INTEGRAL search for magnetar giant flares from the Virgo Cluster and in nearby galaxies with high star formation rate

Giant flares from magnetars can reach, for a fraction of a second, luminosities greater than 1047 erg s-1 in the hard X-ray/soft γ-ray range. This makes them visible at distances of several megaparsecs. Ho we ver, at extragalactic distances (farther than the Magellanic Clouds), they are difficult to distinguish from the short γ-ray bursts, which occur much more frequently. Since magnetars are young neutron stars, nearby galaxies with a high rate of star formation are optimal targets to search for magnetar giant flares (MGFs). Here, we report the results of a search for MGFs in observations of the Virgo cluster and in a small sample of nearby galaxies obtained with the IBIS instrument on the INTE rnational G amma- R ay A strophysics L aboratory ( INTEGRAL) satellite. From the currently known MGF sample, we find that their energy distribution is well described by a power law with slope γ= 2 (with 90 per cent c.l. interval [1.7-2.2]). From the lack of detections in this extensive data set (besides 231115A in M82), we derive a 90 per cent c.l. upper limit on the rate of MGF with E > 3 × 1045 erg of ∼ 2 × 10-3 yr-1 per magnetar and a lower limit on R( > E) of ∼ 4 × 10-4 yr-1 magnetar-1 for E < 1045 erg.