52 research outputs found
Constraints on Black Hole Spin in a Sample of Broad Iron Line AGN
We present a uniform X-ray spectral analysis of nine type-1 active galactic nuclei (AGN) that have been previously found to harbor relativistically broadened iron emission lines. We show that the need for relativistic effects in the spectrum is robust even when one includes continuum "reflection" from the accretion disk. We then proceed to model these relativistic effects in order to constrain the spin of the supermassive black holes in these AGN. Our principal assumption, supported by recent simulations of geometrically-thin accretion disks, is that no iron line emission (or any associated Xray reflection features) can originate from the disk within the innermost stable circular orbit. Under this assumption, which tends to lead to constraints in the form of lower limits on the spin parameter, we obtain non-trivial spin constraints on five AGN. The spin parameters of these sources range from moderate (a approximates 0.6) to high (a > 0.96). Our results allow, for the first time, an observational constraint on the spin distribution function of local supermassive black holes. Parameterizing this as a power-law in dimensionless spin parameter (f(a) varies as absolute value of (a) exp zeta), we present the probability distribution for zeta implied by our results. Our results suggest 90% and 95% confidence limits of zeta > -0.09 and zeta > -0.3 respectively
Relativistic Broadening of Iron Emission Lines in a Sample of AGN
We present a uniform X-ray spectral analysis of eight type-1 active galactic
nuclei (AGN) that have been previously observed with relativistically broadened
iron emission lines. Utilizing data from the XMM-Newton European Photon Imaging
Camera (EPIC-pn) we carefully model the spectral continuum, taking complex
intrinsic absorption and emission into account. We then proceed to model the
broad Fe K feature in each source with two different accretion disk emission
line codes, as well as a self-consistent, ionized accretion disk spectrum
convolved with relativistic smearing from the inner disk. Comparing the
results, we show that relativistic blurring of the disk emission is required to
explain the spectrum in most sources, even when one models the full reflection
spectrum from the photoionized disk.Comment: 50 pages (preprint format), 24 figures. Accepted by Ap
Irradiation of an Accretion Disc by a Jet: General Properties and Implications for Spin Measurements of Black Holes
X-ray irradiation of the accretion disc leads to strong reflection features,
which are then broadened and distorted by relativistic effects. We present a
detailed, general relativistic approach to model this irradiation for different
geometries of the primary X-ray source. These geometries include the standard
point source on the rotational axis as well as more jet-like sources, which are
radially elongated and accelerating. Incorporating this code in the relline
model for relativistic line emission, the line shape for any configuration can
be predicted. We study how different irradiation geometries affect the
determination of the spin of the black hole. Broad emission lines are produced
only for compact irradiating sources situated close to the black hole. This is
the only case where the black hole spin can be unambiguously determined. In all
other cases the line shape is narrower, which could either be explained by a
low spin or an elongated source. We conclude that for all those cases and
independent of the quality of the data, no unique solution for the spin exists
and therefore only a lower limit of the spin value can be given.Comment: accepted by MNRAS for publication; now proof corrected Versio
Self-consistent Black Hole Accretion Spectral Models and the Forgotten Role of Coronal Comptonization of Reflection Emission
Continuum and reflection spectral models have each been widely employed in measuring the spins of accreting black holes. However, the two approaches have not been implemented together in a photon-conserving, self-consistent framework. We develop such a framework using the black hole X-ray binary GX 339–4 as a touchstone source, and we demonstrate three important ramifications. (1) Compton scattering of reflection emission in the corona is routinely ignored, but is an essential consideration given that reflection is linked to the regimes with strongest Comptonization. Properly accounting for this causes the inferred reflection fraction to increase substantially, especially for the hard state. Another important impact of the Comptonization of reflection emission by the corona is the downscattered tail. Downscattering has the potential to mimic the relativistically broadened red wing of the Fe line associated with a spinning black hole. (2) Recent evidence for a reflection component with a harder spectral index than the power-law continuum is naturally explained as Compton-scattered reflection emission. (3) Photon conservation provides an important constraint on the hard state's accretion rate. For bright hard states, we show that disk truncation to large scales R ≫ R[subscript ISCO] is unlikely as this would require accretion rates far in excess of the observed [dotM] of the brightest soft states. Our principal conclusion is that when modeling relativistically broadened reflection, spectral models should allow for coronal Compton scattering of the reflection features, and when possible, take advantage of the additional constraining power from linking to the thermal disk component.United States. National Aeronautics and Space Administration (PF5-160144
An X-Ray View of the Jet-Cycle in the Radio Loud AGN 3C120
We present a study of the central engine in the broad-line radio galaxy 3C120
using a multi-epoch analysis of a deep XMM-Newton observation and two deep
Suzaku pointings (in 2012). In order to place our spectral data into the
context of the disk-disruption/jet-ejection cycles displayed by this object, we
monitor the source in the UV/X-ray bands, and in the radio band. We find three
statistically acceptable spectral models, a disk-reflection model, a jet-model
and a jet+disk model. Despite being good descriptions of the data, the
disk-reflection model violates the radio constraints on the inclination, and
the jet-model has a fine-tuning problem, requiring a jet contribution exceeding
that expected. Thus, we argue for a composite jet+disk model. Within the
context of this model, we verify the basic predictions of the jet-cycle
paradigm, finding a truncated/refilling disk during the Suzaku observations and
a complete disk extending down to the innermost stable circular orbit (ISCO)
during the XMM-Newton observation. The idea of a refilling disk is further
supported by the detection of the ejection of a new jet knot approximately one
month after the Suzaku pointings. We also discover a step-like event in one of
the Suzaku pointings in which the soft band lags the hard band. We suggest that
we are witnessing the propagation of a disturbance from the disk into the jet
on a timescale set by the magnetic field.Comment: 14 pages, 10 figures, accepted for publication in Ap
Iron Line Spectroscopy of NGC4593 with XMM-Newton: Where is the Black Hole Accretion Disk?
