Name: Workshop "Optical GEMS in the Quickly Variable Sky: New Insights on Neutron Star Fundamental Physics from Multi-Messenger Observations"
Start: 2026-05-13T12:00:00+02:00
End: 2026-05-15T14:00:00+02:00
Location: INAF Astronomical Observatory of Rome

Workshop "Optical GEMS in the Quickly Variable Sky: New Insights on Neutron Star Fundamental Physics from Multi-Messenger Observations"

from Wednesday, 13 May 2026 (12:00) to Friday, 15 May 2026 (14:00)

Monday, 11 May 2026
Tuesday, 12 May 2026
Wednesday, 13 May 2026

13:00 Registration
Registration
13:00 - 14:00
Room: Aula Gratton

14:00 Welcome - A. Papitto
Welcome - A. Papitto
14:00 - 14:15
Room: Aula Gratton

14:15 More and more FRBs, more and more questions - Andrea Possenti
More and more FRBs, more and more questions - Andrea Possenti
14:15 - 14:40
Room: Aula Gratton Fast Radio Bursts (FRBs) are short (from millisecond to tens of millisecond) radio flashes originating from sources located across the whole Universe up (so far) to a redshift around 2. Although about 5000 sources have been now catalogued, the engine of the FRB emission is still unconstrained, and the nature of the underlying source(s) debated. This contribution will focus on some recent developments in this blooming astrophysical field, while presenting a new experiment, which INAF is significantly involved in, and which promises to play a major role for both addressing the many still unsolved questions and for fully exploiting the FRBs also in order to perform fundamental physics and cosmology research.

14:40 Fast Radio Bursts outside the radio band - Maura Pilia
Fast Radio Bursts outside the radio band - Maura Pilia
14:40 - 15:05
Room: Aula Gratton Emission outside the radio band is predicted for most models trying to explain the FRB phenomenon. Its nature, however, is still to be determined, with the exception of the possible example provided by the Galactic FRB20200428A, where X-ray emission was observed simultaneously with the radio emission, with an energy ratio E_X/E_radio = 10^5. I will review the targeted attempts to search for the multi-wavelength counterpart of FRBs and I will highlight the results of six years of multi-wavelength campaigns targeting FRB20180916B in optical, X- and gamma-rays, simultaneously with high sensitivity radio observations. Through this campaign the deepest prompt upper limits were obtained in optical and X-rays in terms of E_MWL/E_radio. I will discuss the challenges of such large scale campaigns and the physical implications of our findings.

15:05 Gravitational self-lensing of Fast Radio Bursts in neutron star magnetospheres - Simone Dall'Osso
Gravitational self-lensing of Fast Radio Bursts in neutron star magnetospheres - Simone Dall'Osso
15:05 - 15:30
Room: Aula Gratton Nearly two decades after their discovery, the origin of fast radio bursts (FRBs) remains a mystery. To date their bright, coherent radio emission has no detected counterparts beyond the radio band, with the only exception of FRB-like flares emitted by the galactic magnetar SGR 1935+215. The latter lend support to the proposed association of FRB sources with a cosmic population of magnetars. I will summarize the main properties of FRB emission, and introduce our novel interpretation in terms of strong gravitational lensing of neutron star (NS) flares due to the NS gravitational field, i.e. the gravitational self-lensing (GSL) model. I show how this idea explains in a unified picture the large FRB luminosities, the co-existence of rare repeaters and more numerous one-off sources, and their overall energy budget, allowing at the same time to bridge the gap between the apparent paucity of FRBs in the local universe and their comparatively large all-sky rate. Moreover, the GSL model accounts for (a) the double-peaked energy distribution of individual FRBs observed in the most active repeaters, in terms of a simple, pulsar-like emission geometry, and (b) the redshift (and fluence) distribution of FRBs in the first CHIME catalog, in terms of a cosmic population – consistent with magnetars - following the star formation history.

15:30 Optical monitoring of FRB 20220912A and characterization of fast optical foreground events - Alessia Spolon
Optical monitoring of FRB 20220912A and characterization of fast optical foreground events - Alessia Spolon
15:30 - 15:45
Room: Aula Gratton Repeating fast radio bursts (FRBs) are prime targets for high–time-resolution optical searches aimed at identifying fast optical counterparts. Between October 2022 and December 2023, we monitored the highly active repeater FRB 20220912A at the Asiago Observatory using the fast photon-counting instruments Aqueye+ and IFI+Iqueye. During prolonged optical observations, we identified short (∼1 ms) statistically significant optical pulses, here referred to as fast optical bursts (FOBs). To assess the nature of these events, we performed a detailed foreground characterization using archival Aqueye+ observations of a comparison field, centered on the faint millisecond pulsar PSR J1023+0038. Exploiting the availability of both on-source and on-sky detectors, we find that about 60% of significant events are detected simultaneously in both regions, consistent with diffuse atmospheric contamination, likely associated with meteor activity. A comparable fraction is observed in the FRB 20220912A field, suggesting that the detected FOBs are dominated by foreground events. Further optical monitoring and coordinated multi-wavelength campaigns, including Iqueye at Gemini South, are required to improve the statistics and to search for any excess of isolated on-source events potentially attributable to the FRB.

15:45 A tricky statistical search for Fast Optical Bursts - Carlo Campa
A tricky statistical search for Fast Optical Bursts - Carlo Campa
15:45 - 16:00
Room: Aula Gratton The long unexplored fast optical sky is now accessible thanks to new large ground-based telescopes and new generation instruments. Studying it may lead to new discoveries, but it is also challenging due to optical pollution. In this talk, I will present our preliminary results obtained from an automated search and characterization of mysterious Fast (millisecond) Optical Bursts (FOBs) in about 400 hours of observation with the fast photometer SiFAP2 at the Telescopio Nazionale Galileo. Using a Bayesian Blocks–based algorithm we developed, we found a surprisingly high rate of 2 FOBs per hour. Our analysis suggests that many of these bursts likely have a non-astrophysical origin. However, maybe some bursts show marginally significant evidence to the contrary.

