SIMBAD references

We searched for X-ray flashes (XRFs) - which we defined as ∼10-s duration transient X-ray events observable in the 0.4-15 keV passband - in fields observed using XMM-Newton with the EPIC/pn detector. While we find two non-Poissonian events, the astrophysical nature of the events is not confirmed in fully simultaneous observations with the EPIC/MOS detectors, and we conclude that the events are anomalous to the EPIC/pn detector. We find a 90 per cent upper limit on the number of flashes per sky per year at two different incoming flash fluxes: 4.0x10⁹ events/sky/yr for a flux of 7.1x10^–13 erg/cm2/s and 6.8x10⁷ events/sky/yr for 1.4x10^–11 erg/cm2/s, both assuming a spectral power-law photon index α= 2. These limits are consistent with an extrapolation from the BeppoSAX/WFC XRF rate at much higher fluxes (∼ a factor of 10⁵), assuming a homogenous population, and with a previous, more stringent limit derived from ROSAT pointed observations.