arXiv subjects

Mariafelicia De Laurentis

Publications and source records attributed to Mariafelicia De Laurentis.

At least 19 recordsLinked to original sources

arXiv2026

Probing fundamental physics with ALMA2040 mm-wavelength observations of neutron stars

Bursty or (rotation-induced) pulsed coherent radio emission from pulsars, magnetars, and fast radio transients originates in some of the most extreme environments in the Universe. However, the exact physical mechanism behind the scenes remains poorly understood. ALMA2040 will allow for systematic exploration of the millimeter-wavelength spectral window for pulsars and fast radio transients for the very first time, offering unprecedented opportunities to discover new observational phenomena and advance our understanding of emission physics. Beyond this, ALMA2040 provides a unique means to unveil the neutron-star population in the Galactic Centre (GC), enable novel tests of fundamental physics in the vicinity of the supermassive black hole Sgr A*, probe the potential existence of dark matter in the GC, and investigate the dense, highly dynamic interstellar and magnetic environment of this region.

astro-ph.HE↗

arXiv2026

Broadband multiwavelength properties of the archetypal blazar 3C 279 during the 2017 Event Horizon Telescope campaign

The archetypal blazar 3C 279 hosts a prominent relativistic jet and exhibits strong broadband variability across the electromagnetic spectrum. In April 2017, the Event Horizon Telescope (EHT) observed 3C 279, alongside one of the most extensive quasi-simultaneous multiwavelength (MWL) campaigns ever conducted. With the aim of investigating the physical processes governing 3C 279, we analyzed individual observations and multiband light curves, and constructed a new quasi-simultaneous MWL spectrum. We also performed phenomenological modeling using the turbulent extreme multi-zone (TEMZ) model to constrain the fundamental physical properties of the source. The EHT observations reveal a clear flux increase in the innermost core between April 5 and 11, 2017. Over a broader timescale, radio measurements at longer wavelengths show concurrent enhancements in core flux and polarization around mid-April, coinciding with the ejection of a superluminal knot. Record UV-optical flares with strong polarization variability occurred in late March, followed by gamma-ray activity that declined before the end of the EHT observing period. During this interval, the source remained in a low X-ray state and showed no detectable VHE emission. The TEMZ modeling suggests that the broadband spectrum and variability of 3C 279 can be explained within a jet scenario in which turbulent plasma cells are compressed by a stationary conical shock. However, alternative interpretations, such as magnetic reconnection or a moving shock-in-jet event, remain plausible. This coordinated MWL campaign advances our understanding of the origin of jet and gamma-ray emission in 3C 279, while also providing a comprehensive publicly available dataset that will serve as a valuable reference for future studies.

astro-ph.HE↗

arXiv2026

Comparison of Polarized Radiative Transfer Codes used by the EHT Collaboration

Interpretation of resolved polarized images of black holes by the Event Horizon Telescope (EHT) requires predictions of the polarized emission observable by an Earth-based instrument for a particular model of the black hole accretion system. Such predictions are generated by general relativistic radiative transfer (GRRT) codes, which integrate the equations of polarized radiative transfer in curved spacetime. A selection of ray-tracing GRRT codes used within the EHT collaboration is evaluated for accuracy and consistency in producing a selection of test images, demonstrating that the various methods and implementations of radiative transfer calculations are highly consistent. When imaging an analytic accretion model, we find that all codes produce images similar within a pixel-wise normalized mean squared error (NMSE) of 0.012 in the worst case. When imaging a snapshot from a cell-based magnetohydrodynamic simulation, we find all test images to be similar within NMSEs of 0.02, 0.04, 0.04, and 0.12 in Stokes I, Q, U , and V respectively. We additionally find the values of several image metrics relevant to published EHT results to be in agreement to much better precision than measurement uncertainties.

astro-ph.HE↗

arXiv2026

Dynamics and geometry of the inner sub-parsec-scale jet in 3C 279 observed with the Event Horizon Telescope

The 2021 Event Horizon Telescope observations resolve the innermost jet region of the blazar 3C279 with unprecedented detail. The reconstructed images consistently reveal a compact core elongated nearly orthogonal to the large-scale jet axis. This rarely observed morphology recurs across multiple epochs and from 22-230 GHz and is therefore intrinsic rather than an imaging artifact. Geometric model fitting identifies several components with apparent speeds up to 10c, requiring bulk Lorentz factors greater than 10.3 and constraining viewing angles to extremely small values (smaller than one degree). Rest-frame brightness temperatures are systematically low (between 10^9 and 10^10 K), consistent with optically thin emission at 230 GHz. These results suggest that the jet bends toward the observer on sub-parsec scales, producing strong relativistic beaming. Possible drivers of the observed jet bending and temporal evolution include the jet's interaction with the interstellar medium, kink or Kelvin--Helmholtz instabilities, magnetic reconnection near the horizon, or binary-induced precession. However, the current temporal coverage of VLBI data remains insufficient to distinguish between these mechanisms. Continued multifrequency VLBI monitoring will be essential to constraining the dynamics and geometry of the jet base in 3C279.

