249 research outputs found
Classification of sea-ice types in SAR imagery
We present a supervised three-stage classification (labeling) scheme applied to SAR images of polar regions for detecting different sea-ice types. The three-stage labeling procedure consists of: 1) a speckle noise filtering stage, based on a sequence of contour detection, segmentation and filtering steps, which removes SAR speckle noise (and texture information as well) without losing spatial details;2) a second stage providing Bayesian, maximum-a-posteriori, hierarchical (coarse-tofine),
adaptive (data-driven) and contextual labeling of piecewise constant intensity images featuring little useful texture information;and 3) an output stage providing a many-to-one relationship between second stage output categories (types or clusters) and desired output classes. Modules 1) and 2), which demonstrated their validity in several applications in the existing literature, are briefly recalled in the current paper. The proposed labeling scheme features some interesting functional properties when applied to sea-ice SAR images: it is easy to use, i.e. it requires minor user
interaction, is robust to changes in input conditions and performs better than a noncontextual (per-pixel) classifier. Application results are presented and discussed for a pair of SAR images extracted, respectively, from an ERS-1 scene acquired on November 1992 over the Bellingshausen Sea (Antarctica) and from an ERS-2 scene
of the East Greenland Sea acquired on March 1997 when a field experiment by the research vessel “Jan Mayen” was conducted in the same area
The AFISS web platform for the correlation of high-energy transient events
In the multi-messenger era, facilities share their results with the
scientific community through networks such as the General Coordinates Network
to study transient phenomena (e.g., Gamma-ray bursts) and implement real-time
analysis pipelines to detect transient events, reacting to science alerts
received from other observatories. The fast analysis of transient events is
crucial for detecting counterparts of gravitational waves and neutrino
candidate events. In this context, collecting scientific results from different
high-energy satellites observing the same transient event represents a key step
in improving the statistical significance of the high-energy candidate events.
This project aims to develop a system and a web platform to share information
and scientific results of transient events between high-energy satellites with
INAF participation (AGILE, FERMI, INTEGRAL and SWIFT). The AFISS platform
implements the COMET VO- Event broker and provides a web portal where the users
visualize the list of transient events detected by multi-messenger facilities
and received through the GCN. The web portal could show, for each event, a
summary of the scientific results shared by the real-time analysis pipelines
and a list of time-correlated transient events. In addition, the platform is
ready to receive results from participating facilities on sub-threshold events
(STE) that cannot be shared with the community due to the low statistical
significance. If the platform finds a time correlation between two or more
STEs, it can promote them to science alerts. The web interface shows the list
of STEs with possible time correlation with other STEs or science alerts. The
platform notifies the users with an email when a new transient event is
received.Comment: 4 pages, 4 figures, Astronomical Data Analysis Software and System
XXXII (31 October-4 November 2022
Stellar populations in the bulges of isolated galaxies
open7siWe present photometry and long-slit spectroscopy for 12 S0 and spiral galaxies selected
from the Catalogue of Isolated Galaxies. The structural parameters of the sample galaxies are
derived from the Sloan Digital Sky Survey i-band images by performing a two-dimensional
photometric decomposition of the surface brightness distribution. This is assumed to be the
sum of the contribution of a Sersic bulge, an exponential disc, and a Ferrers bar characterized
by elliptical and concentric isophotes with constant ellipticity and position angles. The rotation
curves and velocity dispersion profiles of the stellar component are measured from the spectra
obtained along the major axis of galaxies. The radial profiles of the Hβ, Mg and Fe line-
strength indices are derived too. Correlations between the central values of the Mg2
and Fe line-strength indices and the velocity dispersion are found. The mean age, total metallicity
and total α/Fe enhancement of the stellar population in the centre and at the radius, where the
bulge gives the same contribution to the total surface brightness as the remaining components,
are obtained using stellar population models with variable element abundance ratios. We
identify intermediate-age bulges with solar metallicity and old bulges with a large spread in
