The seminar of the Astro & Theory Section takes place normally on Tuesdays Wednesdays in D5-106, starting at 11AM 15.15. If you would like to suggest a seminar speaker or want to be added to the email list, please contact the organizer (Raphaelmaksat.Mignon-Risse@ntnusatybaldiev@ntnu.no).
The (planned) seminars in 2024 2025 are
- 0614.0201. Michael Unger (KIT and IFY, NTNU): News from the Galactic Magntic Field (...and the Origin of the Amaterasu Particle)
Abstract: Galaxies are known to be permeated by large-scale magnetic fields with energy densities comparable to the turbulent and thermal energy densities of the interstellar medium. A good knowledge of the global structure of these fields is important to understand their origin and to infer their effect on galactic dynamics and the propagation of charged particles in galaxies. In this talk I will present new studies of the global structure of the magnetic field of our Galaxy based on the analysis of recent new full-sky data of extragalactic rotation measures and the final polarized intensity maps from WMAP and Planck. The analysis employs the latest models for the thermal electron density tuned to the dispersion measures of Galactic pulsars and state-of-the-art cosmic-ray electrons models, needed to predict the rotation measures and synchrotron emission from the Galaxy, respectively. As a result, I will present a major revision of the widely-used Jannson-Farrar 2012 model of the magnetic field of the Galaxy. In addition to a fiducial magnetic field model, a suite of alternative models was studied that fit the data with similar quality, but use different model assumption. This suite of models is then used to place a lower limit on the model uncertainties. As an application, I will discuss the uncertainties of the predicted deflection of ultrahigh-energy cosmic rays in the Galaxy, in particular the origin of the extremely energetic "Amaterasu particle" recently reported by the Telescope Array Collaboration.
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- 13.02. Lena Saurenhaus (MPP Muenchen): Seyfert Galaxies as Astrophysical Neutrino Sources
Abstract: Active galactic nuclei (AGNs) are among the most powerful objects in the Universe and are suspected to be sources of astrophysical neutrinos. Recently, the IceCube Collaboration reported an excess of neutrino events with energies between 1.5 and 15 TeV associated with NGC 1068, a nearby Seyfert galaxy with an extraordinarily high intrinsic X-ray flux. The lack of observable gamma rays in this energy range indicates that these neutrinos are likely to be produced in the AGN corona, which is opaque to high-energy gamma rays. I will give an overview over existing neutrino emission models for NGC 1068-like sources and talk about our current project, which explores the prospects of observing other hidden neutrino sources with similar neutrino production mechanisms and aims to constrain their contribution to astrophysical neutrino observations.
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- 05.03. Triantafyllos Kormpakis (IFY, NTNU): The Particle in Cell method: Theory and astrophysical applications
Abstract: The Particle in Cell (PIC) numerical method (first developed in the 1950s) aims to simulate the behavior of plasmas in the presence of electric and magnetic fields. With it's unique architecture, moving particles on a Langrangian frame and depositing their charge and current densities on a fixed eulerian mesh, it tracks the evolution of systems where high densities of charged particles (mainly electron-positron pairs) and/or strong electromagnetic fields are present. In the parameter space where the Force free magnetic field approximation is valid, such as the magnetospheres of pulsars, magnetars and active galactic nuclei (AGN) jets, the PIC scheme accurately simulates features such as magnetic reconnection phenomena, enables the study of shock acceleration, particle flows and emission regions. In this talk I will first give a basic overview of the PIC method, particularly in its implementation on the Zeltron code. This will lead to the discussion of my application and qualitative reproduction of existing results, in magnetic reconnection in ABC magnetic fields (particular eulerian flows with stable as well as chaotic flow regimes). Lastly, I will also describe my application and results of PIC methodology to a test case: an axially symmetric magnetic field, representing a magnetic field topology present in an AGN jet.s.
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- 14.03. Rita C. Anjos (U Parana): The nature of high-energy multi-messenger sources
Abstract: In this seminar, I will present the main results of high-energy physics, considering charged particles and gamma radiation as multi-messengers. In this context, the primary sources of these particles will be discussed, along with significant challenges in the field and some results from my research group in Brazil. I will also introduce some diversity/outreach initiatives developed by the group to foster the inclusion of children and youth in the subatomic universe.
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- 19.03. Ellis Owen (U Osaka): Cosmic Ray feedback in galaxy evolution
Abstract: Cosmic rays go hand-in-hand with violent and energetic astrophysical conditions. They are an active agent within galactic and circumgalactic ecosystems, where they can deposit energy and momentum, modify the circulation of baryons, and even have the potential to regulate star-formation on local and galactic scales. Their influence in galaxies can be probed using observable signatures across the electromagnetic spectrum, with high energy radiation being particularly important to determine their energy budget, feedback power and hydrodynamic effects. In this talk, I will discuss some of the astrophysical impacts hadronic and leptonic cosmic rays can have in and around galaxies, how their influence can be probed using signatures in X-rays and gamma-rays, and the opportunities soon to open-up that will allow us to map-out the multi-scale effects of cosmic rays in galaxies near and far.
