Astronomers discover kilonova associated with nearby gamma-ray burst

(ORDO NEWS) — An international team of astronomers has discovered a new kilonova associated with a gamma-ray burst (GRB), known as GRB 211211A. The discovery, reported in an article published April 22 on arXiv, could improve our understanding of the origin and nature of the still enigmatic gamma-ray bursts.

Kilons (also known as r-process supernovae) are events that occur when two compact objects, such as neutron stars, collide.

They are thought to emit short gamma-ray bursts and strong electromagnetic radiation due to the radioactive decay of heavy r-process nuclei. To date, kilonovae are the only observed source of r-process nucleosynthesis in the Universe and are possibly responsible for the formation of most elements heavier than iron.

GRB 211211A was identified on December 21, 2021 by the Burst Alert Telescope (BAT) aboard NASA‘s Swift spacecraft at a distance of about 1.14 billion light-years.

It lasted approximately 51.37 seconds, and its spectral parameters turned out to be close to the average value of the gamma-ray burst. The light curve of this burst consists of several overlapping pulses showing little spectral evolution.

A team of researchers led by Gillian Rastinjad of Northwestern University in Evanston conducted a multi-wavelength observational campaign for GRB 211211A to shed more light on its nature. To do this, they used instruments such as the Northern Optical Telescope (NOT), the Calar Alto Observatory, and the Karl Jansky Very Large Array (VLA).

Optical imaging of this event revealed an unrecorded source rapidly fading away during the first three days after the outbreak.

Further K-band observations with the Gemini-North telescope revealed a source with a K-band luminosity of 22.4 mag, indicating a strong infrared excess over the optical afterglow light curve. After that, according to the results of the NOT survey, carried out 17 days after the outbreak, an associated supernova (SN) was discovered.

The results obtained suggest that this SN is indeed a kilonova. The researchers found that the proposed merger ejected about 0.04 solar masses of r-process-rich material. This corresponds to the merger of two neutron stars with masses close to 1.4 solar masses.

“If we assume that the parent binary is composed of two neutron stars and use merger simulation predictions to constrain the relative masses and velocities of the components, we get a good match with a 1.4+1.3 solar mass binary producing ≈ 0.02 solar ejection masses, although matching the luminosity on the first day may require additional heating by the GRB jet during the flare’s one-minute period,” the astronomers explained.

According to the authors of the article, the detection of a kilonova after a long gamma-ray burst means that the current rates of neutron star mergers, calculated from short gamma-ray bursts, may underestimate the true number of such objects.

They suggest that mergers associated with long-duration gamma-ray bursts can make a significant contribution to the merger rate of compact objects.

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