936 research outputs found
Source Size Limitation from Variabilities of a Lensed Quasar
In the case of gravitationally-lensed quasars, it is well-known that there is
a time delay between occurrence of the intrinsic variabilities in each split
image. Generally, the source of variabilities has a finite size, and there are
time delays even in one image. If the origin of variabilities is widely
distributed, say over \gsim 100 pc as whole, variabilities between split
images will not show a good correlation even though their origin is identical.
Using this fact, we are able to limit the whole source size of variabilities in
a quasar below the limit of direct resolution by today's observational
instruments.Comment: 15 pages LaTeX, 3 figures, accepted to ApJ Letter. e-mail:
[email protected]
Recent Progress of RF Cavity Study at Mucool Test Area
In order to develop an RF cavity that is applicable for a muon beam cooling
channel, a new facility, called Mucool Test Area (MTA) has been built at
Fermilab. MTA is a unique facility whose purpose is to test RF cavities in
various conditions. There are 201 and 805 MHz high power sources, a 4-Tesla
solenoid magnet, a cryogenic system including a Helium liquifier, an explosion
proof apparatus to operate gaseous/liquid Hydrogen, and a beam transport line
to send an intense H- beam from the Fermilab Linac accelerator to the MTA hall.
Recent activities at MTA will be discussed in this document.Comment: 4 pp. 13th International Workshop on Neutrino Factories, Superbeams
and Beta beams (NuFact11) 1-6 Aug 2011: Geneva, Switzerlan
Three-dimensional Mapping of CDM Substructure at Submillimeter Wavelengths
The cold dark matter (CDM) structure formation model predicts that about 5-10
percent of a typical galactic halo of mass \sim 10^{12} \ms is in
substructures with masses \lesssim 10^8 \ms. To directly detect such
substructures, we propose to observe dust continuum emission from a strongly
lensed QSO-host galaxy using a large submillimeter interferometer array with a
high angular resolution of arcsec such as the planned Atacama Large
Submillimeter Array (ALMA). To assess their observational feasibility, we
numerically simulate millilensing of an extended circular source by a CDM
substructure modeled as a tidally truncated singular isothermal sphere (SIS)
embedded in a typical QSO-galaxy lens system, B1422+231, modeled as a singular
isothermal ellipsoid (SIE) with an external constant shear and a constant
convergence. Assuming an angular resolution of 0.01arcsec, we find that the
angular positions of \sim 10^8 \ms substructures at several kpc from the
center of the macrolens halo can be directly measured if the size of the dust
continuum emission region and the gradient of the surface brightness at the
position of the perturber are sufficiently large. From the astrometric shift on
a scale of a few times mas of an image perturbed by a subhalo with respect
to an unperturbed macrolensed image, we can break the degeneracy between
subhalo mass and distance provided that macrolensing parameters are determined
from positions and fluxes of multiple images.Comment: 7 pages, 7 EPS files. An assessment of our assumption of constancy in
shear and convergence has been included. Version accepted for publication in
Ap
Evidence for a source size of less than 2000 AU in Quasar 2237+0305
Recently, OGLE team have reported clear quasar microlensing signal in
Q2237+0305. We have analyzed the microlens event of ``image C'' by using their
finely and densely sampled lightcurves. From lightcurve fitting, we can
unambiguously set the source size of \lsim 0.98 Einstein Ring radius as a
conservative limit. This limit corresponds to , if we adopt
obtained by a recent statistical study of
mean mass of lens object. This gives a clear evidence for the existence of an
accretion disk in the central region of the quasar.Comment: 11 pages, including 1 table and 3 figures, accepted to ApJ
Integral field spectroscopy of four lensed quasars: analysis of their neighborhood and evidence for microlensing
CONTEXT: Gravitationally lensed quasars constitute an independent tool to
derive H0 through time-delays; they offer as well the opportunity to study the
mass distribution and interstellar medium of their lensing galaxies and,
through microlensing they also allow one to study details of the emitting
source. AIMS: For such studies, one needs to have an excellent knowledge of the
close environment of the lensed images in order to model the lensing potential:
this means observational data over a large field-of-view and spectroscopy at
high spatial resolution. METHODS: We present VIMOS integral field observations
around four lensed quasars: HE 0230-2130, RX J0911.4+0551, H 1413+117 and B
1359+154. Using the low, medium and high resolution modes, we study the quasar
images and the quasar environments, as well as provide a detailed report of the
data reduction. RESULTS: Comparison between the quasar spectra of the different
images reveals differences for HE 0230-2130, RX J0911.4+0551 and H 1413+117:
flux ratios between the images of the same quasar are different when measured
in the emission lines and in the continuum. We have also measured the redshifts
of galaxies in the neighborhood of HE 0230-2130 and RX J0911.4+0551 which
possibly contribute to the total lensing potential. CONCLUSIONS: A careful
analysis reveals that microlensing is the most natural explanation for the
(de)magnification of the continuum emitting region of the background sources.
In HE 0230-2130, image D is likely to be affected by microlensing
magnification; in RX J0911.4+0551, images A1 and A3 are likely to be modified
by microlensing de-magnification and in H 1413+117, at least image D is
affected by microlensing.Comment: 13 pages, 18 figures. Accepted for publication in A&A: January 7,
200
Imprint of Gravitational Lensing by Population III Stars in Gamma Ray Burst Light Curves
We propose a novel method to extract the imprint of gravitational lensing by
Pop III stars in the light curves of Gamma Ray Bursts (GRBs). Significant
portions of GRBs can originate in hypernovae of Pop III stars and be
gravitationally lensed by foreground Pop III stars or their remnants. If the
lens mass is on the order of and the lens redshift is
greater than 10, the time delay between two lensed images of a GRB is s and the image separation is as. Although it is difficult to
resolve the two lensed images spatially with current facilities, the light
curves of two images are superimposed with a delay of s. GRB light
curves usually exhibit noticeable variability, where each spike is less than
1s. If a GRB is lensed, all spikes are superimposed with the same time delay.
Hence, if the autocorrelation of light curve with changing time interval is
calculated, it should show the resonance at the time delay of lensed images.
Applying this autocorrelation method to GRB light curves which are archived as
the {\it BATSE} catalogue, we demonstrate that more than half light curves can
show the recognizable resonance, if they are lensed. Furthermore, in 1821 GRBs
we actually find one candidate of GRB lensed by a Pop III star, which may be
located at redshift 20-200. The present method is quite straightforward and
therefore provides an effective tool to search for Pop III stars at redshift
greater than 10. Using this method, we may find more candidates of GRBs lensed
by Pop III stars in the data by the {\it Swift} satellite.Comment: 13 pages, 13 figures, accepted for publication in Ap
Beam-Induced Electron Loading Effects in High Pressure Cavities for a Muon Collider
Ionization cooling is a critical building block for the realization of a muon collider. To suppress breakdown in the presence of the external magnetic field, an idea of using an RF cavity filled with high pressure hydrogen gas is being considered for the cooling channel design. One possible problem expected in the high pressure RF cavity is, however, the dissipation of significant RF power through the beam-induced electrons accumulated inside the cavity. To characterize this detrimental loading effect, we develop a simplified model that relates the electron density evolution and the observed pickup voltage signal in the cavity, with consideration of several key molecular processes such as the formation of the polyatomic molecules, recombination and attachment. This model is expected to be compared with the actual beam test of the cavity in the MuCool Test Area (MTA) of Fermilab
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