794 research outputs found
Beam test, simulation, and performance evaluation of PbF and PWO-UF crystals with SiPM readout for a semi-homogeneous calorimeter prototype with longitudinal segmentation
Crilin (Crystal Calorimeter with Longitudinal Information) is a
semi-homogeneous, longitudinally segmented electromagnetic calorimeter based on
high-, ultra-fast crystals with UV-extended SiPM readout. The Crilin design
has been proposed as a candidate solution for both a future Muon Collider
barrel ECAL and for the Small Angle Calorimeter of the HIKE experiment. As a
part of the Crilin development program, we have carried out beam tests of small
(~mm) lead fluoride (PbF) and ultra-fast lead
tungstate (PbWO, PWO) crystals with 120~GeV electrons at the CERN SPS to
study the light yield, timing response, and systematics of light collection
with a proposed readout scheme. For a single crystal of PbF, corresponding
to a single Crilin cell, a time resolution of better than 25~ps is obtained for
3 GeV of deposited energy. For a single cell of \pwo, a time resolution of
better than 45~ps is obtained for the same range of deposited energy. This
timing performance fully satisfies the design requirements for the Muon
Collider and HIKE experiments. Further optimizations of the readout scheme and
crystal surface preparation are expected to bring further improvements
Direct Evidence for Hadronic Cosmic-Ray Acceleration in the Supernova Renmant IC 443
The Supernova Remnant (SNR) IC 443 is an intermediate-age remnant well known
for its radio, optical, X-ray and gamma-ray energy emissions. In this Letter we
study the gamma-ray emission above 100 MeV from IC 443 as obtained by the AGILE
satellite. A distinct pattern of diffuse emission in the energy range 100 MeV-3
GeV is detected across the SNR with its prominent maximum (source "A")
localized in the Northeastern shell with a flux F = (47 \pm 10) 10^{-8} photons
cm^{-2} s^{-1} above 100 MeV. This location is the site of the strongest shock
interaction between the SNR blast wave and the dense circumstellar medium.
Source "A" is not coincident with the TeV source located 0.4 degree away and
associated with a dense molecular cloud complex in the SNR central region. From
our observations, and from the lack of detectable diffuse TeV emission from its
Northeastern rim, we demonstrate that electrons cannot be the main emitters of
gamma-rays in the range 0.1-10 GeV at the site of the strongest SNR shock. The
intensity, spectral characteristics, and location of the most prominent
gamma-ray emission together with the absence of co-spatial detectable TeV
emission are consistent only with a hadronic model of cosmic-ray acceleration
in the SNR. A high-density molecular cloud (cloud "E") provides a remarkable
"target" for nucleonic interactions of accelerated hadrons: our results show
enhanced gamma-ray production near the molecular cloud/shocked shell
interaction site. IC 443 provides the first unambiguous evidence of cosmic-ray
acceleration by SNRs.Comment: 5 pages, 2 figures; accepted by ApJLetters on Jan 21, 201
First AGILE Catalog of High Confidence Gamma-Ray Sources
We present the first catalog of high-confidence gamma-ray sources detected by
the AGILE satellite during observations performed from July 9, 2007 to June 30,
2008. Catalogued sources are detected by merging all the available data over
the entire time period. AGILE, launched in April 2007, is an ASI mission
devoted to gamma-ray observations in the 30 MeV - 50 GeV energy range, with
simultaneous X-ray imaging capability in the 18-60 keV band. This catalog is
based on Gamma-Ray Imaging Detector (GRID) data for energies greater than 100
MeV. For the first AGILE catalog we adopted a conservative analysis, with a
high-quality event filter optimized to select gamma-ray events within the
central zone of the instrument Field of View (radius of 40 degrees). This is a
significance-limited (4 sigma) catalog, and it is not a complete flux-limited
sample due to the non-uniform first year AGILE sky coverage. The catalog
includes 47 sources, 21 of which are associated with confirmed or candidate
pulsars, 13 with Blazars (7 FSRQ, 4 BL Lacs, 2 unknown type), 2 with HMXRBs, 2
with SNRs, 1 with a colliding-wind binary system, 8 with unidentified sources.Comment: Revised version, 15 pages, 3 figures, 3 tables. To be published in
Astronomy and Astrophysics. Text improved and clarified. Refined analysis of
complex regions of the Galactic plane yields a new list of high-confidence
