Articles publicats en revistes (Física Quàntica i Astrofísica)

URI permanent per a aquesta col·leccióhttps://hdl.handle.net/2445/7504

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Machine learning the deuteron: new architectures and uncertainty quantification
(EDP Sciences, 2024-02-25) Rozalén Sarmiento, Javier; Keeble, James; Rios Huguet, Arnau
We solve the ground state of the deuteron using a variational neural network ansatz for the wavefunction in momentum space. This ansatz provides a flexible representation of both the S and the D states, with relative errors in the energy which are within fractions of a percent of a full diagonalization benchmark. We extend the previous work on this area in two directions. First, we study new architectures by adding more layers to the network and by exploring different connections between the states. Second, we provide a better estimate of the numerical uncertainty by taking into account the final oscillations at the end of the minimization process. Overall, we find that the best performing architecture is the simple one-layer, state-disconnected network. Two-layer networks show indications of overfitting, in regions that are not probed by the fixed momentum basis where calculations are performed. In all cases, the errors associated to the model oscillations around the real minimum are larger than the stochastic initilization uncertainties.
Assessment of the a2(1320) tensor-meson contribution to η/η′→π0γγ decays
(American Physical Society, 2025-12-03) Escribano, Rafael; Gonzàlez-Solís, Sergi; Royo, Emilio
In light of the recent measurement of the η→π0γγ decay by the KLOE-2 Collaboration, a previous analysis including vector- and scalar-meson exchange contributions using the vector meson dominance and linear sigma model frameworks, respectively, is extended in the present study to incorporate the effects of the a2(1320) tensor meson within a chiral context. Although the individual contribution of the a2 is negligible, its destructive interference with the vector-meson resonances is found to be significant, representing approximately 18% of the total signal and substantially affecting the diphoton invariant-mass distribution, especially at low mγγ2 values. The total decay rate is calculated to be Γ(η→π0γγ)=0.154(22) eV, which corresponds to a branching ratio of BR(η→π0γγ)=1.17(17)×10-4. This result is approximately 5σ below the reported value of the particle data group, 2.55(22)×10-4, while it is in very good agreement with the KLOE-2 measurement, 0.98(11stat)(14syst)×10-4. In contrast, the total contribution of the a2 is found to be negligible in η′→π0γγ, as this process is completely dominated by the exchange of an on-shell ω vector resonance.
Time-dependent modelling of short-term variability in the TeV-blazar VER J0521+211 during the major flare in 2020
(EDP Sciences, 2025-02-01) MAGIC Collaboration; Aguasca Cabot, Arnau; Carretero-Castrillo, Mar; Paredes i Poy, Josep Maria; Ribó Gomis, Marc
The BL Lacertae object VER J0521+211 underwent a notable flaring episode in February 2020. A short-term monitoring campaign, led by the MAGIC (Major Atmospheric Gamma Imaging Cherenkov) collaboration, covering a wide energy range from radio to very high-energy (VHE, 100 GeV < E < 100 TeV) gamma rays was organised to study its evolution. These observations resulted in a consistent detection of the source over six consecutive nights in the VHE gamma-ray domain. Combining these nightly observations with an extensive set of multi-wavelength data made modelling of the blazar's spectral energy distribution (SED) possible during the flare. This modelling was performed with a focus on two plausible emission mechanisms: (i) a leptonic two-zone synchrotron-self-Compton scenario, and (ii) a lepto-hadronic one-zone scenario. Both models effectively replicated the observed SED from radio to the VHE gamma-ray band. Furthermore, by introducing a set of evolving parameters, both models were successful in reproducing the evolution of the fluxes measured in different bands throughout the observing campaign. Notably, the lepto-hadronic model predicts enhanced photon and neutrino fluxes at ultra-high energies (E > 100 TeV). While the photon component, generated via decay of neutral pions, is not directly observable as it is subject to intense pair production (and therefore extinction) through interactions with the cosmic microwave background photons, neutrino detectors (e.g. IceCube) can probe the predicted neutrino component. Finally, the analysis of the gamma-ray spectra, observed by MAGIC and the Fermi-LAT telescopes, yielded a conservative 95% confidence upper limit of z ≤ 0.244 for the redshift of this blazar.