16:00 Multifrequency observations of Crab giant pulses - Luca Beduzzi
Multifrequency observations of Crab giant pulses - Luca Beduzzi
16:00 - 16:15
Room: Aula Gratton The Crab pulsar is the youngest known neutron star and it has been monitored for over five decades. Its giant pulses (GPs) provide a unique laboratory for probing neutron-star emission physics. Fast radio bursts (FRBs), often linked to neutron stars, offer a complementary framework for studying extreme energy-release processes. Crab GPs have typical fluences larger than a few tens of Jy ms. They may therefore represent a so far missing link between pulsar physics and repeating FRBs emission. We conducted observations at 408 MHz with the Northern Cross radio telescope, 820 MHz with the Green Bank Telescope, and 1500 MHz with the Green Bank and Noto telescopes. Our observations, carried out simultaneously with optical ones, are expected to provide the optical-toradio energy ratio of Crab giant pulses. I will present the analysis of GPs energy and waiting-time distributions. I will compare them with those of the most hyperactive repeating FRBs, such as FRB 121101, FRB 201124A, FRB 220114A, and FRB 220912A, including a search for periodicities.

16:15 Coffee break
Coffee break
16:15 - 16:45
Room: Aula Gratton

16:45 The optical beat of magnetars - Alice Borghese
The optical beat of magnetars - Alice Borghese
16:45 - 17:10
Room: Aula Gratton Magnetars are the most magnetised isolated neutron stars known in the Universe. Their signature is the unpredictable and and variable flaring activity in the X/gamma-ray bands, with bursts lasting from a few milliseconds to tens of seconds and reaching peak luminosities of 1037-1043 erg/s. These flaring events are often accompanied by outbursts in which the persistent X-ray flux increases by a factor of ~10-1000 and then decays over months to years. Magnetars have also been proposed as possible progenitors of some of the most extreme transient events in the Universe, such as fast radio bursts and gamma-ray bursts. Investigating magnetar emission outside the X-ray band is challenging. In this talk, I will focus on the treasure hunt for optical magnetar counterparts, reviewing the few known detections and the ongoing effort with the high-speed optical photometer SiFAP2. I will also discuss possible mechanisms at the origin of magnetar optical emission - a still open problem for which detailed theoretical models are currently lacking.

17:10 CCOs with fast optical photometry - James Turner
CCOs with fast optical photometry - James Turner
17:10 - 17:25
Room: Aula Gratton Central compact objects (CCOs) are a rather unusual manifestation of neutron stars (NSs). They show all the characteristics of being old compared to the bulk NS population; they have slower spin periods, weaker surface magnetic fields and their pulsed emission is almost exclusively comprised of thermal X-rays. We nevertheless know they must be young because they are found in the centre of supernova remnants, hence their namesake. Their formation and evolutionary history is contested, with theories of an intrinsically weak magnetic field at birth (anti-magnetar scenario) being opposed by ideas of rapid spin-down events (fallback disk and B-field crustal emergence) in order to explain their observed properties. A recent detection of radio pulsations from one CCO has suggested that, whilst relatively weakly magnetised, their magnetospheres may possess temporarily favourable configurations for non-thermal emission. Now that the link between CCOs and canonical pulsars has been established, we can probe further at optical and nIR wavelengths. Studying the nIR polarisation and spectra across the rotational phase will be particularly pertinent for constraining atmosphere models, and explaining the true origin of the weak magnetic fields.

17:25 High-time-resolution optical photometry of supernovae with SiFAP2: probing the late-time emission of SN 2023ixf and the compact remnant connection - Fabio Ragosta
High-time-resolution optical photometry of supernovae with SiFAP2: probing the late-time emission of SN 2023ixf and the compact remnant connection - Fabio Ragosta
17:25 - 17:40
Room: Aula Gratton Core-collapse supernovae are the birth sites of neutron stars and black holes, yet the properties of the newly formed compact object remain elusive at optical wavelengths. Fast optical photometry —with sub-second sampling —opens a new window on the rapidly evolving phases of supernovae and on the late-time emission that may betray the presence of an active compact remnant. We report on the first application of the SiFAP2 high-time-resolution photon counter at the TNG (La Palma) to supernova photometry, using the nearby Type II-L SN 2023ixf in M101 as a test case. Observations were carried out at 1 s sampling across six epochs spanning from ~2 days to ~772 days post-explosion, covering the rise, the plateau, the radioactive tail, and the late nebular phase. We describe the methodological challenges of adapting an instrument designed for stellar oscillations and pulsars to the calibration of a spectrally evolving transient, including the development of an empirical time-dependent colour correction. Our late-time photometry reveals a significant excess above the expected radioactive decay at epochs beyond 700 days, consistent with an additional energy source such as ejecta–CSM interaction or emission powered by the nascent compact remnant. We discuss the implications of these findings in the context of neutron star formation and early pulsar activity, and we highlight the potential of high-cadence optical facilities for the multi-messenger follow-up of nearby core-collapse events in the era of gravitational wave astronomy.

17:40 Catching Gamma-Ray Bursts in the Act: Prospects for Prompt Optical Emission Detection with Fast Photometry - Riccardo Brivio
Catching Gamma-Ray Bursts in the Act: Prospects for Prompt Optical Emission Detection with Fast Photometry - Riccardo Brivio
17:40 - 17:55
Room: Aula Gratton Gamma-ray bursts (GRBs) are the most energetic explosions in the Universe, yet the physics of their prompt emission phase remains poorly constrained. Simultaneous optical observations during the prompt γ-ray phase provide a unique and direct diagnostic of the jet structure, emission mechanism, and outflow Lorentz factor. To date, only a handful of events have been captured in optical light during the prompt phase; the most remarkable case, GRB 080319B, reached nakedeye brightness (V ~ 5.3) and was serendipitously observed by the wide-field TORTORA camera, revealing a two-component jet geometry and an extremely relativistic outflow. We discuss the observational requirements and instrument strategies needed to systematically detect GRB prompt optical emission, focusing on two complementary approaches: (i) wide-field, high-cadence imagers capable of monitoring large sky areas without the need for rapid slewing, and (ii) SIFAP-like fast-photometry instruments mounted on telescopes with fast-response capability, which are wellsuited for long-duration events (T90 > 90 s) and ultra-long GRBs. By rescaling from GRB 080319B, we show that O(1) detectable events per year are expected with existing or near-future Italian facilities. The scientific return of each such detection —from sub-second variability to real-time optical–γ correlation —would be transformative for our understanding of the central engine.