sources including 47 sources (compared with the 40 sources appearing in the
first version
Calibration of AGILE-GRID with In-Flight Data and Monte Carlo Simulations
Context: AGILE is a gamma-ray astrophysics mission which has been in orbit
since 23 April 2007 and continues to operate reliably. The gamma-ray detector,
AGILE-GRID, has observed Galactic and extragalactic sources, many of which were
collected in the first AGILE Catalog. Aims: We present the calibration of the
AGILE-GRID using in-flight data and Monte Carlo simulations, producing
Instrument Response Functions (IRFs) for the effective area A_eff), Energy
Dispersion Probability (EDP), and Point Spread Function (PSF), each as a
function of incident direction in instrument coordinates and energy. Methods:
We performed Monte Carlo simulations at different gamma-ray energies and
incident angles, including background rejection filters and Kalman filter-based
gamma-ray reconstruction. Long integrations of in-flight observations of the
Vela, Crab and Geminga sources in broad and narrow energy bands were used to
validate and improve the accuracy of the instrument response functions.
Results: The weighted average PSFs as a function of spectra correspond well to
the data for all sources and energy bands. Conclusions: Changes in the
interpolation of the PSF from Monte Carlo data and in the procedure for
construction of the energy-weighted effective areas have improved the
correspondence between predicted and observed fluxes and spectra of celestial
calibration sources, reducing false positives and obviating the need for
post-hoc energy-dependent scaling factors. The new IRFs have been publicly
available from the Agile Science Data Centre since November 25, 2011, while the
changes in the analysis software will be distributed in an upcoming release
Discovery of extreme particle acceleration in the microquasar Cygnus X-3
The study of relativistic particle acceleration is a major topic of
high-energy astrophysics. It is well known that massive black holes in active
galaxies can release a substantial fraction of their accretion power into
energetic particles, producing gamma-rays and relativistic jets. Galactic
microquasars (hosting a compact star of 1-10 solar masses which accretes matter
from a binary companion) also produce relativistic jets. However, no direct
evidence of particle acceleration above GeV energies has ever been obtained in
microquasar ejections, leaving open the issue of the occurrence and timing of
extreme matter energization during jet formation. Here we report the detection
of transient gamma-ray emission above 100 MeV from the microquasar Cygnus X-3,
an exceptional X-ray binary which sporadically produces powerful radio jets.
Four gamma-ray flares (each lasting 1-2 days) were detected by the AGILE
satellite simultaneously with special spectral states of Cygnus X-3 during the
period mid-2007/mid-2009. Our observations show that very efficient particle
acceleration and gamma-ray propagation out of the inner disk of a microquasar
usually occur a few days before major relativistic jet ejections. Flaring
particle energies can be thousands of times larger than previously detected
maximum values (with Lorentz factors of 105 and 102 for electrons and protons,
respectively). We show that the transitional nature of gamma-ray flares and
particle acceleration above GeV energies in Cygnus X-3 is clearly linked to
special radio/X-ray states preceding strong radio flares. Thus gamma-rays
provide unique insight into the nature of physical processes in microquasars.Comment: 29 pages (including Supplementary Information), 8 figures, 2 tables
version submitted to Nature on August 7, 2009 (accepted version available at
http://www.nature.com/nature/journal/vaop/ncurrent/pdf/nature08578.pdf
The flaring blazars of the first 1.5 years of the AGILE mission
We report the AGILE gamma-ray observations and the results of the
multiwavelength campaigns on seven flaring blazars detected by the mission:
During two multiwavelength campaigns, we observed gamma-ray activity from two
Flat Spectrum Radio Quasars of the Virgo region, e.g. 3C 279 and 3C 273 (the
latter being the first extragalactic source simultaneously observed with the
gamma-ray telescope and the hard X ray imager of the mission). Due to the large
FOV of the AGILE/GRID instrument, we achieved an almost continuous coverage of
the FSRQ 3C 454.3. The source showed flux above 10E-6 photons/cm2/s (E > 100
MeV) and showed day by day variability during all the AGILE observing periods.
