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

Conveners: Emma de Ona Wilhelmi (DESY), Giulia Brunelli

09:00 Welcome

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

2024_11_26_HONEST3_Welcome_Motivation.mp4

2024_11_26_HONEST3_Welcome.pdf

09:05 Introduction and motivation for the workshop

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

HONEST3_Motivation_deOnaWilhelmi2024.pptx

09:20 Lessons learnt from Fermi-LAT pulsars

Speaker: Pablo Saz Parkinson

2024_11_26_HONEST3_Fermi.mp4

241126_Saz_Parkinson_HONEST3_opt.pdf

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)

2024_11_26_Crab_pulsar_HONEST.pdf

2024_11_26_HONEST3_Crab.mp4

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

2024_11_26_HONEST3_Geminga.mp4

HONEST_Geminga_261124.pdf

10:20 Coffee Break

10:50 Vela: the highest pulsed energies ever detected

Speaker: Emma de Oña Wilhelmi (DESY)

2024_11_26_HONEST3_deOnaWilhelmi.mp4

HONEST3_VelaPulsar_26Nov2024.pptx

11:10 Testing for a "Crab-like" Emission Tail above 10 GeV from the Vela Pulsar and PSR B1706-44 using combined H.E.S.S. & Fermi-LAT data

Measuring pulsar spectra in the tens of GeV range is crucial for constraining high-energy emission models, but this effort is hindered by limited Fermi-LAT statistics and the sensitivity constraints of ground-based telescopes. In this study, we analyze data from the largest H.E.S.S. telescope (CT-5) and Fermi-LAT to measure the spectra of the Vela pulsar and PSR B1706-44 in the 1–100 GeV range. Through a joint spectral fit above 10 GeV, which accounts for both instruments' response functions, we detect significant spectral curvature in both sources. This curvature rules out the onset of a power-law tail, setting them apart from the Crab pulsar, and sheds new light on the emission mechanisms in pulsars.

Speaker: Maxime Regeard

2024_11_26_HONEST3_Regeard.mp4

HONEST_Pulsars_HE_joint_RDA.pdf

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

2024_11_26_HONEST3_Illiano.mp4

Illiano_Honest3_Workshop.pdf

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)

similarity_Light_Curves.pdf

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

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

HONEST_Meyer_short.pdf

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

Speaker: Samantha Wong (McGill University)

veritas_pulsars_honest.pdf

Wednesday, 27 November

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

Conveners: Michelle Tsirou (DESY Zeuthen), Tobias Kleiner (DESY)

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.

2024_11_27_HONEST3_Petri.mp4

petri_honest3.pdf

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

2024_11_27_HONEST3_Vigano.mp4

2024.11.27-Honest_Viganò_pub.pdf

13:40 Relativistic winds

Speaker: Dmitry Khangulyan

2024_11_27_HONEST3_Khangulyan.mp4

DKhangulyan.pdf

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

2024_11_27_HONEST3_Venter.mp4

Venter_HONEST2024 (3).pdf

14:20 Coffee Break

14:50 Electron-positron cascades in pulsars

Speaker: Andrey Timokhin

HONEST_2024-.tar.gz

HONEST3_27_Nov_Andrey_Timokhin.mp4

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

Speaker: Claire Guépin

CGuepin_Nov2024.pdf

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

Speaker: Alexander Philippov

HONEST3_27_Nov_Sasha_Philippov.mp4

pulsar_VHE.pdf

16:00 → 17:00 Discussion

Thursday, 28 November

09:00 → 12:00 Prospects

Conveners: David Green (MPP), Rubén López Coto (IAA - CSIC)

09:00 Inverse Compton pulse profiles inferred from global PIC simulations

Speaker: Cerutti Benoît

2024_11_29_HONEST3_Cerutti.mp4

bcerutti_HONEST2024.pdf

09:20 High energy end of pulsar spectra, what is at stake?

The fundamental concepts underlying pulsar mechanics—namely, the central engine, magnetosphere, and wind—date back several decades. It would not be an exaggeration to say that the detection and characterization of gamma-ray emission from pulsars have played a pivotal role in challenging and advancing our understanding of acceleration and radiation processes in these objects. This progress includes significant milestones, such as the historical invalidation of the polar-cap model through MAGIC and Fermi-LAT’s demonstration of the exponential (rather than super-exponential) nature of the pulsed spectrum of the Crab, and the groundbreaking extension of its spectrum into the very high energy (VHE) range by VERITAS. After a brief review, I will focus on the implications of the latest landmark discovery in the field—namely, the detection of the pulsed inverse-Compton component by H.E.S.S. in the multi-TeV range—and outline future prospects with current and upcoming instruments.

Speaker: Arache djannati-Ataï

2024_11_29_HONEST3_Djannati.mp4

Ada_HONEST_2024.pdf

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

2024_11_29_HONEST3_Ceribella.mp4

HONEST2024.pdf

10:00 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

2024_11_29_HONEST3_Duan.mp4

HONEST_duankk_20241128.pdf

10:20 Coffee Break

10:50 Prospects using the Cherenkov Telescope Array Observatory

Speaker: Roberta Zanin

20241128_HONEST.pdf

2024_11_29_HONEST3_Zanin.mp4

11:10 Summary/review of the workshop

Speaker: Felix Aharonian

2024_11_29_HONEST3_Aharonian.mp4

12:00 → 13:00 Discussion