17:55 Fast Optical Variability as a Probe of GRB Central Engine Physics: Opportunities with Italian Facilities - Matteo Ferro
Fast Optical Variability as a Probe of GRB Central Engine Physics: Opportunities with Italian Facilities - Matteo Ferro
17:55 - 18:10
Room: Aula Gratton The physical mechanism powering the prompt emission of gamma-ray bursts (GRBs) —internal shocks, magnetic reconnection, or photospheric dissipation —is one of the longest-standing open questions in high-energy astrophysics. While gamma-ray observations alone cannot break the model degeneracy, simultaneous optical monitoring at sub-second cadence offers a powerful and largely unexploited discriminant: the temporal correlation (or lack thereof) between optical and gamma-ray pulses directly constrains the emission radius, the magnetization of the outflow, and the presence of a reverse shock. We argue that the Italian astronomical community is uniquely positioned to contribute to this field. On one hand, wide-field high-cadence imagers (analogous to TORTORA or the proposed Mezzocielo concept) can serendipitously catch the prompt phase without any slew delay, at the cost of shallow limiting magnitude. On the other hand, SIFAPclass photon-counting instruments on medium-to-large aperture telescopes, if paired with a fastresponse alert system, can reach the field of long-duration GRBs (T90 > 90 s) and ultra-long GRBs (T90 > 1000 s) while the prompt phase is still ongoing, providing photon-by-photon light curves with millisecond resolution. We quantify the expected detection rates under conservative assumptions, discuss the minimum resolvable timescales as a function of telescope aperture and GRB brightness, and outline a realistic observational strategy to maximize the scientific yield of each event. A single well-observed prompt optical light curve, obtained simultaneously with Swift/BAT or Fermi/GBM data, would provide diagnostics unavailable by any other means.
Thursday, 14 May 2026

09:00 The high-speed eye of the TNG: Reviewing SiFAP2 successes starting from the first optical millisecond pulsar - Giulia Illiano
The high-speed eye of the TNG: Reviewing SiFAP2 successes starting from the first optical millisecond pulsar - Giulia Illiano
09:00 - 09:25
Room: Aula Gratton High-time resolution astronomy in the visible band has historically been limited by the readout scales of standard detectors. SiFAP2, a fast optical photometer based on Silicon Photo-Multipliers mounted at the 3.58m Telescopio Nazionale Galileo, overcomes these constraints by recording individual photon arrival times with a sub-nanosecond resolution. This instrument has been pivotal in investigating the rapidly variable optical sky, particularly in the study of millisecond pulsars (MSPs). This talk reviews the key milestones of SiFAP2, starting from the discovery of the first optical millisecond pulsations from the transitional MSP PSR J1023+0038, which overturned our understanding of the emission mechanisms in these systems. The enigma has only deepened with the subsequent detection of optical pulsations from two other sources: the accreting MSP SAX J1808.4-3658 and the rotation-powered MSP PSR J2339-0533. We now face a scenario where three distinct systems exhibit optical pulsations that appear to stem from different physical processes, prompting a deeper exploration of the pulsar-disk interaction and the search for new candidates to test current theoretical models.

09:25 Investigating the long-term timing properties of the transitional millisecond pulsar PSR J1023+0038 with Aqueye+, NICER, and Iqueye@Gemini South - Silvia Conforti
Investigating the long-term timing properties of the transitional millisecond pulsar PSR J1023+0038 with Aqueye+, NICER, and Iqueye@Gemini South - Silvia Conforti
09:25 - 09:40
Room: Aula Gratton PSR J1023+0038 is a transitional millisecond pulsar (tMSP), the only one where coherent pulsations were discovered in both the Optical and X-ray energy bands to date. We present a detailed timing analysis of new Aqueye+ optical data taken from 2021 through 2023, obtaining an updated timing solution for the pulsar. We perform a new measurement of the phase lag between optical and X-ray pulsations and investigate the recent evolution of the binary system, monitoring the variation of the time of passage at the ascending node. We measured a phase lag between the optical and X-ray pulses of 112.3 ± 30.7 μs, confirming a common origin. After 2017, the evolution of the passage at the ascending node follows a well-defined parabolic increasing trend, suggesting a corresponding increment in the orbital period and orbital separation of the system. This evolution is consistent with a scenario in which the binary system is evolving through non-conservative Roche lobe overflow and the donor is interacting with the pulsar wind, losing mass at a rate much higher than the inferred accretion rate. Finally, we offer a glimpse of the results from observations of PSR J1023+0038 obtained with Iqueye recently installed at Gemini South, which achieved unprecedented photon statistics and time resolution.

09:40 Optical spectroscopy of the transitional millisecond pulsars - Marco Messa
Optical spectroscopy of the transitional millisecond pulsars - Marco Messa
09:40 - 09:55
Room: Aula Gratton Transitional millisecond pulsars (tMSPs) represent a dynamic class of systems linking low-mass X-ray binaries to rotation-powered millisecond radio pulsars, providing key laboratories to study accretion–ejection physics and neutron star environments. These sources undergo transitions between accretion- and rotation-powered states, and in their active phase, they display rapid switches between distinct high and low luminosity modes, occasionally accompanied by flares. In this talk, I will present high time-resolution optical spectroscopic observations of the prototypical tMSP J1023+0038 in its sub-luminous disc state. The dataset probes variability on minute timescales, revealing significant changes in colour as well as in the strength and profile of the main emission lines. These variations offer insight into the structure and dynamics of the accretion flow and its interaction with the neutron star during its disc state. I will emphasise how combining high-time resolution optical spectroscopy with fast optical photometry, as enabled by instruments such as SiFAP2, can provide a more complete view of these systems. In particular, the synergy between fast photometry and spectroscopy, combined with X-ray observations, can be used to trace correlations between high/low mode transitions across different energy bands while simultaneously probing the spectral response of the accretion disc. This approach opens the possibility of linking rapid flux variability to changes in emission line properties and disc structure.

