Fast radio bursts are millisecond-duration, extragalactic radio flashes of unknown physical origin. The only known repeating fast radio burst source-FRB 121102-has been localized to a star-forming region in a dwarf galaxy at redshift 0.193 and is spatially coincident with a compact, persistent radio source. The origin of the bursts, the nature of the persistent source and the properties of the local environment are still unclear. Here we report observations of FRB 121102 that show almost 100 per cent linearly polarized emission at a very high and variable Faraday rotation measure in the source frame (varying from +1.46 × 10⁵ radians per square metre to +1.33 × 10⁵ radians per square metre at epochs separated by seven months) and narrow (below 30 microseconds) temporal structure. The large and variable rotation measure demonstrates that FRB 121102 is in an extreme and dynamic magneto-ionic environment, and the short durations of the bursts suggest a neutron star origin. Such large rotation measures have hitherto been observed only in the vicinities of massive black holes (larger than about 10,000 solar masses). Indeed, the properties of the persistent radio source are compatible with those of a low-luminosity, accreting massive black hole. The bursts may therefore come from a neutron star in such an environment or could be explained by other models, such as a highly magnetized wind nebula or supernova remnant surrounding a young neutron star. Scholz, A. P. V. Siemion, S. P. Tendulkar, P. Van Rooy, R. S. Wharton, D. Whitlow Show 14 more Show less * Corresponding author for this work Astronomy Research output : Contribution to journal › Article › Academic › peer-review 461 Citations (Scopus) 461 Downloads (Pure) Abstract Fast radio bursts are millisecond-duration, extragalactic radio flashes of unknown physical origin(1-3). The only known repeating fast radio burst source(4-6)-FRB 121102-has been localized to a star-forming region in a dwarf galaxy(7-9) at redshift 0.193 and is spatially coincident with a compact, persistent radio source(7,10). An extreme magneto-ionic environment associated with the fast radio burst source FRB 121102 . Nature , 553 (7687), 182-185. https://doi.org/10.1038/nature25149 Michilli, D. ; Seymour, A. ; Hessels, J. W. T. et al. / An extreme magneto-ionic environment associated with the fast radio burst source FRB 121102 . In: Nature . 2018 ; Vol. 553, No. 7687. pp. The only known repeating fast radio burst source(4-6)-FRB 121102-has been localized to a star-forming region in a dwarf galaxy(7-9) at redshift 0.193 and is spatially coincident with a compact, persistent radio source(7,10). The origin of the bursts, the nature of the persistent source and the properties of the local environment are still unclear. Whitlow", year = "2018", month = jan, day = "11", doi = "10.1038/nature25149", language = "English", volume = "553", pages = "182--185", journal = "Nature", issn = "0028-0836", publisher = "Nature Publishing Group", number = "7687", } Michilli, D, Seymour, A, Hessels, JWT, Spitler, LG, Gajjar, V, Archibald, AM, Bower, GC, Chatterjee, S, Cordes, JM, Gourdji, K, Heald, GH, Kaspi, VM, Law, CJ, Sobey, C , Adams, EAK , Bassa, CG, Bogdanov, S, Brinkman, C, Demorest, P, Fernandez, F, Hellbourg, G, Lazio, TJW, Lynch, RS, Maddox, N, Marcote, B, McLaughlin, MA, Paragi, Z, Ransom, SM, Scholz, P, Siemion, APV, Tendulkar, SP, Van Rooy, P, Wharton, RS & Whitlow, D 2018, ' An extreme magneto-ionic environment associated with the fast radio burst source FRB 121102 ', Nature , vol. AU - Sobey, C. AU - Adams, E. A. K. AU - Bassa, C. G. AU - Bogdanov, S. AU - Brinkman, C. AU - Demorest, P. AU - Fernandez, F. AU - Hellbourg, G. AU - Lazio, T. J. W. AU - Lynch, R. S. AU - Maddox, N. AU - Marcote, B. AU - McLaughlin, M. A. AU - Paragi, Z. AU - Ransom, S. M. AU - Scholz, P. AU - Siemion, A. P. V. AU - Tendulkar, S. P. AU - Van Rooy, P. AU - Wharton, R. S. AU - Whitlow, D. PY - 2018/1/11 Y1 - 2018/1/11 N2 - Fast radio bursts are millisecond-duration, extragalactic radio flashes of unknown physical origin(1-3). The only known repeating fast radio burst source(4-6)-FRB 121102-has been localized to a star-forming region in a dwarf galaxy(7-9) at redshift 0.193 and is spatially coincident with a compact, persistent radio source(7,10). The origin of the bursts, the nature of the persistent source and the properties of the local environment are still unclear. Such large rotation measures have hitherto been observed(11,12) only in the vicinities of massive black holes (larger than about 10,000 solar masses). Indeed, the properties of the persistent radio source are compatible with those of a low-luminosity, accreting massive black hole(10). The bursts may therefore come from a neutron star in such an environment or could be explained by other models, such as a highly magnetized wind nebula(13) or supernova remnant(14) surrounding a young neutron star. AB - Fast radio bursts are millisecond-duration, extragalactic radio flashes of unknown physical origin(1-3). The only known