Astrophysics Colloquium - Probing Fundamental Physics using X-Ray and Radio Signals from a Magnetar

Abstract:  The last six years have witnessed a substantial number of new
observational manifestations for magnetars, the most magnetic members of
the neutron star family.  These encompass fast radio burst associations,
the detection of giant flares in extragalactic magnetars, high cadence
observations of glitch epochs, and new X-ray polarization information
from IXPE.   Such discoveries have seeded a growth in understanding and
a magnification of their mysterious character.  This talk summarizes
some recent observational and theoretical advances pertaining to
persistent surface X-ray emission.  Polarized magnetar signals are
addressed in the context of atmosphere models that provide a benchmark
for assessing key stellar geometrical parameters.  Characteristics from
the sophisticated radiative transfer simulation MAGTHOMSCATT are
presented, along with how light curves can be used to constrain the
viewing and magnetic geometries.  Evolution of these light curves
suggests dynamic changes in the field structure.  A core focus is on how
the strong-field QED effect of vacuum birefringence impacts the emergent
polarization signals detected in X rays by IXPE.  This culminates in a
recent exposition on combined IXPE data and polarized radio observations
for the magnetar 1E 1547.0-5408, which provide tantalizing suggestion of
the action in Nature of this fundamental physics prediction. 

Short bio:  Prof. Baring is a Professor at Rice University, Houston, Texas, in the
Department of Physics and Astronomy.  He has been there twenty-five
years, having graduated with a PhD from the University of Cambridge,
United Kingdom, in theoretical astrophysics.  In the intervening time,
he occupied positions at several prominent institutions in the US and
Europe, including an eight-year stint at NASA's Goddard Space Flight
Center in Greenbelt, Maryland, where he worked in the Laboratory for
High Energy Astrophysics.  His career started with undergraduate studies
in physics at the University of Melbourne in Australia, and has led him
around the world in the pursuit of knowledge.  His research covers
various sources of radiation in the cosmos, including remnants of
supernovae, cosmic plasma shocks, gamma-ray bursts, jets of active
galaxies, and pulsars, neutron stars and black holes.  Dr. Baring is 
an Associate Scientist for the Large Area Telescope experiment on the
Fermi Gamma-ray Space Telescope, an Associate Science Collaborator for
the XL-Calibur balloon-borne X-ray polarimeter program, and a member of
the AMEGO gamma-ray telescope consortium.  He served two terms as a
Divisional Associate Editor for Physical Review Letters, a four-year
stint as an Associate Editor for Astrophysical Journal Letters, and also
spent four years as the Secretary-Treasurer of the High Energy
Astrophysics Division of the American Astronomical Society.  He is the
current President of Division D of the International Astronomical Union.
He is the recipient of an Outstanding Referee Award from and a Fellow of
the American Physical Society.