GRB 210410A: A twin of short GRB 090510 with complementary observations

GRB 210410A has been announced as a likely long GRB (Fermi GBM Team 2021, GCN 29777), it has been also observed by Swift-XRT (A. Melandri et al 2021, GCN 29778, and A. D'Ai et al, 2021, GCN 29790), by Fermi-LAT (M. Arimoto et al 2021, GCN 29781), by AGILE (A. Ursi et al. 2021, GCN 29782), by Swift BAT (A. Y. Lien et al, 2021 GCN 29793) as well as by Konus-Wind (A. Ridnaia et al 2021, GCN 29797). The Fermi-GBM has determined T90=48 s in 50-300 keV (J. Wood et al 2021, GCN 29788). A possible detection of the host galaxy at redshift z<3.6 was indicated by Butler et al 2021 (GCN 29784). We here propose that GRB 210410A is a twin and covers the complementary observation to the short GRB 090510, with T90=0.3 s. (R. Ruffini et al 2016 ApJ 831 178). We infer that GRB 210410A is a short GRB originating from a black hole formation in view of its observed GeV emission (M. Arimoto et al GCN29781) that and no supernova will be detected. We evidence for the first time an angle dependence of the emission of short GRB: in the polar observation for GRB 090510, with T90=0.3 s and in the equatorial observation for GRB 210410A, with T90=48 s. The spectroscopic determination of the redshift of the host galaxy is essential for the determination of the GeV luminosity and consequently the BH mass (R. Ruffini et al 2019 ApJ 886 82). We indicate the relevance of the redshift determinations in the two enclosed figures. "http://www.icranet.org/documents/GRB210410A-z=0.6-and-GRB090510-z=0.903.pdf"

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