2021/01/13 by O. J. Roberts, P. Veres, P. Vereš +27 · 2 citations
Physics and Astronomy · #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Flare #Galaxy #Gamma-ray bursts and supernovae #Magnetar #Millisecond #Neutron star #Physics #Pulsars and Gravitational Waves Research #Spectral line #astro-ph.HE
paper · pdf · doi:10.1038/s41586-020-03077-8
arxiv created 2021/01/13 · openalex publication_date 2021/01/13 · arxiv updated 2021/01/14 · openalex created_date 2021/01/18 · openalex updated_date 2026/08/05
Magnetars are slowly-rotating neutron stars with extremely strong magnetic fields (1013-15 G), episodically emitting ∼100 ms long X-ray bursts with energies of ∼1040-41 erg. Rarely, they produce extremely bright, energetic giant flares that begin with a short (∼0.2 s), intense flash, followed by fainter, longer lasting emission modulated by the magnetar spin period (typically 2-12 s), thus confirming their origin. Over the last 40 years, only three such flares have been observed in our local group; they all suffered from instrumental saturation due to their extreme intensity. It has been proposed that extra-galactic giant flares likely constitute a subset of short gamma-ray bursts, noting that the sensitivity of current instrumentation prevents us from detecting the pulsating tail, while the initial bright flash is readily observable out to distances ∼ 10-20 Mpc. Here, we report X- and gamma-ray observations of GRB 200415A, which exhibits a rapid onset, very fast time variability, flat spectra and significant sub-millisecond spectral evolution. These attributes match well with those expected for a giant flare from an extra-galactic magnetar, noting that GRB 200415A is directionally associated with the galaxy NGC 253 (∼3.5 Mpc away). The detection of ∼3 MeV photons provides definitive evidence for relativistic motion of the emitting plasma. The observed rapid spectral evolution can naturally be generated by radiation emanating from such rapidly-moving gas in a rotating magnetar.