C. Bleve | University of Salento (original) (raw)

Papers by C. Bleve

The Astrophysical Journal Supplement Series, 2012

Journal of Instrumentation, 2013

ABSTRACT The Pierre Auger Observatory in Malarg¨ue, Argentina, is designed to study the propertie... more ABSTRACT The Pierre Auger Observatory in Malarg¨ue, Argentina, is designed to study the properties of ultra-high energy cosmic rays with energies above 1018 eV. It is a hybrid facility that employs a Fluorescence Detector to perform nearly calorimetric measurements of Extensive Air Shower energies. To obtain reliable calorimetric information from the FD, the atmospheric conditions at the observatory need to be continuously monitored during data acquisition. In particular, light attenuation due to aerosols is an important atmospheric correction. The aerosol concentration is highly variable, so that the aerosol attenuation needs to be evaluated hourly. We use light from the Central Laser Facility, located near the center of the observatory site, having an optical signature comparable to that of the highest energy showers detected by the FD. This paper presents two procedures developed to retrieve the aerosol attenuation of fluorescence light from CLF laser shots. Cross checks between the two methods demonstrate that results from both analyses are compatible, and that the uncertainties are well understood. The measurements of the aerosol attenuation provided by the two procedures are currently used at the Pierre Auger Observatory to reconstruct air shower data.

European Physical Journal Plus, 2012

Astroparticle Physics, 2011

Hadronic interaction models at cosmic ray energies are inherently uncertain due to the lack of a ... more Hadronic interaction models at cosmic ray energies are inherently uncertain due to the lack of a fundamental theoretical description of soft hadronic and nuclear interactions and the large extrapolation required from collider energies to the range of the most energetic Cosmic Rays observed (> 10 20 eV). Model uncertainties are evaluated within the QGSjet-II model, by varying some of the crucial parameters in the limits allowed by collider data, and between QGSjet-II and other models commonly used in air shower simulations. The crucial parameters relate to hard processes, string fragmentation, diffraction and baryon production. Results on inelastic cross sections, on secondary particle production and on the properties of air showers measured by ground detectors from energies of 10 12 to 10 19 eV are discussed.

Physical Review D - Particles, Fields, Gravitation and Cosmology, 2011

Cosmic rays are hampered by the Moon and a deficit in its direction is expected (the so-called Mo... more Cosmic rays are hampered by the Moon and a deficit in its direction is expected (the so-called Moon shadow). The Moon shadow is an important tool to determine the performance of an air shower array. Indeed, the westward displacement of the shadow center, due to the bending effect of the geomagnetic field on the propagation of cosmic rays, allows the setting of the absolute rigidity scale of the primary particles inducing the showers recorded by the detector. In addition, the shape of the shadow permits to determine the detector point spread function, while the position of the deficit at high energies allows the evaluation of its absolute pointing accuracy. In this paper we present the observation of the cosmic ray Moon shadowing effect carried out by the ARGO-YBJ experiment in the multi-TeV energy region with high statistical significance (55 standard deviations). By means of an accurate Monte Carlo simulation of PHYSICAL REVIEW D

Astrophysical Journal Letters, 2011

ARGO-YBJ is an air shower detector array with a fully covered layer of resistive plate chambers. ... more ARGO-YBJ is an air shower detector array with a fully covered layer of resistive plate chambers. It is operated with a high duty cycle and a large field of view. It continuously monitors the northern sky at energies above 0.3 TeV. In this paper, we report a long-term monitoring of Mrk 421 over the period from 2007 November to 2010 February. This source was observed by the satellite-borne experiments Rossi X-ray T iming Explorer and Swif t in the X-ray band. Mrk 421 was especially active in the first half of 2008. Many flares are observed in both X-ray and γ-ray bands simultaneously. The γ-ray flux observed by ARGO-YBJ has a clear correlation with the X-ray flux. No lag between the X-ray and γ-ray photons longer than 1 day is found. The evolution of the spectral energy distribution is investigated by measuring spectral indices at four different flux levels. Hardening of the spectra is observed in both X-ray and γ-ray bands.

Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2011

Detecting and monitoring emissions from flaring gamma-ray sources in the very-high-energy (VHE, &... more Detecting and monitoring emissions from flaring gamma-ray sources in the very-high-energy (VHE, > 100GeV) band is a very important topic in gamma-ray astronomy. The ARGO-YBJ detector is characterized by a high duty cycle and a wide field of view. Therefore, it is particularly capable of detecting flares from extragalactic objects. Based on fast reconstruction and analysis, real-time monitoring of 33

Astrophysical Journal, 2012

As one of the brightest active blazars in both X-ray and very high energy γ -ray bands, Mrk 501, ... more As one of the brightest active blazars in both X-ray and very high energy γ -ray bands, Mrk 501, is very useful for physics associated with jets from active galactic nuclei. The ARGO-YBJ experiment has monitored Mrk 501 for γrays above 0.3 TeV since 2007 November. The largest flare since 2005 was observed from 2011 October and lasted until about 2012 April. In this paper, a detailed analysis of this event is reported. During the brightest γ -ray flaring episodes from 2011 October 17 to November 22, an excess of the event rate over 6σ is detected by ARGO-YBJ in the direction of Mrk 501, corresponding to an increase of the γ -ray flux above 1 TeV by a factor of 6.6 ± 2.2 from its steady emission. In particular, the γ -ray flux above 8 TeV is detected with a significance better than 4σ . Based on time-dependent synchrotron self-Compton (SSC) processes, the broadband energy spectrum is interpreted as the emission from an electron energy distribution parameterized with a single power-law function with an exponential cutoff at its high-energy end. The average spectral energy distribution for the steady emission is well described by this simple one-zone SSC model. However, the detection of γ -rays above 8 TeV during the flare challenges this model due to the hardness of the spectra. Correlations between X-rays and γ -rays are also investigated.

Physical Review D, 2014

ABSTRACT See paper for full list of authors – 12 pages, 6 figures, accepted by Physical Review D

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2011

The advent of the Auger Engineering Radio Array (AERA) necessitates the development of a powerful... more The advent of the Auger Engineering Radio Array (AERA) necessitates the development of a powerful framework for the analysis of radio measurements of cosmic ray air showers. As AERA performs "radio-hybrid" measurements of air shower radio emission in coincidence with the surface particle detectors and fluorescence telescopes of the Pierre Auger Observatory, the radio analysis functionality had to be incorporated in the existing hybrid analysis solutions for fluoresence and surface detector data. This goal has been achieved in a natural way by extending the existing Auger Offline software framework with radio functionality. In this article, we lay out the design, highlights and features of the radio extension implemented in the Auger Offline framework. Its functionality has achieved a high degree of sophistication and offers advanced features such as vectorial reconstruction of the electric field, advanced signal processing algorithms, a transparent and efficient handling of FFTs, a very detailed simulation of detector effects, and the read-in of multiple data formats including data from various radio simulation codes. The source code of this radio functionality can be made available to interested parties on request.

The Astrophysical Journal, 2011

The sun blocks cosmic ray particles from outside the solar system, forming a detectable shadow in... more The sun blocks cosmic ray particles from outside the solar system, forming a detectable shadow in the sky map of cosmic rays detected by the ARGO-YBJ experiment in Tibet. Because the cosmic ray particles are positive charged, the magnetic field between the sun and the earth deflects them from straight trajectories and results in a shift of the shadow from the true location of the sun. Here we show that the shift measures the intensity of the field which is transported by the solar wind from the sun to the earth.

The Astrophysical Journal, 2012

The extended gamma-ray source MGRO J1908+06, discovered by the Milagro air shower detector in 200... more The extended gamma-ray source MGRO J1908+06, discovered by the Milagro air shower detector in 2007, has been observed for ∼4 years by the ARGO-YBJ experiment at TeV energies, with a statistical significance of 6.2 standard deviations. The peak of the signal is found at a position consistent with the pulsar PSR J1907+0602. Parameterizing the source shape with a two-dimensional Gauss function, we estimate an extension of σ ext = 0. • 49 ± 0. • 22, which is consistent with a previous measurement by the Cherenkov Array H.E.S.S. The observed energy spectrum is dN/dE = 6.1 ± 1.4 × 10 −13 (E/4 TeV) −2.54±0.36 photons cm −2 s −1 TeV −1 , in the energy range of ∼1-20 TeV. The measured gamma-ray flux is consistent with the results of the Milagro detector, but is ∼2-3 times larger than the flux previously derived by H.E.S.S. at energies of a few TeV. The continuity of the Milagro and ARGO-YBJ observations and the stable excess rate observed by ARGO-YBJ and recorded in four years of data support the identification of MGRO J1908+06 as the steady powerful TeV pulsar wind nebula of PSR J1907+0602, with an integrated luminosity over 1 TeV ∼ 1.8 times the luminosity of the Crab Nebula.

