Researchers capture the fastest optical flash emitted from a newborn
supernova

Date:
December 9, 2021
Source:
Kavli Institute for the Physics and Mathematics of the Universe
Summary:
A team of astronomers has discovered the fastest optical flash of
a Type Ia supernova.



FULL STORY ==========================================================================
A team of astronomers has discovered the fastest optical flash of a Type
Ia supernova, and reports a study in the Astrophysical Journal Letters published on December 8.


==========================================================================
Many stars end their lives through a spectacular explosion. Most massive
stars will explode as a supernova. Though a white dwarf star is the
remnant of an intermediate mass star like our Sun, it can explode if the
star is part of a close binary star system, where two stars orbit around
each other. This type of supernovae is classified as Type Ia supernovae.

Because of the uniform and extremely high brightness of the Type
Ia supernova, which is about 5 billion times brighter than our Sun,
they are widely used by researchers as a standard candle for distance measurements in astronomy. As the most successful example Type Ia
supernovae helped researchers discover the accelerating expansion of
our universe. But despite the great success of the Type Ia supernova
cosmology, researchers are still puzzled by basic questions such as
what the progenitor systems of Type Ia supernovae are, and how Type Ia supernova explosions are ignited.

To figure out these long-standing issues, a team of astronomers, led
by Kavli Institute for the Physics and Mathematics of the Universe
(Kavli IPMU) Project Researcher Ji-an Jiang, attempted to catch Type
Ia supernovae within one day of their explosions, called early-phase
Type Ia supernovae, using new-generation wide-field survey facilities, including the Tomo-e Gozen camera, the first wide-field mosaic CMOS
sensor imager in the world.

By regularly checking early-phase supernova candidates discovered by
the Tomo- e transient survey, one transient, Tomo-e202004aaelb, caught
Jiang's attention.

"Tomo-e202004aaelb was discovered with high brightness on April 21
in 2020.

Surprisingly, its brightness showed significant variation in the next two
days and then behaved like a normal early-phase Type Ia supernova. We
have discovered several early-phase Type Ia supernovae that show
interesting excess emission in the first few days of their explosions
but have never seen such a fast and prominent early emission in optical wavelengths. Thanks to the high- cadence survey mode and the excellent performance of Tomo-e Gozen, we can perfectly catch this amazing feature
for the first time. Such a prompt early flash should originate from a
different origin compared to previously dis covered early-excess Type
Ia supernovae," said Jiang.



========================================================================== Computational simulations by Kyoto University Associate Professor Keiichi
Maeda showed that the origin of the mysterious fast optical flash can be explained by the energy released from an interaction between supernova
ejecta and a dense and confined circumstellar material (CSM) soon after
the supernova explosion.

"We have not seen such a short and bright flash from Type Ia supernovae
before, even with a recently increasing number of very early discoveries
soon after the supernova explosion in the last few years, including those discovered by our team. The nature of the CSM must reflect the nature
of the progenitor star, and thus this is a key to understanding what
kind of a star explodes and how they do so. A question is what makes
this supernova so special," said Maeda.

Through spectroscopic observations by the Seimei telescope of Kyoto
University, the team found that the SN is a variant of brightest Type
Ia supernovae.

"At the first look of the spectrum taken just after the initial flash,
it stood out as something different from normal supernovae. We noticed
that a brightest class of Type Ia supernovae might look like this one
if they would be observed in such an early phase. Our classification
was subsequently confirmed as the spectra evolve to look more and more
similar to the previously found bright Type Ia supernovae," said Kyoto University Project Researcher Miho Kawabata.

The team's result shows at least a fraction of Type Ia supernovae
originate from a dense CSM environment, which provides a stringent
constraint on the progenitor system of these spectacular phenomena in our universe. Given that Tomo-e202004aaelb (SN 2020hvf) is much brighter than typical Type Ia supernovae used as the distance indicator, the discovery
will enable Jiang and his collaborators to test various theories which
have been proposed for these peculiar overluminous Type Ia supernovae.

"Previously, we have constructed theoretical models of
super-Chandrasekhar-mass rotating white dwarfs and their explosions. Such massive models can be consistent with the peak brightness of SN
2020hvf, but more theoretical work is necessary to explain the detailed observational properties. SN 2020hvf has provided a wonderful opportunity
of collaboration between the theory and observations." said Kavli IPMU
Senior Scientist Ken'ichi Nomoto.

Jiang's team will continue looking for the answer of the long-standing
origin issue of Type Ia supernovae by carrying out transient surveys
with telescopes all over the world.

"We have used Type Ia supernovae to measure the expansion of the universe, although their origins are not well understood. The early-phase photometry
of Type Ia supernovae provides unique information to understand their
origins, and hence, should contribute to more accurate measurements of
the expansion of the universe in near future," said Kavli IPMU Senior
Scientist and University of Tokyo Professor Mamoru Doi.

Details of this study were published in the Astrophysical Journal Letters
on Dec 8, 2021.

========================================================================== Story Source: Materials provided by Kavli_Institute_for_the_Physics_and_Mathematics_of_the Universe. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Ji-an Jiang, Keiichi Maeda, Miho Kawabata, Mamoru Doi, Toshikazu
Shigeyama, Masaomi Tanaka, Nozomu Tominaga, Ken'ichi Nomoto,
Yuu Niino, Shigeyuki Sako, Ryou Ohsawa, Malte Schramm, Masayuki
Yamanaka, Naoto Kobayashi, Hidenori Takahashi, Tatsuya Nakaoka, Koji
S. Kawabata, Keisuke Isogai, Tsutomu Aoki, Sohei Kondo, Yuki Mori,
Ko Arimatsu, Toshihiro Kasuga, Shin-ichiro Okumura, Seitaro Urakawa,
Daniel E. Reichart, Kenta Taguchi, Noriaki Arima, Jin Beniyama,
Kohki Uno, Taisei Hamada. Discovery of the Fastest Early Optical
Emission from Overluminous SN Ia 2020hvf: A Thermonuclear Explosion
within a Dense Circumstellar Environment. The Astrophysical Journal
Letters, 2021; 923 (1): L8 DOI: 10.3847/2041-8213/ ac375f ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/12/211209095621.htm

--- up 5 days, 7 hours, 13 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)