repeating fast radio burst source(4-6)-FRB 121102-has been localized to a star-forming region in a dwarf galaxy(7-9) at redshift 0.193 and is spatially coincident with a compact, persistent radio source(7,10). The origin of the bursts, the nature of the persistent source and the properties of the local environment are still unclear. KW - SAGITTARIUS-A-ASTERISK KW - FARADAY-ROTATION KW - GAMMA-RAY KW - SUPERNOVA REMNANT KW - CRAB-NEBULA KW - HOST GALAXY KW - BLACK-HOLE KW - X-RAY KW - FIELDS KW - POLARIZATION U2 - 10.1038/nature25149 DO - 10.1038/nature25149 M3 - Article SN - 0028-0836 VL - 553 SP - 182 EP - 185 JO - Nature JF - Nature IS - 7687 ER - Michilli D, Seymour A, Hessels JWT, Spitler LG, Gajjar V, Archibald AM et al. An extreme magneto-ionic environment associated with the fast radio burst source FRB 121102 . Nature . 2018 Jan 11;553(7687):182-185. doi: 10.1038/nature25149

The discovery of radio pulsars over a half century ago was a seminal moment in astronomy. It demonstrated the existence of neutron stars, gave a powerful observational tool to study them, and has allowed us to probe strong gravity, dense matter, and the interstellar medium. More recently, pulsar surveys have led to the serendipitous discovery of fast radio bursts (FRBs). While FRBs appear similar to the individual pulses from pulsars, their large dispersive delays suggest that they originate from far outside the Milky Way and hence are many orders-of-magnitude more luminous. While most FRBs appear to be one-off, perhaps cataclysmic events, two sources are now known to repeat and thus clearly have a longer lived central engine. Beyond understanding how they are created, there is also the prospect of using FRBs-as with pulsars-to probe the extremes of the Universe as well as the otherwise invisible intervening medium. Such studies will be aided by the high-implied all-sky event rate: there is a detectable FRB roughly once every minute occurring somewhere on the sky. The fact that less than a hundred FRB sources have been discovered in the last decade is largely due to the small fields-of-view of current radio telescopes. A new generation of wide-field instruments is now coming online, however, and these will be capable of detecting multiple FRBs per day. We are thus on the brink of further breakthroughs in the short-duration radio transient phase space, which will be critical for differentiating between the many proposed theories for the origin of FRBs. In this review, we give an observational and theoretical introduction at a level that is accessible to astronomers entering the field. It demonstrated the existence of neutron stars, gave a powerful observational tool to study them, and has allowed us to probe strong gravity, dense matter, and the interstellar medium. More recently, pulsar surveys have led to the serendipitous discovery of fast radio bursts (FRBs). While FRBs appear similar to the individual pulses from pulsars, their large dispersive delays suggest that they originate from far outside the Milky Way and hence are many orders-of-magnitude more luminous. While most FRBs appear to be one-off, perhaps cataclysmic events, two sources are now known to repeat and thus clearly have a longer lived central engine. We are thus on the brink of further breakthroughs in the short-duration radio transient phase space, which will be critical for differentiating between the many proposed theories for the origin of FRBs. In this review, we give an observational and theoretical introduction at a level that is accessible to astronomers entering the field. Keywords: Fast radio burst, Pulsar, Radio astronomy, Transient status released display-pdf yes is-in-collection-domain yes is-olf no is-manuscript no is-preprint no is-journal-matter no is-scanned no is-retracted no Received 2018 Nov 30; Issue date 2019. These violent processes emit across the electromagnetic spectrum on various timescales—from a few seconds of coherent gamma-ray emission from gamma-ray bursts (GRBs; Gehrels et al. 2009 ) to the sometimes years-long incoherent thermal radio emission from expanding material after a supernova explosion or GRB (Chandra and Frail 2012 ). Binary neutron star mergers can now also be observed through gravitational radiation (Abbott et al. 2017b ). The energetic remnants of stellar explosions such as neutron stars are also known to produce millisecond-duration radio pulses (Hewish et al. 1968 ). ( 2011 ); however, this source was along a sightline in the Galactic plane and thus a Galactic origin (like a RRAT) was also considered possible (see Sect. 5.2 , and Bannister and Madsen 2014 ). Strong support in favor of the Lorimer burst as an astrophysical phenomenon came from Thornton et al. ( 2013 ), who presented four high-DM pulses discovered in the High Time Resolution Universe survey at the Parkes telescope (HTRU; Keith et al. 2010 ). The discoveries by Thornton et al. ( 2013 ) had similar characteristics to the Lorimer burst, and implied an all-sky population of Following gamma-ray burst notation, the FRBs