metallicity. Most of the sample bulges display supersolar α/Fe enhancement, no gradient in
age and negative gradients of metallicity and α/Fe enhancement. These findings support a
formation scenario via dissipative collapse where environmental effects are remarkably less
important than in the assembly of bulges of galaxies in groups and clusters.openMorelli, Lorenzo; Parmiggiani, Marco; Corsini, ENRICO MARIA; Costantin, Luca; DALLA BONTA', Elena; Méndez Abreu, J.; Pizzella, AlessandroMorelli, Lorenzo; Parmiggiani, Marco; Corsini, ENRICO MARIA; Costantin, Luca; DALLA BONTA', Elena; Méndez Abreu, J.; Pizzella, Alessandr
A Deep Learning Method for AGILE-GRID Gamma-Ray Burst Detection
The follow-up of external science alerts received from gamma-ray burst (GRB) and gravitational wave detectors is one of the AGILE Team's current major activities. The AGILE team developed an automated real-time analysis pipeline to analyze AGILE Gamma-Ray Imaging Detector (GRID) data to detect possible counterparts in the energy range 0.1-10 GeV. This work presents a new approach for detecting GRBs using a convolutional neural network (CNN) to classify the AGILE-GRID intensity maps by improving the GRB detection capability over the Li & Ma method, currently used by the AGILE team. The CNN is trained with large simulated data sets of intensity maps. The AGILE complex observing pattern due to the so-called "spinning mode" is studied to prepare data sets to test and evaluate the CNN. A GRB emission model is defined from the second Fermi-LAT GRB catalog and convoluted with the AGILE observing pattern. Different p-value distributions are calculated, evaluating, using the CNN, millions of background-only maps simulated by varying the background level. The CNN is then used on real data to analyze the AGILE-GRID data archive, searching for GRB detections using the trigger time and position taken from the Swift-BAT, Fermi-GBM, and Fermi-LAT GRB catalogs. From these catalogs, the CNN detects 21 GRBs with a significance of >= 3 sigma, while the Li & Ma method detects only two GRBs. The results shown in this work demonstrate that the CNN is more effective in detecting GRBs than the Li & Ma method in this context and can be implemented into the AGILE-GRID real-time analysis pipeline
The Agile Alert System For Gamma-Ray Transients
In recent years, a new generation of space missions offered great
opportunities of discovery in high-energy astrophysics. In this article we
focus on the scientific operations of the Gamma-Ray Imaging Detector (GRID)
onboard the AGILE space mission. The AGILE-GRID, sensitive in the energy range
of 30 MeV-30 GeV, has detected many gamma-ray transients of galactic and
extragalactic origins. This work presents the AGILE innovative approach to fast
gamma-ray transient detection, which is a challenging task and a crucial part
of the AGILE scientific program. The goals are to describe: (1) the AGILE
Gamma-Ray Alert System, (2) a new algorithm for blind search identification of
transients within a short processing time, (3) the AGILE procedure for
gamma-ray transient alert management, and (4) the likelihood of ratio tests
that are necessary to evaluate the post-trial statistical significance of the
results. Special algorithms and an optimized sequence of tasks are necessary to
reach our goal. Data are automatically analyzed at every orbital downlink by an
alert pipeline operating on different timescales. As proper flux thresholds are
exceeded, alerts are automatically generated and sent as SMS messages to
cellular telephones, e-mails, and push notifications of an application for
smartphones and tablets. These alerts are crosschecked with the results of two
pipelines, and a manual analysis is performed. Being a small scientific-class
mission, AGILE is characterized by optimization of both scientific analysis and
ground-segment resources. The system is capable of generating alerts within two
to three hours of a data downlink, an unprecedented reaction time in gamma-ray
astrophysics.Comment: 34 pages, 9 figures, 5 table
The AGILE real-time analysis pipelines in the multi-messenger era
In the multi-messenger era, space and ground-based observatories usually
develop real-time analysis (RTA) pipelines to rapidly detect transient events
and promptly share information with the scientific community to enable
follow-up observations. These pipelines can also react to science alerts shared
by other observatories through networks such as the Gamma-Ray Coordinates
Network (GCN) and the Astronomer's Telegram (ATels). AGILE is a space mission
launched in 2007 to study X-ray and gamma-ray phenomena. This contribution
presents the technologies used to develop two types of AGILE pipelines using
the RTApipe framework and an overview of the main scientific results. The first
type performs automated analyses on new AGILE data to detect transient events
and automatically sends AGILE notices to the GCN network. Since May 2019, this
