Co-I (Black Holes)
I am an associate professor in the Department of Astronomy at Columbia University. My research group investigates the plasma physics of shocks, magnetic reconnection and turbulence in order to explain from first principles the observations of a wide variety of astrophysical objects, especially the most powerful and compact sources in our Universe — neutron stars and black holes.
For neutron stars, I have recently become fascinated by the rich and puzzling phenomenology of Fast Radio Bursts (FRBs). We have demonstrated that relativistic magnetized shocks can self-consistently produce coherent emission via the so-called synchrotron maser instability, thus potentially explaining the origin of FRBs. We have also investigated the physics of FRB propagation through the surrounding medium. FRB waves are so strong that they couple non-linearly with the plasma, thus entering the realm of non-linear optics.
For black holes, I am intrigued by the hard X-ray “coronal” emission of X-ray binaries and active galactic nuclei (AGNs). We have recently proposed a first-principles model that explains the coronal emission as Comptonization by bulk motions in a magnetically-dominated plasma. In addition, I have a decade-long interest in magnetic dissipation and particle acceleration in relativistic black hole jets, focusing both on their multi-wavelength and multi-timescale emission, as well as on their potential role as multi-messenger sources (ultra-high-energy cosmic rays and high-energy neutrinos).
I am honored to be part of this collaboration and help unveiling the extreme physics of the most exotic objects in our Universe.
Five recent relevant references
"Ab Initio Turbulent Comptonization in Magnetized Coronae of Accreting Black Holes", D. Groselj, H. Hakobyan, A. Beloborodov, L. Sironi & A. Philippov, PRL submitted, arXiv:2301.11327 https://ui.adsabs.harvard.edu/abs/2023arXiv230111327G/abstract
"Comptonization by reconnection plasmoids in black hole coronae II: Electron-ion plasma", N. Sridhar, L. Sironi & A. Beloborodov, MNRAS 518, 1301 (2023) https://ui.adsabs.harvard.edu/abs/2023MNRAS.518.1301S/abstract
"Reconnection-driven Particle Acceleration in Relativistic Shear Flows", L. Sironi, M. Rowan & R. Narayan, ApJL 907, L44 (2021)https://ui.adsabs.harvard.edu/abs/2021ApJ...907L..44S/abstract
"Coherent Electromagnetic Emission from Relativistic Magnetized Shocks", L. Sironi, I. Plotnikov, J. Nattila & A. Beloborodov, PRL 127, 035101 (2021) https://ui.adsabs.harvard.edu/abs/2021PhRvL.127c5101S/abstract
"Fast Particle Acceleration in Three-dimensional Relativistic Reconnection", H. Zhang, L. Sironi & D. Giannios, ApJ 922, 161 (2021) https://ui.adsabs.harvard.edu/abs/2021ApJ...922..261Z/abstract