The study found that SN 2017egm is a helium-rich supernova

The study found that SN 2017egm is a helium-rich supernova

Multiscale light curves for SN 2017egm from near ultraviolet to near infrared with galactic extinction correction. Credit: Zhu et al, 2023

Using several ground-based and space-based observatories, an international team of astronomers has investigated a nearby supernova called SN 2017egm. As a result, they found that the investigated explosion belonged to a rare group of superluminous supernovae rich in helium. The finding was reported in a paper published on March 6 in arXiv Prepress server.

Supernovae (SNe) are powerful, luminous stellar explosions. are important to scientific community Because they provide essential evidence for the evolution of stars and galaxies. In general, SNe are divided into two groups based on their atomic spectra: type I and type II. Type I SNe lacks hydrogen in its spectra, while type II displays hydrogen spectral lines.

SLSNe supernovae have exceptionally bright light curves and are often long-lived. The interaction of the SN projectile with the surrounding material (CSM) is an efficient mechanism for converting the kinetic energy of the projectile into radiation and it is hypothesized that such a process may operate SSLNe. As with normal SNe, SLSNe is also classified into two classes based on their spectra around the light maximum: hydrogen-poor (SLSNe-I) and eventual hydrogen-rich (SLSNe-II).

SN 2017egm (also known as Gaia17biu) is a SLSNe-I detected by the Photonic Science Alerts team of ESA’s Gaia mission on May 23, 2017, at a redshift of 0.03. that it host galaxy, NGC 3191, is massive and has a metallic core close to the Sun, unlike the typical dwarf and metal-poor host galaxies of SLSNe-I. SN 2017egm was the closest hydrogen-deficient superluminous supernova when it was detected.

Recently, a team of astronomers led by Jiazheng Zhu of the University of Science and Technology of China in Hefei, China, carried out a photometric and spectroscopic measurement of SN 2017egm in order to gain more insights into its properties.

In this paper, we present the most complete photometric and spectroscopy analysis of SN 2017egm, taking monitoring data and all public data together.”

The study found that long-range multi-scale light curves for SN 2017egm spanning about 300 days have a sharp peak, rapid decline, and many late bumps. Moreover, the SLSN spectra display strong helium lines.

Based on these findings, astronomers have classified SN 2017egm into a subclass of SLSNe-I that slowly evolves according to the luminosity and color evolution near peak brightness. Because of the presence of helium features, they also classified SN 2017egm as a superluminous helium-rich supernova (SLSN-Ib), a rare but cumulative subpopulation of SLSNe-I.

The research also found that SN 2017egm has a large excess of infrared radiation, at the 100 million solar luminosity level, which indicates dust echoes from a pre-existing dust crust or emission from newly formed dust. The paper’s authors estimate that SN 2017egm had an ejected mass of approximately 10.7 solar masses.

more information:
Jiazheng Zhu et al, SN2017egm: A luminous helium-rich supernova with multiple bumps in the light curves, arXiv (2023). doi: 10.48550/arxiv.2303.03424

Journal information:

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