Broad line emission from iron K- and L-shell transitions in the active galaxy 1H0707-495
Larsson, J.; Young, A. J.; Brandt, W. N.; Ponti, G.; Fabian, A. C.; Miller, J. M.; Reynolds, C. S.; Miniutti, G.; Uttley, P.; Reis, R. C.; Gallo, L. C.; Ross, R. R.; Zoghbi, A.; Tanaka, Y.; Blustin, A. J.; Boller, T.; Caballero-Garcia, M. D.
United Kingdom, United States, Canada, Germany, Spain, France
Abstract
Since the 1995 discovery of the broad iron K-line emission from the Seyfert galaxy MCG-6-30-15 (ref. 1), broad iron K lines have been found in emission from several other Seyfert galaxies, from accreting stellar-mass black holes and even from accreting neutron stars. The iron K line is prominent in the reflection spectrum created by the hard-X-ray continuum irradiating dense accreting matter. Relativistic distortion of the line makes it sensitive to the strong gravity and spin of the black hole. The accompanying iron L-line emission should be detectable when the iron abundance is high. Here we report the presence of both iron K and iron L emission in the spectrum of the narrow-line Seyfert 1 galaxy 1H0707-495. The bright iron L emission has enabled us to detect a reverberation lag of about 30s between the direct X-ray continuum and its reflection from matter falling into the black hole. The observed reverberation timescale is comparable to the light-crossing time of the innermost radii around a supermassive black hole. The combination of spectral and timing data on 1H0707-495 provides strong evidence that we are witnessing emission from matter within a gravitational radius, or a fraction of a light minute, from the event horizon of a rapidly spinning, massive black hole.