Global analysis of µ→e interactions in the SMEFT
(Springer Verlag, 2025-07-29) Delzanno, Filippo; Fuyuto, Kaori; Gonzàlez-Solís, Sergi; Mereghetti, E
We study current experimental bounds on charged lepton flavor violating (CLFV) μ – e interactions in the model-independent framework of the Standard Model Effective Field Theory (SMEFT). Assuming a generic flavor structure in the quark sector, we consider the contributions of CLFV operators to low-energy observables, including μ → eγ and μ → e conversion for quark-flavor conserving operators and CLFV meson decays for quark-flavor violating operators. At high energy, we consider limits on CLFV decays of the Higgs and Z bosons and of the top quark, and obtain bounds on operators with light quarks by recasting searches for production of eμ pairs in pp collisions at the Large Hadron Collider (LHC). We connect observables at low- and high-energy by taking into account renormalization group running and matching between CLFV operators. We also discuss the sensitivity of the future Electron-Ion Collider, where the prospective bounds are derived by imposing simple cuts on final state particles. We find that, in a single operator scenario, bounds on purely leptonic operators are dominated by μ → eγ and μ → e conversion. Semileptonic operators with down-type quarks are also dominantly constrained by low-energy observables, while LHC searches lead the bounds on up-type quark-flavor violating operators. Taking simplified multiple-coupling scenarios, we show that it is easy to evade the strongest low-energy bounds from spin-independent μ → e conversion, and that collider searches are competitive and complementary to constraints from spin-dependent μ → e conversion and other low-energy probes.
Relativistic hydrodynamics simulations of supernova explosions within extragalactic jets
(EDP Sciences, 2025-12-05) Longo, B.; Perucho, M.; Bosch i Ramon, Valentí; Martí, José M.; Clairfontaine, G. Fichet de
Context. Jets in active galactic nuclei (AGN) have to cross significant distances within their host galaxies, meeting large numbers of
stars of different masses and evolution stages on their paths. Given enough time, supernova explosions within the jet will eventuallyhappen, and they may have a strong impact on its dynamics, potentially triggering powerful non-thermal activity. Aims. We aim to carry out a detailed numerical study to explore the dynamics of the interaction between the ejecta of a supernovaexplosion and a relativistic extragalactic jet.Methods. By means of relativistic hydrodynamics simulations using the code RATPENAT, we simulated the jet-ejecta interaction in two different geometries or scenarios: a two-dimensional, axisymmetric simulation, and a three-dimensional one, which includes the orbital velocity of the exploding star. In both scenarios, the supernova ejecta is located within the jet at a distance of ∼1 kpc from the central black hole, which is the spatial scale on which these events are most likely. Results. Although initially filling a region much smaller than the jet radius, the ejecta expands and eventually covers most of the jet’s cross-section. The expansion is enhanced as more energy from the jet is converted into kinetic and internal energy of the ejecta, which also favours the ejecta disruption, all of this occurs on timescales of ∼104 yr. Although a complete numerical convergence of the results is unattainable given the subsonic, turbulent nature of the interaction region, the simulations are consistent in their description of the gross morphological and dynamical properties of the interaction process. Conclusions. At the end of the simulations, the supernova ejecta already partially mixed with the relativistic jet. The results also suggest that the jet-ejecta interaction may be a non-negligible non-thermal emitter. Moreover, due to efficient mixing, the interaction region can be a potential source of ultra-high-energy cosmic rays of heavy composition.
Time-dependent modelling of short-term variability in the TeV-blazar VER J0521+211 during the major flare in 2020
(EDP Sciences, 2025-02-01) MAGIC Collaboration; Aguasca Cabot, Arnau; Carretero-Castrillo, Mar; Paredes i Poy, Josep Maria; Ribó Gomis, Marc
The BL Lacertae object VER J0521+211 underwent a notable flaring episode in February 2020. A short-term monitoring campaign, led by the MAGIC (Major Atmospheric Gamma Imaging Cherenkov) collaboration, covering a wide energy range from radio to very high-energy (VHE, 100 GeV < E < 100 TeV) gamma rays was organised to study its evolution. These observations resulted in a consistent detection of the source over six consecutive nights in the VHE gamma-ray domain. Combining these nightly observations with an extensive set of multi-wavelength data made modelling of the blazar's spectral energy distribution (SED) possible during the flare. This modelling was performed with a focus on two plausible emission mechanisms: (i) a leptonic two-zone synchrotron-self-Compton scenario, and (ii) a lepto-hadronic one-zone scenario. Both models effectively replicated the observed SED from radio to the VHE gamma-ray band. Furthermore, by introducing a set of evolving parameters, both models were successful in reproducing the evolution of the fluxes measured in different bands throughout the observing campaign. Notably, the lepto-hadronic model predicts enhanced photon and neutrino fluxes at ultra-high energies (E > 100 TeV). While the photon component, generated via decay of neutral pions, is not directly observable as it is subject to intense pair production (and therefore extinction) through interactions with the cosmic microwave background photons, neutrino detectors (e.g. IceCube) can probe the predicted neutrino component. Finally, the analysis of the gamma-ray spectra, observed by MAGIC and the Fermi-LAT telescopes, yielded a conservative 95% confidence upper limit of z ≤ 0.244 for the redshift of this blazar.
