1,746 research outputs found
Relativistic iron K X-ray Reverberation in NGC 4151
Recent X-ray observations have enabled the study of reverberation delays in
AGN for the first time. All the detections so far are in sources with a strong
soft excess, and the measured delay is between the hard (1-3 keV) direct
continuum and the soft excess (0.5-1 keV), interpreted as the reflection
continuum smeared by relativistic effects. There is however an inherent
ambiguity in identifying and studying the details of the lines in the soft
excess. Here we report the first detection of reverberation in the iron K band
in any AGN. Using XMM-Newton observations of NGC 4151, we find delays of order
2000 s on time-scales of 10e5 s between the 5-6 keV band and 2-3 and 7-8 keV
bands, with a broad lag profile resembling a relativistically-broadened iron
line. The peak of the lag spectra shifts to lower energies at higher
frequencies, consistent with the red wing of the line being emitted at smaller
radii, as expected from reflection off the inner accretion disk. This is a
first detection of a broad iron line using timing studies.Comment: final version, corrected small typo
Discovery of high-frequency iron K lags in Ark 564 and Mrk 335
We use archival XMM-Newton observations of Ark 564 and Mrk 335 to calculate
the frequency dependent time-lags for these two well-studied sources. We
discover high-frequency Fe K lags in both sources, indicating that the red wing
of the line precedes the rest frame energy by roughly 100 s and 150 s for Ark
564 and Mrk 335, respectively. Including these two new sources, Fe K
reverberation lags have been observed in seven Seyfert galaxies. We examine the
low-frequency lag-energy spectrum, which is smooth, and shows no feature of
reverberation, as would be expected if the low-frequency lags were produced by
distant reflection off circumnuclear material. The clear differences in the low
and high frequency lag-energy spectra indicate that the lags are produced by
two distinct physical processes. Finally, we find that the amplitude of the Fe
K lag scales with black hole mass for these seven sources, consistent with a
relativistic reflection model where the lag is the light travel delay
associated with reflection of continuum photons off the inner disc.Comment: 10 pages, 12 figures, accepted for publication in MNRA
1H0707-495 in 2011: An X-ray source within a gravitational radius of the event horizon
The Narrow Line Seyfert 1 Galaxy 1H0707-495 went in to a low state from 2010
December to 2011 February, discovered by a monitoring campaign using the X-Ray
Telescope on the Swift satellite. We triggered a 100 ks XMM-Newton observation
of the source in 2011 January, revealing the source to have dropped by a factor
of ten in the soft band, below 1 keV, and a factor of 2 at 5 keV, compared with
a long observation in 2008. The sharp spectral drop in the source usually seen
around 7 keV now extends to lower energies, below 6 keV in our frame. The 2011
spectrum is well fit by a relativistically-blurred reflection spectrum similar
to that which fits the 2008 data, except that the emission is now concentrated
solely to the central part of the accretion disc. The irradiating source must
lie within 1 gravitational radius of the event horizon of the black hole, which
spins rapidly. Alternative models are briefly considered but none has any
simple physical interpretation.Comment: 9 pages, 19 figures, MNRAS in pres
Detection of a variable ultra-fast outflow in the Narrow Line Seyfert 1 galaxy PG 1448+273
Relativistically blueshifted absorption features of highly ionised ions, the
so-called ultra-fast outflows (UFOs), have been detected in the X-ray spectra
of a number of accreting supermassive black holes. If these features truly
originate from accretion disc winds accelerated to more than 10 per cent of the
speed of light, their energy budget is very significant and they can contribute
to or even drive galaxy-scale feedback from active galactic nuclei (AGN).
However, the UFO spectral features are often weak due to high ionisation of the
outflowing material, and the inference of the wind physical properties can be
complicated by other spectral features in AGN such as relativistic reflection.
Here we study a highly accreting Narrow Line Seyfert 1 galaxy PG 1448+273. We
apply an automated, systematic routine for detecting outflows in accreting
systems and achieve an unambiguous detection of a UFO in this AGN. The UFO
absorption is observed in both soft and hard X-ray bands with the XMM-Newton
observatory. The velocity of the outflow is (26900 +- 600) km/s (~0.09c), with
an ionisation parameter of log ({\xi} / erg cm s^-1)=4.03_{-0.08}^{+0.10} and a
column density above 10^23 cm^-2. At the same time, we detect weak warm
absorption features in the spectrum of the object. Our systematic outflow
search suggests the presence of further multi-phase wind structure, but we
cannot claim a significant detection considering the present data quality. The
UFO is not detected in a second, shorter observation with XMM-Newton,
indicating variability in time, observed also in other similar AGN.Comment: Accepted for publication in MNRAS. 14 pages, 11 figures, 1 tabl
The Closest Look at 1H0707-495: X-ray Reverberation Lags with 1.3 Ms of Data
Reverberation lags in AGN were first discovered in the NLS1 galaxy,
1H0707-495. We present a follow-up analysis using 1.3 Ms of data, which allows
for the closest ever look at the reverberation signature of this remarkable
source. We confirm previous findings of a hard lag of ~100 seconds at
frequencies v ~ [0.5 - 4] e-4 Hz, and a soft lag of ~30 seconds at higher
frequencies, v ~ [0.6 - 3] e-3 Hz. These two frequency domains clearly show
different energy dependences in their lag spectra. We also find evidence for a
signature from the broad Fe K line in the high frequency lag spectrum. We use
Monte Carlo simulations to show how the lag and coherence measurements respond
to the addition of Poisson noise and to dilution by other components. With our
better understanding of these effects on the lag, we show that the lag-energy
spectra can be modelled with a scenario in which low frequency hard lags are
produced by a compact corona responding to accretion rate fluctuations
propagating through an optically thick accretion disc, and the high frequency
soft lags are produced by short light-travel delay associated with reflection
of coronal power-law photons off the disc.Comment: 11 pages, 10 figures. Accepted for publication in MNRA
Neurodegeneration: From cellular concepts to clinical applications
Developing therapies for neurodegenerative diseases will require new scientific approaches that take into account the detrimental effects of altered protein and RNA homeostasis on brain cells, the vulnerabilities of various organelles in certain diseases and aging neurons, and the complex multicellular interactions of the nervous system
X-ray Reverberation close to the black hole in RE J1034+396
In previous work, we discussed the detection of reverberation delays in the
NLS1 1H0707-495. The delays originate close to the black hole. Here, we show
that RE J1034+396 shows very similar lag properties. At low frequencies (< 1
\times 10-4 Hz), the time lag between energy bands increases with energy
separation, similar to that commonly seen in Galactic black holes and other
AGN. At higher frequencies (~ 3.5 \times 10-4 Hz), the soft (< 1 keV) and hard
(> 3 keV) bands lag behind the intermediate band (1-3 keV). The simplest
interpretation is that the intermediate band is dominated by the direct
power-law continuum, while the soft and hard bands are dominated by the
relativistically-smeared reflected emission. The low frequency delays are
present in both available observations. The high frequency lags are only seen
in one observation. In the observation where high frequency reverberation
delays are observed, the spectrum contains a power-law component and there is a
QPO in the light curve. In the other observation, no power-law component is
required and no QPO is seen. The lags originate a few gravitational radii from
the black hole, and the QPO is associated with the power-law emitting corona.Comment: Accepted for publication in MNRA
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