pipeline has sent more than 50 automated notices with a few minutes delay since
data arrival. The second type of pipeline reacts to multi-messenger external
alerts (neutrinos, gravitational waves, GRBs, and other transients) received
through the GCN network and performs hundreds of analyses searching for
counterparts in all AGILE instruments' data. The AGILE Team uses these
pipelines to perform fast follow-up of science alerts reported by other
facilities, which resulted in the publishing of several ATels and GCN
circulars.Comment: 8 pages, 3 figures, Proceedings of the 37th International Cosmic Ray
Conference (ICRC 2021), Berlin, German
AGILE Observations of the LIGO-Virgo Gravitational-wave Events of the GWTC-1 Catalog
We present a comprehensive review of AGILE follow-up observations of the Gravitational Wave (GW) events and the unconfirmed marginal triggers reported in the first LIGO-Virgo (LV) Gravitational Wave Transient Catalog (GWTC-1). For seven GW events and 13 LV triggers, the associated 90% credible region was partially or fully accessible to the AGILE satellite at the T 0; for the remaining events, the localization region was not accessible to AGILE due to passages into the South Atlantic Anomaly, or complete Earth occultations (as in the case of GW170817). A systematic search for associated transients, performed on different timescales and on different time intervals about each event, led to the detection of no gamma-ray counterparts. We report AGILE MCAL upper limit fluences in the 400 keV-100 MeV energy range, evaluated in a time window of T 0 ± 50 s around each event, as well as AGILE GRID upper limit (UL) fluxes in the 30 MeV-50 GeV energy range, evaluated in a time frame of T 0 ± 950 s around each event. All ULs are estimated at different integration times and are evaluated within the portions of GW credible region accessible to AGILE at the different times under consideration. We also discuss the possibility of AGILE MCAL to trigger and detect a weak soft-spectrum burst such as GRB 170817A
AGILE Study of the Gamma-Ray Emission from the SNR G78.2+2.1 (Gamma Cygni)
We present a study of the γ-ray emission detected by the Astrorivelatore Gamma ad Immagini LEggero-Gamma Ray Imaging Detector (AGILE-GRID) from the region of the SNR G78.2+2.1 (Gamma Cygni). In order to investigate the possible presence of γ rays associated with the SNR below 1 GeV, it is necessary to analyze the γ-ray radiation underlying the strong emission from the pulsar PSR J2021+4026, which totally dominates the field. An “off-pulse” analysis has been carried out, by considering only the emission related to the pulsar off-pulse phase of the AGILE-GRID light curve. We found that the resulting off-pulsed emission in the region of the SNR—detected by the AGILE-GRID above 400 MeV—partially overlaps the radio shell boundary. By analyzing the averaged emission on the whole angular extent of the SNR, we found that a lepton-dominated double-population scenario can account for the radio and γ-ray emission from the source. In particular, the MeV-GeV averaged emission can be explained mostly by Bremsstrahlung processes in a high density medium, whereas the GeV-TeV radiation can be explained by both Bremsstrahlung (E ≲ 250 GeV) and inverse Compton processes (E ≳ 250 GeV) in a lower density medium
The Second AGILE MCAL Gamma-Ray Burst Catalog: 13 yr of Observations
We present the results of a systematic search and analysis of GRBs detected by the Astrorivelatore Gamma ad Immagini LEggero (AGILE) MiniCALorimeter (MCAL; 0.4–100 MeV) over a time frame of 13 yr, from 2007 to 2020 November. The MCAL GRB sample consists of 503 bursts triggered by MCAL, 394 of which were fully detected onboard with high time resolution. The sample consists of about 44% short GRBs and 56% long GRBs. In addition, 109 bursts triggered partial MCAL onboard data acquisitions, providing further detections that can be used for joint analyses or triangulations. More than 90% of these GRBs were also detected by the AGILE Scientific RateMeters (RMs), providing simultaneous observations between 20 keV and 100 MeV. We performed spectral analysis of these events in the 0.4–50 MeV energy range. We could fit the time-integrated spectrum of 258 GRBs with a single power-law model, resulting in a mean photon index 〈β〉of−2.3. Among them, 43 bursts could also be fitted with a Band model, with peak energy above 400 keV, resulting in a mean low-energy photon index 〈α〉 = −0.6, a mean high-energy photon index 〈β〉 = −2.5, and a mean peak energy 〈Ep〉 = 640 keV. The AGILE MCAL GRB sample mostly consists of hard-spectrum GRBs, with a large fraction of short-duration events. We discuss properties and features of the MCAL bursts, whose detections can be used to perform joint broad-band analysis with other missions, and to provide insights on the high-energy component of the prompt emission in the tens of mega electron volt energy range.publishedVersio
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