4,074 research outputs found
Outburst Photometry of the Eclipsing Dwarf Nova GY Cancri
We observed the ROSAT-selected eclipsing dwarf nova GY Cnc (=RX J0909.8+1849)
during the 2001 November outburst. We refined the orbital period to be
0.17544251(5) d. The fading portion of the outburst was indistinguishable from
those of typical dwarf novae with similar orbital periods. However, the
signature of orbital humps (or a hot spot) was far less prominently observed in
the orbital light curves and eclipse profiles than in usual dwarf novae with
similar orbital periods. The combination of low frequency of outbursts and the
apparent lack of slowly rising, long outbursts in GY Cnc is difficult to
reconcile within the standard framework of dwarf novae. We suspect that GY Cnc
may be the first above-the-gap counterpart of unusual eclipsing dwarf novae HT
Cas and IR Com.Comment: 6 pages, 7 figures, to appear in Publ. Astron. Soc. Japa
Energy Injection Episodes in Gamma Ray Bursts: The Light Curves and Polarization Properties of GRB 021004
Several GRB afterglow light curves deviate strongly from the power law decay
observed in most bursts. We show that these variations can be accounted for by
including refreshed shocks in the standard fireball model previously used to
interpret the overall afterglow behavior. As an example we consider GRB 021004
that exhibited strong light curve variations and has a reasonably well
time-resolved polarimetry. We show that the light curves in the R-band, X-rays
and in the radio can be accounted for by four energy injection episodes in
addition to the initial event. The polarization variations are shown to be a
consequence of the injections.Comment: 4 pages, 2 figures. To appear in ApJ
Photometric Study of KR Aurigae during the High State in 2001
We photometrically observed the VY Scl-type cataclysmic variable KR Aurigae
after its final rise from the fading episode in 2000-2001. Time-resolved
observation revealed that the light curve is dominated by persistent short-term
variation with time-scales of minutes to tens of minutes. On some nights,
quasi-periodic variations with periods of 10--15 min were observed. No coherent
variation was detected. The power spectral density of the variation has a power
law component (f^(-1.63)). The temporal properties of the short-term variations
in KR Aur present additional support for the possibility that flickering in CVs
may be better understood as a result of self-organized critical state as in
black-hole candidates. The light curve lacks "superhump"-type signals, which
are relatively frequently seen in VY Scl-type systems and which are suggested
to arise from tidal instability of the accretion disk induced by changing
mass-transfer rates. The present observation suggests a borderline of superhump
excitation in VY Scl-type stars between mass ratios q=0.43 (MV Lyr) and q=0.60
(KR Aur).Comment: 8 pages, 6 figures, to appear in Publ. Astron. Soc. Japa
Study of the in-plane magnetic penetration depth in the cuprate superconductor Ca_2-xNa_xCuO_2Cl_2: role of the apical sites
A study of the in-plane magnetic penetration depth \lambda_ab in a series of
the cuprate superconductors Ca_2-xNa_xCuO_2Cl_2 (Na-CCOC) with Na content
x=0.11, 0.12, 0.15, 0.18, and 0.19 is reported. The zero temperature values of
\lambda_ab(0) were obtained by means of the muon-spin rotation technique, as
well as from measurements of the intrinsic susceptibility \chi^int(0) by using
the procedure developed by Kanigel et al. [Phys.Rev.B 71, 224511 (2005)].
\lambda_ab at T=0K was found to increase with decreasing doping from
\lambda_ab(0)=316(19)nm for the x=0.19 sample to \lambda_ab(0)=430(26)nm for
the x=0.11 one. From a comparison of the present Na-CCOC data with those of
Bi2201 and La214 cuprate superconductors it is concluded that substitution of
the apical oxygen by chlorine decreases the coupling between the
superconducting CuO_2 planes, leading to an enhancement of the two-dimensional
properties of Na-CCOC.Comment: 8 pages, 7 figure
Muon spin relaxation studies of incommensurate magnetism and superconductivity in stage-4 LaCuO and LaSrCuO
This paper reports muon spin relaxation (MuSR) measurements of two single
crystals of the title high-Tc cuprate systems where static incommensurate
magnetism and superconductivity coexist. By zero-field MuSR measurements and
subsequent analyses with simulations, we show that (1) the maximum ordered Cu
moment size (0.36 Bohr magneton) and local spin structure are identical to
those in prototypical stripe spin systems with the 1/8 hole concentration; (2)
the static magnetism is confined to less than a half of the volume of the
sample, and (3) regions with static magnetism form nano-scale islands with the
size comparable to the in-plane superconducting coherence length. By
transverse-field MuSR measurements, we show that Tc of these systems is related
to the superfluid density, in the same way as observed in cuprate systems
without static magnetism. We discuss a heuristic model involving percolation of
these nanoscale islands with static magnetism as a possible picture to
reconcile heterogeneity found by the present MuSR study and long-range spin
correlations found by neutron scattering.Comment: 19 pages, 15 figures, submitted to Phys. Rev. B. E-mail:
[email protected]
Probing the magnetic ground state of the molecular Dysprosium triangle
We present zero field muon spin lattice relaxation measurements of a
Dysprosium triangle molecular magnet. The local magnetic fields sensed by the
implanted muons indicate the coexistence of static and dynamic internal
magnetic fields below K. Bulk magnetization and heat capacity
measurements show no indication of magnetic ordering below this temperature. We
attribute the static fields to the slow relaxation of the magnetization in the
ground state of Dy3. The fluctuation time of the dynamic part of the field is
estimated to be ~0.55 s at low temperaturesComment: 5 pages, 5 figures, accepted for publication in Phys. Rev.
Bose-Einstein condensation in multilayers
The critical BEC temperature of a non interacting boson gas in a
layered structure like those of cuprate superconductors is shown to have a
minimum , at a characteristic separation between planes . It is
shown that for , increases monotonically back up to the ideal
Bose gas suggesting that a reduction in the separation between planes,
as happens when one increases the pressure in a cuprate, leads to an increase
in the critical temperature. For finite plane separation and penetrability the
specific heat as a function of temperature shows two novel crests connected by
a ridge in addition to the well-known BEC peak at associated with the
3D behavior of the gas. For completely impenetrable planes the model reduces to
many disconnected infinite slabs for which just one hump survives becoming a
peak only when the slab widths are infinite.Comment: Four pages, four figure
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