Particle and Astroparticle Physics A. A. 2018-19 Lessons 7 and 8 Detection of primary cosmic rays with E < few 100 GeV. Main characteristics of apparatuses on atmospheric balloons, main results. The PAMELA and INTEGRAL and SWIFT observatories on satellites The Compton Gamma Ray Observatory and its components: CGRO, BATSE, Comptel ed EGRET. Gamma Ray Bursts. CGRO Sky Map. A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 1
The starting point: the "all particle" spectrum dn de = [m 2 sr 1 s 1 GeV 1 ] Distribuzione in energia dei raggi cosmici osservati da diversi esperimenti - Simon Swordy - Università di Chicago ~ 1000 particles/(s m 2 ) ionized nuclei: 90% protons 9% α particles heavier nuclei what is the origin of cosmic rays? originated in the solar system? a small amount associated with violent phenomena in the Sun and characterized by great temporal variability originated in the galaxy: most. An anticorrelation with intense solar activities is also noted extragalactic origin: the most energetic part of the spectrum Direct measures of primary cosmic rays in space (satellites) in the high atmosphere (balloons) Indirect measures extended atmospheric showers (EAS) Cherenkov in the air Ground detectors underground laboratories GeV TeV PeV EeVJoule A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 2
Atmospheric Balloons and C.R. physics A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 3
Balloon data: positron fraction before 1990 An evidence for an excess of antimatter?? A first evidence of dark matter? A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 4
Cosmic Rays and Antiparticles The interaction of primary C.R. with the InterStellar Medium (ISM) can explain (at least part of) the observed antimatter A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 5
MASS - Matter Antimatter Space Experiment Designed to measure antiprotons with E ~ 4-20 GeV positrons with E ~ 4-10 GeV. It is the evolution of MASS1 (exp. brought in flight already in 1989), with the tracing apparatus improved thanks to a system of "drift chambers". The identification of particles is possible thanks to the gas-cherenkov (Freon-12) detector and to a calorimeter made of brass-streamer tubes (and Isobutane). The experiment was carried out for 23 hours in September 1991 by Ft. Sumner, after 10 hours the magnetic field was lost. A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 6
Matter Antimatter Space Spectrometer 2 MASS - 1991 A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 7
Isotope Matter Antimatter Experiment Made to be transported in the upper atmosphere with balloons and to measure abundance in galactic C.R. of protons, antiprotons, deuterium, helium-3 and helium-4 in the energy range ~ 0.2 3.2 GeV/nucleon. In this region of energies there is the maximum intensity for the expected flows of the particles to be observed IMAX measures the magnetic rigidity of charged particles that pass through the apparatus (by tracking in the drift chambers (DC) and in the multiwire proportional counters (MWPC)), the charge (via de/dx in the scintillators (S1, S2) that provide also the time -of-flight (TOF)), and the speed (via time-of-flight (TOF) and the Cherenkov aerogel meters (C2 and C3)). By combining these three quantities it is possible to identify the particle by mass, charge and sign of the charge. IMAX was launched in July 1992 starting from Lynn Lake, Manitoba, Canada, has reached the quota of about 36 km (with a residual atmosphere of 5 g/cm 2 ) and during about 16 hours has collected more than 3 million of events (collecting a statistic 10 times greater than previous experiments). IMAX Rigidità = p c/ze [GV]= [energy/charge] sin q/2 = e B L / (2 p) = L / (2 R ) A.A. 2018-2019 q/2 R Prof. Antonio Capone - Particle and AstroParticle Physics L 8
IMAX the flight FLIGHT 16-17 July 16-17, 1992, Lynn Lake, Manitoba, Canada. Float was reached about 7 hours after launch. The instrument took data throughout ascent, recording about 1.4x10 6 events. These data will be used to determine altitude-dependent particle spectra. At the end of the float period, the magnet was ramped down and data was taken with the magnet off in order to check the alignment of the tracking chambers. Landing was near Peace River, Alberta, Canada, with the instrument being recovered in excellent condition. All payload and detector systems appear to have performed well throughout the flight. Over 3.4x10 6 events were recorded during the float period. A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 9
IMAX evidence for an antiproton flux in C.R. A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 10