09:55 What powers millisecond optical pulsations in SAX J1808 and PSR J1023? - Tiziana Di Salvo
What powers millisecond optical pulsations in SAX J1808 and PSR J1023? - Tiziana Di Salvo
09:55 - 10:20
Room: Aula Gratton The discovery of millisecond optical pulsations in SAX J1808.4−3658 and PSR J1023+0038 has opened a new window on the interplay between accretion, magnetic fields, and particle acceleration in neutron-star binaries. In this talk I will review the main physical ideas that have been proposed to explain these signals, from accretion-powered hotspot scenarios to synchrotron models associated with compact magnetospheric interaction regions or striped/pulsar-wind-like dissipation. I will then compare the observational constraints provided by the two prototype systems and discuss how they may point to different radiative regimes: a more clearly two-component picture in SAX J1808, with X-ray pulsations linked to polar accretion and optical/UV pulsations to a non-thermal synchrotron component, versus a more nearly optically thin and spectrally unified pulsed component in PSR J1023. The goal is to identify which elements of the phenomenology may be source-specific and which may reflect a common underlying engine.

10:20 3D particle-in-cell simulations of pulsar wind – disk interaction: application to the transitional millisecond pulsar PSR J1023+0038 - Valentina Richard Romei - REMOTE
3D particle-in-cell simulations of pulsar wind – disk interaction: application to the transitional millisecond pulsar PSR J1023+0038 - Valentina Richard Romei - REMOTE
10:20 - 10:35
Room: Aula Gratton Transitional millisecond pulsars constitute a peculiar subclass of neutron stars in which the pulsar alternates between accretion-powered and rotation-powered states. A third intermediate state, referred to as ‘sub-luminous disk state’, has been identified. During this state, the system exhibits intriguing features, such as broad optical and X-ray pulsations characterized by an unexpectedly high luminosity. To date, no ab initio model of a pulsar wind interacting with an accretion disk has been developed to address these observables. We aim to investigate the origin of the enhanced electromagnetic emission and to reproduce the observable properties of such systems. To model the interaction between the pulsar wind and the disk, we perform 3D particle-in-cell simulations of a pulsar magnetosphere surrounded by a perfectly conducting torus. We find that the presence of the disk induces a significant reconfiguration of the magnetosphere. As a result, the synchrotron radiation is substantially enhanced, and characterized by a strong continuous component and either one or two-peaked light curves, depending on the pulsar’s magnetic obliquity. The polarization properties are also explored. The model successfully reproduces the main features of the optical and X-ray pulsed emission originating from PSR J1023+0038, thereby confirming the scenario in which these pulsations originate from synchrotron radiation generated as the pulsar wind interacts with the inner edge of the disk.

10:35 Coffee break
Coffee break
10:35 - 11:00
Room: Aula Gratton

11:00 Searching for pulsars associated with Fermi sources with MeerKAT - Marta Burgay
Searching for pulsars associated with Fermi sources with MeerKAT - Marta Burgay
11:00 - 11:25
Room: Aula Gratton Pulsars, thanks to their extreme characteristics and their clock-like nature, are unique laboratories to probe many aspects of astrophysics and fundamental physics: from stellar and binary evolution to the study of the interstellar medium and of the Galactic magnetic field, from nuclear physics to relativistic gravity and gravitational waves. The extraordinary sensitivity of the MeerkAT telescope has, in only a few years, led to much progress and many discoveries in this field. In this talk I will describe the pulsar search experiments carried out in the last five years in the framework of the TRAPUM (TRAnsients and Pulsars with Meerkat) Large Survey Projects. I will report on some of the most interesting results, both from pulsar searches and follow-up studies, with a particular focus on searches targeting Fermi unidentified sources, real treasure maps to find exotic binary pulsars, often exhibiting a rich phenomenology across the electromagnetic spectrum.

11:25 The many faces of millisecond pulsars in globular clusters - Alessandro Ridolfi - REMOTE
The many faces of millisecond pulsars in globular clusters - Alessandro Ridolfi - REMOTE
11:25 - 11:50
Room: Aula Gratton About half of all currently known millisecond pulsars (MSPs) reside in globular clusters. These are extremely ancient, self-gravitating, spherical stellar systems that orbit our Galaxy. In their cores, the stellar density can exceed a million solar masses per cubic parsec, providing a formidable breeding ground for the formation of binary systems in which a neutron star can be spun up by a companion and eventually become an MSP. Indeed, over 80% of all the pulsars hosted by GCs are MSPs (with periods smaller than 10 ms). The number of MSPs in GCs has also increased dramatically over the past few years, thanks to major surveys conducted with the most sensitive cm-wavelength radio facilities, most notably MeerKAT and FAST. As of May 2026, more than 300 MSPs are known across 46 different GCs. In this talk, I will review the rich and diverse population of MSPs in globular clusters. I will highlight their general characteristics, relating them to the structural parameters of their host clusters, and briefly discuss some peculiar objects that deserve special attention for their broader scientific implications.

