333 research outputs found
Simulated Gamma-Ray Pulse Profile of the Crab Pulsar with the Cherenkov Telescope Array
We present simulations of the very high energy (VHE) gamma-ray light curve of
the Crab pulsar as observed by the Cherenkov Telescope Array (CTA). The CTA
pulse profile of the Crab pulsar is simulated with the specific goal of
determining the accuracy of the position of the interpulse. We fit the pulse
shape obtained by the MAGIC telescope with a three-Gaussian template and
rescale it to account for the different CTA instrumental and observational
configurations. Simulations are performed for different configurations of CTA
and for the ASTRI mini-array. The northern CTA configuration will provide an
improvement of a factor of ~3 in accuracy with an observing time comparable to
that of MAGIC (73 hours). Unless the VHE spectrum above 1 TeV behaves
differently from what we presently know, unreasonably long observing times are
required for a significant detection of the pulsations of the Crab pulsar with
the high-energy-range sub-arrays. We also found that an independent VHE timing
analysis is feasible with Large Size Telescopes (LSTs). CTA will provide a
significant improvement in determining the VHE pulse shape parameters necessary
to constrain theoretical models of the gamma-ray emission of the Crab pulsar.
One of such parameters is the shift in phase between peaks in the pulse profile
at VHE and in other energy bands that, if detected, may point to different
locations of the emission regions.Comment: 11 pages, 11 figures, 5 table
(Very) Fast astronomical photometry for meter-class telescopes
Our team at the INAF-Astronomical Observatory of Padova and the University of Padova is engaged in the design, construction and operations of instruments with very high time accuracy in the optical band for applications to High Time Resolution Astrophysics and Quantum Astronomy. Two instruments were built to perform photon counting with sub-nanosecond temporal accuracy, Aqueye+ and Iqueye. Aqueye+ is regularly mounted at the 1.8m Copernicus telescope in Asiago, while Iqueye was mounted at several 4m class telescopes around the world and is now attached through the Iqueye Fiber Interface to the 1.2m Galileo telescope in Asiago. They are used to perform coordinated high time resolution optical observations and, for the first time ever, experiments of optical intensity interferometry on a baseline of a few kilometers. We report on recent technological developments and scientific results obtained within the framework of this project...
Evidence of intra-binary shock emission from the redback pulsar PSR J1048+2339
We present simultaneous multiwavelength observations of the 4.66 ms redback
pulsar PSR J1048+2339. We performed phase-resolved spectroscopy with the Very
Large Telescope (VLT) searching for signatures of a residual accretion disk or
intra-binary shock emission, constraining the companion radial velocity
semi-amplitude (), and estimating the neutron star mass ().
Using the FORS2-VLT intermediate-resolution spectra, we measured a companion
velocity of km s and a binary mass ratio of . Combining our results for and , we constrained the mass of
the neutron star and the companion to and ,
respectively, where is the system inclination. The Doppler map of the
H emission line exhibits a spot feature at the expected position of the
companion star and an extended bright spot close to the inner Lagrangian point.
We interpret this extended emission as the effect of an intra-binary shock
originating from the interaction between the pulsar relativistic wind and the
matter leaving the companion star. The mass loss from the secondary star could
be either due to Roche-lobe overflow or to the ablation of its outer layer by
the energetic pulsar wind. Contrastingly, we find no evidence for an accretion
disk. We report on the results of the SRT and the LOFAR simultaneous radio
observations at three different frequencies (150 MHz, 336 MHz, and 1400 MHz).
No pulsed radio signal is found in our search. This is probably due to both
scintillation and the presence of material expelled from the system which can
cause the absorption of the radio signal at low frequencies. Finally, we report
on an attempt to search for optical pulsations using IFI+Iqueye mounted at the
1.2 m Galileo telescope at the Asiago Observatory.Comment: 12 pages, 10 figures, accepted for publication in A&
Limits on WWgamma and WWZ Couplings from W Boson Pair Production
The results of a search for W boson pair production in pbar-p collisions at
sqrt{s}=1.8 TeV with subsequent decay to emu, ee, and mumu channels are
presented. Five candidate events are observed with an expected background of
3.1+-0.4 events for an integrated luminosity of approximately 97 pb^{-1}.