A schematic cross-sectional view of the different detectors making up HEAT, in the first configuration for detection of electrons and positrons. MWPC HEAT - The Transition Radiation Detector The HEAT Transition Radiation Detector The Transition Radiation Detector (built by the University of Chicago) consists of six polyethylene fiber radiator blankets, each with a multi-wire proportional chamber MWPC (filled with a Xenon-methane gas mixture) attached underneath. When a charged particle travels through an interface between materials of different dielectric constants, radiation (in the form of X-rays) is generated with an intensity proportional to the relativistic Lorentz factor gamma of the particle. As it travels through a polyethylene fiber blanket, a high-energy electron (of high Lorentz gamma) encounters many interfaces and generates transition radiation, whereas a proton of the same energy (but a much lower Lorentz factor due to a higher mass) generates essentially no such radiation. X-ray photons are absorbed by the gas mixture in the MWPC. The combination of energy deposited by the X-rays and ionization losses (due to the passage of any charged particle - electron or proton - through the gas in the chambers) is picked up electrically by cathode electrodes running perpendicular to the wires in the chamber (used in the pulse-height analysis below). Additionally, an electrical signal is also picked up by the wires in the chamber, and both a signal amplitude and variation with time are recorded (used in the time slice analysis below). Pulse-height likelihood analysis The total energy deposited in each of the six MWPCs is compared to the known signals (from prior calibrations) obtained when an electron, proton or alpha particle traverses the detector. A parameter is then calculated that indicates the likelihood that the particle was an electron (technically, the parameter is the product for all six chambers of the probability that the signal was produced by an electron or positron divided by the probability that the signal was produced by a proton). Figure A below shows the distribution of this maximum-likelihood parameter with clearly separated proton and electron populations. Time slice analysis A software neural-net classifier (with 3 input nodes, 5 hidden nodes and one output node) was devised, and trained to recognize the difference in the resulting time distribution of charge clusters detected by the wires when an electron or a proton traverses the detector. The output of the neural net analysis is a number between 0 and 1, indicating the probability that the particle was a proton (near 0) or an electron or positron (near 1). The excellent separation between protons and electrons is illustrated in figure B below. A.A. 2018-2019 11
HEAT: the T.O.F. system The HEAT Time-of-Flight system The Time-of-Flight system consists of four paddles of plastic scintillator viewed by eight photomultiplier tubes (built by the University of California at Berkeley), at the top of the instrument, and three paddles of scintillator viewed by three photomultiplier tubes (built by the University of California at Irvine), near the bottom of the instrument. When a charged particle traverses a scintillator slab, a small amount of light (proportional to the square of the charge of the particle but inversely proportional to the square of its velocity) is generated; this light is viewed by the photomultipler tubes and converted to electrical pulses, that are then processed by assorted electronics module. Particle velocity and direction of travel The accurate times at which light is seen at the top and bottom are recorded, and the time difference is used to calculate the velocity of the particle (expressed in units of the speed of light). We are especially interested in discriminating between particles traveling downwards through our instrument and the so-called albedo particles traveling upwards (since an upgoing negatively charged particle could fool us into thinking it was a positively charged particle traveling downwards...). That we have achieved excellent separation between upward and downward-going particles can be seen from figure A below (where by definition positive velocities represent downgoing particles andnegative velocities upgoing). A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 12
HEAT: the magnetic spectrometer The Magnetic Spectrometer consists of two parts: A magnet consisting of two superconducting coils inside a cryogenic vessel filled with liquid Helium, generating a magnetic field of 1 Tesla over a central room-temperature bore of dimensions 51 cm x 51 cm x 61 cm. A precision tracking Drift-Tube Hodoscope, a chamber with 479 thin-walled drift tubes filled with a CO2-hexane gas mixture, arrayedin 26 layers (18 alignedparallelwith the magnetic field, 8 perpendicular), located inside the bore ofthe magnet. When an electrically charged particle travels through the magnetic field permeating the hodoscope, its trajectory is deflected due to the Lorentz force, in a direction perpendicular to the magnetic field. As the particle travels through the gas inside the tubes, it deposits an electrical signal picked up by a thin wire running down the center of the tube, and from the time at which the signal was picked up in the various tubes, it can be determined to high accuracy (about 70 microns) how far from the wire the particle was traveling. We thus obtain a pattern of lined-up "impact parameters" (distance of closest approach), as illustrated in the figure below (black circles inside the gray tubes; the red tubes were rejected in this event althoughtheyhadfired). A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 13
