2,074 research outputs found
Hard X-ray Emission and the Ionizing Source in LINERs
We report X-ray fluxes in the 2--10 keV band from LINERs (low-ionization
nuclear emission-line regions) and low-luminosity Seyfert galaxies obtained
with the ASCA satellite. Observed X-ray luminosities are in the range between
4e39 and 5e41 ergs/s, which are significantly smaller than that of the
``classical'' low-luminosity Seyfert 1 galaxy NGC 4051. We found that X-ray
luminosities in 2--10 keV of LINERs with broad Halpha emission in their optical
spectra (LINER 1s) are proportional to their Halpha luminosities. This
correlation strongly supports the hypothesis that the dominant ionizing source
in LINER 1s is photoionization by hard photons from low-luminosity AGNs. On the
other hand, the X-ray luminosities of most LINERs without broad Halpha emission
(LINER 2s) in our sample are lower than LINER 1s at a given Halpha luminosity.
The observed X-ray luminosities in these objects are insufficient to power
their Halpha luminosities, suggesting that their primary ionizing source is
other than an AGN, or that an AGN, if present, is obscured even at energies
above 2 keV.Comment: 11 pages, 3 figures, To appear in the Astrophyscal Jouna
Detection of an X-ray periodicity in the Seyfert galaxy IRAS18325-5926
We report the detection of a 58 ks (16 hr) periodicity in the 0.5-10 keV
X-ray light curve of the Seyfert galaxy IRAS18325-5926 (Fairall49), obtained
from a 5-day ASCA observation. Nearly 9 cycles of the periodic variation are
seen; it shows no strong energy dependence and has an amplitude of about 15 per
cent. Unlike most other well-studied Seyfert galaxies, there is no evidence for
strong power-law red noise in the X-ray power spectrum of IRAS18325-5926.
Scaling from the QPOs found in Galactic black hole candidates suggests that the
mass of the black hole in IRAS18325-5926 is (6-40) million solar masses.Comment: 5 pages, 4 Postscript figures, to be published in MNRA
Outflow-Dominated Emission from the Quiescent Massive Black Holes in NGC 4621 and NGC 4697
The nearby elliptical galaxies NGC 4621 and NGC 4697 each host a supermassive
black hole with a mass more than 1e8 Solar masses. Analysis of archival Chandra
data and new NRAO Very Large Array data shows that each galaxy contains a
low-luminosity active galactic nucleus (LLAGN), identified as a faint, hard
X-ray source that is astrometrically coincident with a faint 8.5-GHz source.
The latter has a diameter less than 0.3 arcsec (26 pc for NGC 4621, 17 pc for
NGC 4697). The black holes energizing these LLAGNs have Eddington ratios L(2-10
keV) / L(Edd) ~ 1e-9, placing them in the so-called quiescent regime. The
emission from these quiescent black holes is radio-loud, with log Rx = log
nuLnu(8.5 GHz) / L(2-10 keV) ~ -2, suggesting the presence of a radio outflow.
Also, application of the radio-X-ray-mass relation from Yuan & Cui for
quiescent black holes predicts the observed radio luminosities nuLnu(8.5 GHz)
to within a factor of a few. Significantly, that relation invokes X-ray
emission from the outflow rather than from an accretion flow. The faint, but
detectable, emission from these two massive black holes is therefore consistent
with being outflow-dominated. Observational tests of this finding are
suggested.Comment: 11 pages; 4 figures: emulateapj; to appear in Ap
Ghost D-brane, Supersymmetry and Matrix Model
In this note we study the world volume theory of pairs of D-brane and ghost
D-brane, which is shown to have 16 linear supersymmetries and 16 nonlinear
supersymmetries. In particular we study a matrix model based on the pairs of
D(-1)-brane and ghost D(-1)-brane. Since such pairs are supposed to be
equivalent to the closed string vacuum, we expect all 32 supersymmetries should
be unbroken. We show that the world volume theory of the pairs of D-brane and
ghost D-brane has unbroken 32 supersymmetries even though a half of them are
nonlinearly realized.Comment: 12 pages, references adde
Hermitian conjugate measurement
We propose a new class of probabilistic reversing operations on the state of
a system that was disturbed by a weak measurement. It can approximately recover
the original state from the disturbed state especially with an additional
information gain using the Hermitian conjugate of the measurement operator. We
illustrate the general scheme by considering a quantum measurement consisting
of spin systems with an experimentally feasible interaction and show that the
reversing operation simultaneously increases both the fidelity to the original
state and the information gain with such a high probability of success that
their average values increase simultaneously.Comment: 26 pages, 4 figures; a paragraph is added in the introductio
Variability and spectral energy distributions of low-luminosity active galactic nuclei: a simultaneous X-ray/UV look with Swift
We have observed four low-luminosity active galactic nuclei classified as
Type 1 LINERs with the X-ray Telescope (XRT) and the UltraViolet-Optical
Telescope (UVOT) onboard Swift, in an attempt to clarify the main powering
mechanism of this class of nearby sources. Among our targets, we detect X-ray
variability in NGC 3998 for the first time. The light curves of this object
reveal variations of up to 30% amplitude in half a day, with no significant
spectral variability on this time scale. We also observe a decrease of ~30%
over 9 days, with significant spectral softening. Moreover, the X-ray flux is
~40% lower than observed in previous years. Variability is detected in M 81 as
well, at levels comparable to those reported previously: a flux increase in the
hard X-rays (1-10 keV) of 30% in ~3 hours and variations by up to a factor of 2
within a few years. This X-ray behaviour is similar to that of
higher-luminosity, Seyfert-type, objects. Using previous
high-angular-resolution imaging data from the Hubble Space Telescope (HST), we
evaluate the diffuse UV emission due to the host galaxy and isolate the nuclear
flux in our UVOT observations. All sources are detected in the UV band, at
levels similar to those of the previous observations with HST. The XRT (0.2-10
keV) spectra are well described by single power-laws and the UV-to-X-ray flux
ratios are again consistent with those of Seyferts and radio-loud AGNs of
higher luminosity. The similarity in X-ray variability and broad-band energy
distributions suggests the presence of similar accretion and radiation
processes in low- and high-luminosity AGNs.Comment: 12 pages, 6 figures, in press in MNRA
X-ray Properties of the Weak Seyfert 1 Nucleus in NGC 4639
We obtained observations of NGC 4639 with ASCA in order to investigate its
mildly active Seyfert 1 nucleus at hard X-ray energies. Koratkar et al. (1995)
have previously shown that the nucleus is a pointlike source in the ROSAT soft
X-ray band. We detected in the 2-10 keV band a compact central source with a
luminosity of 8.3E+40 erg/s. Comparison of the ASCA data with archival data
taken with the Einstein and ROSAT satellites shows that the nucleus varies on
timescales of months to years. The variability could be intrinsic, or it could
be caused by variable absorption. More rapid variability, on a timescale of
\~10^4 s, may be present in the ASCA data. The spectrum from 0.5 to 10 keV is
well described by a model consisting of a lightly absorbed (N_H = 7.3E+20
cm^-2) power law with a photon index of 1.68. We find no evidence for
significant emission from a thermal plasma; if present, it can account for no
more than 25% of the flux in the 0.5-2.0 keV band. The limited photon
statistics of our data do not allow us to place significant limits on the
presence of iron K emission. (abridged)Comment: To appear in The Astrophysical Journal. LaTex, 18 pages including
embedded figures and table
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