1,720,998 research outputs found
STUDY OF THE DIFFUSE GAMMA-RAY EMISSION FROM THE GALACTIC PLANE WITH ARGO-YBJ
No full textThe events recorded by ARGO-YBJ in more than five years of data collection have been analyzed to determine the diffuse gamma-ray emission in the Galactic plane at Galactic longitudes 25° < l < 100° and Galactic latitudes . The energy range covered by this analysis, from ~350 GeV to ~2 TeV, allows the connection of the region explored by Fermi with the multi-TeV measurements carried out by Milagro. Our analysis has been focused on two selected regions of the Galactic plane, i.e., 40° < l < 100° and 65° < l < 85° (the Cygnus region), where Milagro observed an excess with respect to the predictions of current models. Great care has been taken in order to mask the most intense gamma-ray sources, including the TeV counterpart of the Cygnus cocoon recently identified by ARGO-YBJ, and to remove residual contributions. The ARGO-YBJ results do not show any excess at sub-TeV energies corresponding to the excess found by Milagro, and are consistent with the predictions of the Fermi model for the diffuse Galactic emission. From the measured energy distribution we derive spectral indices and the differential flux at 1 TeV of the diffuse gamma-ray emission in the sky regions investigated.The events recorded by ARGO-YBJ in more than five years of data collection have been analyzed to determine the diffuse gamma-ray emission in the Galactic plane at Galactic longitudes 25 < l < 100 and Galactic latitudes . The energy range covered by this analysis, from â1⁄4350 GeV to â1⁄42 TeV, allows the connection of the region explored by Fermi with the multi-TeV measurements carried out by Milagro. Our analysis has been focused on two selected regions of the Galactic plane, i.e., 40 < l < 100 and 65 < l < 85 (the Cygnus region), where Milagro observed an excess with respect to the predictions of current models. Great care has been taken in order to mask the most intense gamma-ray sources, including the TeV counterpart of the Cygnus cocoon recently identified by ARGO-YBJ, and to remove residual contributions. The ARGO-YBJ results do not show any excess at sub-TeV energies corresponding to the excess found by Milagro, and are consistent with the predictions of the Fermi model for the diffuse Galactic emission. From the measured energy distribution we derive spectral indices and the differential flux at 1 TeV of the diffuse gamma-ray emission in the sky regions investigated
The analog Resistive Plate Chamber detector of the ARGO-YBJ experiment
No full textThe ARGO-YBJ experiment has been in stable data taking from November 2007 till February 2013 at the YangBaJing Cosmic Ray Observatory (4300 m a.s.l.). The detector consists of a single layer of Resistive Plate Chambers (RPCs) (6700 m2) operated in streamer mode. The signal pick-up is obtained by means of strips facing one side of the gas volume. The digital readout of the signals, while allows a high space–time resolution in the shower front reconstruction, limits the measurable energy to a few hundred TeV. In order to fully investigate the 1–10 PeV region, an analog readout has been implemented by instrumenting each RPC with two large size electrodes facing the other side of the gas volume. Since December 2009 the RPC charge readout has been in operation on the entire central carpet (∼5800 m2). In this configuration the detector is able to measure the particle density at the core position where it ranges from tens to many thousands of particles per m2. Thus ARGO-YBJ provides a highly detailed image of the charge component at the core of air showers. In this paper we describe the analog readout of RPCs in ARGO-YBJ and discuss both the performance of the system and the physical impact on the EAS measurements.The ARGO-YBJ experiment has been in stable data taking from November 2007 till February 2013 at the YangBaJing Cosmic Ray Observatory (4300 m a.s.l.). The detector consists of a single layer of Resistive Plate Chambers (RPCs) (6700 m2) operated in streamer mode. The signal pick-up is obtained by means of strips facing one side of the gas volume. The digital readout of the signals, while allows a high space-time resolution in the shower front reconstruction, limits the measurable energy to a few hundred TeV. In order to fully investigate the 1-10 PeV region, an analog readout has been implemented by instrumenting each RPC with two large size electrodes facing the other side of the gas volume. Since December 2009 the RPC charge readout has been in operation on the entire central carpet (â1⁄45800 m2). In this configuration the detector is able to measure the particle density at the core position where it ranges from tens to many thousands of particles per m2. Thus ARGO-YBJ provides a highly detailed image of the charge component at the core of air showers. In this paper we describe the analog readout of RPCs in ARGO-YBJ and discuss both the performance of the system and the physical impact on the EAS measurements
Crab Nebula: five–year observations with ARGO–YBJ
No full textThe ARGO-YBJ air shower detector monitored the Crab Nebula gamma-ray emission from 2007 November to
2013 February. The integrated signal, consisting of
∼
3.3
×
10
5
events, reached the statistical significance of 21.1
standard deviations. The obtained energy spectrum in the energy range 0.3–20 TeV can be described by a power
law function
dN/dE
=
I
0
(
E
/
2TeV)
−
α
, with a flux normalization
I
0
=
(5.2
±
0.2)
×
10
−
12
photons cm
−
2
s
−
1
TeV
−
1
and
α
=
2.63
±
0.05, corresponding to an integrated flux above 1 TeV of 1.97
×
10
−
11
photons cm
−
2
s
−
1
.