astro-ph.GA↗

arXiv2026

VAPOLA -- A multi-year, multi-band polarization survey of AGN and Sgr A* at mm wavelengths with ALMA I. Survey Overview and Science-Ready Archival Products

The Atacama Large Millimeter/submillimeter Array (ALMA) is the most sensitive interferometric array at millimeter and submillimeter wavelengths. Through the ALMA Phasing System (APS), it can participate in global Very Long Baseline Interferometry (VLBI) arrays, enhancing their sensitivity and resolution. However, processing and analzing the ALMA data obtained in APS mode during VLBI observations remains a complex task, requiring specialized expertise and time-consuming calibration and imaging procedures. In this paper, we present VAPOLA-the first online, multi-epoch, multi-band repository of high-level data products from ALMA observations of active galactic nuclei (AGN) and Sgr A* during global VLBI campaigns. Built on an automated pipeline that processes fully calibrated ALMA (QA2) data, generates science-ready products with minimal user intervention. The repository includes fully calibrated interferometric visibilities, full-Stokes images across individual and combined spectral windows, polarimetric and spectral index maps, as well as tabulated polarimetric parameters from visibility-domain polarization fitting. By offering ready-to-use data through a user-friendly web portal, VAPOLA enables non-expert users to perform advanced science analyses without needing in-depth knowledge of ALMA procedures. This resource will facilitate a broad range of scientific investigations, including the characterization of magnetic field properties in accretion flows and relativistic jets, the structure and kinematics of dusty and molecular tori in AGN, and absorption studies of the interstellar medium toward the Galactic Center. In addition, the dataset provides source-integrated parameters and calibration metadata essential for refining VLBI calibration and imaging workflows as well as for placing robust observational constraints on theoretical models of supermassive black holes and their environments.

astro-ph.GA↗

arXiv2026

Shaping the future of Global Interferometric Arrays: Imaging Strong Gravity and Magnetic Fields

The observational validation of General Relativity (GR) has been propelled in recent years by recent breakthroughs in Very Long Baseline Interferometry (VLBI) augmented by ALMA. We explore ALMA2040 opportunities to transform these studies through greatly improved sensitivity and a multi-frequency approach. The focus will be on placing most stringent constraints on GR and alternative theories in the strong-gravity regime, and on understanding the formation and launching of relativistic jets.

astro-ph.IM↗

arXiv2026

Full-polarization millimeter wavelength variability of Sagittarius A* during the 2018 EHT campaign

Sagittarius A* (Srg A*), the supermassive black hole at the center of the Milky Way, provides a unique laboratory to study accretion dynamics and plasma processes near the event horizon. We investigated the variability and polarization properties of Srg A* using ALMA observations during the 2018 Event Horizon Telescope campaign. We analyzed high-cadence full-polarization light curves from ALMA at millimeter wavelengths, performed time-series analysis, and investigated the temporal behavior during an X-ray flare observed by Chandra on 2018 April 24. The variability characteristics are compared with expectations from standard accretion flow models. We find low variability in total intensity ($σ/μ< 10\%$), but significantly higher variability in linear and circular polarization (~ 30% and ~ 50%, respectively). A time-series analysis reveals red-noise variability, with power spectral densities between -2 and -3 across all Stokes parameters. Polarized intensity shows stable intra-day timescales, while total intensity exhibits more variable timescales, suggesting distinct emission regions, with polarization likely arising from a coherent structure. On April 24, a statistically significant inter-band delay in polarized intensity coincides with a near-simultaneous X-ray and millimeter peak that deviates from the typical delayed flare scenario. This event also features enhanced millimeter variability and coherent polarization loop evolution. The observed simultaneity challenges standard models of transient synchrotron emission with cooling delays, favoring instead a scenario of continuous energy injection in an optically thin region. Our results offer new constraints on the physical mechanisms driving variability in Srg A*, and provide key observational input for refining theoretical models of accretion and plasma behavior in the vicinity of supermassive black holes.