11:50 Spider millisecond pulsars with SiFAP2 - Christian Malacaria
Spider millisecond pulsars with SiFAP2 - Christian Malacaria
11:50 - 12:15
Room: Aula Gratton High-time-resolution detectors are playing a crucial role in advancing our understanding of neutron stars and transient phenomena, enabling precise measurements of their properties. SiFAP2, the high-speed optical photometer permanently mounted at the 3.6m INAF Telescopio Nazionale Galileo, obtained significant breakthroughs discovering optical pulsations of three millisecond pulsars in different luminosity states. SiFAP2 is also involved in multiwavelength campaigns on FRBs to search for optical counterparts. In this talk, I will present the improvements applied to the instrument from the point of view of detectors and timing devices within the “GEMS” project. I will also present the enhanced e-SiFAP instrument, a 6-band Vis/SWIR fast photometer with added polarimetric capabilities as well as the new SiFAP-SoFT photometer mounted at the 1.5m Loiano Telescope especially conceived for simultaneous optical measurements targeted on FRBs and their possible link with magnetars.

12:15 Unravelling the web: discovery of nine new spider pulsar candidates - Marco Turchetta - REMOTE
Unravelling the web: discovery of nine new spider pulsar candidates - Marco Turchetta - REMOTE
12:15 - 12:30
Room: Aula Gratton Since its launch in 2008, Fermi-LAT has been uncovering a new nearby population of compact binary millisecond pulsars, also known as “spiders”. Expanding the currently known spider population holds the key to finding the fastest-rotating and most massive neutron stars, which have crucial implications for nuclear physics and gravitational wave astronomy. Although many of these systems are found via radio follow-up of Fermi sources, searching for the variable optical emission of their companions has also proven successful, and holds potential for revealing a hidden population of radio-obscured spiders. We present the discovery of nine variable optical counterparts to pulsar-like Fermi unidentified sources, which we identify as new spider candidates. Their optical light curves show flux modulation larger than 0.2 mag in the sub-day period range and effective temperatures of 4000−6000 K, all properties consistent with the known redback subtype of binary millisecond pulsars. Among our newly discovered candidates, 4FGL J0736.9-3231, if confirmed as millisecond pulsar, would be the closest known spider to Earth (D=659 pc, from Gaia-DR3 parallax). Unlike the mildly irradiated companion in the previous system, 4FGL J1639.3-5146—one of our most promising candidates— shows strong irradiation, with temperature variations up to 1500 K. We also find an X-ray source at the location of another redback candidate, 4FGL J1748.8-3915, which shows direct evidence of the intrabinary shock between the pulsar and its companion’s winds. These results facilitate radio observations of these candidates currently being acquired with the GBT, but also enable neutron star mass estimates via optical light curve modelling, supported by upcoming GTC and VLT spectroscopic follow-ups.

12:30 The power of optical and ultraviolet observations of neutron stars - Roberto Mignani - REMOTE
The power of optical and ultraviolet observations of neutron stars - Roberto Mignani - REMOTE
12:30 - 12:55
Room: Aula Gratton Neutron stars are among the faintest sources of optical radiation. Nonetheless, their study has been pursued since right after the pulsar discovery and has continued through the years with renewed effort. In this review, I will summarise the state of the art of optical and UV observations of neutron stars, with particular emphasis on the scientific implications of such observations and their impact in astrophysics and fundamental physics.

12:55 Lunch
Lunch
12:55 - 14:30
Room: Aula Gratton

14:30 Accreting Millisecond X-ray Pulsars: Spin Evolution and Accretion Physics - Andrea Sanna
Accreting Millisecond X-ray Pulsars: Spin Evolution and Accretion Physics - Andrea Sanna
14:30 - 14:55
Room: Aula Gratton Accreting millisecond X-ray pulsars represent a key phase in the formation of rotation-powered millisecond pulsars, providing a direct observational window onto the interaction between accretion flows and magnetised neutron stars. Their X-ray pulsations offer a unique probe of how angular momentum is transferred to the neutron star and how spin evolution proceeds under the action of accretion torques. In this talk, I will present a review of the observational properties of accreting millisecond X-ray pulsars, focusing on their spin distributions, transient behaviour, and accretion regimes. Recent studies indicate that the observed diversity of these systems cannot be interpreted solely in terms of instantaneous accretion rates, but likely reflects the imprint of their long-term evolutionary history. Within this framework, the observed spin properties can be understood as the result of the interplay among accretion torques, magnetic field strength, and the system’s secular evolution. I will discuss how X-ray timing observations constrain the physics of the disc–magnetosphere interaction and the efficiency of spin-up processes, and how these constraints can be connected to broader evolutionary scenarios. In this context, multi-wavelength observations provide an important complementary perspective. In particular, the detection of optical pulsations at the neutron star spin period in a handful of systems indicates that part of the optical emission can be directly linked to magnetospheric processes operating on millisecond timescales, offering an additional diagnostic of the accretion–ejection interplay. This overview highlights how accreting millisecond X-ray pulsars serve as a laboratory for connecting short-term accretion physics with long-term neutron star spin evolution, offering clear synergies with ongoing efforts to characterise millisecond pulsars across the electromagnetic spectrum, including the optical domain explored within the GEMS project.

14:55 Probing the origin of optical and UV pulsations in the accreting millisecond pulsar SAX J1808.4-3658 - Caterina Ballocco
Probing the origin of optical and UV pulsations in the accreting millisecond pulsar SAX J1808.4-3658 - Caterina Ballocco
14:55 - 15:10
Room: Aula Gratton SAX J1808.4-3658 is the prototype of accreting millisecond X-ray pulsars and the first of this class to show optical and UV pulsations during an accretion outburst. These pulsations challenge standard rotation- or accretion-powered scenarios and provide a unique window into the emission mechanisms of pulsating neutron stars. I will present a multi-band timing study based on XMMNewton, HST/STIS, and TNG/SiFAP2 observations obtained during the 2022 outburst. Optical and UV pulsations observed in 2022 are compared with those first detected in 2019, allowing us to study their evolution across different outbursts. HST observations confirmed the presence of significant UV pulsations at an X-ray luminosity approximately a factor of two lower than during the 2019 outburst, extending the range of mass accretion rates at which UV pulsations have been detected. Analyzing optical observations performed with the fast optical photometer SiFAP2, we find an anti-correlation between the X-ray flux and the amplitude of the optical pulsations, with the latter increasing as the X-ray flux decreases. I will also discuss optical observations obtained during the quiescent state of the source, probing the pulse emission mechanism over a large range of mass accretion rates.

