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Abstract:  The companion to PSR J1622-0315, one of the most compact known redback millisecond pulsars, shows extremely low irradiation despite its short orbital period. We model this system to determine the binary parameters, combining optical observations from NTT in 2017 and NOT in 2022 with the binary modeling code ICARUS. We find a best-fit neutron star mass of $2.3 \pm 0.4\,\text{M}_\odot $, and a companion mass of $0.15 \pm 0.02\,\text{M}_\odot$. We detect for the first time low-level irradiation from asymmetry in the minima as well as a change in the asymmetry of the maxima of its light curves over five years. Using star spot models, we find better fits than those from symmetric direct heating models, with consistent orbital parameters. We discuss an alternative scenario where the changing asymmetry is produced by a variable intrabinary shock. In summary, we find that PSR J1622-0315 combines low irradiation with variable light curve asymmetry, and a relatively high neutron star mass. Slides available here: https://www.ntnu.no/wiki/download/attachments/195538250/Bidisha_Sen_PSR_J1622.pdf?api=v2


  • 08.10. Valentina Richard Romei*  (IPAG, Grenoble): Enhanced particle acceleration in a pulsar wind interacting with a companion *remote seminar

Abstract:Pulsar winds have been shown to be preferred sites of particle acceleration and high-energy radiation. Models have been constructed in order to better characterize their general structure in isolated systems. However, most of the galactic millisecond pulsars find themselves in binary systems. In this talk, I present the first Particle-in-cell (PIC) simulations of both the pulsar magnetosphere and the wind of the pulsar interacting with an unmagnetized spherical companion. This work considers a generic case that could be applied to various companions including planets, asteroids, white dwarfs, or even neutron stars. Our results show evidence of an enhanced conversion of Poynting flux into particle acceleration, via forced reconnection in the outflowing wind near the companion. Hence, the high-energy synchrotron radiation is also amplified and takes the form of an orbital-modulated hollow cone of light. We do not exclude long-period radio transient counterparts, that would be of significant interest, especially in the light of the recently discovered galactic long-period radio transients. Slides available here: https://www.ntnu.no/wiki/download/attachments/195538250/NTNU_seminar_VRR.pdf?api=v2


  • 24.10. Luca Comisso*  (Columbia University): Particle acceleration in highly magnetized plasmas *remote seminar, exceptionally on Thursday 4PM in D5-106

Video available here: https://www.youtube.com/watch?v=_KxfrVZkamE


  • 03.12. Karri Koljonen (IFY, NTNU): Cosmic-neighbor-associated distances to blazars

Abstract: Blazars are active galactic nuclei with relativistic jets directed toward Earth. Relativistic beaming amplifies their brightness, making them appear extremely luminous across multiple wavelengths, from radio to gamma-rays. Consequently, blazars are the most numerous source class among very high-energy gamma-ray emitters. However, determining their redshifts is often challenging because jet emission can obscure spectral lines from the host galaxy or intervening matter. In this talk, I will introduce two methods for estimating blazar distances by associating them with their "cosmic neighborhood". These techniques involve analyzing the optical fields around a blazar using either multi-object spectroscopy or multi-band photometry, combined with the assumption that blazars are typically located in galaxy-rich environments. Accurate redshift estimation for high-redshift blazars is crucial for advancing our understanding of extragalactic very high-energy gamma-ray sources and their interactions with the surrounding universe. Slides available here: https://www.ntnu.no/wiki/download/attachments/195538250/NTNU_seminar_VRRKoljonen.pdf?api=v2