HONEST Workshops: Hot Topics in High Energy Astrophysics

26 Nov 2024, 09:00 → 28 Nov 2024, 14:00 Europe/Madrid

Online

Emma de Oña Wilhelmi (DESY), Rubén López Coto (IAA - CSIC)

Pulsars as rapidly spinning neutron stars have always been excellent laboratories for the study of plasma physics, particle acceleration and cosmic rays. Comprehending how and where particles are accelerated to produce the broadband shape that the pulsed spectra present is subject of enthusiastic discussions and constitute one of the hot topics in high energy astrophysics nowadays. 

Results from the recent years extending pulsar spectra to TeV energies and beyond motivate debates that can only be elucidated through a deep understanding of the high energy end of their spectrum. In this Workshop, we aim to discuss the latest results on pulsars from high energy instruments, their implications for the current theories, and prospects for future observatories.

Tuesday, 26 November

09:00 → 12:00 Experimental part: Review of the latest results

09:00 Welcome

Speakers: Emma de Oña Wilhelmi (DESY), Rubén López Coto (IAA - CSIC)

09:05 Introduction and motivation for the workshop

Speakers: Emma de Oña Wilhelmi (DESY), Rubén López Coto (IAA - CSIC)

09:20 Lessons learnt from Fermi-LAT pulsars

Speaker: Pablo Saz Parkinson

09:40 The Crab Pulsar's Very High Energy emission: Insights from GeV to TeV Energies

The Crab Pulsar is one of the few pulsars detected from GeV up to TeV energies. This talk will review recent gamma-ray observations of the pulsar performed with Imaging Atmospheric Cherenkov Telescopes (IACTs) and analyze their implications for current theoretical models that aim to explain the Very High Energy (VHE) emission from this source.

Speaker: Rubén López Coto (IAA - CSIC)

10:00 Geminga: the first discovered VHE middle-aged pulsar

The detection of Very-High-Energy emission from pulsars is one of the milestone results in the field. Among the few sources know to date, Geminga is the only one with an age of a few hundred kilo-years. From its discovery to the recent observations with Cherenkov Telescopes, Geminga never ceases to surprise us.

Speaker: Giulia Brunelli

10:20 Coffee Break

10:50 Vela: the highest pulsed energies ever detected

Speaker: Emma de Oña Wilhelmi (DESY)

11:10 Other TeV pulsars detected by HESS

Speaker: Maxime Regeard

11:30 The many facets of transitional millisecond pulsars: can accretion- and rotation-powered states coexist?

The increasingly thrilling investigation of millisecond pulsars has recently overturned a long-standing paradigm. Traditionally, these pulsars were thought to shine as rotation-powered radio and/or gamma-ray sources only after a Gyr-long, X-ray bright phase fueled by the accretion of matter from a low-mass donor star. However, transitional millisecond pulsars challenge this classification by swinging between radio and X-ray states. All transitional pulsars have also been caught in an intermediate state, featuring an X-ray luminosity lower than that in the standard accreting phase and gamma-ray emissions up to ten times greater than those recorded during the rotation state. In this context, the recent detection of coherent optical and ultraviolet pulsations from the archetype of transitional millisecond pulsars in this intermediate state hints at the persistence of a rotation-powered magnetospheric process even in the presence of an accretion disk. I will review recent multi-wavelength campaigns on confirmed and candidate transitional millisecond pulsars to test the possible outcomes of the interaction between the pulsar wind of particles and radiation and matter in an accretion disk.

Speaker: Giulia Illiano

12:00 → 13:00 Discussion

13:00 → 14:10 Contributions

13:00 The Pulsar Tree: Visualizing the Pulsar Population using Graph Theory Techniques. Applications from Binary Pulsars to Fast Radio Bursts

Speaker: Carlos Rodríguez García (Institute of Space Science (ICE))

Pulsar_tree&Applications.pdf

13:05 Identification and characterisation of the gamma-ray counterpart of the transitional pulsar candidate CXOU J110926.4–650224

Speaker: Dr Arianna Manca (Università degli Studi di Cagliari/INAF)

J1109-Arianna_Manca.pdf

short_version.mp4

13:10 A quantitative analysis of the similarity of gamma-ray pulsar light curves

Speaker: Diego Torres (ICREA & ICE-CSIC)

13:15 Pulsar wind nebulae meeting the circumstellar medium of their progenitors

Speaker: Dominique Meyer (Institut of Space Science (ICE,CSIC) Barcelona)

13:20 Overview of the VERITAS VHE and optical pulsar programs

Speaker: Samantha Wong (McGill University)

Wednesday, 27 November

13:00 → 16:00 Theoretical models: Pulsar emission mechanisms

13:00 Pulsar striped wind emission: a multi-wavelength and population synthesis perspective

