EPTA meeting 2025 @ SISSA

Nov 17, 2025, 8:00 AM → Nov 21, 2025, 6:00 PM Europe/Rome

128-129 (SISSA (Main building))

 

The European PTA (EPTA) brings together a multinational community of pulsar astronomers with the shared goal of pushing the frontiers of gravitational-wave science. By timing an array of millisecond pulsars with long-term precision, the EPTA probes nano-Hz gravitational waves—far below the reach of terrestrial detectors. This approach opens a unique window on the cosmos, allowing researchers to study merging supermassive black hole binaries, explore extreme early-Universe physics, and gain new insights into galaxy and black hole formation as well as fundamental cosmology.

 

The one-week EPTA meeting in Trieste provides a forum for collaboration, knowledge exchange, and strategic planning within the European pulsar timing community. Researchers present the latest results, discuss technical developments, and coordinate efforts to enhance the array and maximize its scientific output. The meeting also fosters connections across the broader astrophysics and gravitational-wave communities, bringing together diverse expertise within EPTA to reinforce Europe’s role in this global scientific endeavor. 

 

 

 

                                                                                         

 

 

Tuesday, November 18

2:00 PM → 2:15 PM Welcome: day 1

Convener: Enrico Barausse

2:15 PM → 3:30 PM Day 1: EPTA group updates

Convener: Enrico Barausse

2:15 PM MPIfR

Speaker: Jędrzej Jawor (MPIfR)

EPTA_effelsberg_update_2025.pdf

2:30 PM Manchester/Birmingham

Speaker: Bhavnesh Bhat (University of Manchester)

EPTA_JBO_Birm_update.pptx

EPTA_JBO_Birm_update.pptx

2:45 PM FORTH

Speaker: John Antoniadis

EPTA_FORTH_update_2025.pdf

3:15 PM ASTRON

Speaker: Aditya Parthasarathy (ASTRON)

3:30 PM → 3:45 PM Coffee Break

3:45 PM → 5:00 PM Day 1: EPTA Group Updates 2

Convener: Enrico Barausse

3:45 PM Nançay/Orléans

Speaker: Gilles Theureau (Orléans)

EPTA_2025B_frenchgroup.pdf

4:00 PM Shanghai

Speaker: Kuo Liu (SHAO)

4:15 PM MPTA

Speaker: Kathrin Grunthal (MPIfR)

4:30 PM Milan

Speaker: Alberto Sesana (Universita` di Milano Bicocca)

Sesana_EPTA25_update.pdf

4:45 PM InPTA Updates: DR2 and beyond

The Indo-Japanese collaboration InPTA recently published its second data release making high-precision dispersion measures and timing solutions available for 27 millisecond pulsars across a 7 year time baseline, spanning simultaneous frequency coverage of 300-500 MHz and 1260-1460 MHz uGMRT receivers. This data is being combined with global PTA datasets for the upcoming IPTA DR3. The talk would focus on salient features of InPTA DR2 with brief updates on some of the ongoing follow up efforts.

Speaker: Pratik Tarafdar (INAF-OAC)

InPTAUpdate.EPTAFall25.pdf

5:00 PM → 5:10 PM Close: day 1

Wednesday, November 19

9:00 AM → 9:05 AM Welcome: day 2

Convener: Jędrzej Jawor (MPIfR)

9:05 AM → 10:20 AM Day 2: Timing + Data Combination + Noise Analysis

Convener: Jędrzej Jawor (MPIfR)

9:05 AM PPTA - Update

Speaker: Andrew Zic

9:20 AM CPTA - update

Speaker: Siyuan Chen

9:35 AM Updated constraint on the GWB amplitude from the gamma-ray PTA

Speaker: Serena Valtolina

9:50 AM Long term pulse profile variability in millisecond pulsars

Pulsars generally exhibit stable integrated pulse profiles, making them
powerful tools for precision timing experiments. While short-term vari-
ability, such as mode-changing and nulling, is known in young pulsars,
studies suggest that long-term profile changes may also occur, potentially
correlated with the spin-down rate. Millisecond pulsars (MSPs), typi-
cally more stable, have shown hints of such variability in rare cases (e.g
J1022-1001). In this work, we investigate long-term profile evolution in
MSPs using five years of data from the MeerKAT Pulsar Timing Array
(MPTA), covering 83 sources leveraging the high sensitivity of MeerKAT.
We employ a two-dimensional Gaussian Process regression model with a
separable time-phase kernel, following Keith et al. (2025), to detect subtle
variations in pulse shape. Preliminary results reveal measurable long-term
changes in a subset of MSPs. This study explores whether these types of
variations are prevalent in MSPs and if they show correlation with the
spin-down rate as normal pulsars.