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- 21.03. Dmitri Semikoz (APC Paris): Multi-messenger signatures of astrophysical neutrino sources
Abstract: In this talk I’ll review recent observations of galactic and extragalactic neutrino sources comparing them to the predictions of theoretical models. At multi-TeV energies dominant contribution to the neutrino flux of Milky Way is expected from Galactic Ridge, brightest region of our Galaxy, where cosmic rays interact with interstellar gas and produce secondary gamma-rays and neutrinos. In neutrinos first hint of Galactic Ridge was found in ANTARES in 2022. In 2023 IceCube detected it in cascade channel with 4 sigma significance. I’ll discuss perspectives of detection of Galactic Ridge by future neutrino telescopes and by LHAASO, SWGO and CTA in gamma-rays. Also I’ll review recent gamma-ray and neutrino observations from Pevatron source in Cygnus region.For extragalactic neutrino sources I’ll focus on Seyfert galaxies. In addition to well known NGC 1068 only two other sources, based on their hard X-ray properties, NGC 4151 and NGC 3079 are expected to be detectable in 10 years of IceCube data. We find an evidence for neutrino signal from both sources in publicly available ten-year IceCube dataset. The chance coincidence probability to find the observed neutrino count excesses in the directions of the two out of two expected sources, in addition to the previously reported brightest source, is p<2.6e-7. This corresponds to the detection of Seyfert galaxies as a neutrino source class.
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- 25.06. Paul Lai (University College London): Tracking the gas distribution in the Galactic Centre using neutrinos and Alisha Roberts (IFY, NTNU): Investigating Neutrino Emissions from Blazar 3C 454.3
- tbd. Jens Oluf Andersen (IFY, NTNU): Pion condensation and pion stars
Abstract: In this talk I will discuss pion condensation in the context of two and three-flavor chiral perturbation theory. I will present results for quark and pion condensates as functions of the isospin chemical potential. The results compare favorably to those of lattice QCD. As an application, I will discuss pion condensation in a dense neutrino cloud and the possibility of pion stars. These are compact objects with a mass up to 20 solar masses and radii of up to 140km.
- 11.09. Jonas Tjemsland* (previously IFY, NTNU): How are the Norwegian electricity prices set? *Exceptional time: wednesday, 14:15.
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- Matteo Imbrogno (Università di Tor Vergata of Rome): A tale of serendipity: quasi-periodic oscillations in pulsating ULXs and a search for new X-ray pulsators
Abstract: The discovery of pulsating ultraluminous X-ray sources (PULXs) has revealed that accreting neutron stars can shine at extreme luminosities, well above their Eddington limit. This finding has caused a shift in the ULX paradigm and poses significant challenges to our understanding of the physics of accretion onto compact objects. Given their rarity, every new insight into their complex phenomenology can bring us closer to a deeper understanding of these sources. A possible way to find more PULXs is by searching the archives of X-ray missions with good imaging and timing capabilities using a data mining approach. In the process, serendipitous sources are always behind the corner. Both the study of PULXs and the search for new X-ray pulsators through data mining have defined the course of my PhD. I will report my discovery of mHz QPOs in the X-ray flux of the PULXs. These mHz QPOs could represent a signature of super-Eddington accretion. I will also talk about a new pulsar (likely a new candidate magnetar) I discovered in the Large Magellanic Cloud thanks to a data mining project aimed at searching for new pulsators in the XMM-Newton archive. Slides
- 13.02. Yan-Chuan Cai (University of Edinburgh): Peculiar velocities in cosmology
Abstract: On large scales, peculiar velocities refer to the motions of extragalactic objects relative to the background expansion of the Universe, known as the Hubble flow. Coupled with the initial density perturbations of the Universe, peculiar velocities are influenced by the expansion history of the Universe and the strength of gravity. They encode information about the matter-energy content of the Universe and the law of gravity. I will summarise how peculiar velocities of galaxies can be observed, and what we can learn about cosmology from observing them using data from galaxy redshift surveys and the cosmic-microwave background. Slides
- 10.04. Devina Misra (IFY, NTNU): Investigating cannibalistic millisecond pulsar binaries using MESA: New constraints from pulsar spin and mass evolution
