Detection of bursting activity with INTEGRAL/SPI-ACS, possibly from 1E 2259+586 or SGR 1806-20
ATel #4101; V. Savchenko (ISDC/University of Geneva, Switzerland), S. Mereghetti (INAF/IASF-Milano, Italy), C. Ferrigno, E. Bozzo, T. J.-L. Courvoisier (ISDC/University of Geneva, Switzerland), D. Goetz (Cea/Saclay, France), J. Borkowski (CAMK, Torun, Poland), A. von Kienlin, A. Rau, X. Zhang (MPE-Garching, Germany), V. Beckmann (APC Paris, France)
on 8 May 2012; 10:21 UT
Credential Certification: Carlo Ferrigno (Carlo.Ferrigno@unige.ch)
Subjects: Gamma Ray, Neutron Star, Soft Gamma-ray Repeater, Transient, Pulsar
We report on a possible detection of bursting activity
(tentatively from the magnetars 1E 2259+586 or SGR 1806-20) with the SPI
Anti-Coincidence System (ACS) on-board INTEGRAL.
From 2012-04-19T12:03:10 to 2012-04-21 06:28:49 UTC, the ACS detected
25 short (from 50ms to 8s) bursts at a significance level
of 5-10 sigma (peak count-rate of 1×104 - 1×105 counts/s on 50 ms time bin).
Other 7 bursts were detected from 2012-05-05T06:04:47 to
2012-05-07T16:25:07 UTC. The
highest peak count-rate recorded by the ACS was 1.5×105 counts/s
(detection significance up to 50 sigma).
A rough conversion between the ACS count-rate and fluence is 1×10-10 erg/cm2
in the 75keV-1MeV range per one ACS count (Viganò & Mereghetti, 2009,
As no spatial information are available from the ACS, we cannot firmly
associate this activity with any known source. At the best of our
knowledge, two magnetars were recently reported to be active: SGR1806-20
and 1E 2259+586 (ATel #4080, GCN #13237, GCN #13280). The events that we detected have not been
reported by other GRB monitoring experiments. If these are non
detections, it might be due to the intrinsic faintness or (more likely)
a peculiar spectral shape of these events.
We stress that no instrumental issues that could give rise to similar
effects have ever been observed from the ACS in 10 years of operations.
The ACS light curves of all the bursts are available at:
SPI ACS bursts