Speaker: Bhavnesh Bhat (University of Manchester)

BhatBhavnesh_EPTA.pptx

10:05 AM Building a pulsar timing pipeline for ARGOS

ARGOS-CDS is the design study phase for the planned ARGOS telescope, a leading-edge, low-cost radio interferometer to be built in Europe. It will perform continuous wide-field monitoring in between 1 GHz and 3 GHz, and high-cadence, high-SNR observations of all PTA pulsars as the most sensitive instrument in the EPTA.

The pulsar science pipeline, arpa, for ARGOS is being developed as new, open-source software inspired by TOASTER. It is mainly written in rust, a relatively young, high performance systems language with a focus on type and memory safety. Arpa aims to be both modular and efficient, utilising the widely supported Postgresql for database keeping and psrchive for pulsar archive manipulation.

Speaker: Samuel Gullin (Argos / Forth / Univerity of Crete)

EPTA_Sissa2025_Gullin_arpa-2.pptx

10:20 AM → 10:40 AM Coffee Break

10:40 AM → 12:00 PM Day 2: Astrophysics and Interpretation of Gravitational Waves

Convener: Sara Manzini (APC - Université Paris Cité)

10:40 AM Session Introduction

Speaker: Sara Manzini (APC - Université Paris Cité)

10:45 AM Data span and frequency coverage requirements for robust detection and inference in PTAs - A case study with EPTA DR2

Pulsar Timing Arrays (PTAs) are approaching the sensitivity required to make a 5-σ detection of the nanohertz stochastic gravitational wave background (GWB), making it crucial to develop a comprehensive understanding of our data and of the outcomes of our analysis pipelines. Thus, it becomes essential to understand a counterintuitive feature revealed in the recent results from the European Pulsar Timing Array (EPTA) second data release (DR2): when restricting the dataset to its ultimate ∼10.3 years (DR2new), the inferred GWB significance increases from ≲ 2σ for the full 25-year dataset (DR2full), to ≳ 3.5σ for DR2new. In this talk, we show that this behaviour does not reflect an anomaly in the data, but it is a possible outcome of the analysis pipeline. This is done by using realistic DR2-like simulations. We also show that, regardless of the significance, DR2new yields biased GWB parameter estimates, primarily due to spectral leakage effects that are usually disregarded in the analysis and tend to flatten the inferred power-law spectrum. Including leakage in the model, returns unbiased parameter estimates, demonstrating that DR2new is reliable when the signal is appropriately modelled. Furthermore, we show that combining EPTA DR2full data with complementary long-baseline observations from NANOGrav and PPTA and with low frequency observations from LOFAR and NenuFAR significantly improves the GWB evidence and precision and accuracy in the parameter estimation, supporting the case of combining DR2full within the IPTA framework.

Speaker: irene ferranti (University of Milano-Bicocca)

presentazione_Ferranti.pdf

11:00 AM Impact of DM noise modeling on the GWB search

Building on Iraci et al. (2024), we study the impact of our main modelling routines to mitigate the effects of the ionized interstellar medium during the search for the Gravitational Wave Background (GWB) with Pulsar Timing Arrays (PTAs). To this scope, we use synthetic PTA datasets and model the DM variations as Gaussian Processes (DM GP) using the Enterprise software to test the consistency of our routines under controlled conditions. For the first time, we are moving our analysis to the Discovery software suite, which allows us to speed up the parameter estimation process.

Speaker: Danilo Zecca (Università del Salento)

