Multi-wavelength modelling of pulsars and their population

Supervision

Jérôme Petri (OBAS, Strasbourg)

Laboratory and team

OBAS, Strasbourg - Team "GALHECOS"

Subject description

The final product of stellar evolution, neutron stars remain enigmatic today, both in terms of their internal structure and their electrodynamic environment. Most of these compact objects appear as pulsars, emitting pulsed electromagnetic radiation in a broad spectral band, the origin of which is still poorly understood. There are currently around 4,000 pulsars. With the advent of a new generation of radio telescopes such as the SKA (Square Kilometre Array), the number of pulsars detected will increase by an order of magnitude, enabling a precise census of neutron star sub-populations, whether isolated or part of a binary system. Ultimately, we hope to gain a better understanding of the radiative processes taking place in their magnetospheres, and better constrain the stellar evolution of binary systems leading to compact objects (Tauris & van den Heuvel, 2023). The aim of this thesis is first to test scenarios for the evolution of binary pulsar geometry, and in particular the alignment between the stellar rotation axis and the binary's orbital angular momentum. Although theory predicts a very short alignment timescale compared with the pulsar's age, some systems deviate significantly from the assumption of near-perfect alignment. Joint modeling of the radio and gamma-ray pulsation will enable us to assess the deviation from alignment (Benli et al., 2021) (Pétri & Mitra, 2021). In a second step, we will extract the orientation of the magnetic field and the observer with respect to the axis of rotation, for all isolated pulsars, visible in radio and gamma. Thirdly, we will model specific systems, notably the millisecond pulsars observed by the NICER (Neutron Star Interior Composition ExploreR) collaboration, to deduce the geometry of the surface magnetic field (Pétri et al., 2023). Finally, we'll be looking at the statistics of the detection of different pulsar sub-populations, young or millisecond, visible in radio, X-rays and/or gamma rays. The work will be divided into three parts. The first part will involve theoretical modeling of multi-wavelength radio emission at very high energies at GeV/TeV, including in-depth knowledge of curvature, synchrotron and inverse Compton radiation processes. A second part will compare the models with observations gathered in radio (ATNF pulsar catalog) and gamma-ray (Fermi/LAT third pulsar catalog, 3PC) catalogs. The third part will involve implementing modules for calculating light curves in radio, X-rays and gamma rays, in order to compare them directly with data from recent observing campaigns (in X-rays with NICER, in gamma rays with Fermi/LAT and in radio with the Nançay, NRT and NenuFAR radio telescopes). This thesis represents preparatory work for the revolution brought about by the detection of a large population of pulsars in the radio domain thanks to SKA, while maintaining a multi-wavelength view of neutron star emission.

Related mathematical skills

The subject requires basic knowledge of plasma physics (MHD fluid model and kinetic model), magnetospheres of compact objects (neutron stars and black holes) and high-energy emission processes: curvature radiation, synchrotron and inverse Compton. The candidate will be required to implement a code for fitting multi-wavelength data to models derived from numerical simulations, using 2D and 3D interpolation techniques as well as Bayesian inference and Markov chain Monte-Carlo methods. It will also be necessary to identify a 2D surface in 3D physical space, using neural networks or other techniques. The data will come in part from an Indian radio telescope, the GMRT, piloted by my Indian colleague, Dipanjan Mitra.

IRMIA++ is one of the 15 Interdisciplinary Thematic Institute (ITI) of the University of Strasbourg. It brings together a research cluster and a master-doctorate training program, relying on 12 research teams and 9 master tracks.

It encompasses all mathematicians at Université de Strasbourg, with partners in computer science and physics. ITI IRMIA++ builds on the internationally renowned research in mathematics in Strasbourg, and its well-established links with the socio-economic environment. It promotes interdisciplinary academic collaborations and industrial partnerships.

A core part of the IRMIA++ mission is to realize high-level training through integrated master-PhD tracks over 5 years, with common actions fostering an interdisciplinary culture, such as joint projects, new courses and workshops around mathematics and its interactions.

Selection will rely on the professional project of the candidate, his/her interest for interdisciplinarity and academic results.