arXiv subjects

Carlos O. Lousto

Publications and source records attributed to Carlos O. Lousto.

At least 19 recordsLinked to original sources

arXiv2026

Jet variability in small mass ratio supermassive black hole binaries

We present three-dimensional general relativistic magnetohydrodynamic simulations of a precessing supermassive black hole binary with mass ratio q=1/7, embedded in a circumbinary disk. We investigate how dynamics within the binary cavity launch and shape a relativistic jet to thousands of gravitational radii. The primary black hole dominates both accretion and jet power, while the smaller black hole repeatedly crosses and shocks the inner accretion flow. These passages of the secondary drive magnetized gas alternately into the upper and lower jet funnels, producing disturbances that propagate outward as quasi-periodic outflows. Although the inner flow is perturbed twice per orbit, each jet lobe shows one dominant outflow per orbit. On longer timescales, the jet precesses, reverses its magnetic handedness, and undergoes two weak phases. The first results from a reorientation of the primary spin and is followed, after the jet recovers, by a reversal in the circulation of the projected magnetic field. The second weak phase occurs as the secondary's orbit becomes nearly coplanar with the circumbinary disk, reducing the gas and magnetic flux reaching the primary. Together, these results connect cavity dynamics to large-scale jet variability and predict a set of correlated jet signatures whose relative timing and causal ordering may provide stronger evidence for a small-mass-ratio supermassive black hole binary than any one feature alone.

astro-ph.HE↗

arXiv2026

Accretion, Jets, and Recoil in a Merging Supermassive Black Hole Binary: A Prompt Electromagnetic Postmerger Counterpart for LISA

We report the first three-dimensional general relativistic magnetohydrodynamic simulation to follow, self-consistently in a dynamical spacetime, the magnetized gas around a misaligned-spin supermassive binary black hole, from late inspiral through merger to the gravitational-wave recoil of the remnant. The equal-mass binary, in a $\textit{hang-up kick}$ configuration, is embedded in an equilibrated circumbinary disk (CBD), relaxed for 165 binary orbits before we evolve the final $\sim\!40$ orbits. During the inspiral, each black hole hosts a strongly warped minidisk whose jet follows the local spin axis near the horizon before aligning with the binary's angular momentum farther out. The merger imparts a recoil of $\simeq\!1032$ $km\,s$$^{-1}$ to the remnant, which nonetheless retains its gravitationally bound CBD, and the relaunched jet preserves its pre-merger orientation. The bolometric luminosity brightens by a factor $\sim\!2.2$, powered by merger-driven shocks concentrated within $r \lesssim 15\,M$, and the enhancement persists through the recoil. We identify a distinctive postmerger electromagnetic signature: magnetized structures, generated at coalescence, drive correlated quasi-periodic modulations of the horizon magnetic flux, the Poynting flux, and the thermal output, decoupled from the accretion rate. The postmerger radiative efficiency $L_{\rm EM}/\dot{M}c^2$ rises by a factor $\simeq 2.6$ at nearly constant accretion rate, showing that this emission is powered by the merger rather than accretion. The transient turns on within minutes and lasts at least several hours for a $10^6 \ M_{\odot}$ LISA source, establishing recoiling remnants as prompt postmerger counterparts to massive black hole mergers and a first-principles framework for interpreting candidates such as 3C186.

astro-ph.GA↗

arXiv2026

Single-pulse reanalysis of the 2024 Vela glitch and new observations of PSR~J0437$-$4715 and PSR~J1644$-$4559

The Pulsar Monitoring in Argentina (PuMA) collaboration systematically monitors southern glitching pulsars, maintaining high-cadence single-pulse records of the Vela pulsar. We present a pulse-per-pulse reanalysis of the 2024 major glitch of Vela (PSR~J0835$-$4510) with the 400~MHz-bandwidth ROACH backend of the Argentine Institute of Radioastronomy, and extend our machine-learning single-pulse pipeline---Isolation Forest outlier rejection, $β$-Variational-AutoEncoder denoising, and Self-Organizing-Map clustering---to new observations of PSR~J1644$-$4559 and the millisecond pulsar PSR~J0437$-$4715. For Vela, the 4- and 6-cluster decompositions of the eight days bracketing the glitch reproduce, with seven times the previous bandwidth, the behavior found with the narrow-band ETTUS receivers: higher-amplitude clusters peak earlier in phase, are narrower, more skewed, and less populated. With the glitch jump and its two exponential recovery terms included in the timing solution, the mean profile is stable to 1\% across all eight days (width change $-0.5\pm0.9$\% from pre- to post-glitch); omitting the recovery terms would mimic a post-glitch broadening of up to 55\% through a folding-frequency error at the $10^{-7}$ level. The clusters of PSR~J1644$-$4559 differ almost exclusively in amplitude, as expected for a scattering-dominated profile. For PSR~J0437$-$4715, retaining the 10\% of pulses with the highest peak-dominance score doubles the signal-to-noise ratio, and a five-cluster decomposition yields narrow, phase-ordered groups a factor $3.6\pm0.4$ narrower than the average profile, suggesting a $\sim$3.5-fold improvement in cluster-based timing precision for this pulsar-timing-array target, to be confirmed in a follow-up paper.