astro-ph.GA↗

arXiv2026

Ring Asymmetry and Spin in M87*

Event Horizon Telescope (EHT) images of the supermassive black hole M87* depict an asymmetric ring of emission. General relativistic magnetohydrodynamic (GRMHD) models of M87* and its accretion disk predict that the amplitude and location of the ring's peak brightness asymmetry should fluctuate due to turbulence in the source plasma. We compare the observed distribution of brightness asymmetry amplitudes to the simulated distribution in GRMHD models, across varying black hole spin $a_{*}$. We show that, for strongly magnetized (MAD) models, three epochs of EHT data marginally disfavor $|a_{*}| \lesssim 0.2$. This is consistent with the Blandford-Znajek model for M87's jet, which predicts that M87* should have nonzero spin. We show quantitatively how future observations could improve spin constraints, and discuss how improved spin constraints could distinguish between differing jet-launching mechanisms and black hole growth scenarios.

astro-ph.HE↗

arXiv2026

Expanding the Horizon of Black Hole Imaging with AtLAST

The Event Horizon Telescope (EHT) has directly resolved and imaged two supermassive black holes and opening a new window on black hole physics. However, the current array is limited to only these two brightest nearby targets. This white paper outlines how future EHT upgrades, anchored by the Atacama Large Aperture Submillimeter Telescope (AtLAST), will enable a transformative expansion of the accessible population of event-horizon-scale sources. By substantially improving sensitivity and multi-frequency capabilities, EHT+AtLAST will enable demographic studies of black hole growth, accretion physics, and jet launching across a wide range of masses, environments, and accretion states.

astro-ph.IM↗

arXiv2026

Locating the missing large-scale emission in the jet of M87* with short EHT baselines

In Very-Long Baseline Interferometric arrays, nearly co-located stations probe the largest scales and typically cannot resolve the observed source. In the absence of large-scale structure, closure phases constructed with these stations are zero and, since they are independent of station-based errors, they can be used to probe data issues. Here, we show with an expansion about co-located stations, how these trivial closure phases become non-zero with brightness distribution on smaller scales than their short baseline would suggest. When applied to sources that are made up of a bright compact and large-scale diffuse component, the trivial closure phases directly measure the centroid relative to the compact source and higher-order image moments. We present a technique to measure these image moments with minimal model assumptions and validate it on synthetic Event Horizon Telescope (EHT) data. We then apply this technique to 2017 and 2018 EHT observations of M87* and find a weak preference for extended emission in the direction of the large-scale jet. We also apply it to 2021 EHT data and measure the source centroid about 1 mas northwest of the compact ring, consistent with the jet observed at lower frequencies.

astro-ph.HE↗

arXiv2025

Probing jet base emission of M87* with the 2021 Event Horizon Telescope observations

We investigate the presence and spatial characteristics of the jet base emission in M87* at 230 GHz, enabled by the enhanced uv coverage in the 2021 Event Horizon Telescope (EHT) observations. The addition of the 12-m Kitt Peak Telescope and NOEMA provides two key intermediate-length baselines to SMT and the IRAM 30-m, giving sensitivity to emission structures at scales of $\sim250~μ$as and $\sim2500~μ$as (0.02 pc and 0.2 pc). Without these baselines, earlier EHT observations lacked the capability to constrain emission on large scales, where a "missing flux" of order $\sim1$ Jy is expected. To probe these scales, we analyzed closure phases, robust against station-based gain errors, and modeled the jet base emission using a simple Gaussian offset from the compact ring emission at separations $>100~μ$as. Our analysis reveals a Gaussian feature centered at ($Δ$RA $\approx320~μ$as, $Δ$Dec $\approx60~μ$as), a projected separation of $\approx5500$ AU, with a flux density of only $\sim60$ mJy, implying that most of the missing flux in previous studies must arise from larger scales. Brighter emission at these scales is ruled out, and the data do not favor more complex models. This component aligns with the inferred direction of the large-scale jet and is consistent with emission from the jet base. While our findings indicate detectable jet base emission at 230 GHz, coverage from only two intermediate baselines limits reconstruction of its morphology. We therefore treat the recovered Gaussian as an upper limit on the jet base flux density. Future EHT observations with expanded intermediate-baseline coverage will be essential to constrain the structure and nature of this component.

