Cosmic Rays, Gamma Rays and the Universal Rays and the Universal - PowerPoint PPT Presentation

Cosmic Rays, Gamma - - Cosmic Rays, Gamma Rays and the Universal Rays and the Universal Background Radiation Background Radiation Malcolm Longair Malcolm Longair Cavendish Laboratory, Cambridge Cavendish Laboratory, Cambridge

Celebrating Occhialini I met Occhialini I met Occhialini only a few only a few times, in connection with times, in connection with γ - ESA projects and γ - ray ray ESA projects and astronomy. astronomy. The other connection is The other connection is that, as a former director of that, as a former director of the Cavendish Laboratory, the Cavendish Laboratory, his work with Blackett Blackett in in his work with the 1930s is one of the the 1930s is one of the highlights of its scientific highlights of its scientific history. history.

Celebrating Occhialini My charge is to describe My charge is to describe the current state of two the current state of two areas to which he made areas to which he made enormous contributions enormous contributions and which intersect with which intersect with and my interests in High my interests in High Energy Astrophysics and Astrophysics and Energy Cosmology. Cosmology. • • Cosmic ray astrophysics Cosmic ray astrophysics γ - High energy γ • High energy - rays. rays. •

Programme • Brief Historical Notes Brief Historical Notes • • Cosmic ray physics Cosmic ray physics • γ - High energy γ • High energy - rays rays • • Cosmology Cosmology •

1. Brief Historical 1. Brief Historical Notes Notes

The Wilson Cloud Chamber The Wilson Cloud Chamber The first outstanding The first outstanding research involving research involving Occhialini at the at the Occhialini Cavendish Laboratory Cavendish Laboratory concerned development concerned development of the automatic Cloud of the automatic Cloud Chamber. Patrick Chamber. Patrick Blackett had already had already Blackett perfected the techniques perfected the techniques Wilson Wilson ’ ’ s perfected Cloud Chamber s perfected Cloud Chamber of exploiting its of exploiting its capabilities. capabilities.

Blackett ’ ’s s Automatic Cloud Automatic Cloud Blackett Chamber of 1928 Chamber of 1928 In 1924, Blackett Blackett succeeded succeeded In 1924, in taking 23,000 automatic in taking 23,000 automatic cloud chamber photographs cloud chamber photographs which contained about which contained about α - 270,000 tracks of α - 270,000 tracks of particles. Among these particles. Among these were 8 tracks showing the were 8 tracks showing the ejection an energetic proton ejection an energetic proton in the disintegration of a in the disintegration of a nitrogen nucleus. nitrogen nucleus.

Blackett ’ ’ s s Letter to Letter to Occhialini Occhialini ’ ’ s s Blackett Father Father For it was ce rtainly his (Occhialini ’ s ) arrival in Cambridge which stimulate d my e mbarking on the fie ld of cosmic rays which I have ne ve r le ft. And our work toge the r in 1932- 33 was a re al collaboration of the happie st kind. P.M.S. Blackett Letter (1948)

Blackett ’ ’ s s Nobel Prize Lecture Nobel Prize Lecture Blackett Occhialini and I se t about, the re fore , the de vising of a me thod of making cosmic rays take the ir own photographs, using the re ce ntly de ve lope d “ Ge ige r-M ü lle r counte rs ” as de te ctors of the rays. P.M.S. Blackett Nobel Prize Speech (1948)

The Discovery of the Positron The Discovery of the Positron Occhialini had been working with Rossi had been working with Rossi Occhialini using coincidence methods for detecting the using coincidence methods for detecting the arrival of cosmic rays. He arrived in arrival of cosmic rays. He arrived in Cambridge ‘ ‘ for three weeks; he stayed for for three weeks; he stayed for Cambridge three years ’ ’ . They combined the . They combined the three years coincidence technique with the with the cloud cloud coincidence technique chamber so that, whenever a high energy chamber so that, whenever a high energy particle passed through the chamber, its particle passed through the chamber, its track was photographed. track was photographed.