Time-dependent modelling of short-term variability in the TeV-blazar VER J0521+211 during the major flare in 2020
(EDP Sciences, 2025-02-01) MAGIC Collaboration; Aguasca Cabot, Arnau; Carretero-Castrillo, Mar; Paredes i Poy, Josep Maria; Ribó Gomis, Marc
The BL Lacertae object VER J0521+211 underwent a notable flaring episode in February 2020. A short-term monitoring campaign, led by the MAGIC (Major Atmospheric Gamma Imaging Cherenkov) collaboration, covering a wide energy range from radio to very high-energy (VHE, 100 GeV < E < 100 TeV) gamma rays was organised to study its evolution. These observations resulted in a consistent detection of the source over six consecutive nights in the VHE gamma-ray domain. Combining these nightly observations with an extensive set of multi-wavelength data made modelling of the blazar's spectral energy distribution (SED) possible during the flare. This modelling was performed with a focus on two plausible emission mechanisms: (i) a leptonic two-zone synchrotron-self-Compton scenario, and (ii) a lepto-hadronic one-zone scenario. Both models effectively replicated the observed SED from radio to the VHE gamma-ray band. Furthermore, by introducing a set of evolving parameters, both models were successful in reproducing the evolution of the fluxes measured in different bands throughout the observing campaign. Notably, the lepto-hadronic model predicts enhanced photon and neutrino fluxes at ultra-high energies (E > 100 TeV). While the photon component, generated via decay of neutral pions, is not directly observable as it is subject to intense pair production (and therefore extinction) through interactions with the cosmic microwave background photons, neutrino detectors (e.g. IceCube) can probe the predicted neutrino component. Finally, the analysis of the gamma-ray spectra, observed by MAGIC and the Fermi-LAT telescopes, yielded a conservative 95% confidence upper limit of z ≤ 0.244 for the redshift of this blazar.
Hydrodynamics of relativistic superheated bubbles
(American Physical Society, 2025-12-24) Sanchez-Garitaonandia, Mikel; Bea, Yago; Casalderrey Solana, Jorge; Mateos, David (Mateos Solé)
Relativistic, charged, superheated bubbles may play an important role in neutron star mergers if first-order phase transitions are present in the phase diagram of quantum chromodynamics. We describe the properties of these bubbles in the hydrodynamic regime. We find two qualitative differences with supercooled bubbles. First, the pressure at the center of an expanding superheated bubble can be higher or lower than the pressure in the asymptotic, metastable phase. Second, some fluid flows develop metastable regions behind the bubble wall for any choice of the equation of state. We consider the possible role of a conserved charge akin to baryon number. The fluid flow profiles are unaffected by this charge if the speed of sound is constant in each phase, but they are modified for more general equations of state. We compute the efficiency factor relevant for gravitational wave production
Identifying the physical periods in the radio emission from the \u03b3-ray emitting binary LS I +61 303
(EDP Sciences, 2025-12-05) Bosch i Ramon, Valentí; Jaron, Frederic
Context. The γ-ray emitting binary system LS I +61 303 exhibits periodic emission across the electromagnetic spectrum, extending from radio frequencies up to the very-high-energy regime. The most prominent features are three periods with values P1 = 26.5 d, P2 = 26.9 d, and Plong = 4.6 years. Occasionally, a fourth period of 26.7 d is also detected. Mathematically, these four periods are interrelated via the interference pattern of a beating. Competing scenarios that seek to determine which of these periods are physical and which are secondary are under debate. In addition, the detection of a fifth period, P3 = 26.3 d, was recently claimed. Aims. Our aim is to determine which of these periods are intrinsic (i.e., whether they are likely to be related to physical processes) and which of these are secondary (i.e., resulting from interference). We chose to avoid any assumption concerning the physical scenario and restricted our analysis to the phenomenology of the radio emission variability. Methods. We selected intervals from archival radio data and applied the generalized Lomb-Scargle periodogram. We fit the observational data to generate synthetic datasets that only contain specific signals in the form of pure sine waves. We analyzed these synthetic data to assess the impact of these signals and their interference on the light curves and the periodogram. Results. The two-peaked profile, consisting of P1 and P2, was detected in the periodogram of the actual data for intervals that are significantly shorter than Plong, provided that these intervals contain the minimum of the long-term modulation. The characteristics of the observational data and their periodogram could only be reproduced with synthetic data if these explicitly included all of the three periods, P1, P2, and Plong, with the residuals being limited by noise. Conclusions. We have found, for the first time, that all three periods, P1, P2, and Plong, could, in fact, correspond to physically real processes occurring in LS I +61 303. This should be considered when modeling the physical processes in this binary system.
