Discovery of two new fast X-ray transients with INTEGRAL: IGR J03346+4414 and IGR J20344+3913

Abstract

We report on the discovery of two fast X-ray transients (FXTs) from analysis of archival INTEGRAL data. Both are characterized by a remarkable hard X-ray activity above 20 keV, in terms of duration (∼15 and 30 min, respectively), peak flux (∼10^-9 erg cm^-2 s^-1) and dynamic range (∼2400 and 1360, respectively). Swift/X-ray telescope follow-up observations failed to detect any quiescent or low-level soft X-ray emission from either of the two FXTs, providing an upper limit of the order of a few times 10^-12 erg cm^-2 s^-1. The main spectral and temporal Imager on Board INTEGRAL Satellite (IBIS)/INTEGRAL Soft Gamma-Ray Imager (ISGRI) characteristics are presented and discussed with the aim of inferring possible hints on their nature.