Magnetar Magnetospheres under the Microscope

Wed 6 March, 2019 @12:00 PM, level 7, David Caro Building
Dr Matthew Baring, Rice University

Email:  baring[at]


Magnetars are young neutron stars with high surface magnetic fields,
exceeding around 10 TeraGauss. Pulsed, non-thermal quiescent X-ray
emission extending between 10 keV to >150 keV has been observed in about
10 magnetars by RXTE, INTEGRAL, Suzaku, NuSTAR and Fermi-GBM. This talk
describes a model for the generation of such hard X-ray signals, wherein
the emission is produced by resonant Compton upscattering of soft
thermal photons from the neutron star surface. This mechanism is
efficient due to the enhancement of the scattering cross section at the
cyclotron resonance. Spectra that approximately match observations can
be generated by emission volumes within about ten stellar radii of the
magnetar surface. The observed/implied maximum energies of these hard
X-ray signals may require that an attenuation process such as magnetic
photon splitting be active. This prospect can be probed by future
sensitive Compton telescopes with polarimetric capability, for example
the AMEGO concept. Interestingly, key pulsation and spectral signatures
can be used to constrain the viewing geometry and the angle between the
magnetic and spin axes of magnetars, a diagnostic that may improve the
ability to precisely determine the strengths of magnetar fields.