11:15 AM Modeling Non-Gaussianities using Gaussian Mixture Models

In Pulsar Timing Array (PTA) data analysis, noise is typically assumed to be Gaussian, and the marginalized likelihood has a well-established analytical form derived within the framework of Gaussian processes. However, this Gaussianity assumption may break down for certain classes of astrophysical and cosmological signals, particularly for a gravitational wave background (GWB) generated by a population of supermassive black hole binaries (SMBHBs). In this work, we present a new method for testing the presence of non-Gaussian features in PTA data. We go beyond the Gaussian assumption by modeling the noise or signal statistics using a Gaussian mixture model (GMM). An advantage of this approach is that the marginalization of the likelihood remains fully analytical, expressed as a linear combination of Gaussian PTA likelihoods. This makes the method straightforward to implement within existing data analysis tools. Moreover, this method extends beyond the free spectrum analysis by producing posterior probability distributions of higher-order moments inferred from the data, which can be incorporated into spectral refitting techniques. We validate the model using simulations and demonstrate the sensitivity of PTAs to non-Gaussianity by computing the Bayes factor in favor of the GMM as a function of the injected excess moments. We apply the method to a more astrophysically motivated scenario where a single SMBHB is resolved on top of a realistic GWB and show that significant non-Gaussianities are introduced by the individual source. Finally, we search for non-Gaussianities in the EPTA DR2 dataset.

Speaker: Mikel Falxa (Università di Milano Bicocca)

Non-Gaussianities.pdf

11:30 AM Optimizing gravitational-wave sky maps for PTAs

Gravitational-wave sky maps are a key tool for understanding the origin of the gravitational-wave background (GWB) signal in PTA data sets. Moreover, as they depict the gravitational-wave power sky distribution is, close-by supermassive-black-hole binaries are potentially revealed as hot-spots on these maps. A crucial factor for the identification of these hot-spots and the resulting level of anisotropy is the resolution of the PTA, and its proper reflection in the map calculation procedure.
In this talk, we present a novel scheme to calculate the Point-Spread-Function (PSF) of a PTA in terms of the sky map analysis. This scheme is used to illustrate the shortcomings of the currently employed setup of spherical-harmonics-based anisotropy analyses. Based on the findings, we propose a reworked anisotropy analysis setup. At hand of simulated data sets, we demonstrate the improvements it brings to the identification of anisotropies in the GWB.

Speaker: Kathrin Grunthal (MPIfR)

11:45 AM Cosmic Variance in Anisotropy Searches at Pulsar Timing Arrays

In the context of cosmology, the statistical uncertainty induced by a small sample size is typically referred to as cosmic variance. Several works have considered its relevance in the context of gravitational wave (GW) detection using pulsar timing array (PTA) experiments. In this talk, I will discuss the impact of cosmic variance on the measurement of anisotropies in the GW background using PTAs. In particular, I will show that, while low statistics induce apparent anisotropies in each realization of an isotropic GWB, statistical inference remains robust, meaning that the measurements remain consistent with the underlying assumption of isotropy. This talk is based on and briefly summarizes the main results obtained in the recent paper 2508.21131.

Speaker: Mauro Pieroni

12:00 PM → 1:30 PM Lunch

1:30 PM → 3:00 PM EPTA only: EPTA Roadmap

Convener: Aditya Parthasarathy (ASTRON)

3:00 PM → 3:30 PM Coffee Break

3:30 PM → 4:35 PM Day 2: Physics of the ISM and Noise Modelling

Convener: Dr Golam Shaifullah (Dipartimento di Fisica ``G. Occhialini", Universit{\'a} degli Studi di Milano-Bicocca, Piazza della Scienza 3, I-20126 Milano, Italy)

3:30 PM Session Introduction

Speaker: Dr Golam Shaifullah (Dipartimento di Fisica ``G. Occhialini", Universit{\'a} degli Studi di Milano-Bicocca, Piazza della Scienza 3, I-20126 Milano, Italy)

3:35 PM Update on LOFAR and NenuFAR

In this talk, we will discuss on the recent updates on LOFAR and NenuFAR.

Speaker: Mark Brionne (INAF-OACa Cagliari)

LOFAR_GLOW_update_EPTA_fall_2025.pdf

3:50 PM Polarization Calibration in LOFAR Beamformed Data

LOFAR’s beamformed mode enables diverse science cases and data collected in this mode proved to be fundamental for the latest EPTA data release, DR2low (Iraci and Chalumeau et al 2025).
However, polarization analysis in beamformed mode has remained largely out of reach due to the absence of a reliable polarization calibration framework.

Here, I will present our cutting-edge polarization calibration scheme specifically tailored for LOFAR’s beamformed mode. This work faces a number of calibration challenges, and indicates the pitfalls of the currently-used beam model, but also serves as a stepping stone towards a robust polarization calibration for SKA Low.