HEAT - The electromagnetic calorimeter The Electromagnetic Calorimeter (built by the University of California at Irvine) consists of ten plastic scintillator slabs viewed by one photomultiplier tube each, interspersed with ten layers of Lead (each of a thickness equivalent to 0.9 electron radiation length), located at the bottom of the instrument. When an electron or a hadron reaches the Lead layers, a shower of secondary particles is produced and propagates through the rest of the stack (most of the secondary particles themselves produce further showering in deeper Lead layers), until the energy of the parent particle is expended and the particle shower is eventually absorbed. When charged particles traverse the scintillator slabs, light is generated and detected by the photomultipler tubes (and then converted to electrical pulses, processed by assorted electronics module), in amounts proportional to the number of particles in the scintillator. Shower shape discrimination By measuring the number of particles in the shower at each scintillator layer in the stack (the socalled shower profile), we can distinguish between showers initiated by electrons or positrons from those initiated by hadrons
BESS - Balloon Superconducting Solenoid Experiment Primary scientific objectives of the experiment are the measurements of the cosmic antiproton energy spectrum, very sensitive search for antihelium, and the precision measurements of various cosmic ray components. The BESS detector has a unique cylindrical configuration with a large acceptance of 0.4, which is one order of magnitude larger than that of previous spectrometers. Forty low energy cosmic antiprotons were clearly detected for the first time by the BESS detector. Anti-helium BESS experiment already has placed an upper limit on anti-helium to helium ratio of 2 10-6, which is a factor improvement over previous experiments, which is a factor of 50 improvement over previous experiments. A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 15
Do we expect to find an "antimatter" component in primary C.R.? Evaporation of primordial black holes Anti-nucleosyntesis Background: CR interaction with ISM CR + ISM à p-bar + WIMP dark-matter annihilation in the galactic halo A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 16
In 79 Golden et al. they observed antiprotons in cosmic rays. Sign of a symmetrical universe for matter and antimatter???. Expected antiprotons in C.R. interactions (protons, He +, heavier nuclei,...) with interstellar matter (ISM). The comparison between expected and measured fluxes can offer data to "model" the transport of R.C. (particularly the heaviest nuclei) in the ISM. Proton/antiproton ratio Other "exotic" sources have also been considered, such as "evaporation of primordial black holes, decay of" dark matter ", acceleration in relativistic plasma,... The measures of BESS, MASS2, IMAX, and CAPRICE are in agreement with the model that the majority of antiprotons are secondary products of the interaction of R.C. primary A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 17
The Observatory PAMELA 2006-2016 Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 18
The PAMELA Instrument A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 19
PAMELA results: positrons A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 20
Pamela positron fraction A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 21
PAMELA results: antiprotons A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 22
PAMELA Results possible explanations Dark Matter particles annihilate and from the "vacuum à e + e - A local pulsar : the spinning B of the pulsar strips e - that accelerated emit g that originate e + e - PULSAR à e - à g à e + e - A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 23
PAMELA, other results: the B and C fluxes O. Adriani et al. ApJ 791 (2014), 93 A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 24
PAMELA overall results A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 25
INTErnational Gamma-Ray Astrophysics Laboratory A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 26
