11,758 research outputs found
Slim Disk Model for Soft X-Ray Excess and Variability of Narrow-Line Seyfert 1 Galaxies
Narrow-line Seyfert 1 galaxies (NLS1s) exhibit extreme soft X-ray excess and
large variability. We argue that both features can be basically accounted for
by the slim disk model. We assume that a central black-hole mass in NLS1 is
relatively small, , and that a disk shines nearly at
the Eddington luminosity, . Then, the disk becomes a slim disk and
exhibits the following distinctive signatures: (1) The disk luminosity
(particularly of X-rays) is insensitive to mass-flow rates, , since the
generated energy is partly carried away to the black hole by trapped photons in
accretion flow. (2) The spectra are multi-color blackbody. The maximum
blackbody temperature is keV,
and the size of the blackbody emitting region is small, r_{\rm bb} \lsim 3
r_{\rm S} (with being Schwarzschild radius) even for a
Schwarzschild black hole. (3) All the ASCA observation data of NLS1s fall onto
the region of (with being the Eddington
luminosity) on the () plane, supporting our view that a
slim disk emits soft X-rays at in NLS1s. (4) Magnetic energy
can be amplified, at most, up to the equipartition value with the trapped
radiation energy which greatly exceeds radiation energy emitted from the disk.
Hence, energy release by consecutive magnetic reconnection will give rise to
substantial variability in soft X-ray emission.Comment: 9 pages LaTeX including 4 figures, accepted to PASJ. e-mail to
[email protected]
Measuring Black Hole Spin using X-ray Reflection Spectroscopy
I review the current status of X-ray reflection (a.k.a. broad iron line)
based black hole spin measurements. This is a powerful technique that allows us
to measure robust black hole spins across the mass range, from the stellar-mass
black holes in X-ray binaries to the supermassive black holes in active
galactic nuclei. After describing the basic assumptions of this approach, I lay
out the detailed methodology focusing on "best practices" that have been found
necessary to obtain robust results. Reflecting my own biases, this review is
slanted towards a discussion of supermassive black hole (SMBH) spin in active
galactic nuclei (AGN). Pulling together all of the available XMM-Newton and
Suzaku results from the literature that satisfy objective quality control
criteria, it is clear that a large fraction of SMBHs are rapidly-spinning,
although there are tentative hints of a more slowly spinning population at high
(M>5*10^7Msun) and low (M<2*10^6Msun) mass. I also engage in a brief review of
the spins of stellar-mass black holes in X-ray binaries. In general,
reflection-based and continuum-fitting based spin measures are in agreement,
although there remain two objects (GROJ1655-40 and 4U1543-475) for which that
is not true. I end this review by discussing the exciting frontier of
relativistic reverberation, particularly the discovery of broad iron line
reverberation in XMM-Newton data for the Seyfert galaxies NGC4151, NGC7314 and
MCG-5-23-16. As well as confirming the basic paradigm of relativistic disk
reflection, this detection of reverberation demonstrates that future large-area
X-ray observatories such as LOFT will make tremendous progress in studies of
strong gravity using relativistic reverberation in AGN.Comment: 19 pages. To appear in proceedings of the ISSI-Bern workshop on "The
Physics of Accretion onto Black Holes" (8-12 Oct 2012). Revised version adds
a missing source to Table 1 and Fig.6 (IRAS13224-3809) and corrects the
referencing of the discovery of soft lags in 1H0707-495 (which were in fact
first reported in Fabian et al. 2009
Study of the Cir X--1 Broad Band Spectrum at Orbital Phases Close to the Apoastron
We report on the results of a BeppoSAX (1.8--200 keV) observation of the
peculiar X-ray binary source Circinus X--1 (Cir X--1) at the orbital phases
between 0.61 and 0.63. We find that three components are needed to fit the
broad band spectrum: a blackbody component, at a temperature of keV,
a Comptonized component, with a seed-photon temperature of keV,
electron temperature of keV and optical depth of , and a
power-law component dominating the spectrum at energies higher than 20 keV. We
interpret the blackbody as the emission from the accretion disk, while the
Comptonized component probably comes from a corona surrounding the inner part
of the system. This spectrum is different from that observed at the periastron
(Iaria et al. 2001a) because of the presence of the blackbody component. We
discuss the implications of this difference and the presence of the power-law
component.Comment: 15 pages, 6 figures, accepted by Ap
Monthly progress report
This report is the mid-year report intended for the design concepts for the communication network for the Advanced Solid Rocket Motor (ASRM) facility being built at Yellow Creek near Iuka, MS. The overall network is to include heterogeneous computers, to use various protocols, and to have different bandwidths. Performance consideration must be given to the potential network applications in the network environment. The performance evaluation of X window applications was given the major emphasis in this report. A simulation study using Bones will be included later. This mid-year report has three parts: Part 1 is an investigation of X window traffic using TCP/IP over Ethernet networks; part 2 is a survey study of performance concepts of X window applications with Macintosh computers; and the last part is a tutorial on DECnet protocols. The results of this report should be useful in the design and operation of the ASRM communication network
Combined STEREO/RHESSI study of CME acceleration and particle acceleration in solar flares
Using the potential of two unprecedented missions, STEREO and RHESSI, we
study three well observed fast CMEs that occurred close to the limb together
with their associated high energy flare emissions in terms of RHESSI HXR
spectra and flux evolution. From STEREO/EUVI and STEREO/COR1 data the full CME
kinematics of the impulsive acceleration phase up to 4 Rs is measured with a
high time cadence of less equal 2.5 min. For deriving CME velocity and
acceleration we apply and test a new algorithm based on regularization methods.
The CME maximum acceleration is achieved at heights h < 0.4 Rs, the peak
velocity at h < 2.1 Rs (in one case as small as 0.5 Rs). We find that the CME
acceleration profile and the flare energy release as evidenced in the RHESSI
hard X-ray flux evolve in a synchronized manner. These results support the
standard flare/CME model which is characterized by a feed-back relationship
between the large-scale CME acceleration process and the energy release in the
associated flare.Comment: accepted for Ap
Simulating Supersonic Turbulence in Galaxy Outflows
We present three-dimensional, adaptive mesh simulations of dwarf galaxy out-
flows driven by supersonic turbulence. Here we develop a subgrid model to track
not only the thermal and bulk velocities of the gas, but also its turbulent
velocities and length scales. This allows us to deposit energy from supernovae
directly into supersonic turbulence, which acts on scales much larger than a
particle mean free path, but much smaller than resolved large-scale flows.
Unlike previous approaches, we are able to simulate a starbursting galaxy
modeled after NGC 1569, with realistic radiative cooling throughout the
simulation. Pockets of hot, diffuse gas around individual OB associations sweep
up thick shells of material that persist for long times due to the cooling
instability. The overlapping of high-pressure, rarefied regions leads to a
collective central outflow that escapes the galaxy by eating away at the
exterior gas through turbulent mixing, rather than gathering it into a thin,
unstable shell. Supersonic, turbulent gas naturally avoids dense regions where
turbulence decays quickly and cooling times are short, and this further
enhances density contrasts throughout the galaxy- leading to a complex, chaotic
distribution of bubbles, loops and filaments as observed in NGC 1569 and other
outflowing starbursts.Comment: 22 pages, 13 figures, MNRAS, in pres
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