INTEGRAL IBIS and SPI-ACS detection of a hard X-ray counterpart of the radio burst from SGR 1935+2154

ATel #13685; S. Mereghetti (INAF, IASF-Milano), V. Savchenko (ISDC, Versoix), D. Gotz, J. Rodriguez (CEA, Saclay), L. Ducci, C. Ferrigno, E. Bozzo (ISDC, Versoix), J. Borkowski (CAMK, Torun) and A. Bazzano (INAF, IAPS-Roma)
on 29 Apr 2020; 10:53 UT
Credential Certification: Lorenzo Ducci (lorenzo.ducci@unige.ch)

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A bright short burst has been detected by IBAS in the IBIS/ISGRI data at 14:34:24 UT of April 28 (Alert Packet n. 8611), and promptly identified as originating from the currently active SGR 1935+2154 (GCN #27667, #27666, #27665, #27664, #27663, #27662, #27661, #27659, #27657, #27631, ATel #13682, #13679, #13678, #13675). Note that the above time is not corrected for the light-travel but it is consistent with the one of the radio burst from the same source reported in ATel #13681, #13684.

The burst was at an off-axis angle of 8.1 degrees, in the field of view of the IBIS and SPI instruments, but outside those of JEM-X and OMC. It was detected during the INTEGRAL monitoring campaign on GRS 1915+105.

A preliminary analysis indicates that the burst had a duration of about 0.3 s, a fluence of 3.9±0.2e-7 erg/cm² in the 25-80 keV range and a peak flux of 1.2±0.1 e-6 erg/cm²/s on 10 ms timescale, assuming Crab-like spectra.

The burst was also marginally detected in the SPI-ACS with S/N=4.65 on a 0.65s time scale. The ACS observation independently derives a FAP at the level of 0.0019 (2.9 σ).

We note that another weaker burst from SGR 1935+2154, lasting about 0.1 s was detected by IBAS at 09:51:05 UT of April 28 (Weak Alert Packet n. 8610).

ISGRI and SPI-ACS lightcurves of the bright event are available at:

SPI-ACS and ISGRI light curves of the SGR 1935+2154 burst detected by INTEGRAL**