214,293 research outputs found
Cancellations Amongst Kloosterman Sums
We obtain several estimates for bilinear form with Kloosterman sums. Such
results can be interpreted as a measure of cancellations amongst with
parameters from short intervals. In particular, for certain ranges of
parameters we improve some recent results of Blomer, Fouvry, Kowalski, Michel,
and Mili\'cevi\'c (2014) and Fouvry, Kowalski and Michel (2014).Comment: 10 page
Discovery of Two Simultaneous Kilohertz QPOs in the Persistent Flux of GX 349+2
We report the discovery of two simultaneous quasi-periodic oscillations in
the persistent flux of GX 349+2 at frequencies 712 +/- 9 and 978 +/- 9 Hz, with
rms amplitudes 1.25% +/- 0.34% and 1.34 +/- 0.32%, respectively. During our 152
ks observation with the Rossi X-ray Timing Explorer, GX 342+2 was in either the
normal branch or the flaring branch with count rates in the nominal 2-60 keV
RXTE-PCA band ranging from a low of 8,000 cps to a high of 15,000 cps. The kHz
QPOs were observed only when the source was at the top of the normal branch
when the count rate was about 8,200 cps corresponding to a flux of 1.4E-8
ergs/cm**2/s in the 2-10 keV band. With this report, now kHz QPOs have been
observed in all the 6 Z sources.Comment: 5 pages, LaTex (aas2pp4), Accepted for publication in ApJ Let
Observing Zitterbewegung for photons near the Dirac point of a two-dimensional photonic crystal
It is shown, for the first time, that the zitterbewegung of photon can appear
near the Dirac point in two-dimensional photonic crystal. The superiority of
such a phenomenon for photons is that it can be found in different scaling
structures with wide frequency regions. It can be observed by measuring the
time dependence of the transmission coefficient through photonic crystal slabs.
Thus, it is particularly suited for experimentally observing this effect. We
have observed such a phenomenon by exact numerical simulations, confirming a
long-standing theoretical prediction
Kilohertz QPO Frequency and Flux Decrease in AQL X-1 and Effect of Soft X-ray Spectral Components
We report on an RXTE/PCA observation of Aql X-1 during its outburst in March
1997 in which, immediately following a Type-I burst, the broad-band 2-10 keV
flux decreased by about 10% and the kilohertz QPO frequency decreased from
813+-3 Hz to 776+-4 Hz. This change in kHz QPO frequency is much larger than
expected from a simple extrapolation of a frequency-flux correlation
established using data before the burst. Meanwhile a very low frequency noise
(VLFN) component in the broad-band FFT power spectra with a fractional
root-mean-square (rms) amplitude of 1.2% before the burst ceased to exist after
the burst. All these changes were accompanied by a change in the energy
spectral shape. If we characterize the energy spectra with a model composed of
two blackbody (BB) components and a power law component, almost all the
decrease in flux was in the two BB components. We attribute the two BB
components to the contributions from a region very near the neutron star or
even the neutron star itself and from the accretion disk, respectively.Comment: 12 pages with 4 figures, accepted for publication in ApJ Letters,
typos corrected and references update
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