Speaker: Caterina Tiburzi (inaf-oac)

4:05 PM DR2low and IISM turbulence with LOFAR

Low-frequency radio data are highly valuable for studying propagation effects in pulsar signals, such as dispersion measure (DM) variations. In this work, we combine for the first time observations from LOFAR (100–200 MHz) and NenuFAR (30–90 MHz) with EPTA DR2new+ data to build a new dataset, the so-called DR2low. It consists of 12 pulsars observed over a time span of ∼11 years with radio frequencies spanning from ~30 to ~2500 MHz. We perform the same noise analysis as for EPTA DR2 to compare the results and update the favoured noise models for these pulsars. The extended frequency coverage improves the ability to disentangle red noise from chromatic effects, constrains DM variations more tightly, and reveals scattering in several sources.

Beyond the noise characterisation, these data open up new opportunities to study the turbulent ionised interstellar medium. In a separate work, I focus on LOFAR observations to identify and characterise discrete H II regions along the lines of sight to nearby pulsars, investigating their possible role in shaping the observed DM variations.

Speaker: Francesco Iraci (INAF-OAC)

DR2low_and_HII.key

DR2low_and_HII.pdf

4:20 PM Simulating the IISM to improve PTAs noise modelling

The Ionised interstellar medium (IISM) is a major source of unmodelled noise in Pulsar Timing Array (PTA) data. Spatial effects like scattering and scintillation lead to short-term diffractive and long-term refractive noise. These overlaid with variations in electron density further complicate and bias PTA noise models - directly impacting sensitivity to low-frequency gravitational waves. Achieving a more precise characterization of the IISM is essential for a proper characterization of the gravitational wave background. In this talk, I will introduce a novel method for simulating the IISM and noise in pulsar timing data. This approach begins with simulating IISM screens and imprinting the computed group and scattering delays on pulsar timing data. These simulated data are used to test the efficacy of current noise algorithms and how they can be improved. I will present the results obtained and the future perspective of this technique.

Speaker: Ruggero Valdata

4:35 PM → 4:50 PM Close: day 2

Convener: Jędrzej Jawor (MPIfR)

8:00 PM → 10:00 PM Group Dinner

Thursday, November 20

9:00 AM → 9:05 AM Welcome: day 3

Convener: Jędrzej Jawor (MPIfR)

9:05 AM → 10:00 AM EPTA only: LEAP-2 Discussion

Conveners: Aditya Parthasarathy (ASTRON), Delphine Perrodin (INAF - Osservatorio Astronomico di Cagliari)

10:00 AM → 10:25 AM Coffee Break

10:25 AM → 12:00 PM Day 3: New Physics / CWs / Discrete Sources

Convener: irene ferranti (University of Milano-Bicocca)

10:25 AM Session Introduction

Speaker: irene ferranti (University of Milano-Bicocca)

10:30 AM Constraints on Ultralight Scalar and Dark photon Dark Matter from PPTA-DR3 and EPTA-DR2

The cold dark matter (CDM) model successfully describes the Universe on large scales, yet faces challenges at sub-galactic scales. Ultralight dark matter (ULDM), with particle masses around $10^{-22}$ eV, offers a promising solution to these small-scale issues. Pulsar timing arrays (PTAs), originally designed to detect nanohertz gravitational waves, also provide a sensitive probe for ULDM signals. In this work, we perform a Bayesian search for ULDM using PTAs, focusing on two types of signals: the oscillatory gravitational potential from scalar ULDM and the fifth-force interaction mediated by dark photon dark matter (DPDM). Both signals are searched for using the PPTA-DR3 dataset, while the EPTA-DR2 data are employed to constrain the DPDM. No statistically significant evidence for ULDM is found, and we place 95% confidence-level upper limits on the relevant parameters. For scalar ULDM, our constraints show improved sensitivity over PPTA-DR1 at low frequencies, are comparable to those from the NANOGrav 15-year dataset, but are weaker than the latest EPTA-DR2 limits. For DPDM, the obtained bounds are comparable to existing constraints.

Speaker: XiaoSong Hu (Beijing Normal University)

10:45 AM Exploring Neural Network Methods for Sky Localisation of PTA sources

Accurate localisation of continuous gravitational waves (CGWs) from supermassive black hole binaries (SMBHBs) remains one of the key challenges in Pulsar Timing Array (PTA) data analysis. Traditional searches based on the $\mathcal{F}_e$ statistic provide a robust analytic framework, but the resulting sky maps are strongly affected by the PTA antenna pattern, which redistributes signal power across the sky and generates secondary peaks that complicate the identification of the true source position. This degeneracy motivates the development of alternative approaches capable of disentangling instrumental artefacts from true localisation information.

