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X-ray short-time lags in the Fe-K energy band produced by scattering clouds in active galactic nuclei
- Source :
- Monthly notices of the Royal Astronomical Society, 2018, Vol.478(1), pp.971-982 [Peer Reviewed Journal]
- Publication Year :
- 2018
- Publisher :
- arXiv, 2018.
-
Abstract
- X-rays illuminating the accretion disc in active galactic nuclei give rise to an iron K line and its associated reflection spectrum which are lagged behind the continuum variability by the light-travel time from the source to the disc. The measured lag timescales in the iron band can be as short as $\sim R_g/c$, where $R_g$ is the gravitational radius, which is often interpreted as evidence for a very small continuum source close to the event horizon of a rapidly spinning black hole. However, the short lags can also be produced by reflection from more distant material, because the primary photons with no time-delay dilute the time-lags caused by the reprocessed photons. We perform a Monte-Carlo simulation to calculate the dilution effect in the X-ray reverberation lags from a half-shell of neutral material placed at $100\,R_g$ from the central source. This gives lags of $\sim2\,R_g/c$, but the iron line is a distinctly narrow feature in the lag-energy plot, whereas the data often show a broader line. We show that both the short lag and the line broadening can be reproduced if the scattering material is outflowing at $\sim0.1c$. The velocity structure in the wind can also give shifts in the line profile in the lag-energy plot calculated at different frequencies. Hence we propose that the observed broad iron reverberation lags and shifts in profile as a function of frequency of variability can arise from a disc wind at fairly large distances from the X-ray source.<br />Comment: 12 pages, accepted for publication in MNRAS
- Subjects :
- Physics
High Energy Astrophysical Phenomena (astro-ph.HE)
Reverberation
Photon
Active galactic nucleus
010308 nuclear & particles physics
Scattering
Event horizon
Astrophysics::High Energy Astrophysical Phenomena
black hole physics
galaxies: active
FOS: Physical sciences
Astronomy and Astrophysics
Astrophysics
01 natural sciences
K-line
galaxies: Seyfert
X-rays: galaxies
Space and Planetary Science
0103 physical sciences
Electronic band structure
Astrophysics - High Energy Astrophysical Phenomena
010303 astronomy & astrophysics
Schwarzschild radius
Astrophysics::Galaxy Astrophysics
Subjects
Details
- Database :
- OpenAIRE
- Journal :
- Monthly notices of the Royal Astronomical Society, 2018, Vol.478(1), pp.971-982 [Peer Reviewed Journal]
- Accession number :
- edsair.doi.dedup.....d0fe0ab852bca63fbc147ee4bc8d8015
- Full Text :
- https://doi.org/10.48550/arxiv.1805.00046