The SWIFT Gamma Ray Burst Explorer Swift is mission mainly dedicated to the observations of Gamma-ray bursts (GRBs. GRBs are the most powerful explosions the Universe has seen since the Big Bang. They occur approximately once per day and are brief, but intense flashes of gamma radiation. They come from all different directions of the sky and last from a few milliseconds to a few hundred seconds. So far scientists do not know what causes them. Do they signal the birth of a black hole in a massive stellar explosion? Are they the product of the collision of two neutron stars? Or is it some other exotic phenomenon that causes these bursts? Swift was launched on Nov 20th, 2004. It contains 3 instruments: The Burst Alert Telescope (BAT) The X-Ray Telescope (XRT) The Ultra Violet-Optical Telescope (UVOT) Swift is a MIDEX Gamma Ray Burst mission led by NASA with participation of Italy and the UK. A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 27
Astrophysical gamma rays sources The extragalactic high energy sources most relevant for us are active galactic nuclei (AGNs) and Gamma Ray Bursts (GRBs). All AGNs are believed to be powered by a supermassive black hole at the center of a galaxy. The supermassive black hole will accrete gas in a disk-like configuration. Sketch of the typical geometry of an AGN on a logarithmic length scale. Depending on the viewing direction, the AGN appears as a BL Lac object or flat spectrum radio quasar (FSRQ), a Seyfert-I galaxy or steep spectrum radio quasar (SSRQ), or as an high luminosity Faranoff Riley-II (FR-II) galaxy, a low luminosity Faranoff Riley-I (FR-I) galaxy or a Seyfert-II galaxy, respectively, as indicated. Perpendicular to the accretion disk two jets are emitted that consist of relativistic matter and magnetic fields and whose formation is probably related to MHD effects. Immersed in these jets are shocks that form knots and hot spots in which particles can be accelerated to very high energies. Particle acceleration can also occur in the immediate environment of the supermassive black hole but due to the intense radiation fields there the maximal energies achieved are expected to be lower. A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 28
A source of Gamma Ray Burst (in brief) Sketch of the typical geometry of a GRB in the fireball model. Apart from the distance from the centre also plotted are the emission timescales of the various stages of the explosion are plotted along the horizontal axis. Also listed are the most relevant electromagnetic and photo-hadronic processes. If photons are emitted roughly isotropically in the comoving plasma rest frame, in the observer frame the emission appears to be beamed into a cone with opening angle θ 1/Γ with Γ the Lorentz factor of the plasma in the observer frame. GRBs were first discovered in the late 1960s by the Vela satellites and were originally thought to be linked to nuclear testing. However, it soon became clear that these objects have an extra-terrestrial origin. In the following 20 years it was thought that GRBs are originated as explosions at the surfaces of neutron stars within our own Galaxy. There are two types of GRBs, the short GRBs with a duration < 2 s and a higher than average peak energy, and the long GRBs with a duration > 2 s that are observed up to higher redshifts. The catastrophic event linked to the former is believed to be the merger of two neutron stars or of a neutron star and a black hole, whereas the latter are thought to be triggered by the collapse of a very massive star. A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 29
Searching for astrophysical EM radiation Soft X-ray to high-energy gamma-ray observatories in operation The list below is not complete!!! low medium High energy X rays g rays A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 30
The INTEGRAL Gamma Ray Observatory IBIS The gamma-ray Imager: 15 kev-10 MeV (ISGRI/PICsIT) 12 FWHM imaging <30 source location OMC Optical Monitor Camera: 500-600 nm IBIS, SPI, Jem-X: coded mask Launched 17/10/2002, still in operation! high elliptical orbit (~72h) 58h of continuous science Jem-X - The Joint European X-ray Monitor: 3-35 kev; 3 SPI The gamma-ray Spectrometer: 20 kev 8 MeV E/DE ~ 500 1.3 source location Is the link between soft X-ray and high energy g-ray science High Sensitivity for photons 3 kev < E g <10 MeV Wide Field Of View ~ 100 1000 deg 2 All-Sky monitor capability for 80 kev < E g <2.5 MeV Real time transmission of transient to Earth laboratory A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 31
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INTEGRAL: some results THE GALAXY IN HARD-X/SOFT GAMMA-RAYS A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 33
INTEGRAL: ANNIHILATION IN THE GALAXY The SPI instrument onboard INTEGRAL has performed a search for 511 kev emission (resulting from positron-electron annihilation) all over the sky. A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 34