The systematic error is estimated to be less than 30% for the flux normalization and 0.06 for the spectral index.
Assuming a power law spectrum with an exponential cutoff
dN/dE
=
I
0
(
E/
2TeV)
−
α
exp (
−
E/E
cut
), the lower
limit of the cutoff energy
E
cut
is 12 TeV, at 90% confidence level. Our extended data set allows the study of the TeV
emission over long timescales. Over five years, the light curve of the Crab Nebula in 200-day bins is compatible
with a steady emission with a probability of 7.3
×
10
−
2
. A correlated analysis with
Fermi
-LAT data over
∼
4.5 yr
using the light curves of the two experiments gives a Pearson correlation coefficient
r
=
0.56
±
0.22. Concerning
flux variations on timescales of days, a “blind” search for flares with a duration of 1–15 days gives no excess
with a significance higher than four standard deviations. The average rate measured by ARGO-YBJ during the
three most powerful flares detected by
Fermi
-LAT is 205
±
91 photons day
−
1
, consistent with the average value of
137
±
10 day
TeV GAMMA-RAY SURVEY OF THE NORTHERN SKY USING THE ARGO-YBJ DETECTOR
No full textThe Astrophysical Radiation with Ground-based Observatory at Yang Ba Jing (ARGO-YBJ) detector is an extensive
air shower array that has been used to monitor the northern
γ
-ray sky at energies above 0.3 TeV from 2007 November
to 2013 January. In this paper, we present the results of a sky survey in the declination band from
−
10
◦
to 70
◦
,
using data recorded over the past five years. With an integrated sensitivity ranging from 0.24 to
∼
1 Crab units
depending on the declination, six sources have been detected with a statistical significance greater than five standard
deviations. Several excesses are also reported as potential
γ
-ray emitters. The features of each source are presented
and discussed. Additionally, 95% confidence level upper limits of the flux from the investigated sky region are
shown. Specific upper limits for 663 GeV
γ
-ray active galactic nuclei inside the ARGO-YBJ field of view are
reported. The effect of the absorption of
γ
-rays due to the interaction with extragalactic background light is
estimateThe Astrophysical Radiation with Ground-based Observatory at Yang Ba Jing (ARGO-YBJ) detector is an extensive air shower array that has been used to monitor the northern Î3-ray sky at energies above 0.3 TeV from 2007 November to 2013 January. In this paper, we present the results of a sky survey in the declination band from -10° to 70°, using data recorded over the past five years. With an integrated sensitivity ranging from 0.24 to â1⁄41 Crab units depending on the declination, six sources have been detected with a statistical significance greater than five standard deviations. Several excesses are also reported as potential Î3-ray emitters. The features of each source are presented and discussed. Additionally, 95% confidence level upper limits of the flux from the investigated sky region are shown. Specific upper limits for 663 GeV Î3-ray active galactic nuclei inside the ARGO-YBJ field of view are reported. The effect of the absorption of Î3-rays due to the interaction with extragalactic background light is estimated. © 2013. The American Astronomical Society. All rights reserved.
Cosmic ray proton plus helium energy spectrum measured by the ARGO-YBJ experiment in the energy range 3-300 TeV
No full textThe ARGO–YBJ experiment is a full-coverage air shower detector located at the Yangbajing Cosmic
Ray Observatory (Tibet, People
’
s Republic of China, 4300 m a.s.l.). The high altitude, combined with the
full-coverage technique, allows the detection of extensive air showers in a wide energy range and offer the
possibility of measuring the cosmic ray proton plus helium spectrum down to the TeV region, where direct
balloon/space-borne measurements are available. The detector has been in stable data taking in its full
configuration from November 2007 to February 2013. In this paper the measurement of the cosmic ray
proton plus helium energy spectrum is presented in the region 3
–
300 TeV by analyzing the full collected
data sample. The resulting spectral index is
γ
1⁄4
−
2
.
