Pulsars: the Magnetosphere and the γ-ray emission Gabriele Brambilla Supervisors: P. M. Pizzochero (Unimi), A. K. Harding (NASA GSFC)

The pulsar radio emission lead to the conclusion they are fast rotating compact objects www.cv.nrao.edu C. Kalapotharakos

Neutron star and Pulsar wind Pulsars are formed in supernovae explosions, and they accelerate particles that emit in X and γ rays Supernova shell Jet Neutron star and Pulsar wind Pulsar wind nebula Pulsar Credit: NASA/CXC/ISDC/L. Pavan et al Credit: NASA/CXC/Eureka Scientific/M. Roberts et al.

Measuring the pulsar period and its deceleration, we get a lot of information about the pulsar For a spinning magnetic dipole:     Harding from ATNF data     Harding 2013

Particle’s acceleration produces light -> dissipation Pulsars behaves like a dynamo; currents dissipate, emitting light when particles are accelerated www.physicsforums.com Google images Particle’s acceleration produces light -> dissipation

magnetosphere J = σ ( E + v x B) =0 E·B=0 Pulsars cannot be surrounded by vacuum. The opposite limit is called force-free plasma Ω J = σ ( E + v x B) E   =0 (force free) magnetosphere PULSAR B   E·B=0

The magnetosphere can get close to the force-free condition by electron-positron pair cascades A. K. Harding QED: g + B  e e+ Pair Formation Front e-

Finite conductivity implies particles’ acceleration and emission along the magnetic field lines   E·B≠0 B A. A. Abdo et al. The second Fermi Large Area Telescope catalog of gamma-ray pulsars. The Astrophysical Journal Supplement Series, 2013. ρ

The geometry of the emission depends on the location of particles’ acceleration and on relativistic effects ζ ϕ C. Kalapotharakos

The global magnetosphere structure was explored with MHD models, which matched up well with the data Gruzinov 1999 I. Contopoulos et al 1999 A. Spitkovsky 2006 Bai & Spitkovsky 2010 b C. Kalapotharakos et al 2014

PIC codes allow for the exploration of feedback mechanisms in the magnetosphere including both e+ and e- Philippov et al 2015 A. Marocchino

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RETARDATION Ω µ B ABERRATION CAUSTIC µ LEADING EDGE TRAILING EDGE ●

Particle-in-cell simulations: Spitkovsky & Arons 2002 Torus develops diocotron instability Petri, Heyvaerts & Bonazzola 2002b

Time scale (limit cycle): µs Timokhin & Arons, 2013 Pair multiplicity: 103 ÷ 105 Timokhin & Harding, 2015 g + g  e

The magnetospheric gaps models are not self-consistent but they partly describe the Fermi data Radio beam from the polar cap Slot gap Striped wind Outer gap J. G. Kirk et al 2009 A. K. Harding

C. Kalapotharakos et al, 2014

Observed Model: a = 600, z = 500, s = 10W DeCesar 2013 Brambilla et al. 2015

Observed Model: a = 600, z = 500, s = 10W Fermi 2nd Pulsar Catalog, Abdo et al. 2013 Brambilla et al. 2015

Age vs σ Brambilla et al. 2015

Non-uniform conductivity C. Kalapotharakos et al, 2015 (in prep.) a = 150 450 750 s finite The first results show a significant dependence of Lγ on α This dependence together with the fΩ variability with ζ may be able to explain the Lγ scattering