INTEGRAL TRACES THE LOW LUMINOSITY POPULATION OF GAMMA RAY BURSTS THE RADIO-ACTIVE DECAY OF 26 AL AS REVEALED BY INTEGRAL/SPI The 1.809 MeV line emission associated with the radio-active of 26 Al A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 35
Compton Gamma Ray Observatory CGRO (1991-2000) A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 36
Compton Gamma Ray Observatory Oriented Scintillation Spectrometer Experiment 50 KeV-10 MeV 1-30 MeV 20 MeV - 30 GeV Burst And Transient Source Experiment 20 KeV - 1 MeV These four instruments are much larger and more sensitive than any gamma-ray telescopes previously flown in space. The large size is necessary because the number of gamma-ray interactions that can be recorded is directly related to the mass of the detector. Since the number of gamma-ray photons from celestial sources is very small compared to the number of optical photons, large instruments are needed to detect a significant number of gamma rays in a reasonable amount of time. The combination of these instruments can detect photon energies from 20 thousand electron volts (20 kev) to more than 30 billion electron volts (30 GeV). A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 37
CGRO BATSE: GRB and transient events At the heart of the BATSE detectors are NaI crystals which produce a flash of visible light when struck by gamma rays. The flashes are recorded by light-sensitive detectors whose output signal is digitized and analyzed to determine the arrival time and energy of the gamma ray which caused the flash. Each BATSE detector unit consists of a large area detector sensitive to faint transient events along with a smaller detector optimized for spectroscopic studies of bright events. The Burst And Transient Source Experiment (BATSE) served as the all-sky monitor for the Compton Observatory, detecting and locating strong transient sources called gammaray bursts as well as outbursts from other sources over the entire sky. There were eight BATSE detectors, one facing outward from each corner of the satellite, which are sensitive to gamma-ray energies from 20 kev to 1 MeV. A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 38
CGRO - OSSE The Oriented Scintillation Spectrometer Experiment (OSSE) consists of four NaI scintillation detectors, sensitive to energies from 50 kev to 10 MeV. Each of these detectors can be individually pointed. This allows observations of a gamma-ray source to be alternated with observations of nearby background regions. An accurate subtraction of background contamination can then be made. The OSSE instrument has produced observations of the energy spectrum of nuclear lines in solar flares, the radioactive decay of nuclei in supernova remnants, and the signature of matter-antimatter (electron-positron) annihilation in the Galactic center region. A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 39
The bursts are isotropically distributed on the sky: no significant quadrupole moment or dipole moment is found. The nature of the sources remains unknown. At the same time, a deficiency has been detected in the number of faint bursts, interpreted as an indication that the spatial extent of the burst distribution is limited and that BATSE has seen the limit or edge of the distribution. BATSE main results The Gamma Ray Bursts isotropic distribution on the sky along with the deficiency of faint bursts can be naturally explained if the bursts are located at cosmological distances (far beyond the Milky Way). A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 40
The sources of GRB are therefore isotropic, galactic and extragalactic: if such events would have been originated in our galaxy then they would be distributed preferably on the plane of the Milky Way; even if they were associated with the galactic halo, they would be distributed above all towards the galactic centre, unless the size of the halo is enormously greater than estimated. GRBs were classified into two seemingly distinct categories: Flashes of short duration and hard spectrum (short bursts or short flashes) they typically last less than two seconds and emissions are dominated by high-energy photons Long-lasting flashes and soft spectrum (long bursts or long flashes) they typically last more than two seconds and emissions are dominated by low-energy photons. Beppo-SAX In 1997 the Italian satellite Beppo-SAX allowed to identify the coordinates of the lightning with unprecedented precision, definitively confirming how these flashes were generated in distant galaxies. A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 41
