349 research outputs found
The bright optical flash from GRB 060117
We present a discovery and observation of an extraordinarily bright prompt
optical emission of the GRB 060117 obtained by a wide-field camera atop the
robotic telescope FRAM of the Pierre Auger Observatory from 2 to 10 minutes
after the GRB. We found rapid average temporal flux decay of alpha = -1.7 +-
0.1 and a peak brightness R = 10.1 mag. Later observations by other instruments
set a strong limit on the optical and radio transient fluxes, unveiling an
unexpectedly rapid further decay. We present an interpretation featuring a
relatively steep electron-distribution parameter p ~ 3.0 and providing a
straightforward solution for the overall fast decay of this optical transient
as a transition between reverse and forward shock.Comment: Accepted to A&A, 4 pages, corected few typos pointed out by X.F. W
Search for microwave emission from ultrahigh energy cosmic rays
We present a search for microwave emission from air showers induced by
ultrahigh energy cosmic rays with the microwave detection of air showers
experiment. No events were found, ruling out a wide range of power flux and
coherence of the putative emission, including those suggested by recent
laboratory measurements.Comment: 5 pages, 3 figure
The MIDAS telescope for microwave detection of ultra-high energy cosmic rays
We present the design, implementation and data taking performance of the
MIcrowave Detection of Air Showers (MIDAS) experiment, a large field of view
imaging telescope designed to detect microwave radiation from extensive air
showers induced by ultra-high energy cosmic rays. This novel technique may
bring a tenfold increase in detector duty cycle when compared to the standard
fluorescence technique based on detection of ultraviolet photons. The MIDAS
telescope consists of a 4.5 m diameter dish with a 53-pixel receiver camera,
instrumented with feed horns operating in the commercial extended C-Band (3.4
-- 4.2 GHz). A self-trigger capability is implemented in the digital
electronics. The main objectives of this first prototype of the MIDAS telescope
- to validate the telescope design, and to demonstrate a large detector duty
cycle - were successfully accomplished in a dedicated data taking run at the
University of Chicago campus prior to installation at the Pierre Auger
Observatory.Comment: 13 pages, 18 figure
Operations of and Future Plans for the Pierre Auger Observatory
Technical reports on operations and features of the Pierre Auger Observatory,
including ongoing and planned enhancements and the status of the future
northern hemisphere portion of the Observatory. Contributions to the 31st
International Cosmic Ray Conference, Lodz, Poland, July 2009.Comment: Contributions to the 31st ICRC, Lodz, Poland, July 200
Measurement of the Depth of Maximum of Extensive Air Showers above 10^18 eV
We describe the measurement of the depth of maximum, Xmax, of the
longitudinal development of air showers induced by cosmic rays. Almost four
thousand events above 10^18 eV observed by the fluorescence detector of the
Pierre Auger Observatory in coincidence with at least one surface detector
station are selected for the analysis. The average shower maximum was found to
evolve with energy at a rate of (106 +35/-21) g/cm^2/decade below 10^(18.24 +/-
0.05) eV and (24 +/- 3) g/cm^2/decade above this energy. The measured
shower-to-shower fluctuations decrease from about 55 to 26 g/cm^2. The
interpretation of these results in terms of the cosmic ray mass composition is
briefly discussed.Comment: Accepted for publication by PR
The Pierre Auger Observatory III: Other Astrophysical Observations
Astrophysical observations of ultra-high-energy cosmic rays with the Pierre
Auger ObservatoryComment: Contributions to the 32nd International Cosmic Ray Conference,
Beijing, China, August 201
A search for point sources of EeV photons
Measurements of air showers made using the hybrid technique developed with
the fluorescence and surface detectors of the Pierre Auger Observatory allow a
sensitive search for point sources of EeV photons anywhere in the exposed sky.
A multivariate analysis reduces the background of hadronic cosmic rays. The
search is sensitive to a declination band from -85{\deg} to +20{\deg}, in an
energy range from 10^17.3 eV to 10^18.5 eV. No photon point source has been
detected. An upper limit on the photon flux has been derived for every
direction. The mean value of the energy flux limit that results from this,
assuming a photon spectral index of -2, is 0.06 eV cm^-2 s^-1, and no celestial
direction exceeds 0.25 eV cm^-2 s^-1. These upper limits constrain scenarios in
which EeV cosmic ray protons are emitted by non-transient sources in the
Galaxy.Comment: 28 pages, 10 figures, accepted for publication in The Astrophysical
Journa
Reconstruction of inclined air showers detected with the Pierre Auger Observatory
We describe the method devised to reconstruct inclined cosmic-ray air showers
with zenith angles greater than detected with the surface array of
the Pierre Auger Observatory. The measured signals at the ground level are
fitted to muon density distributions predicted with atmospheric cascade models
to obtain the relative shower size as an overall normalization parameter. The
method is evaluated using simulated showers to test its performance. The energy
of the cosmic rays is calibrated using a sub-sample of events reconstructed
with both the fluorescence and surface array techniques. The reconstruction
method described here provides the basis of complementary analyses including an
independent measurement of the energy spectrum of ultra-high energy cosmic rays
using very inclined events collected by the Pierre Auger Observatory.Comment: 27 pages, 19 figures, accepted for publication in Journal of
Cosmology and Astroparticle Physics (JCAP
Azimuthal asymmetry in the risetime of the surface detector signals of the Pierre Auger Observatory
The azimuthal asymmetry in the risetime of signals in Auger surface detector
stations is a source of information on shower development. The azimuthal
asymmetry is due to a combination of the longitudinal evolution of the shower
and geometrical effects related to the angles of incidence of the particles
into the detectors. The magnitude of the effect depends upon the zenith angle
and state of development of the shower and thus provides a novel observable,
, sensitive to the mass composition of cosmic rays
above eV. By comparing measurements with predictions from
shower simulations, we find for both of our adopted models of hadronic physics
(QGSJETII-04 and EPOS-LHC) an indication that the mean cosmic-ray mass
increases slowly with energy, as has been inferred from other studies. However,
the mass estimates are dependent on the shower model and on the range of
distance from the shower core selected. Thus the method has uncovered further
deficiencies in our understanding of shower modelling that must be resolved
before the mass composition can be inferred from .Comment: Replaced with published version. Added journal reference and DO
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