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

Abstract

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.

Properties of flat-spectrum radio-loud narrow-line Seyfert 1 galaxies

“…More details about the Metsähovi, and Effelsberg/Pico Veleta observations on RLNLS1s will be published by Lähteenmäki et al (in preparation) and Angelakis et al (in preparation), respectively. Some of the data have already been published by Abdo et al (2009a,b), Foschini et al ( , 2012, Fuhrmann et al (2011), and Angelakis et al (2012a,b).…”

“…Fig. 6 displays the two extreme states from the available data: the lowest activity state (LS, 2009 May 15, see also Abdo et al 2009b, Foschini et al 2012) and the highest state (HS, 2012 December 30). In both cases, we model the synchrotron emission (dotted grey line) with a power-law model with an exponential cutoff.…”

“…The disk emission (dashed grey line) is the standard Shakura-Sunyaev model as expected from a black hole of M = 7.5 × 10 7 M ⊙ (see Table 2). Previous modelling (Abdo et al 2009b, Foschini et al 2012) supposed constant disk luminosity equal to L disk ∼ 0.4L Edd , as measured by fitting the optical/UV emission with a standard Shakura-Sunyaev disk. In the present work, we obtained from the emission lines a value of L disk ∼ 0.12L Edd .…”

“…During the 2009 MW campaign, these values ranged from 44.9 to 45.54 for the radiative power, and from 45.67 to 46.2 for the kinetic power (Abdo et al 2009b). During more than three years of monitoring, log P rad spanned the interval 44.55-45.97, while log P kinetic was in the range 46.19-47.61 (Foschini et al 2012). The present estimate (Table 3) is an average of several measurements done directly at 15 GHz (mostly by the MOJAVE project and Effelsberg), and is reasonably consistent with the previously published values (see also Angelakis et al, in preparation).…”

FERMIMONITORING OF RADIO-LOUD NARROW-LINE SEYFERT 1 GALAXIES

“…The peak flux is observed in the bin centered at MJD 56,297, which is not covered by Foschini et al (2012). Few significant flaring activities are observed and we consider two of them for further analysis.…”