The Compton "telescope": COMPTEL The Imaging Compton Telescope (COMPTEL) utilizes the Compton Effect and two layers of gamma-ray detectors to reconstruct an image of a gamma-ray source in the energy range 1 to 30 million electron volts (MeV). Gamma rays from active galaxies, radioactive supernova remnants, and diffuse gamma rays from giant molecular clouds can be studied with this instrument. COMPTEL's upper layer of detectors are filled with a liquid scintillator which scatters an incoming gamma-ray photon according to the Compton Effect. This photon is then absorbed by NaI crystals in the lower detectors. The instrument records the time, location, and energy of the events in each layer of detectors which makes it possible to determine the direction and energy of the original gamma-ray photon and reconstruct an image and energy spectrum of the source. A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 42
Fotoelettrico in Piombo Compton A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 43
CGRO - EGRET The Energetic Gamma Ray Experiment Telescope (EGRET) provides the highest energy gamma-ray window for the Compton Observatory. Its energy range is from 20 million electron volts (20 MeV) to 30 billion electron volts (30 GeV). EGRET is 10 to 20 times larger and more sensitive than previous detectors operating at these high energies and has made detailed observations of high-energy processes associated with diffuse gamma-ray emission, gamma-ray bursts, cosmic rays, pulsars, and active galaxies known as blazars. The EGRET instrument produces images at these energies (20 MeV- 30 GeV) using high-voltage gas-filled spark chambers. High-energy gamma rays enter the chambers and produce an electron-positron pair of particles which cause sparks. The path of the particles is recorded allowing the determination of the direction of the original gamma ray. The particle energies are recorded by a NaI crystal beneath the spark chambers providing a measure of the original gamma-ray energy. A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 44
CGRO - EGRET Detectors on satellites - Detect the primary photons - They need to anticoincide e+- - Tracking detector needed for e+e- - Calorimeter (e.m. energy measur.) Effective area: A eff ( E) = N φ( E) T Given by the convolution of the geometrical detector area and the detector efficiency CARATTERISTICHE DI EGRET Eγ Δ E/E Δ θ (FWHM) Aeff (cm2) (MeV) FWHM gradi 100 26% 5.5 930 500 20% 2 1570 1,000 19% 1.2 1300 10,000 26% 0.4 690 A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 45
CGRO - EGRET EGRET was the most sensitive instrument on board the Compton Gamma Ray Observatory (CGRO). It has collected data from 5 April 1991 to 2000. Sensitive for 20 MeV < E g < 30 GeV. EGRET was made up of a multilayer "spark chamber" with tantalum converters. The energy was measured by a sodium iodide calorimeter of 8 radiation lengths A time-of-flight system allowed the measurement of the propagation direction of the incoming particles in the apparatus. The minimum flux of photons (sensitivity) of energy greater than 100 MeV, detectable by EGRET was equal to about F min =5x10-8 fotoni/cm 2 /s.. He realized for the first time a complete map of the gamma radiation of the celestial vault, leading to the discovery of new high-energy sources and of the diffused galactic radiation (Galactic Diffuse Radiation). A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 46
EGRET sky map E g >100 MeV The EGRET all-sky map shows an image of the sky at gamma-ray energies above 100 MeV in Galactic coordinates. The diffuse emission, which appears brightest along the Galactic plane, is primarily due to cosmic-ray interactions with the interstellar medium. The Vela, Geminga and Crab pulsars are clearly visible as bright knots of emission in the Galactic plane in the right portion of the image. The blazar 3C279 is seen as the brightest knot of emission above the plane. This map was produced by combining EGRET observations from the first year of Compton Observatory operations. A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 47
CRAB and GEMINGA This EGRET image shows Geminga (above and left of center) and the Crab nebula (below and right of center), two bright sources of gamma rays in the direction of the Galactic anticenter. Both Geminga and the Crab contain pulsars which pulse at gamma-ray energies. Strikingly, Geminga mainly pulses in the X-ray and gamma-ray regimes with very little pulsation at other wavelengths, while the Crab pulsar is observed to generate optical and radio pulses as well. The faint source visible just below center is the active galaxy designated PKS 0528+134. A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 48
A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 49
The "today" γ telescope in the space: FERMI A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 50
END for the moment A.A. 2018-2019 Prof. Antonio Capone - Particle and AstroParticle Physics 51