1,980 research outputs found
High-resolution X-ray spectroscopy of the low and high states of the Seyfert 1 galaxy NGC 4051 with Chandra LETGS
Methods. We analyse two observations taken with the Low Energy Transmission
Grating Spectrometer of Chandra. We investigated the spectral response to a
sudden flux decrease by a factor of 5, which occurred during the second
observation. Results. We detect a highly ionised absorption component with an
outflow velocity of -4670 km/s, one of the highest outflow velocity components
observed in a Seyfert 1 galaxy. The spectra contain a relativistic O VIII Ly
alpha line, and four absorption components spanning a range in ionisation
parameter xi between 0.07 and 3.19. An emission component producing radiative
recombination continua of C VI and C V appears during the low state. The black
body temperature decreases with the drop in flux observed in the second
observation. Conclusions. For all absorber components we exclude that the
ionisation parameter linearly responded to the decrease in flux by a factor of
5. The variability of the absorber suggest that at least three out of four
detected components are located in the range 0.02-1 pc. ABRIDGEDComment: Accepted by A&A, 14 pages, 9 figure
Deep Optical Imaging of A Compact Group of Galaxies, Seyfert's Sextet
In order to investigate the dynamical status of Seyfert's Sextet (SS), we
have obtained a deep optical () image of this group. Our image shows that
a faint envelope, down to a surface brightness (AB) mag arcsec, surrounds the member galaxies. This envelope is
irregular in shape. It is likely that this shape is attributed either to
recent-past or to on-going galaxy interactions in SS. If the member galaxies
have experienced a number of mutual interactions over a long timescale, the
shape of the envelope should be rounder. Therefore, the irregular-shaped
morphology suggests that SS is in an early phase of dynamical interaction among
the member galaxies. It is interesting to note that the soft X-ray image
obtained with ROSAT (Pildis et al. 1995) is significantly similar in
morphology. We discuss the possible future evolution of SS briefly.Comment: 7 pages text (emulateapj LaTeX), 8 figures (3 EPS files, 1 PostScript
file, and 4 jpeg files) figures, The Astronomical Journal, 120, No. 5 inpres
Supermassive Black Holes in Galactic Nuclei: Past, Present and Future Research
This review discusses the current status of supermassive black hole research,
as seen from a purely observational standpoint. Since the early '90s, rapid
technological advances, most notably the launch of the Hubble Space Telescope,
the commissioning of the VLBA and improvements in near-infrared speckle imaging
techniques, have not only given us incontrovertible proof of the existence of
supermassive black holes, but have unveiled fundamental connections between the
mass of the central singularity and the global properties of the host galaxy.
It is thanks to these observations that we are now, for the first time, in a
position to understand the origin, evolution and cosmic relevance of these
fascinating objects.Comment: Invited Review, 114 pages. Because of space requirements, this
version contains low resolution figures. The full resolution version can be
downloaded from http://www.physics.rutgers.edu/~lff/publications.htm
Validity and Reproducibility of Measurement of Islet Autoreactivity by T-Cell Assays in Subjects With Early Type 1 Diabetes
Measurement of the ratio of branching fractions BR(B0 -> K*0 gamma)/BR(Bs0 -> phi gamma)
The ratio of branching fractions of the radiative B decays B0 -> K*0 gamma
and Bs0 -> phi gamma has been measured using 0.37 fb-1 of pp collisions at a
centre of mass energy of sqrt(s) = 7 TeV, collected by the LHCb experiment. The
value obtained is BR(B0 -> K*0 gamma)/BR(Bs0 -> phi gamma) = 1.12 +/- 0.08
^{+0.06}_{-0.04} ^{+0.09}_{-0.08}, where the first uncertainty is statistical,
the second systematic and the third is associated to the ratio of fragmentation
fractions fs/fd. Using the world average for BR(B0 -> K*0 gamma) = (4.33 +/-
0.15) x 10^{-5}, the branching fraction BR(Bs0 -> phi gamma) is measured to be
(3.9 +/- 0.5) x 10^{-5}, which is the most precise measurement to date.Comment: 15 pages, 1 figure, 2 table
Search for CP violation in decays
A model-independent search for direct CP violation in the Cabibbo suppressed
decay in a sample of approximately 370,000 decays is
carried out. The data were collected by the LHCb experiment in 2010 and
correspond to an integrated luminosity of 35 pb. The normalized Dalitz
plot distributions for and are compared using four different
binning schemes that are sensitive to different manifestations of CP violation.
No evidence for CP asymmetry is found.Comment: 13 pages, 8 figures, submitted to Phys. Rev.
Measurement of the lifetime
Using a data set corresponding to an integrated luminosity of ,
collected by the LHCb experiment in collisions at centre-of-mass energies
of 7 and 8 TeV, the effective lifetime in the
decay mode, , is measured to be ps. Assuming
conservation, corresponds to the lifetime of the light
mass eigenstate. This is the first measurement of the effective
lifetime in this decay mode.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2016-017.htm
Opposite-side flavour tagging of B mesons at the LHCb experiment
The calibration and performance of the oppositeside
flavour tagging algorithms used for the measurements
of time-dependent asymmetries at the LHCb experiment
are described. The algorithms have been developed using
simulated events and optimized and calibrated with
B
+ âJ/ÏK
+, B0 âJ/ÏK
â0 and B0 âD
ââ
Ό
+
ΜΌ decay
modes with 0.37 fbâ1 of data collected in pp collisions
at
â
s = 7 TeV during the 2011 physics run. The oppositeside
tagging power is determined in the B
+ â J/ÏK
+
channel to be (2.10 ± 0.08 ± 0.24) %, where the first uncertainty
is statistical and the second is systematic
Strong constraints on the rare decays Bs -> mu+ mu- and B0 -> mu+ mu-
A search for Bs -> mu+ mu- and B0 -> mu+ mu- decays is performed using 1.0
fb^-1 of pp collision data collected at \sqrt{s}=7 TeV with the LHCb experiment
at the Large Hadron Collider. For both decays the number of observed events is
consistent with expectation from background and Standard Model signal
predictions. Upper limits on the branching fractions are determined to be BR(Bs
-> mu+ mu-) mu+ mu-) < 1.0 (0.81) x 10^-9 at
95% (90%) confidence level.Comment: 2+6 pages; 4 figures; Accepted for publication in Physical Review
Letter
Measurements of the branching fractions of the decays B°s â Dâs K± and B°s â DÂŻsÏ+
The decay mode B°s â Dâs K± allows for one of the theoretically cleanest measurements of the CKM angle Îł through the study of time-dependent CP violation. This paper reports a measurement of its branching fraction relative to the Cabibbo-favoured mode B°s â DÂŻsÏ+ based on a data sample corresponding to 0.37 fbÂŻÂč of proton-proton collisions at âs = 7TeV collected in 2011 with the LHCb detector. In addition, the ratio of B meson production fractions fs/fd, determined from semileptonic decays, together with the known branching fraction of the control channel B°s â DÂŻsÏ+ is used to perform an absolute measurement of the branching fractions: B(B°s â DÂŻsÏ+) = (2.95 ± 0.05 ± 0.17 -0.22 +0.18) Ă 10ÂŻÂł ; B(B°s â Dâs K±) = (1.90 ± 0.12 ± 0.13 -0.14 +0.12) Ă 10ÂŻ4 ; where the first uncertainty is statistical, the second the experimental systematic uncertainty, and the third the uncertainty due to f s/f
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