Physics Letters B, 2010

We report a measurement of the flux of cosmic rays with unprecedented precision and statistics us... more We report a measurement of the flux of cosmic rays with unprecedented precision and statistics using the Pierre Auger Observatory. Based on fluorescence observations in coincidence with at least one surface detector we derive a spectrum for energies above 10 18 eV. We also update the previously published energy spectrum obtained with the surface detector array. The two spectra are combined addressing the systematic uncertainties and, in particular, the influence of the energy resolution on the spectral shape. The spectrum can be described by a broken power law E −γ with index γ = 3.3 below the ankle which is measured at log 10 (E ankle /eV) = 18.6. Above the ankle the spectrum is described by a power law with index 2.6 followed by a flux suppression, above about log 10 (E/eV) = 19.5, detected with high statistical significance.

Physical Review D, 2012

ð5 Ä 200Þ TeV is reported. The method exploited to analyze the experimental data is based on a Ba... more ð5 Ä 200Þ TeV is reported. The method exploited to analyze the experimental data is based on a Bayesian procedure. The measured intensities of the light component are consistent with the recent CREAM results and higher than that obtained adding the proton and helium spectra reported by the RUNJOB experiment.

Physical Review D, 2011

The Surface Detector of the Pierre Auger Observatory is sensitive to neutrinos of all flavours ab... more The Surface Detector of the Pierre Auger Observatory is sensitive to neutrinos of all flavours above 0.1 EeV. These interact through charged and neutral currents in the atmosphere giving rise to extensive air showers. When interacting deeply in the atmosphere at nearly horizontal incidence, neutrinos can be distinguished from regular hadronic cosmic rays by the broad time structure of their shower signals in the water-Cherenkov detectors. In this paper we present for the first time an analysis based on down-going neutrinos. We describe the search procedure, the possible sources of background, the method to compute the exposure and the associated systematic uncertainties. No candidate neutrinos have been found in data collected from 1 January 2004 to 31 May 2010. Assuming an E^-2 differential energy spectrum the limit on the single flavour neutrino is (E^2 * dN/dE) < 1.74x10^-7 GeV cm^-2 s^-1 sr^-1 at 90% C.L. in the energy range 1x10^17 eV < E < 1x10^20 eV.

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2009

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2008

We report on the search for Gamma Ray Bursts (GRBs) in the energy range 1-100 GeV in coincidence ... more We report on the search for Gamma Ray Bursts (GRBs) in the energy range 1-100 GeV in coincidence with the prompt emission detected by satellites using the Astrophysical Radiation with Ground-based Observatory at YangBaJing (ARGO-YBJ) air shower detector. Thanks to its mountain location (Yangbajing, Tibet, P.R. China, 4300 m a.s.l.), active surface (∼6700 m 2 of Resistive Plate Chambers), and large field of view (∼2 sr, limited only by the atmospheric absorption), the ARGO-YBJ air shower detector is particularly suitable for the detection of unpredictable and short duration events such as GRBs. The search is carried out using the "single particle technique", i.e. counting all the particles hitting the detector without measurement of the energy and arrival direction of the primary gamma rays. Between 2004 December 17 and 2009 April 7, 81 GRBs detected by satellites occurred within the field of view of ARGO-YBJ (zenith angle θ ≤ 45 • ). It was possible to examine 62 of these for > 1 GeV counterpart in the ARGO-YBJ data finding no statistically significant emission. With a lack of detected spectra in this energy range fluence upper limits are profitable, especially when the redshift is known and the correction for the extragalactic absorption can be considered. The obtained fluence upper limits reach values as low as 10 −5 erg cm −2 in the 1-100 GeV energy region.

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2006

The layout of the RPCs, used in the Argo-YBJ experiment to image with a high space-time granulari... more The layout of the RPCs, used in the Argo-YBJ experiment to image with a high space-time granularity the atmospheric shower, is described in this paper. The detector has been assembled to provide both digital and analog informations in order to cover a wide particle density range with a ...

