GRB 200415A: Magnetar Giant Flare or Short Gamma-Ray Burst?

A detailed analysis of the GBM/Fermi experiment data is carried out to classify GRB 200415A. It is shown that, on the one hand, this event exhibits typical for type I (short) gamma-ray bursts (GRBs) properties, such as duration, variability, and the character of spectral evolution (lag). On the other hand, the localization of the event source on the celestial plane, obtained by the triangulation method (IPN), indicates the nearby ( $$D_{L}=3.5$$ Mpc) galaxy NGC 253 (Sculptor) as a possible host galaxy for this burst. It introduces significant restrictions on the energetics of the event ( $$E_{iso}\sim 10^{46}$$ erg) and gives an alternative interpretation of GRB 200415A as a giant flare (GF) of a soft gamma repeater (SGR). This interpretation is supported by the atypically hard energy spectrum. In addition, according to the position of the burst on the $$E_{p,i}{-}E_{iso}$$ (the position of the maximum in the energy spectrum $$\nu F_{\nu}$$ in the source frame depending on the isotropic equivalent of the total energy, emitted in gamma rays) and $$T_{90,i}{-}EH$$ (duration in the source frame depending on the combination of parameters $$EH=E_{p,i,2}E_{iso,51}^{-0.4}$$ ) diagrams, GRB 200415A is unambiguously classified as a giant flare of a magnetar, assuming its association with the galaxy NGC 253. In these diagrams, known giant flares in the Galaxy and candidates for giant flares in nearby galaxies form a well-defined group, which includes the GRB 200415A.