reflare

A reflare is a term used in astronomy to describe a renewed increase in brightness in the light curve of a transient astronomical event after an initial bright phase or decay. It denotes a secondary flare or rebrightening episode rather than the primary peak, and can appear across multiple wavelengths, including X-ray, optical, and radio bands.

Reflares are discussed in the context of various violent astrophysical sources. They are commonly reported in gamma-ray burst afterglows, where the optical or X-ray brightness can rise again days after the burst, sometimes with little spectral change. They are also observed in active galactic nuclei with relativistic jets, such as blazars, and in X-ray binaries, where renewed emission can occur due to changes in the accretion flow or jet dynamics. The term is often used interchangeably with “rebrightening,” though reflares typically imply a distinct secondary energy release rather than a smooth continuation of the original trend.

Possible mechanisms behind reflares include delayed energy injection from slower ejecta catching up with a decelerating blast wave (refreshed shocks), variations in the ambient medium density, changes in the microphysical parameters of the shock, late-time activity of the central engine, or geometric effects related to jet structure and viewing angle. In some cases, microlensing or observational biases can mimic rebrightening.

Observationally, reflares are characterized by a temporary deviation from the overall decay, with timing ranging from hours to days or weeks after the initial event and varying degrees of chromatic or achromatic behavior. Analyzing reflares involves multiwavelength light curves, spectral energy distributions, and theoretical modeling of potential energy-release scenarios.