A short hard X-ray flare from the blazar NRAO 530 observed by INTEGRAL
Maraschi, L.; Ghisellini, G.; Pian, E.; Tosti, G.; Tavecchio, F.; Foschini, L.; Di Cocco, G.; Malaguti, G.; Raiteri, C. M.
Italy
Abstract
We report about a short flare from the blazar NRAO 530 occurred on 17 February 2004 and detected serendipitously by the IBIS/ISGRI detector on board INTEGRAL. In the 20-40 keV energy range, the source, that is otherwise below the detection limit, is detected at a level of ≈2 × 10-10 erg cm-2 s-1 during a time interval of less than 2000 s, which is about a factor 2 above the detection threshold. At other wavelengths, only nearly-simultaneous radio data are available (1 observation at 2 cm on 11 February 2004), indicating a moderate increase of the polarization. This appears to be the shortest time variability episode ever detected in a high luminosity blazar at hard X-rays, unless the blazar is contaminated by the presence of an unknown unresolved rapidly varying source.