (LOSS) ). The original Harvard Smithsonian Center for Astrophysics press release had a typo noting SN2012gc. We have informed Harvard and as you will now see in Gary's link above this has now been corrected.
No cigar for Greg/BOSS on this one, but we did our bit in making sure the correct credit was acknowledged where due.
Again thanks to Gary for posting as it indeed shows there is still much science is finding out about Supernova.
Hmmm, a bit of detective work from Greg and I found that the actual science paper that refers to this research notes that the Supernova was infact SN2012cg discovered by LOSS ([Discoverer=Kandrashoff, Cenko et al. (LOSS) ). The original Harvard Smithsonian Center for Astrophysics press release had a typo noting SN2012gc. We have informed Harvard and as you will now see in Gary's link above this has now been corrected.
No cigar for Greg/BOSS on this one, but we did our bit in making sure the correct credit was acknowledged where due.
Again thanks to Gary for posting as it indeed shows there is still much science is finding out about Supernova.
Thanks for the correction notice and though it transpires Greg didn't discover
this specific one, we know all the SN the BOSS team have discovered have
been the subject of professional scientific investigation.
Thanks also for the quote that appeared in your response on the
Standard Candle question but unfortunately got chopped when you
edited about the correction.
Perhaps the transition points as one comes off the plateaus are giving
astronomers further standard candle references. Prior to the discovery
perhaps they were reliant on just the peak intensity point.
Well, as you can imagine, I was quite surprised and disappointed to find the typo in the Harvard article once I obtained a copy of the original paper.
However, have set the record straight, Harvard have changed the reference, but there may be more articles out there that won't be changed.
So, its back to the scope for me, and try to find some more worthwhile discoveries.....
Thanks for the correction notice and though it transpires Greg didn't discover
this specific one, we know all the SN the BOSS team have discovered have
been the subject of professional scientific investigation.
Thanks also for the quote that appeared in your response on the
Standard Candle question but unfortunately got chopped when you
edited about the correction.
Perhaps the transition points as one comes off the plateaus are giving
astronomers further standard candle references. Prior to the discovery
perhaps they were reliant on just the peak intensity point.
Ooops!
Abstract
The light curves of type Ia supernovae are routinely used to constrain cosmology models. Driven by radioactive decay of 56Ni, the light curves steadily decline over time, but after 150 d post-explosion the near-infrared portion is poorly characterized. We report a year-long plateau in the near-infrared light curve at 150–500 d, followed by a second decline phase accompanied by a possible appearance of [Fe I] emission lines. This near-infrared plateau contrasts sharply with type IIP plateaux and requires a new physical mechanism. We suggest a masking of the ‘near-infrared catastrophe’—a predicted, yet unobserved, sharp light-curve decline—by scattering of ultraviolet photons to longer wavelengths. The transition off the plateau could be due to a change in the dominant ionization state of the supernova ejecta. Our results help explain the complex radiative transfer processes that take place in type Ia supernovae and enhance their use as ‘standard candles’.