Impact of the hot inner crust on compact stars at finite temperature
(EDP Sciences, 2024-07-16) Dehman, Clara; Centelles Aixalà, Mario; Viñas Gausí, Xavier
We conducted a study on the thermal properties of stellar matter with the nuclear energy density functional BCPM. This functionalis based on microscopic Brueckner–Hartree–Fock calculations and has demonstrated success in describing cold neutron stars. Toenhance its applicability in astrophysics, we extended the BCPM equation of state to finite temperature for β-stable neutrino-freematter, taking into consideration the hot inner crust. Such an equation of state holds significant importance for hot compact objects,particularly those resulting from a binary neutron star merger event. Our exploration has shown that with increasing temperature,there is a fast decrease in the crust-core transition density, suggesting that for hot stars it is not realistic to assume a fixed value ofthis density. The microscopic calculations also reveal that the presence of nuclear clusters persists up to T = 7.21 MeV, identified asthe limiting temperature of the crust. Above this threshold, the manifestation of clusters is not anticipated. Below this temperature,clusters within the inner crust are surrounded by uniform matter with varying densities, allowing for the distinction between the upperand lower transition density branches. Moreover, we computed mass–radius relations of neutron stars, assuming an isothermal profilefor β-stable neutron star matter at various temperature values. Our findings highlight the significant influence of the hot inner crust onthe mass–radius relationship, leading to the formation of larger and more inflated neutron stars. Consequently, under our prescription,the final outcome is a unified equation of state at finite temperature.
Full 5D characterisation of the Sagittarius stream with Gaia DR2 RR Lyrae
(EDP Sciences, 2020) Ramos, Pau; Mateu, Cristina; Antoja Castelltort, M. Teresa; Helmi, Amima; Castro Ginard, Alfred; Balbinot, Eduardo; Carrasco Martínez, José Manuel
Context. The Sagittarius (Sgr) stream is one of the best tools that we currently have to estimate the mass and shape of our Galaxy. However, assigning membership and obtaining the phase-space distribution of the stars that form the tails of the stream is quite challenging. Aims. Our goal is to produce a catalogue of the RR Lyrae stars of Sgr and obtain an empiric measurement of the trends along the stream in sky position, distance, and tangential velocity. Methods. We generated two initial samples from the Gaia DR2 RR Lyrae catalogue: one selecting only the stars within ±20◦ of the orbital plane of Sagittarius (Strip), and the other resulting from application of the Pole Count Map (nGC3) algorithm. We then used the model-independent, deterministic method developed in this work to remove most of the contamination by detecting and isolating the stream in distance and proper motions. Results. The output is two empiric catalogues: the Strip sample (higher-completeness, lower-purity) which contains 11 677 stars,and the nGC3 sample (higher-purity, lower-completeness) with 6608 stars. We characterise the changes along the stream in all the available dimensions, namely the five astrometric dimensions plus the metallicity, covering more than 2π rad in the sky, and obtain new estimates for the apocentres and the mean [Fe/H] of the RR Lyrae population. Also, we show the first map of the two components of the tangential velocity thanks to the combination of distances and proper motions. Finally, we detect the bifurcation in the leading arm and report no significant difference between the two branches in terms of metallicity, kinematics, or distance. Conclusions. We provide the largest sample of RR Lyrae candidates of Sgr, which can be used as input for a spectroscopic follow-up or as a reference for the new generation of models of the stream through the interpolators in distance and velocity that we constructed.
