Scientific Context
The recent milestone detection of the nanohertz gravitational wave background by Pulsar Timing Arrays has opened an entirely new observational window into the Universe. As we move towards the most sensitive datasets ever assembled, the astrophysical interpretation of these signals is limited by two key challenges: poor models of the intervening interstellar medium (ISM), and uncertainties in pulsar distance measurements.
This workshop brings together, for the first time, leading experts in gravitational wave science, interstellar medium studies, and Very Long Baseline Interferometry (VLBI) to collaboratively identify and address these limitations. Through keynote talks, interactive tutorials, and structured breakout sessions, we aim to produce actionable research plans and observing strategies that integrate cutting-edge techniques across all three fields.
The workshop is particularly timely given significant upgrades to the European VLBI Network, the advent of next-generation radio facilities like the SKA and DSA-2000, and the forthcoming third data release of the International Pulsar Timing Array.
Characterising the nanohertz GW background from supermassive black hole binaries using Pulsar Timing Arrays. Understanding the signal's spectrum and spatial correlations to constrain SMBHB populations.
Modelling time-variable dispersion, scattering, and scintillation. Integrating ISM measurements into timing models and developing robust correction techniques for next-generation PTA datasets.
Precision parallax-based pulsar distances using VLBI. Identifying and mitigating systematic errors from ionospheric and ISM propagation effects to achieve sub-parsec distance determinations.
Programme
Keynotes, interactive tutorials, and structured breakout sessions designed to produce concrete, actionable outcomes.
Opening Day — Setting the Scene
Lorentz Centre introduction + workshop goals (Aditya Parthasarathy)
~30 participants: 1-minute introductions sharing expertise, interests, and goals for the week
The first inroads into the low-frequency gravitational-wave spectrum: Results and Challenges — Michael Keith
The interstellar medium in space and time: current state-of-the-art in scintillometry and imaging techniques — Stella Ocker
Precision astrometry on compact objects with VLBI and avenues for advancements — Adam Deller
~25 participants
PTA: Challenges & Solutions
Moderators Rutger van Haasteren, Caterina Tiburzi, Matthew Miles, James Cordes
Trainers Kathrin Grunthal, Aurelien Chalumeau, Sara Manzini
Pulsar Timing Array Foreground Signals: Origins, Models, and Consequences for Gravitational-Wave Astronomy
Daniel Reardon
Prioritise topics and questions emerging from Keynote 1
Continuous waves from supermassive black hole binaries: facing the challenge of detection and localisation — Niccolò Veronesi
Finalise shortlist of breakout questions + key ideas
PTA observables → constraints → how they plug into timing
8 teams of 6–7: one PTA challenge + actionable solution
Moderator synthesis + 1 reporter per team
All participants: shortlisted topics, define success criteria
ISM: Challenges & Solutions
Moderators Dylan Jow, Jacob Turner, Marten van Kerkwijk
Trainers Atharva Kulkarni, Nina Gusinskaia, Daniel Baker
Advances in pulsar scintillometry techniques — Robert Main
Prioritise topics emerging from Keynote 1
High-resolution VLBI astrometry of pulsar scintillation screens — Ashley Stock
Finalise breakout questions + key ideas
ISM observables → constraints → how they plug into timing
8 teams of 6–7: one ISM challenge + actionable solution
Moderator synthesis + 1 reporter per team
All participants: shortlisted topics, define success criteria
VLBI: Challenges & Solutions
Moderators John McKean, Robert Wharton, Silke Britzen
Trainers Shami Chatterjee, Florian Eppel
VLBI and AGN variability — Andreas Brunthaler
Prioritise topics emerging from Keynote 1
A large-scale astrometric project for millisecond pulsars — Bailee Wolfe (remote)
Finalise breakout questions + key ideas
VLBI observables → constraints → how they plug into timing
8 teams of 6–7: one VLBI challenge + actionable solution
Moderator synthesis + 1 reporter per team
All participants: shortlisted topics, define success criteria
Synthesis & Roadmap
Participants collaboratively draft actionable research plans, grant proposals, and observing strategies based on the week's discussions.
Culminating in a community roadmap document to guide future collaborative efforts across PTA, ISM, and VLBI communities.
Participants
Experts spanning pulsar timing, ISM studies, VLBI astrometry, and instrumentation.
Scientific Organising Committee
Chair · ASTRON & University of Amsterdam
Expert in precision pulsar timing and gravitational wave science. Led key efforts in the European and International PTA collaborations. ERC Starting Grant and NWO-I Veni fellow.
Sternberg Astronomical Institute & MPIfR
Specialist in gravitational wave science and dark matter searches with PTAs. Executive committee member of the EPTA, steering committee of the IPTA.
ASTRON
Expert in VLBI astrometry and compact object studies. WISE fellow leading observing campaigns with major VLBI facilities worldwide.
MPIfR, Germany
Specialist in pulsar scintillation and novel data analysis methods. Developing theoretical models for anisotropic interstellar scattering screens.
National Astronomical Observatories of China
Precision radio astrometry using VLBI. Led the largest astrometric survey of millisecond pulsars. IAU PhD Prize honourable mention.
Workshop Coordinator: Emmy Verlek-Hage, Lorentz Center · verlek@lorentzcenter.nl · +31 71 527 5659
Practical Information
Everything you need to know about attending the workshop in Leiden.
Lorentz Center@Omega
Niels Bohrweg 1, Leiden (Bio Science Park)
2nd floor of the Snellius building
For navigation systems, please use destination: Niels Bohrweg 4, or plan your route via 9292.nl.
By train: A direct train leaves from Schiphol Airport to Leiden Central Station every 15 minutes. From Leiden station:
Plan your journey at 9292.nl
By car: Please email the organisers by 11 May to register for parking lot access.
If you have requested a hotel, an updated hotel confirmation will be mailed to you. Please check this carefully and notify the workshop coordinator of any changes. Do not contact the hotel directly — the workshop coordinator is the contact person for the hotel.
Lunch vouchers: At the start of the workshop you will receive lunch vouchers for the week, usable in the restaurant on the first floor of the Snellius building.
Welcome reception: On Monday afternoon we will host a welcome reception at the Lorentz Center.
Workshop dinner: A dinner has been arranged for Wednesday evening. A sign-up list will circulate at the start of the workshop where you can confirm attendance and dietary requirements.
Bring your own device: You need your own laptop to present in the lecture room.
ClickShare: Share your presentation wirelessly. Please download the ClickShare app before the workshop. USB and HDMI connections are also available.
Internet: Wireless internet via eduroam is available throughout the Lorentz Center. You will receive an automated email from Leiden University with temporary login credentials.
Bicycle rental is available at the Lorentz Center for €5 per person per day (cash only, limited availability). Ask upon arrival. ATMs are available at the airport and near the train station.
This workshop is partially open to specific online participants. Please download the Zoom app (laptop/PC recommended over tablet or phone). The Zoom link will be shared via email.
The Lorentz Center is accessible to people with disabilities. A quiet/prayer room and a nursing room are available — please don't hesitate to ask.
Please review the Lorentz Center Code of Conduct ahead of the workshop.
Updates
March 2026
The full programme with breakout topic assignments, interactive session details, and topic cards has been posted. See the detailed programme.
March 2026
The workshop website is now live. Programme details and logistics information will be updated as we approach May.
Coming Soon
Science documents and background materials will be shared with all participants ahead of the workshop to facilitate productive discussions from day one.