astro-ph.HE↗

arXiv2026

First fast radio burst search campaign at the Argentine Institute of Radio Astronomy

Fast radio bursts (FRBs) are intense millisecond-duration radio transients of extragalactic origin whose physical nature remains under active investigation, and which also serve as probes of the intergalactic medium. We report on the first FRB search campaign carried out at the Argentine Institute of Radio Astronomy (IAR) between December 2024 and March 2026, targeting nearby galaxy superclusters in the southern sky. We observed fields in the Ophiuchus, Shapley, and Sculptor/Phoenix supercluster regions with one of the two 30~m antennas of the IAR, using a ROACH-based backend with 400~MHz of bandwidth centred at 1400~MHz and a time resolution of 41--82~$μ$s, for a total net observing time of 212~h. The data were searched for dispersed single pulses with \texttt{PRESTO} in the dispersion measure range $100 \leq \mathrm{DM} \leq 500$, and candidates were classified with the FETCH machine learning classifier. The pipeline was validated on archival Parkes data containing known FRBs and on synthetic bursts injected into IAR observations. One FRB candidate, FRB~20251018, was identified on 18 October 2025 in an observation pointed towards the galaxy cluster A2870, in the Phoenix supercluster, with a dispersion measure of $243$, a signal-to-noise ratio of 8.2, and a FETCH probability of $p=0.99$. To the best of our knowledge, this would be the first FRB detected from South America. A set of more marginal candidates is also presented. These results demonstrate the capability of the IAR antennas to detect FRBs and support the continuation and extension of the monitoring campaign, including coincident dual-antenna observations and cross-matches with gravitational-wave events and electromagnetic transients.

astro-ph.HE↗

arXiv2026

Antikick Relation in High-Energy Head-On Collisions of Spinning Black Holes

The collision of black holes at relativistic speeds probes gravity in its most extreme dynamical regime. While the maximum gravitational recoil from \emph{grazing} high-energy collisions ($\approx28\,562$~km/s, i.e., $\sim0.1c$) and the maximum radiated energy $E_{\rm rad}$ and remnant spin $α_f^{\max}$ from such encounters ($E_{\rm rad}/M_{\rm ADM}\approx32\%$ where $M_{\rm ADM}$ is the ADM mass, and $α_f^{\max}\approx0.987$) have been established previously~\cite{Healy:2022jbh,Healy:2024lhl}, here we focus on the \emph{head-on} high-energy collision of equal-mass spinning black holes and on the detailed structure of the resulting recoil. Performing a sequence of full numerical simulations for spin magnitudes $s=0.5,0.65$, and $0.8$ over a range of initial momenta $γv$, we characterize the peak recoil $V_p$, the final recoil $V_f$, and the antikick $ΔV\equiv V_f-V_p$, and we provide phenomenological fits of their dependence on $γv$ and $s$. We complement these results with a zero-frequency-limit (ZFL) analysis of the radiated energy and momentum, a quasinormal-mode model of the antikick, and a superposed boosted double-Kerr close-limit estimate. We find that in the relativistic regime ($γv>1$) the peak and final recoil are directly proportional, $V_p\approx7.4\,V_f$ (equivalently $ΔV \approx-6.4\,V_f$), largely independent of both the initial momentum and the spin magnitude, pointing to a common post-merger relaxation. While the ZFL predicts a leading linear-in-spin dependence, the close-limit analysis predicts a leading $s^3$ dependence of the recoil amplitude; with the three spin magnitudes studied here the empirical exponent is $s^{1.27\pm0.08}$, motivating an even higher energy collision spin sequence study.

