Introduction to the AGILE symposium

AGILE development and silicon detector Abstract In the years 1980s and 1990s, a very fast and important progress on position and energy loss measurements of elementary particles was obtained by the use of Si strip detector in high energy (HE) experiments. The number of strips has been increasing at any improvement of the tracker device. The high number of strip density also pushed the power reduction of the readout electronic amplifiers. The Si tracker became at certain moment a challenging substitute of the classical spark chambers (Fichtel et al. NASA-TM-X-70761, 1995; Thompson arXiv:e:0811.0738, 2008), in use for tracking particles in space experiments. In particular in HE \(\gamma \)-strophysics, the photon direction was derived by measuring that of the positron electron pair produced in high Z material interlaid in the planes of the spark chamber. See for instance the EGRET figure in the text. AGILE and GLAST (renamed Fermi after launch) are the most successful examples of the Si revolution.

A multi-wavelength pipeline for pulsar searches Abstract Pulsar studies in the recent years have shown, more than others, to have benefited from a multi-wavelength approach. The INAF-Astronomical Observatory in Cagliari (INAF-OAC) is a growing facility with a young group devoted to pulsar and fast-transient studies across the electromagnetic spectrum. Taking advantage of this expertise, we have worked to provide a suite of multi-wavelength software and databases for the observations of pulsars and compact Galactic objects at the Sardinia Radio Telescope (SRT). In turn, radio pulsar observations at SRT will be made available, in a processed format, to gamma-ray searches using AGILE and FERMI gamma-ray satellites and, in a near future, they will be complementary to polarimetric X-ray observations with IXPE.

The future of ground-based gamma-ray astronomy Abstract Ground-based gamma-ray astronomy is a young branch of high-energy astrophysics, addressing the highest energies in the electromagnetic spectrum. TeV photons cannot be produced by “ordinary” stars since they require quite extreme conditions, thus they allow the study of extreme astrophysical objects such as supernova remnants, neutron stars, black holes, both stellar and supermassive, as well as the elusive dark matter. To make it possible to go a step further in this exciting field, a world-wide collaboration is building the Cherenkov telescope array, an ambitious global observatory, to which the Italian community is strongly committed. The foreseen contribution of the Istituto Nazionale di Astrofisca (INAF) will be briefly outlined.

The fermi view of gamma-ray bursts at the dawn of the multi-messenger era Abstract Gamma-Ray Bursts (GRBs) are among the most powerful astrophysical phenomena. Recent observations are shedding light into their high-energy emission properties. Here I will review GRB observations made by the Fermi instruments, the Gamma-Ray Burst Monitor (GBM), and the Large Area Telescope (LAT). I will discuss the main observational properties of the detected bursts presented in the more recent GBM and LAT GRB catalogs.

Measurement of the low-energy charged particle background with the space detector HEPD Abstract Spaceborne gamma-ray telescopes are operated within a dominant background of charged particles, mainly primary cosmic rays and Earth albedo particles. Dedicated anti-coincidence devices and on-board rejection techniques are needed to reject this background, as well as the best available background models. The high-energy particle detector (HEPD) is a space detector for high-energy particles, which can identify electrons, protons and light nuclei in the energy range from few MeV to many hundreds of MeV, and measure their fluxes. It consists of a high-precision silicon tracker, a versatile trigger system, a range calorimeter, and an anti-coincidence system. HEPD will extend PAMELA and the AMS-02 measurements to lower energies and characterize the orbital radiation environment, then providing very useful data for the future gamma-ray mission development, especially for the optimization of the on-board background rejection.

A search for new sources below 100 MeV in the Fermi -LAT data Abstract The Fermi Large Area Telescope (LAT) has discovered more than 3000 sources between 100 MeV and 300 GeV (3FGL), including over 200 \(\gamma \)-ray pulsars. The majority of these pulsars have their spectral energy peaks (in \(\nu F_{\nu }\)) above 1 GeV. There exists another population of very energetic, young rotation-powered pulsars having non-thermal hard X-ray emission with spectral energy distributions (SEDs) peaking around 1 MeV, but having no detected emission by Fermi LAT above 100 MeV. Previous analyses of point sources in the gamma ray range were done only below 30 MeV (COMPTEL) or above 100 MeV (Fermi-LAT). Below 30 MeV, the imaging Compton telescope (COMPTEL) detected 26 steady sources in the energy range from 0.75 to 30 MeV. Since the Fermi LAT detects gamma rays down to 20 MeV, we create a list of sources detected in the energy range between 30 MeV and 100 MeV, using PGWave, a background-independent tool that makes use of a wavelet transform. This closes a gap of point source analysis between the COMPTEL catalog and the Fermi-LAT catalog and provides information and constraint for this missing MeV pulsar population.

The BL Lac PG 1553+113: a supermassive binary black hole candidate Abstract We present updated observations of the blazar PG 1553+113, a bright BL Lac Object that yields quasi-periodic gamma-ray emission every 2.2 years, strongly suggesting the activity of a super-massive binary black hole. Such binary systems are widely held to emit low-frequency gravitational waves. Confirming the binary nature of PG 1553+113 is very relevant for upcoming searches of nHz gravitational waves.

A decade of AGILE: Closing remarks

The crab nebula and its mysteries: some facts and puzzles Abstract We discuss and summarize five results that we and various colleagues have produced over the last few years in the study of the wonderful, yet enigmatic, Crab Nebula and its pulsar. The results, in turn, have to do with the geometry inferred from Chandra X-ray observations, the surprising results of pulse phase polarimetry at 1.4 GHz, the search for an X-ray location of the γ-ray flares for which we have Agile and Fermi to thank, and seeing if the optical and infrared inner knot might be the location of these flares.