arXiv subjects

Luís Felipe Longo Micchi

Publications and source records attributed to Luís Felipe Longo Micchi.

5 recordsLinked to original sources

arXiv2026

Magnetar Formation from Accretion Induced Collapse of White Dwarfs

We aim to characterize the post-collapse evolution of accretion-induced collapse (AIC) remnants of rapidly rotating, magnetized white dwarfs, focusing on their rotational, magnetic, and thermal structure, as well as the development of instabilities and their energy content. We perform nine axis-symmetric general-relativistic neutrino magnetohydrodynamic (MHD) simulations of collapsing, rapidly rotating, magnetized white dwarfs. The simulations follow the system from collapse through bounce and up to $\sim$1 s post-bounce. The simulations are performed by the conformally flat general relativistic neutrino MHD code \texttt{Gmunu}. The collapse produces a rapidly rotating proto-magnetar surrounded by a persistent accretion disk lasting at least $\sim 1$ s after bounce. The remnant mass and spin span 1.15--1.45 $M_{\odot}$ and 2.9--4.9 kHz, respectively, with stronger initial magnetic fields generally leading to lower rotation rates. During the first $\sim 10$ ms, the proto-magnetar exhibits global oscillations that drive both gravitational-wave emission and coherent modulation of the poloidal magnetic field energy. The magnetic energy evolution, normalized to its bounce value, follows an approximately universal behavior across all models. The remnant interior remains strongly magnetized ($\gtrsim 10^{13}$ G) and hot ($\gtrsim 20$ MeV) up to 1 s after bounce, with maxima of both quantities co-located in the inner $\sim 10$ km. The magnetic field topology shows surface poloidal fields of ${\sim}10^{12}$ G and toroidal fields of ${\sim}10^{14}$ G, with strong toroidal components extending into the equatorial region. When the magnetic energy exceeds the rotational energy ($\sim 10^{52}$ erg), the remnant core becomes unstable, leading to episodic magnetic flux expulsion, mass ejection, and flare-like activity in which magnetic energy is released and thermalized in the surrounding material.

astro-ph.HE↗

arXiv2025

Gamma-ray bursts and kilonovae from the accretion-induced collapse of white dwarfs

We present the first seconds-long 2D general relativistic neutrino magnetohydrodynamic simulations of accretion-induced collapse (AIC) in rapidly rotating, strongly magnetized white dwarfs (WDs), which might originate as remnants of double-WD mergers. This study examines extreme combinations of magnetic fields and rotation rates, motivated both by the need to address the limitations of 2D axisymmetric simulations and to explore the physics of AIC under rare conditions that, while yet to be observationally confirmed, may be consistent with current theoretical models and account for unusual events. Under these assumptions, our results demonstrate that, if realizable, such systems can generate relativistic jets and neutron-rich outflows with properties consistent with long gamma-ray bursts (LGRBs) accompanied by kilonovae, such as GRB 211211A and GRB 230307A. These findings highlight the potential role of AIC in heavy $r$-process element production and offer a framework for understanding rare LGRBs associated with kilonova emission. Longer-duration 3D simulations are needed to fully capture magnetic field amplification, resolve instabilities, and determine the fate of the energy retained by the magnetar at the end of the simulations.

astro-ph.HE↗

arXiv2024

Spectrogram correlated stacking: A novel time-frequency domain analysis of the Stochastic Gravitational Wave Background

The astrophysical stochastic gravitational wave background (SGWB) originates from numerous faint sub-threshold gravitational wave (GW) signals arising from the coalescing binary compact objects. This background is expected to be discovered from the current (or next-generation) network of GW detectors by cross-correlating the signal between multiple pairs of GW detectors. However, detecting this signal is challenging and the correlation is only detectable at low frequencies due to the arrival time delay between different detectors. In this work, we propose a novel technique, \texttt{Spectrogram Correlated Stacking} (or \texttt{SpeCs}), which goes beyond the usual cross-correlation (and to higher frequencies) by exploiting the higher-order statistics in the time-frequency domain which accounts for the \textit{chirping} nature of the individual events that comprise SGWB. We show that \texttt{SpeCs} improves the signal-to-noise for the detection of SGWB by a factor close to $8$, compared to standard optimal cross-correlation methods which are tuned to measure only the power spectrum of the SGWB signal.\texttt{SpeCs} can probe beyond the power spectrum and its application to the GW data available from the current and next-generation GW detectors would speed up the SGWB discovery.

gr-qc↗

arXiv2023

Multimessenger Emission from the Accretion Induced Collapse of White Dwarfs

We present fully general-relativistic three-dimensional numerical simulations of accretion-induced collapse (AIC) of white dwarfs (WDs). We evolve three different WD models (nonrotating, rotating at 80% and 99% of the Keplerian mass shedding limit) that collapse due to electron capture. For each of these models, we provide a detailed analysis of their gravitational waves (GWs), neutrinos and electromagnetic counterpart and discuss their detectability. Our results suggest that fast rotating AICs could be detectable up to a distance of 8 Mpc with third-generation GW observatories, and up to 1 Mpc with LIGO. AIC progenitors are expected to have large angular momentum due to their accretion history, which is a determining factor for their stronger GW emission compared to core-collapse supernovae (CCSNe). Regarding neutrino emission, we found no significant difference between AICs and CCSNe. In the electromagnetic spectrum, we find that AICs are two orders of magnitude fainter than type Ia supernovae. Our work places AICs as realistic targets for future multimessenger searches with third generation ground-based GW detectors.

astro-ph.HE↗

arXiv2023

GW190521: Search for Echoes due to Stimulated Hawking Radiation from Black Holes

Being arguably the most massive binary black hole merger event observed to date, GW190521 deserves special attention. The exceptionally loud ringdown of this merger makes it an ideal candidate to search for gravitational wave echoes, a proposed smoking gun for the quantum structure of black hole horizons. We perform an unprecedented multi-pronged search for echoes via two well-established and independent pipelines: a template-based search for stimulated emission of Hawking radiation, or Boltzmann echoes, and the model-agnostic coherent WaveBurst (cWB) search. Stimulated Hawking radiation from the merger is expected to lead to post-merger echoes at horizon mode frequency of $\sim50$ Hz (for quadrupolar gravitational radiation), repeating at intervals of $\sim1$ second, due to partial reflection off Planckian quantum structure of the horizon. A careful analysis using dynamic nested sampling yields a Bayesian evidence of $8^{+4}_{-2}$ (90\% confidence level) for this signal following GW190521, carrying an excess of $6^{+10}_{-5}\%$ in gravitational wave energy, relative to the main event (consistent with the predicted amplitude of Boltzmann echoes). The "look-elsewhere" effect is estimated by using General Relativity (plus Boltzmann echoes) injections in real data, around the event, giving a false (true) positive detection probability for higher Bayes factors of $1.5^{+1.2}_{-0.9}\%$ ($35\pm7\%$). Similarly, the reconstructed waveform of the first echo in cWB carries an energy excess of $13^{+16}_{-7}\%$. While the current evidence for stimulated Hawking radiation does not reach the gold standard of $5σ$ (or p-value $<3\times10^{-7}$), our findings are in line with expectations for stimulated Hawking radiation at current detector sensitivities. The next generation of gravitational wave observatories can thus draw a definitive conclusion on the quantum nature of black hole horizons.

gr-qc↗