are named in YYMMDD format to indicate the year (YY) month (MM) and day (DD) on which the burst was detected. Also listed to the right of each pulse are the observed dispersion measures (DMs) in units of cm - 3 pc Observed properties The FRB search process is described in detail in Sect. 4 . In brief, it consists of looking for dispersed pulses like the one shown in Fig. 1 in radio astronomical data that are sampled in frequency and time. Searches are most commonly done by forming a large number of time series corresponding to different amounts of dispersion over a wide range. Given that such galaxies are also known to be the common hosts of superluminous supernovae (SLSNe) and long gamma-ray bursts (LGRBs), this presented a tantalizing possible link between FRBs and these other types of extreme astrophysical transients (Metzger et al. 2017 ; Murase et al. 2016 ). Deeper observations of the host using the Hubble Space Telescope (HST) revealed that FRB 121102 is coincident with an intense star-forming region (Bassa et al. 2017b ). The EVN radio position is offset from the optical centroid of the star-forming region by 55 mas, statistically significant, but within the half-light radius. Magnetically powered bursts from neutron stars have also been considered in the literature. Flares from magnetars were first proposed by Popov and Postnov ( 2010 ) and Popov and Postnov ( 2013 ). A flaring magnetar model for FRB 121102 was proposed by Beloborodov ( 2017 ), and was partially motivated to explain the source’s compact, persistent radio counterpart (Chatterjee et al. 2017 ; Marcote et al. 2017 ). In this model, the FRBs are from a giga-Hertz maser and originate in shocks far from the neutron star itself. Hessels et al. ( 2018 ) show that FRB 121102 bursts have complex time–frequency structures.

The dispersive sweep of fast radio bursts (FRBs) has been used to probe the ionized baryon content of the intergalactic medium¹, which is assumed to dominate the total extragalactic dispersion. Although the host-galaxy contributions to the dispersion measure appear to be small for most FRBs², in at least one case there is evidence for an extreme magneto-ionic local environment^3,4 and a compact persistent radio source⁵. Here we report the detection and localization of the repeating FRB 20190520B, which is co-located with a compact, persistent radio source and associated with a dwarf host galaxy of high specific-star-formation rate at a redshift of 0.241 ± 0.001. The estimated host-galaxy dispersion measure of approximately [Formula: see text] parsecs per cubic centimetre, which is nearly an order of magnitude higher than the average of FRB host galaxies^2,6, far exceeds the dispersion-measure contribution of the intergalactic medium. Caution is thus warranted in inferring redshifts for FRBs without accurate host-galaxy identifications.

gamma-ray burst. On 28 April 2020, a pair of millisecond-timescale bursts (FRB 200428) consistent with observed fast radio bursts, with a fluence of >1.5 million In radio astronomy, a fast radio burst (FRB) is a transient radio wave of duration ranging from a fraction of a millisecond, for an ultra-fast radio burst, to 3 seconds, caused by a high-energy astrophysical process that is not yet understood. Astronomers estimate the average FRB releases as much energy in a millisecond as the Sun puts out in three days. While extremely energetic at their source, In radio… The first fast radio burst to be described, the Lorimer Burst FRB 010724, was found in 2007 in archived data recorded by the Parkes Observatory on 24 July 2001. Since then, many FRBs have been found in previously recorded data. On 19 January 2015, astronomers at Australia's national science agency (CSIRO) reported that a fast radio burst had been observed for the first time live, by the Parkes Observatory. Many FRBs have been detected in real time by the CHIME radio telescope since it became operational in 2018, including the first FRB detected from within the Milky Way in April 2020. In January 2025, astronomers discovered radio waves from a galaxy that is roughly 2-billion light years away from Earth and is believed to be more than 11 billion years old. These FRBs are associated with a galaxy that was believed to be dead. This established magnetars as, at least, one ultimate source of fast radio bursts, although the exact cause remains unknown. Further studies support the notion that magnetars may be closely associated with FRBs. On 13 October 2021, astronomers reported the detection of hundreds of FRBs from a single system. In 2024, an international team led by astrophysicists of INAF, using detections from VLA, NOEMA interferometer, and Gran Telescopio Canarias has conducted a research campaign about FRB20201124A, one of the two known persistent FRB, located about 1.3 billion light-years away. On 19 January 2015, astronomers at Australia's national science agency (CSIRO) reported that a fast radio burst had been observed for the first time live, by the Parkes Observatory. Many FRBs have been