In the EGRET era, the source was found in high gamma-ray activity only once. An
other blazar, PKS 1510-089 was frequently found in high gamma-ray activity. S5
0716+71, an intermediate BL Lac object, exhibited a very high gamma-ray
activity and fast gamma-ray variability during a period of intense optical
activity. We observed high gamma-ray activity from W Comae, a BL Lac object,
and Mrk 421, an high energy peaked BL Lac object. For this source, a
multiwavelength campaign from optical to TeV has been performed
Episodic Transient Gamma-Ray Emission from the Microquasar Cygnus X-1
Cygnus X-1 is the archetypal black hole (BH) binary system in our Galaxy. We
report the main results of an extensive search for transient gamma-ray emission
from Cygnus X-1 carried out in the energy range 100 MeV - 3 GeV by the AGILE
satellite, during the period 2007 July - 2009 October. The total exposure time
is about 300 days, during which the source was in the "hard" X-ray spectral
state. We divided the observing intervals in 2 or 4 week periods, and searched
for transient and persistent emission. We report an episode of significant
transient gamma-ray emission detected on 2009, October 16 in a position
compatible with Cygnus X-1 optical position. This episode, occurred during a
hard spectral state of Cygnus X-1, shows that a 1-2 day time variable emission
above 100 MeV can be produced during hard spectral states, having important
theoretical implications for current Comptonization models for Cygnus X-1 and
other microquasars. Except for this one short timescale episode, no significant
gamma-ray emission was detected by AGILE. By integrating all available data we
obtain a 2 upper limit for the total integrated flux of
in the energy range
100 MeV - 3 GeV. We then clearly establish the existence of a spectral cutoff
in the energy range 1-100 MeV that applies to the typical hard state outside
the flaring period and that confirms the historically known spectral cutoff
above 1 MeV.Comment: Accepted for publication by ApJ on the 9th of Feb 2010, 5 pages, 3
figure
Detection of Gamma-ray Emission from the Eta-Carinae Region
We present the results of extensive observations by the gamma-ray AGILE
satellite of the Galactic region hosting the Carina nebula and the remarkable
colliding wind binary Eta Carinae (Eta Car) during the period 2007 July to 2009
January. We detect a gamma-ray source (1AGL J1043-5931) consistent with the
position of Eta Car. If 1AGL J1043-5931 is associated with the Eta Car system
our data provide the long sought first detection above 100 MeV of a colliding
wind binary. The average gamma-ray flux above 100 MeV and integrated over the
pre-periastron period 2007 July to 2008 October is F = (37 +/- 5) x 10-8 ph
cm-2 s-1 corresponding to an average gamma-ray luminosity of L = 3.4 x 10^34
erg s-1 for a distance of 2.3 kpc. We also report a 2-day gamma-ray flaring
episode of 1AGL J1043-5931 on 2008 Oct. 11-13 possibly related to a transient
acceleration and radiation episode of the strongly variable shock in the
system.Comment: 5 pages, 4 figure, accepted for publication in ApJ Letter
Detection of Gamma-Ray Emission from the Vela Pulsar Wind Nebula with AGILE
Pulsars are known to power winds of relativistic particles that can produce
bright nebulae by interacting with the surrounding medium. These pulsar wind
nebulae (PWNe) are observed in the radio, optical, x-rays and, in some cases,
also at TeV energies, but the lack of information in the gamma-ray band
prevents from drawing a comprehensive multiwavelength picture of their
phenomenology and emission mechanisms. Using data from the AGILE satellite, we
detected the Vela pulsar wind nebula in the energy range from 100 MeV to 3 GeV.
This result constrains the particle population responsible for the GeV
emission, probing multivavelength PWN models, and establishes a class of
gamma-ray emitters that could account for a fraction of the unidentified
Galactic gamma-ray sources.Comment: Accepted by Science; first published online on December 31, 2009 in
Science Express. Science article and Supporting Online Material are available
at http://www.sciencemag.or
- …