We present an analysis of the 2-10keV XMM-Newton/EPIC-pn spectrum of the
Seyfert-1 galaxy NGC4593. Apart from the presence of two narrow emission lines
corresponding to the Kalpha lines of cold and hydrogen-like iron, this spectrum
possesses a power-law form to within 3-5%. There is a marked lack of spectral
features from the relativistic regions of the black hole accretion disk. We
show that the data are, however, consistent with the presence of a
radiatively-efficient accretion disk extending right down to the radius of
marginal stability if it possesses low iron abundance, an appropriately ionized
surface, a very high inclination, or a very centrally concentrated emission
pattern (as has been observed during the Deep Minimum State of the Seyfert
galaxy MCG-6-30-15). Deeper observations of this source are required in order
to validate or reject these models.Comment: 6 pages, 3 postscript figures. Accepted for publication in the
Monthly Notices of the Royal Astronomical Societ
3C 273 with NuSTAR: Unveiling the Active Galactic Nucleus
We present results from a 244 ks NuSTAR observation of 3C 273 obtained during a cross-calibration campaign with the Chandra, INTEGRAL, Suzaku, Swift, and XMM-Newton observatories. We show that the spectrum, when fit with a power-law model using data from all observatories except INTEGRAL over the 1–78 keV band, leaves significant residuals in the NuSTAR data between 30 and 78 keV. The NuSTAR 3–78 keV spectrum is well described by an exponentially cutoff power law (Γ = 1.646 ± 0.006, E_(cutoff) = 202_(-34)^(+51) keV) with a weak reflection component from cold, dense material. There is also evidence for a weak (EW = 23 ± 11 eV) neutral iron line. We interpret these features as arising from coronal emission plus reflection off an accretion disk or distant material. Beyond 80 keV INTEGRAL data show clear excess flux relative to an extrapolation of the active galactic nucleus model fit to NuSTAR. This high-energy power law is consistent with the presence of a beamed jet, which begins to dominate over emission from the inner accretion flow at 30–40 keV. Modeling the jet locally (in the NuSTAR + INTEGRAL band) as a power law, we find that the coronal component is fit by Γ_(AGN) = 1.638 ± 0.045, E_(cutoff) = 47 ± 15 keV, and jet photon index by Γ_(jet) = 1.05 ± 0.4. We also consider Fermi/LAT observations of 3C 273, and here the broadband spectrum of the jet can be described by a log-parabolic model, peaking at ~2 MeV. Finally, we investigate the spectral variability in the NuSTAR band and find an inverse correlation between flux and Γ
The Interaction of 3C401 with the Surrounding Intracluster Medium
We present an observation of the radio-galaxy 3C401 and the surrounding
intracluster medium (ICM) of its host galaxy cluster by the Chandra X-ray
Observatory. This luminous radio-galaxy is notable in that it has
characteristics intermediate between the FRI and FRII morphologies. We clearly
detect point-like emission coincident with the radio-core of 3C401, although
the spatial resolution of even Chandra is only 2kpc at the distance of 3C401
(z=0.201) and so the possibility remains that this is a dense (and rapidly
cooling) thermal gaseous core in the center of the ICM atmosphere. Strong
departures from spherical symmetry in the central 10-20kpc of the ICM clearly
suggest interaction between the ICM and the radio-lobes of 3C401. A central
X-ray bar probably results from the evacuation of two ICM cavities by the
expanding radio lobes. Beyond these central regions, the cluster possesses a
flatter profile than many clusters of comparable mass suggesting the importance
of ICM heating and entropy injection by 3C401. We detect an interesting
cross-like structure in the ICM on 100kpc scales. We speculate that this could
be a radio-galaxy induced disturbance corresponding to a time when 3C401 was
substantially more powerful. A particularly exciting possibility is that this
cross-like structure corresponds to a large scale global g-mode oscillation
excited by a past outburst of 3C401.Comment: 7 pages, 5 postscript figures. Accepted for publication in MNRA
Constraining Black Hole Spin Via X-ray Spectroscopy
We present an analysis of the observed broad iron line feature and putative
warm absorber in the long 2001 XMM-Newton observation of the Seyfert-1.2 galaxy
MCG-6-30-15. The new "kerrdisk" model we have designed for simulating line
emission from accretion disk systems allows black hole spin to be a free
parameter in the fit, enabling the user to formally constrain the angular
momentum of a black hole, among other physical parameters of the system. In an
important extension of previous work, we derive constraints on the black hole
spin in MCG-6-30-15 using a self-consistent model for X-ray reflection from the
surface of the accretion disk while simultaneously accounting for absorption by
dusty photoionized material along the line of sight (the warm absorber). Even
including these complications, the XMM-Newton/EPIC-pn data require extreme
relativistic broadening of the X-ray reflection spectrum; assuming no emission
from within the radius of marginal stability, we derive a formal constraint on
the dimensionless black hole spin parameter of a > 0.987 at 90% confidence. The
principal unmodeled effect that can significantly reduce the inferred black
hole spin is powerful emission from within the radius of marginal stability.
Although significant theoretical developments are required to fully understand
this region, we argue that the need for a rapidly spinning black hole is robust
to physically plausible levels of emission from within the radius of marginal
stability. In particular, we show that a non-rotating black hole is strongly
ruled out.Comment: 42 pages, 10 figures, accepted for publication in the Astrophysical
Journal as of 7/06. To download the models used in this paper, please go to
http://www.astro.umd.edu/~chris/kerrdisk/kerrdisk_model.htm
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