64
0
.
01
, the error is dominated by sys uncertainties. The accurate measurement of the spectrum of light elements with a ground based air shower
detector demonstrates the possibility of extending these measurements at larger energies, where galactic
cosmic ray sources should run out of power in acceleratingThe ARGO-YBJ experiment is a full-coverage air shower detector located at the Yangbajing Cosmic Ray Observatory (Tibet, People's Republic of China, 4300 m a.s.l.). The high altitude, combined with the full-coverage technique, allows the detection of extensive air showers in a wide energy range and offer the possibility of measuring the cosmic ray proton plus helium spectrum down to the TeV region, where direct balloon/space-borne measurements are available. The detector has been in stable data taking in its full configuration from November 2007 to February 2013. In this paper the measurement of the cosmic ray proton plus helium energy spectrum is presented in the region 3-300 TeV by analyzing the full collected data sample. The resulting spectral index is Î3=-2.64±0.01, the error is dominated by systematic uncertainties. The accurate measurement of the spectrum of light elements with a ground based air shower detector demonstrates the possibility of extending these measurements at larger energies, where galactic cosmic ray sources should run out of power in accelerating light elements
Calibration of the RPC charge readout in the ARGO-YBJ experiment with the iso-gradient method
No full textThe ARGO-YBJ experiment is a full coverage array of Resistive Plate Chambers (RPCs) with an active area
of 5800 m
2
. In order to eliminate the response difference of the charge readout from the RPCs, a
calibration procedure is carried out with the iso-gradient method. This method also allows the extension
of the absolute calibration with the muon telescope including scintillation detectors to all the RPCs in the
array. The overall systematic uncertainty in measurements o10.7%. In general, the method gives results consistent with those from a totally different approach also
used in the experiment.The ARGO-YBJ experiment is a full coverage array of Resistive Plate Chambers (RPCs) with an active area of 5800 m2. In order to eliminate the response difference of the charge readout from the RPCs, a calibration procedure is carried out with the iso-gradient method. This method also allows the extension of the absolute calibration with the muon telescope including scintillation detectors to all the RPCs in the array. The overall systematic uncertainty in measurements of the number of particles by the RPCs is 10.7%. In general, the method gives results consistent with those from a totally different approach also used in the experiment
Energy spectrum of cosmic protons and helium nuclei by a hybrid measurement at 4300 m a.s.l.
No full textThe energy spectrum of cosmic Hydrogen and Helium nuclei has been measured below the so-called
“knee” by using a hybrid experiment with a wide field-of-view Cherenkov telescope and the Resistive Plate Chamber
(RPC) array of the ARGO-YBJ experiment at 4300 m above sea level. The Hydrogen and Helium nuclei have been
well separated from other cosmic ray components by using a multi-parameter technique. A highly uniform energy
resolution of about 25% is achieved throughout the whole energy range (100–700 TeV). The observed energy spectrum
is compatible with a single power law with index
γ
=−2.63±0.0
Very high energy gamma-ray astronomy and cosmic ray physics with the ARGO-YBJ experiment
No full textGamma ray astronomy at energies 10^11-10^13 eV, which are strictly related to the identification
and study of the cosmic ray acceleration sites, is the main scientific goal of the ARGO-YBJ experiment.
The detector, which is now being assembled in Tibet (China) at 4300 m a.s.l., is a full coverage Extensive Air Shower array consisting of a carpet of Resistive Plate Chambers covering a surface of about 7000 m2. The high altitude ( atmospheric depth
600 g/cm2 ) and the full coverage ensure a very low primary photon energy threshold at few hundreds GeV (close to the limits of the satellite technology), while the detector time resolution sigma_t=1ns gives a good pointing accuracy,
thus allowing a high sensitivity to gamma -ray sources. Moreover the large field of view and the high duty-cycle ensure the continuous monitoring of the sky.
The detector layout, performance and location, offer a unique possibility to make also a deep study of several characteristics of the hadronic component of the cosmic ray flux up to energies of
hundreds of TeV. In particular, the structure of the shower core, the lateral distribution, the energy spectra and the angular (e.g. anisotropies) and time (e.g. solar flares) flux modulations can be
measured with high sensitivity. Moreover, the use of a full coverage detector with a high space
granularity gives detailed images of the shower front, that can be used to test different hypotheses on the cosmic ray interactions, the shower development in the atmosphere and particle physics at
very high energies. In this work the general layout of the detector and its performance will be described, together
with some of the first results coming from the data analysis of a relevant fraction of the apparatus that is already operating
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