Fast radio burst

A fast radio burst (FRB) is a high-energy astrophysical phenomenon manifested as a transient radio pulse lasting only a few milliseconds. These are bright, unresolved, broadband, millisecond flashes found in parts of the sky outside the Milky Way. Each burst is delayed by different amounts of time, depending on the wavelength. This delay is described by a value referred to as a dispersion measure. Fast radio bursts have dispersion measures which are: much larger than expected for a source inside the Milky Way; and consistent with propagation through an ionized plasma.

The origin of fast radio bursts is not known. It is conjectured to be extragalactic because of the anomalously high value of pulse dispersion observed. Some have speculated that these signals might be signs of extraterrestrial intelligence.

Fast radio bursts are named by the date the signal was recorded, as "YYMMDD" . For example, one on 26 June 2011 would be called FRB 110626. The first FRB found was FRB 010621. On 19 January 2015, astronomers at Australia's national science agency (CSIRO) reported from Parkes that a fast radio burst had been observed for the first time live.

Lorimer Burst

The Lorimer Burst was discovered in archived data taken in 2001 by the Parkes radio dish in Australia. Analysis of the survey data found a 30-jansky dispersed burst which occurred on 24 August 2001, less than 5 milliseconds in duration, located 3° from the Small Magellanic Cloud. The reported burst properties argue against a physical association with the Milky Way galaxy or the Small Magellanic Cloud. The burst became known as the Lorimer Burst. The discoverers argue that current models for the free electron content in the universe imply that the burst is less than 1 gigaparsec distant. The fact that no further bursts were seen in 90 hours of additional observations implies that it was a singular event such as a supernova or merger of relativistic objects. It is suggested that hundreds of similar events could occur every day and, if detected, could serve as cosmological probes.

Further developments

In 2010 there was a new report of 16 similar pulses: clearly of terrestrial origin; detected by the Parkes radio telescope; and given the name perytons. In 2015 perytons were shown to be generated when microwave oven doors were suddenly opened during a heating cycle, with emission generated by the magnetron.

An observation in 2012 of a fast radio burst (FRB 121102) in the direction of Auriga in the northern hemisphere using the Arecibo radio telescope confirmed the extragalactic origin of fast radio pulses by an effect known as plasma dispersion. Victoria Kaspi of the McGill University estimates that as many as 10,000 fast radio bursts may occur per day over the entire sky.

In 2013 four bursts were identified that supported the likelihood of extragalactic sources.

FRB 140514, caught 'live', was found to be 21% (+/- 7%) circularly polarised.

Fast radio bursts discovered up until 2015 had dispersion measures that were close to multiples of 187.5 cm⁻³ pc. However subsequent observations do not fit this pattern.

In 2015, FRB 110523 was discovered in archival data from the Green Bank Telescope. It was the first FRB for which linear polarization was detected (allowing, with the detection of circular polarisation, a calculation of Faraday rotation). Measurement of the signal's dispersion delay suggested that this burst is of extragalactic origin, possibly up to 6 billion light years away.

The upcoming and unusual Canadian radio telescope called CHIME will also be used to detect "hundreds" of fast radio bursts as its secondary objective.

FRB 150418

On 18 April 2015, FRB 150418 was detected by the Parkes observatory and within hours, several telescopes including the Australia Telescope Compact Array caught an "afterglow" of the flash, which took six days to fade. The Subaru telescope was used to find what was thought to be the host galaxy and determine its redshift and the implied distance to the burst.

However, the origin of the burst was soon disputed, and by April 2016 it was established that the emission instead originates from an active galactic nucleus that is powered by a supermassive black hole with dual jets blasting outward from the black hole. It was also noted that what was thought to be an "afterglow", never goes away, meaning that it cannot be associated with the fast radio burst.

FRB 121102

In November 2015, astronomer Paul Scholz at McGill University in Canada, found ten non-periodically repeated fast radio pulses in archival data gathered in May and June 2015 by the Arecibo radio telescope. The ten bursts have dispersion measures and sky positions consistent with the original burst FRB 121102, detected in 2012. Like the 2012 burst, the 10 bursts have three times the maximum plasma dispersion measure from a source in the Milky Way Galaxy. According to the Canadian team, the data support "an origin in a young, highly magnetized, extragalactic neutron star."

Hypotheses

Because of the isolated nature of the observed phenomenon, the nature of the source remains speculative. As of 2016, there is no generally accepted explanation. The emission region is estimated to be no larger than a few hundred kilometers. If the bursts come from cosmological distances, their sources must be very bright. One possible explanation would be a collision between very dense objects like collapsing black holes or neutron stars. Blitzars are another proposed explanation. It has been suggested that there is a connection to gamma-ray bursts.

In 2007, just after the publication of the e-print with the first discovery, it was proposed that fast radio bursts could be related to hyperflares of magnetars. In 2015 three studies supported the magnetar hypothesis. It has also been proposed that if fast radio bursts originate in black hole explosions, FRBs would be the first detection of quantum gravity effects.

List of bursts

name	date-time UTC for 1581.804688 MHz	RA J2000	dec J2000	DM cm−3pc	width ms	peak flux Jy	notes
FRB 010724	2001/07/24 19:50:01.63	01h18′	-75°12′	375	4.6	30	"Lorimer Burst"
FRB 010621	2001/06/21 13:02:10.795	18h52′	-08°29′	746	7.8	0.4
FRB 110220	2011/02/20 01:55:48.957	22h34′	-12°24′	944.38	5.6	1.3
FRB 110627	2011/06/27 21:33:17.474	21h03′	-44°44′	723.0	<1.4	0.4
FRB 110703	2011/07/03 18:59:40.591	23h30′	-02°52′	1103.6	<4.3	0.5
FRB 120127	2012/01/27 08:11:21.723	23h15′	-18°25′	553.3	<1.1	0.5
FRB 011025	2001/10/25 00:29:13.23	19h07′	-40°37′	790	9.4	0.3
FRB 121002	2012/10/02 13:09:18.402	18h14′	-85°11′	1628.76	2.1; 3.7	0.35	double pulse 5.1 ms apart
FRB 121002	2012/10/02 13:09:18.50	18h14'	-85°11'	1629.18	<0.3	>2.3
FRB 121102	2012/11/02 06:35:53.244	05h32′	33°05'	557	3.0	0.4	by Arecibo radio telescope
	2015	05h32′~	33°05'~	557~			10 repeat bursts: 6 bursts in 10 minutes, 3 bursts weeks apart.
FRB 131104	2013/11/04 18:04:01.2	06h44′	-51°17′	779.0	<0.64	1.12	'near' Carina Dwarf Spheroidal Galaxy
FRB 140514	2014/05/14 17:14:11.06	22h34′	-12°18′	562.7	2.8	0.47	21 ± 7 per cent (3σ) circular polarization
FRB 090625	2009/06/25 21:53:52.85	03h07'	-29°55′	899.6	<1.9	>2.2
FRB 130626	2013/06/26 14:56:00.06	16h27'	-07°27'	952.4	<0.12	>1.5
FRB 130628	2013/06/28 03:58:00.02	09h03'	+03°26'	469.88	<0.05	>1.2
FRB 130729	2013/07/29 09:01:52.64	13h41'	-05°59'	861	<4	>3.5
FRB 110523	2011/05/23	21h45'	-00°12'	623.30	1.73	0.6	700-900 MHz at Green Bank radio telescope, detection of both circular and linear polarization.
FRB 150418	2015/04/18 04h29'	07h16'	−19° 00′	776.2	0.8	2.4	Detection of linear polarization. The origin of the burst is disputed.