Abstract: Compact binary millisecond pulsars (MSPs) with orbital periods less than 1d are key to understanding binary evolution involving massive neutron stars (NSs). Due to the ablation of the companion by the rapidly spinning pulsar, these systems are also known as spiders and categorized into two main branches: redbacks (RBs; companion mass in the range of 0.1 to 0.5Msun) and black widows (BWs; companion mass less than 0.1 Msun ). We present models of low- and intermediate-mass X-ray binaries and compare them with observations of Galactic spiders (including the presence or absence of hydrogen lines in their optical spectra), and we constrain and quantify the interaction between the pulsar and the companion. For the first time in MESA, we also included the detailed evolution of the pulsar spin and modeled the irradiation of the companion by the pulsar wind. Efficient mass accretion onto the NS (i.e., at least 70% of the mass transferred is accreted) with an X-ray irradiated disk followed by strong irradiation of the companion can explain most of the properties of the observed spiders. Our RB evolutionary tracks continue to the BW regime, connecting the two branches of spiders. Our models explain the lack of hydrogen in some observed BWs with ultra-light companions. During accretion-induced spin up, the mass required to spin up an NS to sub-milliseconds is high enough to collapse into a black hole. Cannibalistic MSP binary formation depends heavily on the interplay between accretion onto the pulsar and pulsar wind irradiation. Our work supports earlier claims that RBs evolve into BWs. We also show that the fastest-spinning pulsars may collapse before reaching sub-millisecond spin periods. Slides
- 15.05. Hosein Gholami (TU Darmstadt): Renormalization Group Consistent Treatment of Color Superconductivity in the NJL Model
Abstract: The Nambu–Jona-Lasinio (NJL) model—and particularly its extension to color superconductivity—is a powerful framework for investigating dense quark matter. However, its reliability is limited by regularization artifacts that emerge near the cutoff energy scales. In this talk, we present a mean-field Functional Renormalization Group (FRG) approach, referred to as the RG-consistent treatment, which effectively eliminates these artifacts. Our study reveals substantial modifications to the previously established phase diagram of three-flavor, neutral, color superconducting matter within the NJL model. Notably, the RG-consistent treatment not only removes the regularization artifacts but also aligns with earlier Ginzburg-Landau analyses, suggesting the emergence of a so-called dSC phase in the melting pattern of the Color-Flavor Locked (CFL) phase. Finally, I present our recent results on the renormalized Quark-Meson-Diquark (QMD) model and compare them with those obtained via the RG-consistent treatment of the QMD framework.
- 01.10. Vittoria Vecchiotti (IFY, NTNU; INAF-OAA; TDLI): Very high-energy gamma-ray and neutrino emission from hadronic interaction in compact binary millisecond pulsars
Abstract: Black widow and redback systems are millisecond pulsars in compact orbits with ultra-light and low-mass companions, respectively, collectively known as "spider pulsars". In such systems, an intrabinary shock can form between the pulsar and the companion winds, serving as a site for particle acceleration and associated non-thermal emission. Assuming that protons can be extracted from the neutron star surface and accelerated at the intrabinary shock and/or within the pulsar wind, we model the very high-energy gamma-ray and neutrino emissions (0.1−10^3~TeV) produced through interactions with the companion wind and the companion star. We first calculate the high-energy emissions using an optimistic combination of parameters to maximize the gamma-ray and neutrino fluxes. We find that, for energetic spider pulsars with a spin-down power ≳10^35 erg s−1 and a magnetic field of ∼10^3G in the companion region, the gamma-ray emission could be detectable as point sources by CTA and LHAASO, while the neutrino emission could be detectable by the future TRIDENT detector. Finally, we build a synthetic population of these systems, compute the cumulative neutrino flux expected from spider pulsars, and compare it with the Galactic neutrino diffuse emission measured by IceCube. We find that, under realistic assumptions on the fraction of the spin-down power converted into protons, the contribution of spiders to the diffuse Galactic neutrino flux is negligible.
- 27.11. Markus Ahlers (University of Copenhagen, Niels Bohr Institute): High Energy Astrophysical Neutrinos: An Overview
Abstract: Neutrino astronomy has achieved a number of milestones in the past decade. The IceCube Observatory discovered a diffuse flux of TeV-PeV neutrinos in 2013. Neutrino emission at the observed flux level has been predicted from a variety of sources. However, none of these candidate sources has been unambiguously identified as the origin of IceCube’s observation. Recent evidence of neutrino emission from the gamma-ray blazar TXS 0506+056 as well as the Seyfert galaxy NGC 1068 might be the first glimpses of extragalactic neutrino point-sources. IceCube has also now observed a neutrino glow of the Milky Way, consistent with model predictions of cosmic ray diffusion in our Galaxy. Very recently, the KM3NeT telescope announced the discovery of an ultra-high-energy neutrino with an energy exceeding 100 PeV, the most energetic astrophysical neutrino observed so far. I will give an overview of these results and their interpretation in terms of multi-messenger astronomy. Slides
- 17.09. Bidisha Sen (IFY, NTNU): The Orbit and Companion of PSR J1622-0315: Variable Asymmetry and a Massive Neutron Star
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
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- 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_Koljonen.pdf?api=v2