FRB Detection

FRBs are bright millisecond-duration radio emissions discovered in 2007 during a survey for radio pulsars — rapidly rotating neutron stars that emit beams of radio emission from their magnetic poles. The first burst was found in archival data from a 1.4 GHz survey of the Magellanic Clouds using the 64m Parkes radio telescope.

It is estimated that the average FRB releases as much energy in a millisecond as the Sun puts out in three days. While FRBs appear similar to individual pulses from pulsars, their large dispersive delays indicate they originate from far outside the Milky Way, making them many orders of magnitude more luminous. Over 600 FRBs have been detected to date.

Some FRBs repeat. The first repeating FRB, FRB121102, was identified in November 2012, disproving the cataclysmic origin models that required the destruction of the source. Spectroscopic observations of its host galaxy revealed a low-metallicity, star-forming dwarf galaxy at redshift z = 0.193, confirming the extragalactic origin.

The origins of FRBs remain unknown. Numerous theoretical models have been proposed, driven by observations from radio observatories including Parkes, Green Bank Telescope, Arecibo, ASKAP, CHIME, FAST, and STARE2. Current leading candidates include magnetars, neutron star mergers, and giant pulses from exotic rotating sources.

Beyond the intrinsic astrophysics, FRBs are a promising probe of the intergalactic medium. The dispersion measure — the delay in arrival time as a function of radio frequency — encodes information about electron density along the line of sight, potentially allowing FRBs to be used to measure the distribution of baryonic matter in the universe.

The implied all-sky event rate is high: a detectable FRB occurs somewhere in the sky approximately every minute. The limiting factor has been the narrow field of view of radio telescopes.

The research project at TIFR's Department of Astronomy and Astrophysics used the Schechter luminosity function to model the distribution of FRB luminosities and estimate detection rates for radio telescope arrays of varying design.

The Schechter function — originally developed to describe the luminosity distribution of galaxies — provides a parametric model where the number density of sources as a function of luminosity follows a power law with an exponential cutoff at the bright end. Applied to FRBs, it lets us predict how many bursts above a given flux threshold a telescope with a given sensitivity should detect per unit time.

The project optimised the field-of-view versus sensitivity trade-off for radio telescope array design. Increasing the field of view increases the sky volume monitored, capturing more FRBs, but at the cost of per-beam sensitivity. The Schechter model provided the framework for quantifying this trade-off and identifying the optimal aperture and array configuration for maximising detection rates of high-energy events.