Towards a global analysis of the b → cuq puzzle
(Springer Verlag, 2025-06-03) Meiser, Stefan; van Dyk, Danny; Virto, Javier
We study the nonleptonic decays B0 s → D (∗)+ s π − and B0 → D(∗)+K− within the Weak Effective Theory (WET) up to mass-dimension six. We revisit the calculation of the hadronic matrix elements within QCD Factorization including the full set of WET operators. We recalculate the two-particle contributions to the hard-scattering kernels at next-to-leading order in αs, confirming recent results in the literature. We also calculate the three-particle contributions at leading order in αs, clarifying the procedure, refining the SM results in the literature, and providing for the first time the complete set of contributions within the WET. We use these results to perform a global phenomenological study of the effective couplings, putting bounds on the size of the WET Wilson coefficients in four distinct fit models. The fits include constraints from the nonleptonic B-meson decay width, which we calculate at the leading order for the full set of WET operators for the first time. This study is the first one to account for simultaneous variation of up to six effective couplings. We identify two distinct modes in all fit models and discuss how future measurements can be used to distinguish between them.
Spinodal Gravitational Waves
(Springer Verlag, 2025-11-17) Bea, Yago; Giannakopoulos, Thanasis; Jansen, Andreas; Krippendorf, Sven; Mateos, David (Mateos Solé); Sanchez-Garitaonandia, Mikel; Zilhão, Miguel; Casalderrey Solana, Jorge
We uncover a new gravitational-wave production mechanism in cosmological, first-order, thermal phase transitions. These are usually assumed to proceed via the nucleationof bubbles of the stable phase inside the metastable phase. However, if the nucleationrate is sufficiently suppressed, then the Universe may supercool all the way down themetastable branch and enter the spinodal region. In this case the transition proceeds via theexponential growth of unstable modes and the subsequent formation, merging and relaxationof phase domains. We use holography to follow the real-time evolution of this process in astrongly coupled, four-dimensional gauge theory and compute the resulting gravitational-wavespectrum. We discuss the possibility that the spinodal dynamics may be preceded by aperiod of thermal inflation.
Benefits of Image Deconvolution in CCD Imagery
(Instituto de Astronomi?a, Universidad Nacional Auto?noma de Me?xico., 2006-01) Fors Aldrich, Octavi; Merino, M.T.; Otazu Porter, Xavier; Cardinal, Robert D.; Núñez de Murga, Jorge, 1955-; Hildebrand, A.R.
We show how wavelet-based image deconvolution can provide to wide-field CCD telescopes an increase in limiting magnitude of Δ R ∼ 0.6 and significant deblending improvement. Astrometric accuracy is not distorted, therefore, the feasibility of the technique for astrometric projects is validated. We apply the deconvolution process to a set of images from the recently refurbished Baker-Nunn camera at Rothney Astrophysical Observatory.
The Calar Alto Lunar Ocultation program: a status report
(Instituto de Astronomía, Universidad Nacional Autónoma de México, 2006-01) Fors Aldrich, Octavi; Richichi, Andrea; Merino, M.T.; Otazu Porter, Xavier; Núñez de Murga, Jorge, 1955-; Prades, Albert; Pérez-Ramírez, D.
The status of the Calar Alto Lunar Occultation Program is presented. This has been conducted at IR and optical wavelengths through OAN 1.5-m and CAHA 2.2-m telescopes, operating either with fast IR array or CCD. The scientific throughput is double: first, angular diameter determinations (>1-2 mas) of late-type stars and circumstellar matter detection of astrophysically interesting targets (YSOs, T Taus, carbon stars, masers). Second, new binaries detection with projected separations > 5mas, and brightness ratios up to 1:50. We detail the runs carried out so far and summarize the scientific results obtained.