In this work, we investigate whether neural networks (NNs) can improve CGW sky localisation by learning the correct position directly from $\mathcal{F}_e$ maps. We design and train a fully connected residual NN that takes as input the full sky map and outputs the source coordinates on the celestial sphere, encoded as $(\sin\phi, \cos\phi, \cos\theta)$. The loss function is dominated by the Haversine distance between predicted and true positions, providing a direct measure of angular separation.

The results show that the neural network consistently improves localisation performance relative to analytic expectations. In particular exceeding Fisher predictions by an order of magnitude in some of the cases. The network remains robust to changes in SNR, maintaining superior accuracy specially in low-SNR conditions. However, as expected, when the pulsar term is included in the signal model, performance decreases substantially.

Speaker: Ludovica Carbone (Università degli Studi di Milano-Bicocca)

pres_EPTA_nov_2025 (1).pdf

11:00 AM Studying eccentric supermassive black hole binaries in PTA

The most plausible astrophysical sources for PTA experiments are supermassive black hole binaries (SMBHBs), which emit gravitational waves (GWs) that incoherently superpose to form a stochastic GW background (SGWB). Particularly massive and nearby SMBHBs produce strong signals that may stand out above the GWB. PTAs will observe the early inspiral of these systems at large orbital separations, where the orbits may have significant eccentricity.
In this talk, I will present the results of parameter estimation performed using a gravitational waveform model based on the Effective-One-Body (EOB) approach applied to individually resolvable binaries. I will focus on relevant binaries for an EPTA-like mock dataset, spanning the parameter space in eccentricity, chirp mass, and orbital frequency for various signal-to-noise ratio (SNR) values.
Furthermore, since the template includes high post-Newtonian (PN) order corrections, which depend explicitly on the total mass of the binary, I will investigate the possibility of disentangling the two component masses for relativistic systems in the high-frequency region of the PTA band.

Speaker: Sara Manzini (APC - Université Paris Cité)

EPTA meeting trieste (7).pdf

11:15 AM Constraining Preferred-Frame Effects in Gravity with Binary Pulsars

We constrain Einstein-Aether gravity, a leading alternative to General Relativity that introduces a preferred-frame via a dynamical time-like vector field, using high-precision pulsar timing observations from EPTA. Our analysis incorporates both conservative and dissipative first post-Newtonian corrections and utilizes full times of arrival from multiple pulsars, processed with Vela.jl, a Bayesian tool based on PINT. The model spans many parameters, including binary component masses, Einstein-Aether coupling constants and center-of-mass velocity components. We extract posteriors on post-Keplerian parameters from timing data and employ normalizing flows combined with resampling techniques to map these onto constraints for the fundamental theory parameters. Our results demonstrate the power of pulsar timing to probe deviations from General Relativity and provide insights into the phenomenology of preferred-frame gravity.

Speaker: Massimo Vaglio (SISSA)

Constrain_LV-gravity_with_pulsars - Vaglio.pdf

11:30 AM Light Bending Under General Relativity: A study of pulsar blackhole binaries

We present a fully general relativistic formalism to study propagation delays in the radio signals of pulsars in binary systems, arising from the gravitational bending of light. This bending delay is a significant contribution in neutron star–neutron star systems and becomes even more pronounced in neutron star–black hole binaries. Applying our framework to hypothetical neutron star–black hole systems, we find excellent agreement with previous approximate treatments near superior conjunction, while demonstrating that our method remains valid across all orbital configurations. Our formalism also reveals new features, including a characteristic discontinuity in the delay curve near conjunction. For the first time, we extend the calculation of bending delays to systems with rotating (Kerr) black hole companions. Finally, we show that light bending induces distortions in the apparent intensity distribution across the pulsar beam, leading to measurable pulse profile modifications and broadening.

Speaker: Jyotijwal Debnath (INAF Cagliari)

Light_bending_PSRBH.pdf

11:45 AM Sardinia/Cagliari

Speaker: Delphine Perrodin (INAF - Osservatorio Astronomico di Cagliari)

Cagliari_EPTA_Fall2025.pdf

12:00 PM → 1:30 PM Lunch

1:30 PM → 2:30 PM EPTA only: Open Discussion

Convener: Aditya Parthasarathy (ASTRON)

2:30 PM → 3:00 PM Close

Convener: Alberto Sesana (Universita` di Milano Bicocca)