Modelling the variable broad-band optical/UV/X-ray spectrum of PG1211+143: implications for the ionized outflow
1 Department of Physics & Institute of Theoretical & Computational Physics, University of Crete, PO Box 2208, 710 03 Heraklion, Crete, Greece
2 IESL, Foundation for Research and Technology-Hellas, 71110 Heraklion, Crete, Greece
3 Osservatorio Astronomico di Roma-INAF, Via di Frascati 33, 00040 Monte Porzio Catone, RM, Italy
4 Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA
Received: 2 October 2015
Accepted: 26 April 2016
Context. We present the results from a detailed analysis of the 2007 Swift monitoring campaign of the quasar PG1211+143.
Aims. We study its broad-band optical/UV-X-ray spectral energy distribution and its variations, with the use of physically motivated models.
Methods. We constructed broad-band, optical/UV-X-ray spectral energy distributions over three X-ray flux intervals, and we fitted them with a model which accounts for the disc and the X-ray coronal emission. We also added a spectral model component to account for the presence of the warm absorber which has been well established from past observations of the source.
Results. We detected no optical/UV variations over the two-month period of the monitoring campaign. On the other hand, the X-rays are highly variable in a correlated way in the soft and hard X-ray bands with an amplitude larger than has been commonly observed in nearby Seyferts, even on longer time scales. The three flux spectra are well fitted by the model we considered. The disc inner temperature remains constant at ~2 eV, while X-rays are variable in slope and normalization. The absorber covers almost 90% of the central source. It is outflowing with a velocity less than 2.3 × 104 km s-1 (3σ upper limit), and has a column density of log NH ~ 23.2. Its ionization parameter varies by a factor of 1.6, and it is in photo-ionizing equilibrium with the ionizing flux. It is located at a distance of less than 0.35 pc from the central source, and its relative thickness, ΔR/R, is less than 0.1. The absorber’s ionization parameter variations can explain the larger than average amplitude of the X-ray variations.
Conclusions. The absence of optical/UV variations are consistent with the high black hole mass estimate of ~108M⊙ for this object, which implies variability time scales longer than the period of the Swift observations. It argues against the presence of inward propagating fluctuations in the disc as the reason for the flux variability in this source and against the hypothesis that X-ray illumination singificantly affects the disc emission. This is consistent with the low ratio of X-ray over the bolometric luminosity of ~20–35 in this source. Based on the properties of the ionized outflow, we estimate an upper limit for the mass outflow of ~5 M⊙ per year, which is ~2.3 times the Eddington mass accretion rate for PG1211+143. If the outflow rate is indeed that high, then it must be a short-lived episode in the quasar’s life time. Finally, we estimate an upper limit for the kinetic power of the outflow of ~1.4 × 1043 ergs s-1. As a result, the outflow cannot deploy significant mechanical energy to the surrounding ISM of the quasar’s host galaxy, but is sufficient to heat the ISM to 107 K and to produce a fast decline to the star formation rate of the galaxy.
Key words: galaxies: active / galaxies: Seyfert / quasars: individual: PG1211+134 / X-rays: galaxies
© ESO, 2016