astro-ph.HE↗

arXiv2025

Stellar Objects From Quantum Gravity

This paper explores the theoretical implications of quantum gravity by analyzing compact stellar objects, presenting three distinct models that serve as alternatives to traditional black holes. These models are characterized by their extreme compactness and incorporation of a quantum core, successfully avoiding the curvature singularities typically associated with classical general relativity. Central to these models is the noncommutative parameter, which plays a crucial role in determining stellar properties and enables the exploration of various astrophysical regimes. While pure Planckian effects pose significant challenges for observational detection, our findings suggest that lower energy scales may reveal exotic stellar objects with Earth and Sun-like masses that lack classical counterparts, potentially providing the first experimental evidence of non-classical gravity. We propose that the metrics derived in this study can be tested against known neutron stars, offering promising avenues for future research aimed at understanding the interplay between quantum effects in gravity and stellar evolution, ultimately enhancing our comprehension of the universe's fundamental properties.

gr-qc↗

arXiv2025

Gravitational signatures beyond Newton: exploring hierarchical three-body dynamics

Hierarchical three-body systems offer a compelling framework to explore the subtle interplay between Newtonian and relativistic gravitational effects in astrophysical environments. In this work, we investigate post-Newtonian corrections to the periastron shift within such systems, focusing on the impact of orbital eccentricity. Modeling the secondary body's influence as a quadrupolar perturbation, we compare Newtonian, Schwarzschild, and post-Newtonian quadrupolar contributions to orbital precession. Our analysis demonstrates that Newtonian quadrupolar effects could be observable, for a long monitoring time, in the orbit of the S87 star around Sagittarius A* if an intermediate-mass black hole is present, under the assumptions of our model. Additionally, post-Newtonian quadrupolar corrections may influence the dynamics of small Solar System bodies in the presence of massive companions. Although the predicted effects are minute and require long monitoring periods to be measurable, our analysis clarifies how relativistic corrections enter the dynamics of the third body and outlines the conditions under which future observations could reveal them.

gr-qc↗

arXiv2025

Time Delay of Pulsar Signals in Astrophysical Black Hole Spacetimes

In this paper, we investigate the fully relativistic time delay of pulsar signals propagating in the vicinity of a rotating black hole and its potential mimickers, including a deformed Kerr black hole and the Janis-Newman-Winicour naked singularity. We aim to compute and compare the pulsar time delays caused by different spacetime geometries to explore possible observational signatures that distinguish between black holes and their alternatives. We begin by solving the equations of motion for null geodesics in these background geometries. Subsequently, we address the emitter-observer problem to compute the time delay of pulsar signals in Kerr, deformed Kerr, and JNW spacetimes. A comparative analysis between Schwarzschild and Kerr black holes allows us to observe the effect of spin on propagation delay in pulsar timing. Further, we examine the impact of the deformation parameter in the deformed Kerr black hole and the influence of the scalar field on the rotating JNW spacetime. Our study considers both direct and indirect photons emitted by a source in the equatorial circular orbit. We find that the variations in the spin parameter show very small but detectable changes when we compare the time delay cases of a Kerr black hole with deformed Kerr and rotating JNW spacetimes. Our pulsar time delay results suggest a potential observable distinguishing feature of these astrophysical black hole geometries which could be useful for the forthcoming observational facilities such as Square Kilometer Array Observatory, Five-hundred-meter Aperture Spherical Telescope and Event Horizon Telescope.

gr-qc↗

arXiv2025

Origin of the ring ellipticity in the black hole images of M87*

We investigate the origin of the elliptical ring structure observed in the images of the supermassive black hole M87*, aiming to disentangle contributions from gravitational, astrophysical, and imaging effects. Leveraging the enhanced capabilities of the Event Horizon Telescope (EHT) 2018 array, including improved $(u,v)$-coverage from the Greenland Telescope, we measure the ring's ellipticity using five independent imaging methods, obtaining a consistent average value of $τ= 0.08_{-0.02}^{+0.03}$ with a position angle $ξ= 50.1_{-7.6}^{+6.2}$ degrees. To interpret this measurement, we compare against General Relativistic Magnetohydrodynamic (GRMHD) simulations spanning a wide range of physical parameters including thermal or non-thermal electron distribution function, spins, and ion-to-electron temperature ratios in both low and high-density regions. We find no statistically significant correlation between spin and ellipticity in GRMHD images. Instead, we identify a correlation between ellipticity and the fraction of non-ring emission, particularly in non-thermal models and models with higher jet emission. These results indicate that the ellipticity measured from the \m87 emission structure is consistent with that expected from simulations of turbulent accretion flows around black holes, where it is dominated by astrophysical effects rather than gravitational ones. Future high-resolution imaging, including space very long baseline interferometry and long-term monitoring, will be essential to isolate gravitational signatures from astrophysical effects.

