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DeepHMC : a deep-neural-network acclerated Hamiltonian Monte Carlo algorithm for binary neutron star parameter estimation
No full textInternational audienceWe present a deep neural network (DNN) accelerated Hamiltonian Monte Carlo (HMC) algorithm called DeepHMC for the inference of binary neutron star systems. The HMC is a non-random walk sampler that uses background gradient information to accelerate the convergence of the sampler. While faster converging than a random-walk sampler, in theory by a factor of the dimensionality of the problem, a known computational bottleneck for HMC algorithms is the calculation of gradients of the log-likelihood. We demonstrate that Hamiltonian trajectories based on a DNN gradients are 30 times faster than those based on the relative binning gradients, and 7000 times faster than trajectories based on a naive likelihood gradient calculation. Using the publicly available 128 second LVK data set for the binary neutron star mergers GW170817 and GW190425, we show that not only does DeepHMC produce produces highly accurate and consistent results with the LVK public data, but acquires 5000 statistically independent samples (SIS) in the parameter space in approximately two hours on a Macbook pro for GW170817, with a cost of second/SIS, and 2.5 days for GW190425, with a cost of seconds/SIS
Numerical Simulations for Optimizing Small Satellite Constellations for TGF Studies
No full textInternational audienceThe detection of Terrestrial Gamma ray Flashes (TGFs) from space is mostly made by astrophysics satellites, which only provide single-point measurements. Future TGF missions could consist in performing simultaneous detection by a detector array in space. In order to prepare such a scientific objective, we simulate the detection of TGFs by a nanosatellite, or small satellite, constellation. The objective is to quantify the impact of six parameters defining such a constellation, in order to maximize the scientific return of the mission. The parameters characterized in this work are the number of satellites, their relative distance, their altitude, their orbital configuration, the effective detection surface, and their orbital inclination. We use a Monte Carlo simulation code to propagate photons in the atmosphere and simulate the satellite positions and photons hits on satellites. Finally, we quantify the number of TGFs detected by the fleet, multi-detected, the number of photons received, and draw conclusions about the impact of each parameter
Robust direction-dependent gain-calibration of beam-modelling errors far from the target field
No full textInternational audienceMany astronomical questions require deep, wide-field observations at low radio frequencies. Phased arrays like LOFAR and SKA-low are designed for this, but have inherently unstable element gains, leading to time, frequency and direction-dependent gain errors. Precise direction-dependent calibration of observations is therefore key to reaching the highest possible dynamic range. Many tools for direction-dependent calibration utilise sky and beam models to infer gains. However, these calibration tools struggle with precision calibration for relatively bright (e.g. A-team) sources far from the beam centre. Therefore, the point-spread-function of these sources can potentially obscure a faint signal of interest. We show that, and why, the assumption of a smooth gain solution per station fails for realistic radio interferometers, and how this affects gain-calibration results. Subsequently, we introduce an improvement for smooth spectral gain constraints for direction-dependent gain-calibration algorithms, in which the level of regularisation is weighted by the expected station response to the sky model. We test this method using direction-dependent calibration method DDECal and physically-motivated beam modelling errors for LOFAR-HBA stations. The new method outperforms the standard method for various calibration settings near nulls in the beam, and matches the standard inverse-variance-weighted method's performance for the remainder of the data. The proposed method is especially effective for short baselines, both in visibility and image space. Improved direction-dependent gain-calibration is critical for future high-precision SKA-low observations, where higher sensitivity, increased antenna beam complexity, and mutual coupling call for better off-axis source subtraction, which may not be achieved through improved beam models alone
Holomorphic Discrete Series of SU(1,1): Orthogonality Relations, Character Formulas, and Multiplicities in Tensor Product Decompositions
No full textInternational audienceThe SU group plays a fundamental role in various areas of physics, including quantum mechanics, quantum optics, and representation theory. In this work we revisit the holomorphic discrete series representations of SU, with a focus on orthogonality relations for matrix elements, character formulas of unitary irreducible representations (UIRs), and the decomposition of tensor products of these UIRs. Special attention is given to the structure of these decompositions and the associated multiplicities, which are essential for understanding composite systems and interactions within SU symmetry frameworks. These findings offer deeper insights into the mathematical foundations of SU representations and their significance in theoretical physics
Limits on the Ejecta Mass During the Search for Kilonovae Associated with Neutron Star-Black Hole Mergers: A case study of S230518h, GW230529, S230627c and the Low-Significance Candidate S240422ed
No full textInternational audienceNeutron star-black hole (NSBH) mergers, detectable via their gravitational-wave (GW) emission, are expected to produce kilonovae (KNe). Four NSBH candidates have been identified and followed-up by more than fifty instruments since the start of the fourth GW Observing Run (O4), in May 2023, up to July 2024; however, no confirmed associated KN has been detected. This study evaluates ejecta properties from multi-messenger observations to understand the absence of detectable KN: we use GW public information and joint observations taken from 05.2023 to 07.2024 (LVK, ATLAS, DECam, GECKO, GOTO, GRANDMA, SAGUARO, TESS, WINTER, ZTF). First, our analysis on follow-up observation strategies shows that, on average, more than 50% of the simulated KNe associated with NSBH mergers reach their peak luminosity around one day after merger in the - bands, which is not necessarily covered for each NSBH GW candidate. We also analyze the trade-off between observation efficiency and the intrinsic properties of the KN emission, to understand the impact on how these constraints affect our ability to detect the KN, and underlying ejecta properties for each GW candidate. In particular, we can only confirm the kilonova was not missed for 1% of the GW230529 and S230627c sky localization region, given the large sky localization error of GW230529 and the large distance for S230627c and, their respective KN faint luminosities. More constraining, for S230518h, we infer the dynamical ejecta and post-merger disk wind ejecta . Similarly, the non-astrophysical origin of S240422ed is likely further confirmed by the fact that we would have detected even a faint KN at the time and presumed distance of the S240422ed event candidate, within a minimum 45% credible region of the sky area, that can be larger depending on the KN scenario
