Insights into Supernova 2021gmj: A Low Luminosity Event

Supernovae are massive explosions that occur at the end of a star's life cycle. Supernova 2021gmj is a type II supernova discovered shortly after it exploded. This supernova is classified as low luminosity, meaning it is not as bright as many others. This article details the observations and features of SN 2021gmj, shedding light on its characteristics and significance.

#Discovery and Initial Observations

SN 2021gmj was discovered on March 20, 2021, in the galaxy NGC 3310, just one day after the explosion. This quick detection allowed for thorough monitoring right from the start. When it was first spotted, SN 2021gmj had an apparent brightness of 15.98 magnitudes. Initial follow-up observations captured its brightness fluctuations, revealing a peak brightness of 15.45 magnitudes.

Due to its low luminosity classification, SN 2021gmj reached its peak brightness more slowly compared to other supernovae, taking about 8.4 days to rise to maximum brightness. Following this peak, it plateaued for around 100 days, slowly fading in brightness.

#Characteristics of SN 2021gmj

#Light Curve Analysis

A light curve represents the brightness of an astronomical object over time. The light curve of SN 2021gmj shows a slow decline in brightness during its plateau phase. This is characteristic of low luminosity supernovae, indicating that they release energy more gradually than their more luminous counterparts. The eventual drop in brightness by two magnitudes signifies the transition from the plateau phase into the radioactive decay phase, where the light output is primarily driven by radioactive elements formed during the explosion.

#Circumstellar Material

Circumstellar material (CSM) refers to the gas and dust surrounding a star before it goes supernova. Observations of SN 2021gmj suggest the presence of CSM. Early light curves and spectra displayed features indicative of this material, implying that the rapid brightness rise may have been influenced by interactions between the supernova's ejecta and the local environment.

The inferred low CSM mass, determined through hydrodynamic modeling, aligns with the spectral observations that hint at the interaction between the SN ejecta and the surrounding material.

#Spectral Features

Spectroscopy allows scientists to study the different elements present in a supernova by examining the light emitted. The early spectra of SN 2021gmj show evidence of high-velocity hydrogen, which may indicate an interaction with the CSM. A notable spectral feature near 4600 angstroms could be linked to high ionization lines from elements such as carbon or nitrogen. This finding is significant as it indicates that similar spectral features may be common in other low luminosity supernovae.

#Host Galaxy: NGC 3310

SN 2021gmj is located in the galaxy NGC 3310, a starburst galaxy characterized by intense star formation. This galaxy features an unusual morphology, showing structures that indicate past interactions and mergers with other galaxies, leading to the current starburst activity.

Studies of the host galaxy's composition suggest that it contains regions with lower metallicity, which affects the characteristics of stars that form within it. This metallicity plays a role in the properties and evolution of supernova progenitors.

#Distance Measurement

Accurate distance measurement is crucial for understanding the properties of supernovae. For SN 2021gmj, researchers applied a method called the expanding photosphere method (EPM). This technique estimates distance based on the brightness and apparent size of the expanding photosphere of the supernova. This method derived a distance consistent with previous measurements for the host galaxy, NGC 3310.

#Progenitor Star Characteristics

The progenitor star of a supernova is the massive star that exploded. Two potential scenarios for the progenitor of SN 2021gmj were considered based on its characteristics. One scenario involves a high mass star that collapses to form a black hole, while another suggests a lower mass red supergiant star.

Studies of progenitors generally indicate that low luminosity supernovae like SN 2021gmj often come from stars with lower masses, typically between 8 to 12 solar masses. Observations of SN 2021gmj align with this conclusion, supporting the idea that its progenitor star was a red supergiant.

#Late Phase Observations

As the supernova fades into its later phases, the optical spectra evolve significantly. The early blue continuum seen in the first observations gradually transforms into a redder spectrum over time. This shift signifies the cooling and expansion of the ejecta.

By about 50 days after the explosion, the spectrum reveals emission lines from heavier elements, including iron. The evolution of these lines provides insight into the physical processes occurring in the ejecta and offers a means to estimate the progenitor's mass and the energy released during the explosion.

#Nickel Mass Calculation

The radioactive decay of nickel plays a critical role in powering the light curves of supernovae in their late phases. For SN 2021gmj, the nickel mass was calculated by constructing a pseudo-bolometric light curve based on photometric data collected after maximum brightness.

The nickel mass obtained falls within the expected range for low luminosity supernovae, supporting the idea that SN 2021gmj did not produce a significant amount of nickel compared to more energetic events.

#Comparison with Other Supernovae

When comparing SN 2021gmj with other supernovae, it becomes clear that it shares many characteristics with other low luminosity type II supernovae. Its light curve shape, expansion velocities, and spectral features correspond with those of other similar events. This reinforces the classification of SN 2021gmj as a low luminosity supernova and helps to build an understanding of this class of stellar explosions.

#Conclusion

The observations of SN 2021gmj provide valuable insights into low luminosity type II supernovae. The rapid rise to brightness, evidence of circumstellar material, and the spectral features observed early on all contribute to a deeper understanding of the processes at play. Observations from the host galaxy indicate a connection between the supernova and its environment, demonstrating how surrounding material can influence the properties of stellar explosions.

This supernova illustrates the diversity of supernova phenomena and how low luminosity events can reveal essential details about massive stars and their end stages. Further studies on SN 2021gmj and similar events will undoubtedly enhance our knowledge of the life cycles of stars and the dramatic processes that unfold during their final moments.