15:10 Millisecond pulsars phenomenology under the light of graph theory - Carlos Rodriguez - REMOTE
Millisecond pulsars phenomenology under the light of graph theory - Carlos Rodriguez - REMOTE
15:10 - 15:25
Room: Aula Gratton Millisecond pulsars (MSPs) in binary systems display a rich phenomenology, including spider pulsars, commonly classified as black widows or redbacks, as well as transitional millisecond pulsars. Understanding how these systems relate to one another within the broader MSP population remains an open question. In this talk, I present a set of algorithms in the context of graph theory, specifically those based on the Minimum Spanning Tree (MST), to analyze and classify the binary MSP population in a multidimensional parameter space. The MST provides a graph-based representation in which distinct pulsar classes naturally emerge as separate branches. In particular, we show that black widows, redbacks, and transitional systems occupy well-defined regions of the tree, enabling their separation without relying on predefined boundaries. We also define a similarity-based ranking to identify candidate systems associated with specific classes. This approach enables the promotion of new candidates. Building on this structure, we apply an algorithm to partition the MST into statistically meaningful subgroups and systematically explore their phenomenological classification. Finally, we introduce a method for locating pulsars with uncertain measurements within the MST. By analyzing their positions relative to well-characterized sources, we constrain the plausible ranges of unknown parameters and guide targeted observational searches. These results demonstrate that MST-based methods offer an interpretable and flexible framework for classifying and exploring MSP populations, with direct applicability to current and future pulsar surveys.

15:25 Optical and X-ray Polarised Emission from Transitional Millisecond Pulsars - Cristina Baglio
Optical and X-ray Polarised Emission from Transitional Millisecond Pulsars - Cristina Baglio
15:25 - 15:50
Room: Aula Gratton Transitional millisecond pulsars (tMSPs) switch between a rotation-powered radio pulsar state and an X-ray active state in which an accretion disc is present. What powers the emission in this active state (pulsar rotation, mass accretion, or some combination of both) has been debated for over a decade. Multiwavelength polarimetry offers a powerful tool to break this degeneracy. In this talk, I will present results from the first multiwavelength polarimetric campaign of the prototypical tMSP PSR J1023+0038, combining simultaneous observations with IXPE, the VLT, and the VLA. I will show how these results provide direct evidence that both the polarised and pulsed emission arise from synchrotron radiation at the boundary region where the pulsar particle wind collides with the inner accretion disk. Moreover, the same multiwavelength polarimetric campaign also allowed us to shed new light on the mechanisms powering the flaring mode. Looking ahead, fast-time resolved polarimetry with photon-counting optical instruments, combined with the expected capabilities of eXTP in the X-rays, promises to take this field to a new level, enabling us to probe the geometry and emission mechanisms of these systems on the timescales of the pulsations.

15:50 Time variability of X-ray polarization as a tool to investigate the geometry of the accretion flow in NS-LMXBs - Alessandro Di Marco
Time variability of X-ray polarization as a tool to investigate the geometry of the accretion flow in NS-LMXBs - Alessandro Di Marco
15:50 - 16:15
Room: Aula Gratton Millisecond pulsars (MSPs) are the quickest-spinning neutron stars (NSs) known. The X-ray pulsations produced by hot spots on the NS surface encode information about the mass and size of these compact objects; in this context, accreting MSPs (AMSPs) are among the best targets because they become relatively bright X-ray sources during X-ray outbursts. Yet, breaking the degeneracy among the many parameters that shape their pulse profiles was not possible due to the limited effective area of X-ray instruments flown to date. X-ray polarimetry is a potential game-changer, providing an independent measure of the geometry of the hot spots. In this talk, the IXPE results obtained by observations of the two AMSPs, SRGA J144459.2-604207 and SAX J1808.4-3658, are presented. Although the spin-phase variability of the normalized Stokes parameters is not highly significant, applying the relativistic rotating vector model, the geometry of the hot spots was determined for SRGA J144459.2-604207. On the other hand, unexpected time variability on longer time scales has been observed in non-pulsating NS-LMXBs, particularly in response to intensity drop during dips. These variations could be explained by a possible contribution from an extended accretion-disk corona or a disk-wind component. In this talk, results for GX 13+1 and XTE J1701- 462 are presented, along with possible constraints on the geometry of the extended accretion-disk corona or the disk wind.

16:15 New insights from X-ray polarimetry into emission geometry of Z sources - Fabio La Monaca
New insights from X-ray polarimetry into emission geometry of Z sources - Fabio La Monaca
16:15 - 16:30
Room: Aula Gratton X-ray timing and broadband spectroscopy have been the main methods for studying the rich and complex phenomenology of neutron stars with weak magnetic fields for a long time. Nowadays, X-ray polarimetry offers the missing, independent set of observables that are directly relevant to comprehending the geometry and nature of the emission regions: polarization degree and angle. This allows breaking degeneracies because different geometries and physical conditions might yield equivalent spectral and timing signatures. Some of the main results obtained in this frame by using the Imaging X-ray Polarimetry Explorer (IXPE) will be reported in this talk. In particular, IXPE observations of Z sources have shown that the polarization properties are not constant but evolve significantly with spectral state. A common trend has emerged in all the Z sources studied so far: the polarization decreases markedly during the transition from the horizontal branch (HB) to the normal branch (NB), indicating substantial changes as the accretion flow evolves.