Axial perturbations of black holes with primary scalar hair
No full textInternational audienceWe study axial perturbations of static black holes with primary hair in a family of degenerate higher-order scalar-tensor (DHOST) theories. These solutions possess a scalar charge, fully independent of the mass, leading to a continuous one-parameter deformation of the standard Schwarzschild black hole. Starting from these solutions, we also construct new black holes, solutions of other DHOST theories, obtained via disformal transformations of the metric. In particular, we investigate two specific types of disformal transformations: the first leading to a theory where gravitational waves propagate at the speed of light, the second to a Horndeski theory, where the equations of motion remain second order. The dynamics of axial perturbations can be formally related to the general relativistic equations of motion of axial perturbations in an effective metric. The causal structure of the effective metric differs from that of the background metric, leading to distinct gravitational and luminous horizons. Using a WKB approximation, we compute the quasi-normal modes for the Schrödinger-like equation associated with the effective metric outside the gravitational horizon
Broad line region echo from rapidly accreting intermediate-mass black hole candidate SDSS J144850.08+160803.1. The first probe of intra-night variability and reverberation mapping
No full textInternational audienceContext. Elusive intermediate-mass black holes (IMBHs; ) can act as ``time-squeezing'' machines, enabling studies of AGN geometry through reverberation mapping (RM) on much shorter timescales than their supermassive siblings. Aims. The broad line region (BLR) radius constraints for IMBH candidates with different Eddington ratios probe the unexplored faint end of radius--luminosity () relations and allow us to build a robust estimator. This study aims to (a) confirm a rapidly accreting IMBH candidate; (b) demonstrate the feasibility of the first photometric BLR reverberation mapping (RM) campaign for this class of objects. Methods. The IMBH candidate J1448+16 was identified in the broad H-selected spectroscopic sample from SDSS. We carried out narrow-band H and broad-band SDSS~g~́monitoring to check small-scale variability and extract the time lag between the BLR and accretion disk (AD) continuum during 5 months (March--July 2024) using a 60-cm telescope at the Caucasus Mountain Observatory. Results. We confirmed the candidate as an active IMBH using XMM-Newton as a bright X-ray point source with the photon index , suggesting the high accretion rate. From a combination of SDSS optical spectra and XMM-Newton observations, we estimate the black hole mass in the range and the Eddington rate from . We report high-amplitude intra-night (~h) H variability in this highly accreting IMBH. In addition, we extracted a tentative measurement of a BLR RM radius . Conclusions. This work is a proof of concept for further IMBH variability studies and BLR RM campaigns, which will be essential for the calibration of the relation at the faint end
Euclid Quick Data Release (Q1). The active galaxies of Euclid
No full textInternational audienceWe present a catalogue of candidate active galactic nuclei (AGN) in the Quick Release (Q1) fields. For each source we collect multi-wavelength photometry and spectroscopy information from Galaxy Evolution Explorer (GALEX), , Dark Energy Survey (DES), Wise-field Infrared Survey Explorer (WISE), , Dark Energy Survey (DESI), and Sloan Digital Sky Survey (SDSS), including spectroscopic redshift from public compilations. We investigate the AGN contents of the Q1 fields by applying selection criteria using colours and WISE-AllWISE cuts finding respectively 292,222 and 65,131 candidates. We also create a high-purity QSO catalogue based on DR3 information containing 1971 candidates. Furthermore, we utilise the collected spectroscopic information from DESI to perform broad-line and narrow-line AGN selections, leading to a total of 4392 AGN candidates in the Q1 field. We investigate and refine the Q1 probabilistic random forest QSO population, selecting a total of 180,666 candidates. Additionally, we perform SED fitting on a subset of sources with available , and by utilizing the derived AGN fraction, we identify a total of 7766 AGN candidates. We discuss purity and completeness of the selections and define two new colour selection criteria (_ and _) to improve on purity, finding 313,714 and 267,513 candidates respectively in the Q1 data. We find a total of 229,779 AGN candidates equivalent to an AGN surface density of 3641 deg for , and a subsample of 30,422 candidates corresponding to an AGN surface density of 482 deg when limiting the depth to . The surface density of AGN recovered from this work is in line with predictions based on the AGN X-ray luminosity functions
The Atacama Cosmology Telescope: DR6 Maps
No full textInternational audienceWe present Atacama Cosmology Telescope (ACT) Data Release 6 (DR6) maps of the Cosmic Microwave Background temperature and polarization anisotropy at arcminute resolution over three frequency bands centered on 98, 150 and 220 GHz. The maps are based on data collected with the AdvancedACT camera over the period 2017--2022 and cover 19,000 square degrees with a median combined depth of 10 uK arcmin. We describe the instrument, mapmaking and map properties and illustrate them with a number of figures and tables. The ACT DR6 maps and derived products are available on LAMBDA at https://lambda.gsfc.nasa.gov/product/act/actadv_prod_table.html. We also provide an interactive web atlas at https://phy-act1.princeton.edu/public/snaess/actpol/dr6/atlas and HiPS data sets in Aladin (e.g. https://alasky.cds.unistra.fr/ACT/DR4DR6/color_CMB)