8,006 research outputs found
Multifrequency observations of XTE J0421+560/CI Cam in outburst
We report on two X-ray observations of the transient source XTE J0421+560
performed by BeppoSAX, and on a series of observations performed by the 0.7m
Teramo-Normale Telescope. Outburst peak occurrence time and duration depend on
photon energy: the outburst peak is achieved first in the X-ray band, then in
the optical and finally in the radio. An exponential decay law fits well the
X-ray data except in the TOO2 0.5-1.0 keV band, where erratic time variability
is detected. During TOO1 the e-folding time scale decreases with energy up to ~
20 keV, when it achieves a saturation; during TOO2 it decreases up to ~ 2 keV
and then increases. This change is correlated with a spectral change,
characterized by the onset of a soft (< 2 keV) component in TOO2 (Orr et al.
1998). This component might originate from the relativistic jets, while the
hard component is more likely associated to processes occurring in the
circumstellar matter and/or near the compact object. Optical observations show
that the object appears intrinsically red even during the outburst. The nature
of the compact object is discussed.Comment: Four pages. Accepted for publication in A&A Lette
Structural and electrical transport properties of superconducting Au{0.7}In{0.3} films: A random array of superconductor-normal metal-superconductor (SNS) Josephson junctions
The structural and superconducting properties of Au{0.7}In{0.3} films, grown
by interdiffusion of alternating Au and In layers, have been studied. The films
were found to consist of a uniform solid solution of Au{0.9}In{0.1}, with
excess In precipitated in the form of In-rich grains of various Au-In phases
(with distinct atomic compositions), including intermetallic compounds. As the
temperature was lowered, these individual grains became superconducting at a
particular transition temperature (Tc), determined primarily by the atomic
composition of the grain, before a fully superconducting state of zero
resistance was established. From the observed onset Tc, it was inferred that up
to three different superconducting phases could have formed in these
Au{0.7}In{0.3} films, all of which were embedded in a uniform Au{0.9}In{0.1}
matrix. Among these phases, the Tc of a particular one, 0.8 K, is higher than
any previously reported for the Au-In system. The electrical transport
properties were studied down to low temperatures. The transport results were
found to be well correlated with those of the structural studies. The present
work suggests that Au{0.7}In{0.3} can be modeled as a random array of
superconductor-normal metal-superconductor (SNS) Josephson junctions. The
effect of disorder and the nature of the superconducting transition in these
Au{0.7}In{0.3} films are discussed.Comment: 8 text pages, 10 figures in one separate PDF file, submitted to PR
Direct Measurement of the Top Quark Charge at Hadron Colliders
We consider photon radiation in tbar-t events at the upgraded Fermilab
Tevatron and the CERN Large Hadron Collider (LHC) as a tool to measure the
electric charge of the top quark. We analyze the contributions of tbar-t-gamma
production and radiative top quark decays to p-p, pbar-p -> gamma l^+/- nu
bbar-b jj, assuming that both b-quarks are tagged. With 20~fb^{-1} at the
Tevatron, the possibility that the ``top quark'' discovered in Run I is
actually an exotic charge -4/3 quark can be ruled out at the 95% confidence
level. At the LHC, it will be possible to determine the charge of the top quark
with an accuracy of about 10%.Comment: Revtex, 24 pages, 2 tables, 9 figure
The low-energy theory for the Bose-Hubbard model and the normal ground state of bosons
A bosonic realization of the SU(2) Lie algebra and of its vector
representation is constructed, and an effective low-energy description of the
Bose-Hubbard model in the form of anisotropic theory of quantum rotors is
proposed and discussed. A possibility of a normal zero-temperature bosonic
phase with neither crystalline nor superfluid order around the tip of the
checkerboard-solid lobe at half-integer fillings is examined.Comment: 8 pages, LaTex, one postscript figur
On the nature of XTE J0421+560/CI Cam
We present the results of the analysis of RXTE, BATSE and optical/infrared
data of the 1998 outburst of the X-ray transient system XTE J0421+560 (CI Cam).
The X-ray outburst shows a very fast decay (initial e-folding time ~0.5 days,
slowing down to ~2.3 days). The X-ray spectrum in the 2-25 keV band is complex,
softening considerably during decay and with strongly variable intrinsic
absorption. A strong iron emission line is observed. No fast time variability
is detected (<0.5 % rms in the 1-4096 Hz band at the outburst peak). The
analysis of the optical/IR data suggests that the secondary is a B[e] star
surrounded by cool dust and places the system at a distance of >~ 2 kpc. At
this distance the peak 2-25 keV luminosity is ~4 x 10^37 erg/s. We compare the
properties of this peculiar system with those of the Be/NS LMC transient A
0538-66 and suggest that CI Cam is of similar nature. The presence of strong
radio emission during outburst indicates that the compact object is likely to
be a black hole or a weakly magnetized neutron star.Comment: Accepted for publication on The Astrophysical Journal, July 199
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