detected in real time by the CHIME radio telescope since it became operational in 2018, including the first FRB detected from within the Milky Way in April 2020. In January 2025, astronomers discovered radio waves from a galaxy that is roughly 2-billion light years away from Earth and is believed to be more than 11 billion years old. These FRBs are associated with a galaxy that was believed to be dead. In 2015 it was suggested that FRBs are caused by explosive decays of axion miniclusters. Another exotic possible source are cosmic strings that produced these bursts as they interacted with the plasma that permeated the early Universe. In 2016 the collapse of the magnetospheres of Kerr–Newman black holes were proposed to explain the origin of the FRBs' "afterglow" and the weak gamma-ray transient 0.4 s after GW 150914. 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. In July 2019, astronomers reported that non-repeating Fast Radio Bursts may not be one-off events, but actually FRB repeaters with repeat events that have gone undetected and, further, that FRBs may be formed by events that have not yet been seen or considered. Additional possibilities include that FRBs may originate from nearby stellar flares. A FRB with multiple periodic component peaks lasting over 3 seconds was reported in 2022. A neutron star has been proposed as the origin of this FRB. It was the first FRB for which linear polarization was detected (allowing a measurement of Faraday rotation). Measurement of the signal's dispersion delay suggested that this burst was of extragalactic origin, possibly up to 6 billion light-years away. === 2012 === Victoria Kaspi of McGill University estimated that as many as 10,000 fast radio bursts may occur per day over the entire sky. ==== FRB 121102 ==== 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. However, the association of the burst with the afterglow was soon disputed, and by April 2016 it was established that the "afterglow" originated from an active galactic nucleus (AGN) 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 did not fade away as would be expected, supporting the interpretation that it originated in the variable AGN On 6 April 2020, followup studies by the Global MASTER-Net were reported on The Astronomer's Telegram. On 25 August 2021, further observations were reported. ==== FRB 181112 ==== FRB 181112 was mysteriously unaffected after believed to have passed through the halo of an intervening galaxy. === 2019 === ==== FRB 180924 ==== FRB 180924 is the first non-repeating FRB to be traced to its source. The source is a galaxy 3.6 billion light-years away. The galaxy is nearly as large as the Milky Way and about 1000 times larger than the source galaxy of FRB 121102. The detected FRB is "one of the faintest FRB sources detected so far", according to the report. ==== FRB 200428 ==== On 28 April 2020, astronomers at the Canadian Hydrogen Intensity Mapping Experiment (CHIME), reported the detection of a bright radio burst from the direction of the Galactic magnetar SGR 1935+2154 about 30,000 light years away in the Vulpecula constellation. The burst had a DM of 332.8 pc/cc. The STARE2 team independently detected the burst and reported that the burst had a fluence of >1.5 MJy ms, establishing the connection between this burst and FRBs at extragalactic distances. The burst was then referred to as FRB 200428.

We report on the lowest-frequency detection to date of three bursts from the fast radio burst FRB 180916.J0158+65, observed at 328 MHz with the Sardinia Radio Telescope (SRT). The SRT observed the periodic repeater FRB 180916.J0158+65 for five days from 2020 February 20 to 24 during a time interval of active radio bursting, and detected the three bursts during the first hour of observations; no more bursts were detected during the remaining ∼30 hr. Simultaneous SRT observations at 1548 MHz did not detect any bursts. Burst fluences are in the range 37 to 13 Jy ms. No relevant scattering is observed for these bursts. We also present the results of the multiwavelength campaign we performed on FRB 180916.J0158+65, during the five days of the active window. Simultaneously with the SRT observations, others with different time spans were performed with the Northern Cross at 408 MHz, with XMM-Newton, NICER, INTEGRAL, AGILE, and with the TNG and two optical telescopes in Asiago, which are equipped with fast photometers. XMM-Newton obtained data simultaneously with the three bursts detected by the SRT, and determined a luminosity upper limit in the 0.3–10 keV energy range of ∼10(exp 45) erg/s for the burst emission. AGILE obtained data simultaneously with the first burst and determined a fluence upper limit in the MeV range for millisecond timescales of 10(exp -8) erg/sq.cm. Our results show that absorption from the circumburst medium does not significantly affect the emission from FRB

identifying unusual, transient events. At radio wavelengths, this includes the recent discovery of fast radio bursts , which astronomers are still struggling