16:30 X-ray Polarimetry as a Geometrical Probe of Neutron-Star Low-Mass X-ray Binaries - Alessio Anitra
X-ray Polarimetry as a Geometrical Probe of Neutron-Star Low-Mass X-ray Binaries - Alessio Anitra
16:30 - 16:45
Room: Aula Gratton Fast X-ray timing of transient sources has historically been the domain of large, monolithic space observatories. Here we show that, for the first time, sub-millisecond timing can be achieved with a wide-field nanosatellite instrument operating without collimation. Using data from the HERMES X/γ-ray spectrometer on board the SpIRIT CubeSat, we demonstrate sub-millisecond timing capabilities in the keV range. This performance is enabled by an algorithmic framework based on cross-correlation techniques applied to photon Time-of-Arrival (ToA) data, combined with adaptive binning and Monte Carlo methods to robustly recover fast variability in the low-count regime typical of CubeSat observations. These results establish CubeSats as a viable platform for fast X-ray photometry, opening new opportunities for timing studies of both transient and persistent high-energy sources. This methodology naturally enables cross-band lag measurements and delay studies between optical and high-energy emission, as targeted by the Optical GEMS project.

16:45 Coffee break
Coffee break
16:45 - 17:15
Room: Aula Gratton

17:15 Unveiling the accretion-ejection interplay in black hole transients with multi-band variability - Alessio Marino
Unveiling the accretion-ejection interplay in black hole transients with multi-band variability - Alessio Marino
17:15 - 17:40
Room: Aula Gratton Black Hole Transients (BHTs) are binary systems composed of a stellar-mass BH and a companion star typically less massive than the Sun. These sources emit over a wide range of electromagnetic frequencies, from radio to gamma-rays. Their multi-band spectral energy distribution is dominated by two main components: an accretion disk, emitting from the optical to the X-rays, and a jet, emitting from radio to NIR. Despite being apparently opposite phenomena, matter inflows (in the disk) and matter outflows (in the jet) are profoundly intertwined, to the extent that we can call them two faces of the same medal. Unfortunately, the details of such a coupling are far to be fully understood, including the physical engine that launches jets and the role that the mass and/or spin of the BH (if any) plays in this scenario. In this context, multi-band observations, especially in the optical-NIR band, as it lies at the interface between jet and disk emission, are fundamental to solve these questions. Fast optical photometry has in particular emerged as a powerful tool to disentangle these components in the time domain, providing unique insights into the causal connection between inflow and outflow. IIn this talk, I will review our current understanding of the disk–jet connection in black hole transients and highlight how fast optical photometry has advanced, and will continue to advance, the field, providing access to physical source scales, jet speeds, the origin of quasi-periodic oscillations, and the coupling between accretion and ejection.

17:40 Sub-second multi-wavelength emission from X-ray binaries - Federico Vincentelli
Sub-second multi-wavelength emission from X-ray binaries - Federico Vincentelli
17:40 - 18:05
Room: Aula Gratton Accretion onto compact objects is a fundamental process in astrophysics, powering some of the brightest sources in the sky. It also drives powerful outflows that can shape the surrounding environment, making accretion central to the broader inflow–outflow cycle. In recent years, subsecond optical and infrared observations of accreting X-ray binaries have opened a new window onto this connection, uncovering a rich variety of previously inaccessible phenomena. For example, the discovery of a 0.1 s lag between the X-ray and optical/infrared variable emission has provided a powerful probe of the inner jet physics, while also placing constraints on the jet speed and inclination. In this talk, I will review the current observational picture and discuss the main physical components responsible for rapid optical/infrared variability. I will then show how new data are placing stringent constraints on the properties of jets and accretion discs, highlighting the need for more realistic physical models.

18:05 Quickly variable optical polarization and e-SiFAP - Francesco Leone
Quickly variable optical polarization and e-SiFAP - Francesco Leone
18:05 - 18:30
Room: Aula Gratton e-SIFAP has been designed to study sources characterized by quickly-variable polarized emission. After a brief overview of polarimetric measurement methods, we provide a detailed description of e-SIFAP. The discussion focuses on its unique capabilities, particularly its ultra-high temporal resolution and its broad spectral coverage. e-SIFAP operates across an extensive range that includes the full SLOAN filter set and extends into the near-infrared with the J and H bands. e-SIFAP is a full-Stokes polarimeter designed for high-fidelity measurements. The instrument is capable of measuring the Stokes Q and U parameters simultaneously, while the Stokes V parameter is acquired independently. Both measurement modes benefit from the implementation of the dual-beam swapping technique. This method is essential to cancel out instrumental polarization and systematic errors, allowing us to accurately measure even the most subtle linear and circular polarization signals. While e-SIFAP is crucial for probing rotating magnetospheres, mapping the underlying magnetic field geometry requires solving the radiative transfer equation in polarized light within the magnetized medium. This step is necessary to correctly interpret the observed polarization signatures. In this context, the knowledge gained from modeling the magnetic Ap stars is essential, as their magnetospheres have been extensively studied through phase-resolved Stokes parameters in both the visible and radio bands.
Friday, 15 May 2026

09:30 On searches for optical pulsations from NSs in binaries - Riccardo La Placa
On searches for optical pulsations from NSs in binaries - Riccardo La Placa
09:30 - 09:55
Room: Aula Gratton Timing neutron star systems is crucial to follow the evolution of binary and the interplay between the two objects, test strong-field general relativity, and study the neutron star itself. Millisecond pulsars in particular are ideal targets to probe the strong interaction at supranuclear densities and search for continuous gravitational wave (CW) sources. I will review the main techniques behind the efforts to find these pulsations across the EM spectrum, comparing their main use cases. Moreover, I will describe our implementation of a semi-coherent algorithm paricularly suited for binary systems for which standard blind searches would prove computationally unfeasible. I will explain the main workflow of the technique and show our first results in its application to optical data of one of the strongest candidates for CW emission, Scorpius X-1, using the fast photometer SiFAP2 mounted at the TNG.

09:55 Genetic and evolutionary algorithms for finding pulsations - Nicolò Pinciroli
Genetic and evolutionary algorithms for finding pulsations - Nicolò Pinciroli
09:55 - 10:10
Room: Aula Gratton Detecting periodic signals from accreting pulsars, including millisecond pulsars, is challenging due to distortions introduced by orbital motion in binary systems. This talk presents the use of evolutionary algorithms, specifically genetic algorithms, to efficiently explore the orbital parameter space and reconstruct a corrected light curve, reducing computational cost compared to exhaustive grid searches. This approach is particularly useful for millisecond pulsars, whose search is both resource- and time-consuming when using traditional grid-search methods.