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arXiv2026

The Fifth RIT Catalog of Binary Black Hole Simulations: Multiple-Resolution Studies of Eccentric Orbits

This fifth release of the RIT public catalog of numerical relativity binary black hole waveforms http://ccrg.rit.edu/~RITCatalog introduces an additional 248 configurations, prioritizing 197 newly simulated eccentric orbits. This update brings the catalog to a total of 2129 cases. All waveforms are corrected for center-of-mass drift and extrapolated to future null infinity. To rigorously estimate waveform errors, we conduct multiple-resolution convergence studies on 10 eccentric simulations (up to 33 orbits to merger) using three global resolutions increasing by factors of 1.2, plus a comprehensive six-resolution study for a single 18-orbit configuration. We evaluate waveform accuracy by computing mismatches against theoretical infinite-resolution extrapolations. Additionally, we analyze the convergence properties of key physical observables: merger times, number of orbits, final masses, final spins, recoil velocities, and the peak amplitude, frequency, and luminosity of the gravitational radiation.

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arXiv2026

Parameter Estimation with Targeted Eccentric Numerical-Relativity Simulations for GW200208_22 and GW190620

We have analyzed LVK gravitational wave events that show some evidence of eccentricity from TEOBResumS modeling parameter estimations and have confronted them independently with full numerical generated waveforms from our bank of nearly two thousand simulations of binary black holes. We have used RIFT for Bayesian parameter estimation and found that GW200208_22 KDE estimates favor eccentricities $e_{20} = 0.198_{-0.180}^{+0.119}$ upon entering the LVK band at $\sim20$Hz within a $90\%$ confidence interval. Within this event analysis we employed 42 new targeted full numerical relativity simulations and we have thus found a top improved likelihood $\ln\mathcal{L}$ matching waveform, compared to model-based analysis, with an estimated eccentricity at 20Hz, $e_{20}=0.200$, thus reinforcing the eccentric hypothesis of the binary. We have also used our full bank of numerical waveforms on GW190620 finding that the KDE estimate favors eccentricities at 10 Hz in $e_{10}=0.190_{-0.186}^{+0.046}$. New specifically targeted simulations will be required to narrow these eccentricity ranges.

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arXiv2026

Waveform Modelling for the Laser Interferometer Space Antenna

LISA, the Laser Interferometer Space Antenna, will usher in a new era in gravitational-wave astronomy. As the first anticipated space-based gravitational-wave detector, it will expand our view to the millihertz gravitational-wave sky, where a spectacular variety of interesting new sources abound: from millions of ultra-compact binaries in our Galaxy, to mergers of massive black holes at cosmological distances; from the beginnings of inspirals that will venture into the ground-based detectors' view to the death spiral of compact objects into massive black holes, and many sources in between. Central to realising LISA's discovery potential are waveform models, the theoretical and phenomenological predictions of the pattern of gravitational waves that these sources emit. This white paper is presented on behalf of the Waveform Working Group for the LISA Consortium. It provides a review of the current state of waveform models for LISA sources, and describes the significant challenges that must yet be overcome.

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arXiv2025

The maximum radiated energy and final spin of high speed collision of two black holes

We performed a series of 769 full numerical simulations of high energy collision of black holes to search for the maximum gravitational energy emitted $E_{rad}$, during their merger. We consider equal mass binaries with spins pointing along their orbital angular momentum $\vec{L}$ and perform a search over impact parameters $b$ and initial linear momenta $p/m=γv$ to find the maximum $E_{rad}$ for a given spin $\vec{S}$. The total radiated energy proves to have a weak dependence on the intrinsic spin $s$ of the holes, for the sequence $s=+0.8, 0.0, -0.8$ studied here. We thus estimate the maximum $E_{rad}^{max}/M_{ADM}\approx32\%\pm2\%$ for these direct merger encounters. We also explore the radiated angular momentum and the maximum spin of the merger remnant (within these configurations), finding $α_f^{max}=0.987$. We then use the zero frequency limit expansion to analytically model the radiated energy in the small impact parameter and large initial linear momentum regime.

