Denise Riquelme

Simultaneous Planck, Swift, and Fermi observations of X-ray and γ-ray selected blazars

We present simultaneous Planck, Swift, Fermi, and ground-based data for 105 blazars belonging to three samples with flux limits in the soft X-ray, hard X-ray, and -ray bands, and we compare our results to those of a companion paper presenting simultaneous Planck and multi-frequency observations of 104 radio-loud northern active galactic nuclei selected at radio frequencies. While we confirm several previous results, our unique data set has allowed us to demonstrate that the selection method strongly influences the results, producing biases that cannot be ignored. Almost all the BL Lac objects have been detected by Fermi Large Area Telescope (LAT), whereas 30 to 40% of the flat-spectrum radio quasars (FSRQs) in the radio, soft X-ray, and hard X-ray selected samples are still below the -ray detection limit even after integrating 27 months of Fermi-LAT data. The radio to sub-millimetre spectral slope of blazars is quite flat, withh i 0 up to about 70 GHz, above which it steepens toh i 0:65. BL Lacs have significantly flatter spectra than FSRQs at higher frequencies. The distribution of the rest-frame synchrotron peak frequency ( S ) in the spectral energy distribution (SED) of FSRQs is the same in all the blazar samples withh S i = 10 13:1 0:1 Hz, while the mean inverse-Compton peak frequency,h IC i, ranges from 10 21 to 10 22 Hz. The distributions of S and of IC of BL Lacs are much broader and are shifted to higher energies than those of FSRQs; their shapes strongly depend on the selection method. The Compton dominance of blazars ranges from less than 0.2 to nearly 100, with only FSRQs reaching values larger than about 3. Its distribution is broad and depends strongly on the selection method, with -ray selected blazars peaking at 7 or more, and radio-selected blazars at values close to 1, thus implying that the common assumption that the blazar power budget is largely dominated by high-energy emission is a selection e ect. A comparison of our multi-frequency data with theoretical predictions shows that simple homogeneous SSC models cannot explain the simultaneous SEDs of most of the -ray detected blazars in all samples. The SED of the blazars that were not detected by Fermi-LAT may instead be consistent with SSC emission. Our data challenge the correlation between bolometric luminosity and S predicted by the blazar sequence.

Radio and γ-ray follow-up of the exceptionally high-activity state of PKS 1510−089 in 2011

We investigate the radio and γ-ray variability of the flat spectrum radio quasar PKS 1510−089 in the time range between 2010 November and 2012 January. In this period the source showed an intense activity, with two major γ-ray flares detected in 2011 July and October. During the latter episode both the γ-ray and the radio flux density reached their historical peak. Multiwavelength analysis shows a rotation of about 380° of the optical polarization angle close in time with the rapid and strong γ-ray flare in 2011 July. An enhancement of the optical emission and an increase of the fractional polarization both in the optical and in radio bands are observed about three weeks later, close in time with another γ-ray outburst. On the other hand, after 2011 September a huge radio outburst has been detected, first in the millimetre regime followed with some time delay at centimetre down to decimetre wavelengths. This radio flare is characterized by a rising and a decaying stage, in agreement with the formation of a shock and its evolution, as a consequence of expansion and radiative cooling. If the γ-ray flare observed in 2011 October is related to this radio outburst, then this strongly indicates that the region responsible for the γ-ray variability is not within the broad line, but a few parsecs downstream along the jet.

Radio-to-[gamma]-ray monitoring of the narrow-line Seyfert 1 galaxy PMN J0948+0022 from 2008 to 2011

We present more than three years of observations at different frequencies, from radio to high-energy γ-rays, of the Narrow-Line Seyfert 1 (NLS1) Galaxy PMN J0948+0022 (z = 0.585). This source is the first NLS1 detected at energies above 100 MeV and therefore can be considered the prototype of this emerging new class of γ-ray emitting active galactic nuclei (AGN). The observations performed from 2008 August 1 to 2011 December 31 confirmed that PMN J0948+0022 generates a powerful relativistic jet, which is able to develop an isotropic luminosity at γ-rays of the order of 10 48 erg s −1 , at the level of powerful quasars. The evolution of the radiation emission of this source in 2009 and 2010 followed the canonical expectations of relativistic jets with correlated multiwavelength variability (γ-rays followed by radio emission after a few months), but it was difficult to retrieve a similar pattern in the light curves of 2011. The comparison of γ-ray spectra before and including 2011 data suggested that there was a softening of the highenergy spectral slope. We selected five specific epochs to be studied by modelling the broad-band spectrum, which are characterised by an outburst at γ-rays or very low/high flux at other wavelengths. The observed variability can largely be explained by changes in the injected power, the bulk Lorentz factor of the jet, or the electron spectrum. The characteristic time scale of doubling/halving flux ranges from a few days to a few months, depending on the frequency and the sampling rate. The shortest doubling time scale at γ-rays is 2.3 ± 0.5 days. These small values underline the need of highly sampled multiwavelength campaigns to better understand the physics of these sources.