10:10 Fast X-ray Timing with CubeSats: An Adaptive Approach to the Low-Count Regime - Wladimiro Leone
Fast X-ray Timing with CubeSats: An Adaptive Approach to the Low-Count Regime - Wladimiro Leone
10:10 - 10:25
Room: Aula Gratton Fast X-ray timing of transient sources has historically been the domain of large, monolithic space observatories. Here we show that, for the first time, sub-millisecond timing can be achieved with a wide-field nanosatellite instrument operating without collimation. Using data from the HERMES X/γ-ray spectrometer on board the SpIRIT CubeSat, we demonstrate sub-millisecond timing capabilities in the keV range. This performance is enabled by an algorithmic framework based on cross-correlation techniques applied to photon Time-of-Arrival (ToA) data, combined with adaptive binning and Monte Carlo methods to robustly recover fast variability in the low-count regime typical of CubeSat observations. These results establish CubeSats as a viable platform for fast X-ray photometry, opening new opportunities for timing studies of both transient and persistent high-energy sources. This methodology naturally enables cross-band lag measurements and delay studies between optical and high-energy emission, as targeted by the Optical GEMS project.

10:25 Coffee break
Coffee break
10:25 - 11:00
Room: Aula Gratton

11:00 Fast optical photometry with TNG@SiFAP2, e-SiFAP@TNG and SiFAP-SoFT@Loiano - Filippo Ambrosino
Fast optical photometry with TNG@SiFAP2, e-SiFAP@TNG and SiFAP-SoFT@Loiano - Filippo Ambrosino
11:00 - 11:25
Room: Aula Gratton High-time-resolution detectors are playing a crucial role in advancing our understanding of neutron stars and transient phenomena, enabling precise measurements of their properties. SiFAP2, the high-speed optical photometer permanently mounted at the 3.6m INAF Telescopio Nazionale Galileo, obtained significant breakthroughs discovering optical pulsations of three millisecond pulsars in different luminosity states. SiFAP2 is also involved in multiwavelength campaigns on FRBs to search for optical counterparts. In this talk, I will present the improvements applied to the instrument from the point of view of detectors and timing devices within the “GEMS” project. I will also present the enhanced e-SiFAP instrument, a 6-band Vis/SWIR fast photometer with added polarimetric capabilities as well as the new SiFAP-SoFT photometer mounted at the 1.5m Loiano Telescope especially conceived for simultaneous optical measurements targeted on FRBs and their possible link with magnetars.

11:25 Future of Aqueye+, Iqueye and synergies with SiFAP2 - Michele Fiori - REMOTE
Future of Aqueye+, Iqueye and synergies with SiFAP2 - Michele Fiori - REMOTE
11:25 - 11:50
Room: Aula Gratton Aqueye+ and Iqueye are two astronomical instruments designed to exploit the highest time resolution achievable using modern electronics and detectors in the optical band. They are used to explore the quantum properties of light (e.g., through intensity interferometry measurements) and to enable the study of rapid optical variability down to the sub-millisecond level. This extreme timing capability is crucial for characterising certain important classes of astrophysical sources, in particular (millisecond) pulsars and X-ray binaries. Along with SiFAP2, Aqueye+ and Iqueye are among the most powerful optical timing facilities currently in operation. In this presentation, I will highlight some of the most recent results that we have obtained, emphasising the multiinstrument and multi-wavelength synergies. I will also present future instrumental developments of this project and the scientific prospects for the coming years, including the possibility of offering Iqueye at Gemini South.

11:50 Einstein Probe and Synergies with Fast Optical Photometry - Francesco Coti Zelati
Einstein Probe and Synergies with Fast Optical Photometry - Francesco Coti Zelati
11:50 - 12:10
Room: Aula Gratton Einstein Probe, launched in January 2024, is opening a new window on the transient X-ray Universe through the wide-field capabilities of its Wide-field X-ray Telescope and the rapid, sensitive follow-up provided by the Follow-up X-ray Telescope. In this talk, I will present the main characteristics of the mission and its role in the discovery and characterization of X-ray transients, with a focus on accreting compact objects. I will then discuss the synergy between Einstein Probe and fast optical photometry, highlighting simultaneous Einstein Probe and TNG/SiFAP2 observations of the accreting millisecond pulsar SAX J1808.4-3658 during its 2025 outburst. These data include a thermonuclear burst observed simultaneously in X-rays and optical wavelengths, as well as coordinated observations probing the connection between X-ray and optical pulsations across different stages of the outburst.

12:10 The new SOXS instrument for the ESO NTT: overview and synergies with fast optical photometry - Paolo D'Avanzo
The new SOXS instrument for the ESO NTT: overview and synergies with fast optical photometry - Paolo D'Avanzo
12:10 - 12:30
Room: Aula Gratton SOXS (Son Of X-Shooter) will be a unique spectroscopic facility built by an international consortium for the ESO-NTT 3.6-m telescope in La Silla (Chile). The design foresees a single-object, high-efficiency spectrograph with a resolution-slit product of ~ 4,500, capable of simultaneously observing the complete spectral range 350 - 2000 nm with a good sensitivity and with imaging capabilities in the visible band (ugrizY). It is designed to observe all kind of transients and variable sources over a wide range of time scales with a highly flexible schedule maintained by the consortium, based on the Target of Opportunity concept. SOXS is going to be a fundamental spectroscopic partner for any kind of imaging survey, becoming one of the premier transient follow-up instruments in the Southern hemisphere.

12:30 TDT and synergies with fast optical photometry - Simone Scaringi - REMOTE
TDT and synergies with fast optical photometry - Simone Scaringi - REMOTE
12:30 - 12:50
Room: Aula Gratton

12:50 Quantum Gravity With Pulsars - Luciano Burderi
Quantum Gravity With Pulsars - Luciano Burderi
12:50 - 13:10
Room: Aula Gratton

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