astro-ph.HE↗

arXiv2025

Future prospects for measuring 1PPN parameters using observations of S2 and S62 at the Galactic Center

The Parameterized Post-Newtonian (PPN) formalism offers an agnostic framework for evaluating theories of gravity that extend beyond General Relativity. Departures from General Relativity are represented by a set of dimensionless parameters that, at the first order in the expansion, reduce to $β$ and $γ$, which describe deviations in spatial curvature and non-linear superposition effects of gravity, respectively. We exploit future observations of stars at the Galactic Center, orbiting the supermassive black hole Sagittarius A*, to forecast the ability to constrain the first-order PPN parameters $γ$ and $β$. We have generated a mock catalog of astrometric and spectroscopic data for S2, based on the Schwarzschild metric, simulating observations over multiple orbital periods with the GRAVITY and SINFONI instruments. Our analysis includes the effects of relativistic orbital precession and line-of-sight (LOS) velocity gravitational redshift. Since future data for S2 can provide constraints only on a linear combination of the PPN parameters $β$ and $γ$ we also analyzed the impact of future observations of the gravitational lensing for stars that pass closer in the sky to Sgr A*, like the known star S62, which can potentially provide tight constraints on the parameter $γ$, that alone regulates the amplitude of the astrometric deviations due to lensing. When combining lensing observations for S62, and the precise orbital tracking of S2, one obtains independent constraints on both $γ$ (with a potential precision as good as $\sim 1\%$) and $β$ (with a corresponding precision of $\sim 2\%$), providing a precision test of General Relativity and its extensions.

astro-ph.GA↗

arXiv2025

The putative center in NGC 1052

Many active galaxies harbor powerful relativistic jets, however, the detailed mechanisms of their formation and acceleration remain poorly understood. To investigate the area of jet acceleration and collimation with the highest available angular resolution, we study the innermost region of the bipolar jet in the nearby low-ionization nuclear emission-line region (LINER) galaxy NGC 1052. We combined observations of NGC 1052 taken with VLBA, GMVA, and EHT over one week in the spring of 2017. For the first time, NGC 1052 was detected with the EHT, providing a size of the central region in-between both jet bases of 250 RS (Schwarzschild radii) perpendicular to the jet axes. This size estimate supports previous studies of the jets expansion profile which suggest two breaks of the profile at around 300 RS and 10000 RS distances to the core. Furthermore, we estimated the magnetic field to be 1.25 Gauss at a distance of 22 μas from the central engine by fitting a synchrotron-self absorption spectrum to the innermost emission feature, which shows a spectral turn-over at about 130 GHz. Assuming a purely poloidal magnetic field, this implies an upper limit on the magnetic field strength at the event horizon of 26000 Gauss, which is consistent with previous measurements. The complex, low-brightness, double-sided jet structure in NGC 1052 makes it a challenge to detect the source at millimeter (mm) wavelengths. However, our first EHT observations have demonstrated that detection is possible up to at least 230 GHz. This study offers a glimpse through the dense surrounding torus and into the innermost central region, where the jets are formed. This has enabled us to finally resolve this region and provide improved constraints on its expansion and magnetic field strength.

astro-ph.HE↗

arXiv2025

A multi-frequency study of sub-parsec jets with the Event Horizon Telescope

The 2017 observing campaign of the Event Horizon Telescope (EHT) delivered the first very long baseline interferometry (VLBI) images at the observing frequency of 230 GHz, leading to a number of unique studies on black holes and relativistic jets from active galactic nuclei (AGN). In total, eighteen sources were observed: the main science targets, Sgr A* and M87 along with various calibrators. We investigated the morphology of the sixteen AGN in the EHT 2017 data set, focusing on the properties of the VLBI cores: size, flux density, and brightness temperature. We studied their dependence on the observing frequency in order to compare it with the Blandford-Königl (BK) jet model. We modeled the source structure of seven AGN in the EHT 2017 data set using linearly polarized circular Gaussian components and collected results for the other nine AGN from dedicated EHT publications, complemented by lower frequency data in the 2-86 GHz range. Then, we studied the dependences of the VLBI core flux density, size, and brightness temperature on the frequency measured in the AGN host frame. We compared the observations with the BK jet model and estimated the magnetic field strength dependence on the distance from the central black hole. Our results indicate a deviation from the standard BK model, particularly in the decrease of the brightness temperature with the observing frequency. Either bulk acceleration of the jet material, energy transfer from the magnetic field to the particles, or both are required to explain the observations.

astro-ph.HE↗