Fast Radio Bursts (FRBs)
Fast Radio Bursts (FRBs) are millisecond-duration coherent radio pulses (100 MHz to 8 GHz) originating primarily from extragalactic galaxies at cosmological distances (z = 0.01 to >1.0), releasing as much radio energy in a thousandth of a second as the Sun emits over several days (E_iso ≈ 10³⁸–10⁴² erg). The April 2020 detection of FRB 20200428 from the Galactic magnetar SGR 1935+2154 confirmed that magnetar crust quakes and relativistic magnetospheric/shock flares are a primary physical engine.
Physical Mechanism & Dynamics
Discovered in 2007 by Duncan Lorimer and collaborators in archival 2001 Parkes telescope data ('the Lorimer Burst', FRB 010724), FRBs exhibit light-travel times of Δt ≈ 0.1–5 ms (requiring emission regions smaller than c Δt ≈ 30–1,500 km) coupled with peak flux densities of ~1–100 Jy at gigaparsec distances. The implied brightness temperature T_B ≈ 10³⁵–10³⁶ K exceeds any incoherent synchrotron or thermal limit (T_B < 10¹² K) by over 20 orders of magnitude, demanding coherent radiation—either coherent curvature radiation by bunched relativistic pairs inside a magnetar magnetosphere (B ≈ 10¹⁴–10¹⁵ G) or synchrotron maser emission in magnetized relativistic shocks.
As an FRB pulse propagates through ionized plasma along its path, lower radio frequencies travel slightly slower than higher frequencies according to the cold plasma group velocity, arriving with a time delay Δt ∝ DM × ν⁻², where the Dispersion Measure DM = ∫ n_e dl / (1 + z) integrates the column of free electrons. By localizing dozens of FRBs to specific host galaxies with ASKAP, DSA-110, MeerKAT, and CHIME Outriggers, Macquart et al. (2020) established the 'Macquart Relation' (DM_IGM vs. z), directly weighing the diffuse ionized baryons of the intergalactic medium and confirming Planck's Ω_b h² = 0.0224.
Quantitatively, this mechanism is governed by Cold Plasma Dispersion Delay & Macquart IGM Relation (Δt(ν) = (e^2 / (2 π m_e c)) DM ν⁻² ≈ 4.149 ms × (DM / pc cm⁻³) (ν / GHz)⁻², ⟨DM_IGM(z)⟩ ≈ 930 × z pc cm⁻³). Separates the observed dispersion measure DM_obs = DM_MW + DM_IGM(z) + DM_host/(1+z) to measure the cosmic electron column ⟨DM_IGM(z)⟩.
Cold Plasma Dispersion Delay & Macquart IGM Relation
Δt(ν) = (e^2 / (2 π m_e c)) DM ν⁻² ≈ 4.149 ms × (DM / pc cm⁻³) (ν / GHz)⁻², ⟨DM_IGM(z)⟩ ≈ 930 × z pc cm⁻³Separates the observed dispersion measure DM_obs = DM_MW + DM_IGM(z) + DM_host/(1+z) to measure the cosmic electron column ⟨DM_IGM(z)⟩.
Quantitative Benchmarks & Parameters
| Parameter / Observable | Measured Value / Scale | Method & Context |
|---|---|---|
| Pulse duration & isotropic radio energy | Δt = 0.05–10 ms; E_radio = 10³⁵ (SGR 1935) to 10⁴³ erg | CHIME/FRB, FAST, ASKAP & DSA-110 catalogs |
| Brightness temperature (coherent emission) | T_B ≈ 10³⁵–10³⁶ K (exceeds 10¹² K incoherent limit by 10²³×) | Sub-millisecond variability + cosmological luminosity distance |
| Galactic magnetar bridge FRB 20200428 | E_radio ≈ 3 × 10³⁴ erg from SGR 1935+2154 (d ≈ 6.6 kpc) | CHIME + STARE2 + Integral/Insight-HXMT X-ray burst (2020) |
| Cataloged FRBs & repeating fraction | > 1,000 unique sources (~3–5% observed to repeat, e.g. FRB 20121102A) | CHIME/FRB Catalog 1/2 & FAST ultra-deep monitoring |
Observational Evidence & How Scientists Know
On 28 April 2020, CHIME and STARE2 simultaneously detected a 1.5-megajansky millisecond radio burst (FRB 20200428) from the Milky Way magnetar SGR 1935+2154 in coincidence with a hard X-ray burst detected by Integral, Konus-Wind, and Insight-HXMT—bridging the luminosity gap between Galactic radio pulsars and extragalactic FRBs.
Across reference datasets (SIMBAD Astronomical Database (CDS), Planck 2018 Cosmological Parameters (PR3)), quantitative benchmarks for fast radio bursts (frbs) are anchored by: Pulse duration & isotropic radio energy (Δt = 0.05–10 ms; E_radio = 10³⁵ (SGR 1935) to 10⁴³ erg, via CHIME/FRB, FAST, ASKAP & DSA-110 catalogs); Brightness temperature (coherent emission) (T_B ≈ 10³⁵–10³⁶ K (exceeds 10¹² K incoherent limit by 10²³×), via Sub-millisecond variability + cosmological luminosity distance); Galactic magnetar bridge FRB 20200428 (E_radio ≈ 3 × 10³⁴ erg from SGR 1935+2154 (d ≈ 6.6 kpc), via CHIME + STARE2 + Integral/Insight-HXMT X-ray burst (2020)); Cataloged FRBs & repeating fraction (> 1,000 unique sources (~3–5% observed to repeat, e.g. FRB 20121102A), via CHIME/FRB Catalog 1/2 & FAST ultra-deep monitoring).
Uncertainties, Systematics & Open Questions
Why a small fraction of FRBs repeat prolifically (some with periodic activity windows, such as FRB 20180916B's 16.35-day cycle, and some inside globular clusters like M81's FRB 20200120E requiring accretion-induced collapse or binary white dwarf mergers) while ~95% appear only once remains under active investigation.
Real Astronomical Benchmarks & Cross-Domain Links
FRB 20200428 (from Magnetar SGR 1935+2154)
First Fast Radio Burst detected inside the Milky Way, directly linking FRBs to magnetar X-ray flares
FRB 20121102A (The First Repeater)
Prolific repeating FRB in a z = 0.193 dwarf galaxy associated with a compact persistent radio nebula, producing >1,600 bursts in a 47-day FAST campaign
FRB 20220610A (at z = 1.016)
High-redshift FRB localized by ASKAP and VLT/HST to an interacting galaxy group ~8 billion light-years away with DM = 1,458 pc cm⁻³
Guided Learning Path
Related Concepts, Methods & Explorers
Scientific Sources & Provenance
- SIMBAD Astronomical Database (CDS) (2026-10 release) — Wenger, M., et al. 2000, A&AS, 143, 9 (The SIMBAD astronomical database). Archive / Reference ↗
- Planck 2018 Cosmological Parameters (PR3) (PR3 (2020 A&A 641, A6)) — Planck Collaboration, Aghanim, N., et al. 2020, A&A, 641, A6. Archive / Reference ↗
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