Masers

TL;DR

This paper provides an overview of astrophysical masers, detailing their sources, molecular emissions, and distinctive properties such as high brightness, narrow lines, polarization, and variability across various cosmic environments.

Contribution

It offers a comprehensive summary of the types, origins, and characteristics of astrophysical masers, highlighting recent observations and their significance in astrophysics.

Findings

Masers are observed in diverse cosmic environments.

They emit from various molecules like H2O, OH, and CH3OH.

Masers exhibit high brightness, narrow spectral lines, and polarization.

Abstract

An astrophysical MASER (Microwave Amplification by Stimulated Emission of Radiation) is a source of stimulated spectral line emission. Maser emission is observed from the circumstellar envelopes of evolved stars, molecular clouds/star-forming regions, active galactic nuclei, supernova remnants, comets, and the Saturnian moons. It arises from molecules such as water (H2O), hydroxyl radicals (OH), methanol (CH3OH), formaldehyde (CH2O), silicon monoxide (SiO), ammonia (NH3), silicon sulphide (SiS), hydrogen cyanide (HCN), and from atomic hydrogen recombination lines. Masers are compact, of high brightness temperature, and often display narrow spectral line widths, polarized emission and variability. Free electron-cyclotron astrophysical masers additionally exist.