The Astrophysical Journal Supplement Series, 2012

Journal of Instrumentation, 2013

ABSTRACT The Pierre Auger Observatory in Malarg¨ue, Argentina, is designed to study the propertie... more ABSTRACT The Pierre Auger Observatory in Malarg¨ue, Argentina, is designed to study the properties of ultra-high energy cosmic rays with energies above 1018 eV. It is a hybrid facility that employs a Fluorescence Detector to perform nearly calorimetric measurements of Extensive Air Shower energies. To obtain reliable calorimetric information from the FD, the atmospheric conditions at the observatory need to be continuously monitored during data acquisition. In particular, light attenuation due to aerosols is an important atmospheric correction. The aerosol concentration is highly variable, so that the aerosol attenuation needs to be evaluated hourly. We use light from the Central Laser Facility, located near the center of the observatory site, having an optical signature comparable to that of the highest energy showers detected by the FD. This paper presents two procedures developed to retrieve the aerosol attenuation of fluorescence light from CLF laser shots. Cross checks between the two methods demonstrate that results from both analyses are compatible, and that the uncertainties are well understood. The measurements of the aerosol attenuation provided by the two procedures are currently used at the Pierre Auger Observatory to reconstruct air shower data.

European Physical Journal Plus, 2012

Astroparticle Physics, 2011

Hadronic interaction models at cosmic ray energies are inherently uncertain due to the lack of a ... more Hadronic interaction models at cosmic ray energies are inherently uncertain due to the lack of a fundamental theoretical description of soft hadronic and nuclear interactions and the large extrapolation required from collider energies to the range of the most energetic Cosmic Rays observed (> 10 20 eV). Model uncertainties are evaluated within the QGSjet-II model, by varying some of the crucial parameters in the limits allowed by collider data, and between QGSjet-II and other models commonly used in air shower simulations. The crucial parameters relate to hard processes, string fragmentation, diffraction and baryon production. Results on inelastic cross sections, on secondary particle production and on the properties of air showers measured by ground detectors from energies of 10 12 to 10 19 eV are discussed.

Physical Review D - Particles, Fields, Gravitation and Cosmology, 2011

Cosmic rays are hampered by the Moon and a deficit in its direction is expected (the so-called Mo... more Cosmic rays are hampered by the Moon and a deficit in its direction is expected (the so-called Moon shadow). The Moon shadow is an important tool to determine the performance of an air shower array. Indeed, the westward displacement of the shadow center, due to the bending effect of the geomagnetic field on the propagation of cosmic rays, allows the setting of the absolute rigidity scale of the primary particles inducing the showers recorded by the detector. In addition, the shape of the shadow permits to determine the detector point spread function, while the position of the deficit at high energies allows the evaluation of its absolute pointing accuracy. In this paper we present the observation of the cosmic ray Moon shadowing effect carried out by the ARGO-YBJ experiment in the multi-TeV energy region with high statistical significance (55 standard deviations). By means of an accurate Monte Carlo simulation of PHYSICAL REVIEW D

Astrophysical Journal Letters, 2011

ARGO-YBJ is an air shower detector array with a fully covered layer of resistive plate chambers. ... more ARGO-YBJ is an air shower detector array with a fully covered layer of resistive plate chambers. It is operated with a high duty cycle and a large field of view. It continuously monitors the northern sky at energies above 0.3 TeV. In this paper, we report a long-term monitoring of Mrk 421 over the period from 2007 November to 2010 February. This source was observed by the satellite-borne experiments Rossi X-ray T iming Explorer and Swif t in the X-ray band. Mrk 421 was especially active in the first half of 2008. Many flares are observed in both X-ray and γ-ray bands simultaneously. The γ-ray flux observed by ARGO-YBJ has a clear correlation with the X-ray flux. No lag between the X-ray and γ-ray photons longer than 1 day is found. The evolution of the spectral energy distribution is investigated by measuring spectral indices at four different flux levels. Hardening of the spectra is observed in both X-ray and γ-ray bands.

Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2011

Detecting and monitoring emissions from flaring gamma-ray sources in the very-high-energy (VHE, &... more Detecting and monitoring emissions from flaring gamma-ray sources in the very-high-energy (VHE, > 100GeV) band is a very important topic in gamma-ray astronomy. The ARGO-YBJ detector is characterized by a high duty cycle and a wide field of view. Therefore, it is particularly capable of detecting flares from extragalactic objects. Based on fast reconstruction and analysis, real-time monitoring of 33

Astrophysical Journal, 2012

As one of the brightest active blazars in both X-ray and very high energy γ -ray bands, Mrk 501, ... more As one of the brightest active blazars in both X-ray and very high energy γ -ray bands, Mrk 501, is very useful for physics associated with jets from active galactic nuclei. The ARGO-YBJ experiment has monitored Mrk 501 for γrays above 0.3 TeV since 2007 November. The largest flare since 2005 was observed from 2011 October and lasted until about 2012 April. In this paper, a detailed analysis of this event is reported. During the brightest γ -ray flaring episodes from 2011 October 17 to November 22, an excess of the event rate over 6σ is detected by ARGO-YBJ in the direction of Mrk 501, corresponding to an increase of the γ -ray flux above 1 TeV by a factor of 6.6 ± 2.2 from its steady emission. In particular, the γ -ray flux above 8 TeV is detected with a significance better than 4σ . Based on time-dependent synchrotron self-Compton (SSC) processes, the broadband energy spectrum is interpreted as the emission from an electron energy distribution parameterized with a single power-law function with an exponential cutoff at its high-energy end. The average spectral energy distribution for the steady emission is well described by this simple one-zone SSC model. However, the detection of γ -rays above 8 TeV during the flare challenges this model due to the hardness of the spectra. Correlations between X-rays and γ -rays are also investigated.

Physical Review D, 2014

ABSTRACT See paper for full list of authors – 12 pages, 6 figures, accepted by Physical Review D

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2011

The advent of the Auger Engineering Radio Array (AERA) necessitates the development of a powerful... more The advent of the Auger Engineering Radio Array (AERA) necessitates the development of a powerful framework for the analysis of radio measurements of cosmic ray air showers. As AERA performs "radio-hybrid" measurements of air shower radio emission in coincidence with the surface particle detectors and fluorescence telescopes of the Pierre Auger Observatory, the radio analysis functionality had to be incorporated in the existing hybrid analysis solutions for fluoresence and surface detector data. This goal has been achieved in a natural way by extending the existing Auger Offline software framework with radio functionality. In this article, we lay out the design, highlights and features of the radio extension implemented in the Auger Offline framework. Its functionality has achieved a high degree of sophistication and offers advanced features such as vectorial reconstruction of the electric field, advanced signal processing algorithms, a transparent and efficient handling of FFTs, a very detailed simulation of detector effects, and the read-in of multiple data formats including data from various radio simulation codes. The source code of this radio functionality can be made available to interested parties on request.

The Astrophysical Journal, 2011

The sun blocks cosmic ray particles from outside the solar system, forming a detectable shadow in... more The sun blocks cosmic ray particles from outside the solar system, forming a detectable shadow in the sky map of cosmic rays detected by the ARGO-YBJ experiment in Tibet. Because the cosmic ray particles are positive charged, the magnetic field between the sun and the earth deflects them from straight trajectories and results in a shift of the shadow from the true location of the sun. Here we show that the shift measures the intensity of the field which is transported by the solar wind from the sun to the earth.

The Astrophysical Journal, 2012

The extended gamma-ray source MGRO J1908+06, discovered by the Milagro air shower detector in 200... more The extended gamma-ray source MGRO J1908+06, discovered by the Milagro air shower detector in 2007, has been observed for ∼4 years by the ARGO-YBJ experiment at TeV energies, with a statistical significance of 6.2 standard deviations. The peak of the signal is found at a position consistent with the pulsar PSR J1907+0602. Parameterizing the source shape with a two-dimensional Gauss function, we estimate an extension of σ ext = 0. • 49 ± 0. • 22, which is consistent with a previous measurement by the Cherenkov Array H.E.S.S. The observed energy spectrum is dN/dE = 6.1 ± 1.4 × 10 −13 (E/4 TeV) −2.54±0.36 photons cm −2 s −1 TeV −1 , in the energy range of ∼1-20 TeV. The measured gamma-ray flux is consistent with the results of the Milagro detector, but is ∼2-3 times larger than the flux previously derived by H.E.S.S. at energies of a few TeV. The continuity of the Milagro and ARGO-YBJ observations and the stable excess rate observed by ARGO-YBJ and recorded in four years of data support the identification of MGRO J1908+06 as the steady powerful TeV pulsar wind nebula of PSR J1907+0602, with an integrated luminosity over 1 TeV ∼ 1.8 times the luminosity of the Crab Nebula.