Since the launch of the Fermi/LAT telescope in June 2008, several hundred radio-loud gamma-ray pulsars have been detected. Observing simultaneously their radio and gamma-ray pulse profiles helps to constrain the geometry and radiation mechanisms within their magnetosphere and to localize the photon production sites. In this talk I show how time-aligned gamma-ray light curve fitting of young pulsars reveals their geometry, namely the magnetic axis and line-of-sight inclination angles. To this end, I assume a dipole force-free magnetosphere where radio photons emanate from high altitudes above the polar caps and gamma-rays originate from the pulsar striped wind, close to the light-cylinder. The striped wind emission model agrees well with the time-aligned single- or double-peaked gamma-ray pulses. Moreover the distinction between radio-loud, radio-quiet gamma-ray pulsars and radio-only pulsars is entirely related to the geometry of the associated emitting regions. The high-altitude polar cap model combined with the striped wind represents a minimalistic approach able to reproduce a wealth of gamma-ray pulse profiles for the whole young pulsar population.

13:20 Modeling the observed spectra and light curves of synchro-curvature emission of pulsars

In this talk, we will review the synchro-curvature modeling of high-energy radiation from pulsars. Through a minimalist model containing only three essential free parameters, the model is able to fit the spectra of the entire population of pulsars, showing trends between the magnitude of the electric field and the parameter associated to the typical lengthscale of the acceleration region. We also incorporate the high-energy maps assuming the emission from a simplified current sheet region beyond the light cylinder, and show preliminary results on successful simultaneous spectral and light curve fitting, which give constraints on the inclination and viewing angles. The underlying model is a useful tool to approach the pulsar population, since it is intrinsically simple but gives hints on the relevant physical parameters at play. It can indeed be complicated to include more realistic physics and overcome some current caveats.

Speaker: Daniele Viganò

13:40 Relativistic winds

Speaker: Dmitry Khangulyan

14:00 Pulsed TeV emission from pulsars in the sychrocurvature/inverse-Compton framework

A number of pulsars have now been detected by ground-based Cherenkov telescopes, including PSR B1706-44, Geminga, Crab, and Vela. Vela exhibits a TeV component that is distinct from its GeV one, in contrast to the other detected pulsars. In the synchro-curvature radiation / inverse Compton (SCR-IC) framework, the same particles that are responsible for the GeV emission via SCR (with Lorentz factors of around 5e7) near the current sheet (CS) beyond the light cylinder radius, upscatter optical-near-infrared to X-ray photons to form a pulsed TeV component via inverse Compton (IC) scattering. The target photons may be synchrotron radiation (SR) from secondary pairs. I will review the assumptions of this model as well as its reasonably successful reproduction of available spectral and light curve data of some pulsars. I will also touch on recent work to develop and calibrate a visibility metric for TeV pulsars that may be used to focus future Cherenkov observations of plausible pulsar candidates.

Speaker: Venter Christo

14:20 Coffee Break

14:50 Electron-positron cascades in pulsars

Speaker: Andrey Timokhin

15:10 Analytical approaches for the study of the VHE emission of pulsar spectra

Speaker: Claire Guépin

15:30 Numerical approaches for the study of the VHE emission of pulsar spectra

Speaker: Alexander Philippov

16:00 → 17:00 Discussion

Thursday, 28 November

09:00 → 12:00 Prospects

09:00 Review and prospects of pulsar models

Speaker: Cerutti Benoît

09:20 Phenomenology and implications for current and next generation instruments

Speaker: Arache djannati-Ataï

09:40 Timing the future: pulsar ephemerides

The field of high-energy pulsars is experiencing a fast development driven by the observations of Fermi-LAT, the current IACT experiments (MAGIC, VERITAS, H.E.S.S.), and CTAO. The detailed study of the emission properties and the proper accumulation of events require more and more advanced techniques to precisely determine the rotation parameters of pulsars and their evolution (rotational ephemerides). In this talk I will briefly discuss the methods currently in use to obtain a rotational solution, and review the prospects for the future.

Speaker: Giovanni Ceribella

10:00 Prospects using the Cherenkov Telescope Array Observatory

Speaker: Roberta Zanin

10:20 Coffee Break

10:50 Prospects for the detection of very-high-energy pulsars with LHAASO and SWGO

Pulsations from the Crab pulsar and the Vela pulsar have been detected at high energies by IACT. Potential candidates for detection with EAS experiments at very-high-energy (VHE) ranges have been identified. Our findings indicate that LHAASO and SWGO could detect these signal within a few years which will enhance understanding of VHE pulsar emissions.

Speaker: Kaikai Duan

11:10 Summary/review of the workshop

Speaker: Felix Aharonian

12:00 → 13:00 Discussion