Blackett and and Occhialini Occhialini, 1933 , 1933 Blackett In the key experiment, In the key experiment, the cloud the cloud chamber was chamber was placed on its side and placed on its side and solenoids placed above solenoids placed above and below it. it. The The and below upper solenoid acted upper solenoid acted as a converter for the as a converter for the cosmic rays. cosmic rays. P.M S. P.M S. Blackett Blackett and G.P.S. and G.P.S. Occhialini Occhialini, 1933,. Proc. Roy. Soc. A139, 699 , 1933,. Proc. Roy. Soc. A139, 699

Blackett and and Occhialini Occhialini, 1933 , 1933 Blackett They discovered They discovered showers of high energy showers of high energy electrons, accompanied electrons, accompanied by positively charged by positively charged particles which were particles which were deflected by the same deflected by the same amount in the opposite amount in the opposite direction. This was the direction. This was the discovery of the positron, positron, discovery of the the first antiparticle to be the first antiparticle to be discovered. discovered. P.M S. Blackett Blackett and G.P.S. and G.P.S. Occhialini Occhialini, 1933,. Proc. Roy. Soc. A139, 699 , 1933,. Proc. Roy. Soc. A139, 699 P.M S.

COS - B γ - ray Satellite As soon as space As soon as space astronomy became astronomy became feasible, Occhialini Occhialini feasible, became a leader of became a leader of European efforts, European efforts, γ - particularly in γ - ray ray particularly in astronomy. Perhaps astronomy. Perhaps his greatest his greatest achievement was the achievement was the success of COS - - B. B. success of COS

COS - B Map of the Galaxy in γ - rays

The Compton γ - ray Observatory (CGRO)

Beppo - - SAX Satellite SAX Satellite Beppo The Beppo Beppo - - The SAX satellite SAX satellite was a was a remarkable remarkable success – – we we success will discuss will discuss some of the some of the results later. results later.

The INTEGRAL Space The INTEGRAL Space Observatory Observatory INTEGRAL is the γ γ - - ray ray INTEGRAL is the observatory mission of observatory mission of ESA launched on ESA launched on October 17 2002 on a October 17 2002 on a Proton rocket. It is an Proton rocket. It is an ESA - - led mission in led mission in ESA collaboration with collaboration with Russia and the USA. Russia and the USA.

SWIFT NASA project to understand the physics of γ - ray bursts. Launched November 20 2004

2. Cosmic Rays 2. Cosmic Rays

The Cosmic Ray Spectrum 3 x E 3 Replot as Replot as E x N(E) N(E) There is encouraging There is encouraging agreement about the observed agreement about the observed spectrum except at the very spectrum except at the very highest energies. highest energies.

The Universal Mechanism The Universal Mechanism Power - - law energy law energy Power spectra are found spectra are found commonly in high energy commonly in high energy astrophysical systems. astrophysical systems. E - 2.7 Radio, optical, X - - ray and ray and Radio, optical, X γ - γ - ray spectra of quasars ray spectra of quasars and active galaxies and and active galaxies and γ - γ E - 3.1 - ray bursts require ray bursts require x dE dE ∝ ∝ E - x E - N(E) dE N(E) dE x ~ 2.5 - - 3 3 x ~ 2.5

First - order Fermi Acceleration The great merit of of The great merit Shock front the first first order shock order shock the acceleration acceleration mechanism that it is that it is mechanism not sensitive to the not sensitive to the precise strength of precise strength of the shock, so long as the shock, so long as it is reasonably it is reasonably strong. strong.

First - - order Fermi Acceleration order Fermi Acceleration First in Strong Shocks, U U » » v v s in Strong Shocks, s U v 2 = ¼ v 1 v 1 = |U| p 2 , T 2 , ρ 2 p 1 , T 1 , ρ 1 ¾ U ¾ U

First - order Fermi Acceleration In the simplest calculation for non - - relativistic relativistic In the simplest calculation for non shocks, a power - - law spectrum is found which law spectrum is found which shocks, a power only depends upon the shock being strong. only depends upon the shock being strong.

The Acceleration of Charged Particles The Acceleration of Charged Particles Three Shock Acceleration mechanisms work together. • First • First - - order Fermi mechanism: scattering order Fermi mechanism: scattering across the shock dominant at quasi - - parallel parallel across the shock dominant at quasi shocks ( θ θ Bn o ) < 45 o ) shocks ( Bn < 45 • Shock Drift Acceleration: drift along the shock Shock Drift Acceleration: drift along the shock • surface dominant at quasi - - perpendicular perpendicular surface dominant at quasi θ Bn shocks ( θ o ) < 45 o ) shocks ( Bn < 45 • Second • Second - - order Fermi mechanism: Stochastic order Fermi mechanism: Stochastic � add process, turbulent acceleration � process, turbulent acceleration add momentum diffusion term momentum diffusion term