Physics Letters B, 2010

We report a measurement of the flux of cosmic rays with unprecedented precision and statistics us... more We report a measurement of the flux of cosmic rays with unprecedented precision and statistics using the Pierre Auger Observatory. Based on fluorescence observations in coincidence with at least one surface detector we derive a spectrum for energies above 10 18 eV. We also update the previously published energy spectrum obtained with the surface detector array. The two spectra are combined addressing the systematic uncertainties and, in particular, the influence of the energy resolution on the spectral shape. The spectrum can be described by a broken power law E −γ with index γ = 3.3 below the ankle which is measured at log 10 (E ankle /eV) = 18.6. Above the ankle the spectrum is described by a power law with index 2.6 followed by a flux suppression, above about log 10 (E/eV) = 19.5, detected with high statistical significance.

Physical Review D, 2012

ð5 Ä 200Þ TeV is reported. The method exploited to analyze the experimental data is based on a Ba... more ð5 Ä 200Þ TeV is reported. The method exploited to analyze the experimental data is based on a Bayesian procedure. The measured intensities of the light component are consistent with the recent CREAM results and higher than that obtained adding the proton and helium spectra reported by the RUNJOB experiment.

Physical Review D, 2011

The Surface Detector of the Pierre Auger Observatory is sensitive to neutrinos of all flavours ab... more The Surface Detector of the Pierre Auger Observatory is sensitive to neutrinos of all flavours above 0.1 EeV. These interact through charged and neutral currents in the atmosphere giving rise to extensive air showers. When interacting deeply in the atmosphere at nearly horizontal incidence, neutrinos can be distinguished from regular hadronic cosmic rays by the broad time structure of their shower signals in the water-Cherenkov detectors. In this paper we present for the first time an analysis based on down-going neutrinos. We describe the search procedure, the possible sources of background, the method to compute the exposure and the associated systematic uncertainties. No candidate neutrinos have been found in data collected from 1 January 2004 to 31 May 2010. Assuming an E^-2 differential energy spectrum the limit on the single flavour neutrino is (E^2 * dN/dE) < 1.74x10^-7 GeV cm^-2 s^-1 sr^-1 at 90% C.L. in the energy range 1x10^17 eV < E < 1x10^20 eV.

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2009

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2008

We report on the search for Gamma Ray Bursts (GRBs) in the energy range 1-100 GeV in coincidence ... more We report on the search for Gamma Ray Bursts (GRBs) in the energy range 1-100 GeV in coincidence with the prompt emission detected by satellites using the Astrophysical Radiation with Ground-based Observatory at YangBaJing (ARGO-YBJ) air shower detector. Thanks to its mountain location (Yangbajing, Tibet, P.R. China, 4300 m a.s.l.), active surface (∼6700 m 2 of Resistive Plate Chambers), and large field of view (∼2 sr, limited only by the atmospheric absorption), the ARGO-YBJ air shower detector is particularly suitable for the detection of unpredictable and short duration events such as GRBs. The search is carried out using the "single particle technique", i.e. counting all the particles hitting the detector without measurement of the energy and arrival direction of the primary gamma rays. Between 2004 December 17 and 2009 April 7, 81 GRBs detected by satellites occurred within the field of view of ARGO-YBJ (zenith angle θ ≤ 45 • ). It was possible to examine 62 of these for > 1 GeV counterpart in the ARGO-YBJ data finding no statistically significant emission. With a lack of detected spectra in this energy range fluence upper limits are profitable, especially when the redshift is known and the correction for the extragalactic absorption can be considered. The obtained fluence upper limits reach values as low as 10 −5 erg cm −2 in the 1-100 GeV energy region.

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2006

The layout of the RPCs, used in the Argo-YBJ experiment to image with a high space-time granulari... more The layout of the RPCs, used in the Argo-YBJ experiment to image with a high space-time granularity the atmospheric shower, is described in this paper. The detector has been assembled to provide both digital and analog informations in order to cover a wide particle density range with a ...