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GCN Circular 27627

Subject
GRB 200415A (possible magnetar Giant Flare in Sculptor Galaxy): INTEGRAL observations
Date
2020-04-22T22:33:18Z (4 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
A. Pozanenko (IKI), P. Minaev (IKI), I. Chelovekov (IKI), S. Grebenev 
(IKI) report on behalf of GRB IKI FuN:

We analysed publicly available INTEGRAL data around the time of GRB 
200415A (Fermi GBM team, GCN 27579; Omodei et al., GCN 27586; Frederiks 
et al., GCN 27596; Marisaldi et al., GCN 27622).  Direction to GRB 
200415A localization  by IPN (Svinkin et al., GCN 27585) and Fermi LAT 
(Omodei et al., GCN 27597) is 89 degrees off-axis for INTEGRAL 
telescopes, which is nearly optimal for the SPI-ACS detector. This event 
did not trigger IBAS (see 
http://www.isdc.unige.ch/integral/science/grb#ACS).

The GRB 200415A is clearly visible in SPI-ACS, IBIS/ISGRI and 
IBIS/PICsIT (for latter two - outside the FoV). Using IBIS/ISGRI we 
derived the GRB 200415A time interval from T0+0.38 up to T0+0.52, where 
T0 = 2020-04-15T08:48:05.56  (UT) is the trigger time of GRB Fermi.

Duration of GRB 200415A is 0.20 s as seen in SPI-ACS and 0.14 c in 
IBIS/ISGRI in 30-500 keV energy band. The fluence of the event in 
SPI-ACS is 27800 +/- 300 cts, which is equivalent to 6.7��-6 ergs/cm2 in 
10-1000 keV energy (1.2��-6 -- 3.8��-5 ergs/cm2 is the 95% confident 
region using calibration of SPI-ACS for short Pozanenko et al., 
Astronomy Letters, 45, 11, 710 (2019). The fluence of the event in ISGRI 
is  3.2 +/- 2.2e-6 ergs/cm2 (30-100 keV) and  3.7 +/- 2.4e-6 ergs/cm2 
(100-500 keV) after calibration of ISGRI (Chelovekov et al., Astronomy 
Letters, 45, 10, 635 (2019).
We detected neither any precursor within 200 s prior the trigger, nor 
significant extended emission up to +100 s.

Light curves of the GRB 200415A registered by INTEGRAL detectors can be 
found at
http://grb.rssi.ru/GRB200415A_ISGRI_PICSIT_ACS.png

We note a possible multi-pulse structure of the event as can be seen in 
the IBIS/ISGRI light curve.

We also put the spectral data reported  (Bissaldi et al., GCN 27587; 
Frederiks et al., GCN 27596) onto E_iso -- E_p diagram (AKA Amati 
relation) and EHD diagram (Minaev et al., MNRAS, 492, 1919 (2020).

If GRB 200415A is a real gamma-ray burst its redshift should be z > 0.03 
as it is seen from the event trajectory in the diagrams.

We put the Giant Flare (GF) of SGR 1806-20 on 2004-12-27 on the E_iso -- 
E_p diagram and found that position of GRB 200415A, if its source in 
Sculptor galaxy (NGC 253) at 3.5 Mpc,  is compatible with the position 
of the GF of SGR 1806-20 on 2004-12-27 (see Figures below).

E_iso -- E_p diagram (AKA Amati relation) and EHD diagram can be found at
http://grb.rssi.ru/GRB200415A/GRB200415A_Amati_SGR.png
http://grb.rssi.ru/GRB200415A/GRB200415A_EHD_SGR.png
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