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arXiv2025

Study of the 2024 major Vela glitch at the Argentine Institute of Radioastronomy

We report here on new results of the systematic monitoring of southern glitching pulsars at the Argentine Institute of Radioastronomy. In particular, we study in this work the new major glitch in the Vela pulsar (PSR J0835$-$4510) that occurred on 2024 April 29. We aim to thoroughly characterise the rotational behaviour of the Vela pulsar around its last major glitch and investigate the statistical properties of its individual pulses around the glitch. We characterise the rotational behaviour of the pulsar around the glitch through the pulsar timing technique. We measured the glitch parameters by fitting timing residuals to the data collected during the days surrounding the event. In addition, we study Vela individual pulses during the days of observation just before and after the glitch. We selected nine days of observations around the major glitch on 2024 April 29 and studied their statistical properties with the Self-Organizing Maps (SOM) technique. We used Variational AutoEncoder (VAE) reconstruction of the pulses to separate them clearly from the noise. We obtain a precise timing solution for the glitch. We find two recovery terms of $\sim 3~\mathrm{days}$ and $\sim 17~\mathrm{days}$. We find a correlation of high amplitude with narrower pulses while not finding notable qualitative systematic changes before and after the glitch.

astro-ph.HE↗

arXiv2025

Eccentric Binary Black Hole Simulations with Numerical Relativity

We perform a systematic study of eccentric orbiting nonspinning black hole binaries. We first make a technical study of the optimal full numerical techniques to apply to these studies. We choose different gauge parameters and Courant factors, $c=dx/dt$, and find an optimal value for it of 0.45. We also find the grid structure and global resolution that optimize accuracy and speed of current computational resources. With these choices we perform a study of the merger times $t_m$ as a function of eccentricity for configurations with comparable orbital energy content and find that they are well represented by the post-Newtonian factor $F(e)=(1+73e^2/24+37e^4/96)/(1-e^2)^{7/2}$ when merger times are normalized to their quasicircular values, i.e. $t_m(e)/t_m\approx F(e)$. We then perform a systematic coverage of five small-medium eccentricities up to $e\sim0.45$ and six mass ratios up to 8.5:1 producing a total of 30 simulations covering up to 25 orbits to merger to further model merger times and as a seed to a forthcoming new systematic catalog of gravitational waveforms from eccentric binary black holes to directly perform parameter estimations of gravitational waves events.

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arXiv2024

Quasicircular Orbital Parameters for Numerical Relativity Revisited

In the post-Newtonian (PN) expansion, we extend the determination of quasicircular orbital parameters to be used by subsequent full numerical simulations to the 3.5PN order, and find that this leads to lower eccentricities, $e$, than with our previous method that used up to 3PN order. We also supplement the computation of the radial infall due to radiation reaction and the location of the center of mass to 3.5PN order, providing explicit formulas. In addition, we consider the small mass ratio limit by explicitly including the Schwarzschild and Kerr limits, the later in quasi-isotropic as well as in our standard use of ADMTT coordinates. We evolve binaries with a $q=1/16$ mass ratio by using 3PN, 3.5PN, 3.5PN+Schwarzschild, 3.5PN+KerrQISO and 3.5PN+KerrADMTT quasicircular data for three different configurations where the larger hole intrinsic spins are $χ^z=-0.8$, $-0.4$ and $+0.8$. Using different measures of eccentricity from the black hole trajectories and from the waveform amplitudes and phases, we determine a systematic reduction of eccentricities with respect to the 3PN initial values by factors of up to an order of magnitude, and reaching the desired $e\sim10^{-3}$ threshold.

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arXiv2024

Close Encounter of Three Black Holes III

We revisit the three black hole scenario with numerical relativity techniques to study hierarchical configurations where the inner binary contains highly spinning black holes. We find that the merger time of the binary gets a delay (with a number of orbits to merger increase), depending strongly with the distance to the orbiting third hole $D$ as $\sim1/D^{1.6\pm0.1}$. Notably, a different dependence from what we had found in the nonspinning case, $\sim1/D^{2.5}$. We interpret this effect as mostly due to a spin-orbit coupling between the third hole and the closest member of the binary in the successive approaches. This lead us next to study scattering configurations of the third hole with the binary in order to evaluate the extent of this ``sudden'' interactions, finding also a correlation of the delay in merger times with the closest distance, even for the nonspinning cases. We then explore the mass ratio dependence of the triple system by modeling binaries orbiting a larger black hole bearing masses ratios 8:1:1 and 18:1:1 in co-orbiting or counter-orbiting configurations, finding merger times increasing with increasing mass ratios and for the counter-orbiting cases.

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arXiv2024

Ultimate Black Hole Recoil: What the maximum high energy collisions kick is?