Limits on the anomalous couplings are obtained from a maximum likelihood fit of
the E_T spectra of the leptons in the candidate events. Assuming identical
WWgamma and WWZ couplings, the 95 % C.L. limits are -0.62<Delta_kappa<0.77
(lambda = 0) and -0.53<lambda<0.56 (Delta_kappa = 0) for a form factor scale
Lambda = 1.5 TeV.Comment: 10 pages, 1 figure, submitted to Physical Review
Search for R-parity Violating Supersymmetry in Dimuon and Four-Jets Channel
We present results of a search for R-parity-violating decay of the neutralino
chi_1^0, taken to be the Lightest Supersymmetric Particle. It is assumed that
this decay proceeds through one of the lepton-number violating couplings
lambda-prime_2jk (j=1,2; k=1,2,3). This search is based on 77.5 pb-1 of data,
collected by the D0 experiment at the Fermilab Tevatron in ppbar collisions at
a center of mass energy of 1.8 TeV in 1992-1995.Comment: 10 pages, 3 figure
The lowest frequency Fast Radio Bursts: Sardinia Radio Telescope detection of the periodic FRB 180916 at 328 MHz
We report on the lowest-frequency detection to date of three bursts from the
fast radio burst FRB 180916, observed at 328 MHz with the Sardinia Radio
Telescope (SRT). The SRT observed the periodic repeater FRB 180916 for five
days from 2020 February 20 to 24 during a time interval of active radio
bursting, and detected the three bursts during the first hour of observations;
no more bursts were detected during the remaining ~ 30 hours. Simultaneous SRT
observations at 1548 MHz did not detect any bursts. Burst fluences are in the
range 37 to 13 Jy ms. No relevant scattering is observed for these bursts. We
also present the results of the multi-wavelength campaign we performed on FRB
180916, during the five days of the active window. Simultaneously with the SRT
observations, others with different time spans were performed with the Northern
Cross at 408 MHz, with XMM-Newton, NICER, INTEGRAL, AGILE, and with the TNG and
two optical telescopes in Asiago, which are equipped with fast photometers.
XMM-Newton obtained data simultaneously with the three bursts detected by the
SRT, and determined a luminosity upper limit in the 0.3-10 keV energy range of
~ erg/s for the burst emission. AGILE obtained data simultaneously
with the first burst and determined a fluence upper limit in the MeV range for
millisecond timescales of erg cm.Our results show that
absorption from the circumburst medium does not significantly affect the
emission from FRB 180916, thus limiting the possible presence of a
superluminous supernova around the source, and indicate that a cutoff for the
bursting mechanism, if present, must be at lower frequencies. Our
multi-wavelength campaign sensitively constrains the broadband emission from
FRB 180916, and provides the best limits so far for the electromagnetic
response to the radio bursting of this remarkable source of fast radio bursts.Comment: ApJL, 896 L4
Probing BFKL Dynamics in the Dijet Cross Section at Large Rapidity Intervals in ppbar Collisions at sqrt{s}=1800 and 630 GeV
Inclusive dijet production at large pseudorapidity intervals (delta_eta)
between the two jets has been suggested as a regime for observing BFKL
dynamics. We have measured the dijet cross section for large delta_eta in ppbar
collisions at sqrt{s}=1800 and 630 GeV using the DO detector. The partonic
cross section increases strongly with the size of delta_eta. The observed
growth is even stronger than expected on the basis of BFKL resummation in the
leading logarithmic approximation. The growth of the partonic cross section can
be accommodated with an effective BFKL intercept of
a_{BFKL}(20GeV)=1.65+/-0.07.Comment: Published in Physical Review Letter
A Quasi-Model-Independent Search for New Physics at Large Transverse Momentum
We apply a quasi-model-independent strategy ("Sleuth") to search for new high
p_T physics in approximately 100 pb^-1 of ppbar collisions at sqrt(s) = 1.8 TeV
collected by the DZero experiment during 1992-1996 at the Fermilab Tevatron.
Over thirty-two e mu X, W+jets-like, Z+jets-like, and 3(lepton/photon)X
exclusive final states are systematically analyzed for hints of physics beyond
the standard model. Simultaneous sensitivity to a variety of models predicting
new phenomena at the electroweak scale is demonstrated by testing the method on
a particular signature in each set of final states. No evidence of new high p_T
physics is observed in the course of this search, and we find that 89% of an
ensemble of hypothetical similar experimental runs would have produced a final
state with a candidate signal more interesting than the most interesting
observed in these data.Comment: 28 pages, 17 figures. Submitted to Physical Review
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