Paper detail

INTEGRAL observations of the GeV blazar PKS1502+106 and of the hard X-ray bright Seyfert Galaxy Mkn841

Extragalactic nuclear activity is best explored with observations at high energies, where the most extreme flux and spectral variations are expected to occur, witnessing changes in the accretion flow or in the kinematics of the plasma. In active galactic nuclei of blazar type, these variations are the most dramatic. By following blazar outbursts from their onset and by correlating the observed variations at many different wavelengths we can reconstruct the behavior of the plasma and map out the development of the flare within the jet. The advent of the Fermi satellite has allowed the start of a systematic and intensive monitoring program of blazars. Blazar outbursts are very effectively detected by the LAT instrument in the MeV-GeV domain, and these can be promptly followed up with other facilities. Based on a Fermi LAT detection of a high MeV-GeV state, we have observed the blazar PKS 1502+106 with the INTEGRAL satellite between 9 and 11 August 2008. Simultaneous Swift observations have been also accomplished, as well as optical follow-up at the Nordic Optical Telescope. The IBIS instrument onboard INTEGRAL detected a source at a position inconsistent with the optical coordinates of PKS 1502+106, but consistent with those of the Seyfert 1 galaxy Mkn 841, located at 6.8 arcmin south-west from the blazar, which is therefore responsible for all the hard X-ray flux detected by IBIS. At the location of the blazar, IBIS sets an upper limit of ~10^{-11} erg/s/cm2 on the 15-60 keV flux, that turns out to be consistent with a model of inverse Compton scattering accounting for the soft X-ray and gamma-ray spectra measured by Swift XRT and Fermi LAT, respectively. The gamma-ray spectrum during the outburst indicates substantial variability of the characteristic energy of the inverse Compton component in this blazar.(abridged).