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

2. The pulsar radio emission lead to the conclusion they are fast rotating compact objects
C. Kalapotharakos

3. 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.

4. 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

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

6. 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

7. 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-

8. 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

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

10. 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

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

13. ^3)

17. RETARDATION Ω B
ABERRATION
CAUSTIC
LEADING EDGE
TRAILING EDGE ●

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

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

23. 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

25. C. Kalapotharakos et al, 2014

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

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

28. Age vs σ
Brambilla et al. 2015

29. Non-uniform conductivity
C. Kalapotharakos et al, 2015 (in prep.)
a =
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