We performed a series of 1381 full numerical simulations of high energy collision of black holes to search for the maximum recoil velocity after their merger. We consider equal mass binaries with opposite spins pointing along their orbital plane and perform a search of spin orientations, impact parameters, and initial linear momenta to find the maximum recoil for a given spin magnitude $s$. This spin sequence for $s=0.4, 0.7, 0.8, 0.85, 0.9$ is then extrapolated to the extreme case, $s=1$, to obtain an estimated maximum recoil velocity of $28,562\pm 342$ km/s, thus approximately bounded by $10\%$ the speed of light.

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arXiv2023

Pulsar Observations at low latitudes and low frequencies

The Pulsar Monitoring in Argentina (PuMA) is a collaboration between the Argentine Institute for Radioastronomy (IAR) and the Rochester Institute of Technology (RIT) that since 2017 has been observing southern sky pulsars with high cadence using the two restored IAR antennas in the L-Band (1400MHz). We briefly review the first set of results of this program to study transient phenomena, such as magnetars and glitching pulsars, as well as to perform precise timing of millisecond pulsars. Access to lower frequency bands, where most of the pulsars are brighter, would allow us to reach additional pulsars, currently buried into the background noise. We identify two dozen additional glitching pulsars that could be observable in the 400MHz band by the IAR's projected Multipurpose Interferometer Array (MIA). We also discuss the relevance and challenges of single-pulse pulsar timing at low frequencies and the search for Fast Radio Burst (FRB) in the collected data since 2017 using machine learning techniques.

astro-ph.IM↗

arXiv2023

Study of the Intermediate Mass Ratio Black Hole Binary Merger up to 1000:1 with Numerical Relativity

We explicitly demonstrate that current numerical relativity techniques are able to accurately evolve black hole binaries with mass ratios of the order of 1000:1. This proof of principle is relevant for future third generation (3G) gravitational wave detectors and space mission LISA, as by purely numerical methods we would be able to accurately compute gravitational waves from the last stages of black hole mergers, as directly predicted by general relativity. We perform a sequence of simulations in the intermediate to small mass ratio regime, $m_1^p/m_2^p = 1/7, 1/16, 1/32, 1/64, 1/128, 1/256, 1/512, 1/1024$, with the small hole starting from rest at a proper distance $D\approx13M$. We compare these headon full numerical evolutions with the corresponding semianalytic point particle perturbative results finding an impressive agreement for the total gravitational radiated energy and linear momentum as well as for the waveform spectra. We display numerical convergence of the results and identify the minimal numerical resolutions required to accurately solve for these very low amplitude gravitational waves. This work represents a first step towards the considerable challenge of applying numerical-relativity waveforms to interpreting gravitational-wave observations by LISA and next-generation ground-based gravitational-wave detectors.

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arXiv2023

First results of the glitching pulsars monitoring program at the Argentine Institute of Radioastronomy

We report here on the first results of a systematic monitoring of southern glitching pulsars at the Argentine Institute of Radioastronomy that started in the year 2019. We detected a major glitch in the Vela pulsar (PSR J0835$-$4510) and two small-glitches in PSR J1048$-$5832. For each glitch, we present the measurement of glitch parameters by fitting timing residuals. We then make an individual pulses study of Vela in observations before and after the glitch. We selected 6 days of observations around the major glitch on 2021 July 22 and study their statistical properties with machine learning techniques. We use Variational AutoEncoder (VAE) reconstruction of the pulses to separate them clearly from the noise. We perform a study with Self-Organizing Maps (SOM) clustering techniques to search for unusual behavior of the clusters during the days around the glitch not finding notable qualitative changes. We have also detected and confirm recent glitches in PSR J0742$-$2822 and PSR J1740$-$3015.

astro-ph.HE↗

arXiv2022

Eccentricity estimation from initial data for Numerical Relativity Simulations

We describe and study an instantaneous definition of eccentricity to be applied at the initial moment of full numerical simulations of binary black holes. The method consists of evaluating the eccentricity at the moment of maximum separation of the binary. We estimate it using up to third post-Newtonian (3PN) order, and compare these results with those of evolving (conservative) 3PN equations of motion for a full orbit and compute the eccentricity $e_r$ from the radial turning points, finding excellent agreement. We next include terms with spins up to 3.5PN, and then compare this method with the corresponding estimates of the eccentricity $e_r^{NR}$ during full numerical evolutions of spinning binary black holes, characterized invariantly by a fractional factor $0\leq f\leq1$ of the initial tangential momenta. It is found that our initial instantaneous definition is a very useful tool to predict and characterize even highly eccentric full numerical simulations.

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