The thermal index of neutron-star matter in the virial approximation
(Institute of Physics (IOP), 2025-06-27) Rivieccio, Giuseppe; Nadal Matosas, Adriana; Rios Huguet, Arnau; Ruiz Revuelta, Mònica
Motivated by gravitational-wave observations of binary neutron-star mergers, we study the thermal index of low-density, high-temperature dense matter. We use the virial expansion to account for nuclear interaction effects. We focus on the region of validity of the expansion, which reaches 10−3 fm−3 at T = 5 MeV up to almost saturation density at T = 50 MeV. In pure neutron matter, we find an analytical expression for the thermal index, and show that it is nearly density and temperature independent, within a fraction of a percent of the noninteracting, nonrelativistic value of Γth ≈ 5/3. When we incorporate protons, electrons, and photons, we find that the density and temperature dependence of the thermal index changes significantly. We predict a smooth transition between an electron-dominated regime with Γth ≈ 4/3 at low densities to a neutron-dominated region with Γth ≈ 5/3 at high densities. This behavior is by and large independent of the proton fraction and is not affected by nuclear interactions in the region where the virial expansion converges. We model this smooth transition analytically and provide a simple but accurate parameterization of the inflection point between these regimes. When compared to tabulated realistic models of the thermal index, we find an overall agreement at high temperatures that weakens for colder matter. The discrepancies can be attributed to the missing contributions of nuclear clusters. The virial approximation provides a clear and physically intuitive framework for understanding the thermal properties of dense matter, offering a computationally efficient solution that makes it particularly well suited for the regimes relevant to neutron-star binary remnants.
Khuri-Treiman analysis of J=ψ → π + π − π0
(American Physical Society, 2023-07-28) Albaladejo Miguel; Gonzàlez-Solís, Sergi; Bibrzycki, Ł; Fernandez-Ramirez, César; Hammoud, Nadine; Mathieu, Vincent; Mikhasenko, Mikhail; Montaña Faiget, Glòria; Perry, Robert J.; Pilloni, Alessandro; Rodas Bilbao, Arkaitz; Smith, Wyatt A.; Szczepaniak, Adam Pawel; Winney, Daniel
We study the decay J/ψ→π+π-π0 within the framework of the Khuri-Treiman equations. We find that the BESIII experimental dipion mass distribution in the ρ(770)-region is well reproduced with a once-subtracted P-wave amplitude. Furthermore, we show that F-wave contributions to the amplitude improve the description of the data in the ππ mass region around 1.5 GeV. We also present predictions for the J/ψ→π0γ* transition form factor.
Quasiparticle pairing encoding of atomic nuclei for quantum annealing
(Elsevier B.V., 2025-12-06) Costa, Emanuele; Pérez-Obiol, A.; Menéndez Sánchez, Javier; Rios Huguet, Arnau ; García-Sáez, A.; Juliá-Díaz, Bruno
Quantum computing is emerging as a promising tool in nuclear physics. However, the cost of encoding fermionic operators hampers the application of algorithms in current noisy quantum devices. In this work, we analyze an encoding scheme based on pairing nucleon modes. This approach significantly reduces the complexity of the encoding, while maintaining a high accuracy for the ground states of semimagic nuclei across the sd and pf shells and for tin isotopes. In addition, we also explore the encoding ability to describe open-shell nuclei within the above configuration spaces. When this scheme is applied to a trotterized quantum adiabatic evolution, our results demonstrate a computational advantage of up to three orders of magnitude in CNOT gate count compared to the standard Jordan-Wigner encoding. Our approach paves the way for efficient quantum simulations of nuclear structure using quantum annealing, with applications to both digital and hybrid quantum computing platforms.
VHE γ-ray observations of bright BL Lacs with the Large-Sized Telescope prototype (LST-1) of the CTAO
(Royal Astronomical Society, 2025-11-01) Aguasca Cabot, Arnau; Ribó Gomis, Marc; Paredes i Poy, Josep Maria; Pihet, Marine; Bordas Coma, Pol; CTAO-LST Collaboration
Cherenkov Telescope Array Observatory (CTAO) is the next-generation ground-based γ-ray observatory operating in the energy range from 20GeV up to 300TeV, with two sites in La Palma (Spain) and Paranal (Chile). It will consist of telescopes of three sizes, covering different parts of the large energy range. We report on the performance of Large-Sized Telescope prototype (LST-1) in the detection and characterization of extragalactic γ-ray sources, with a focus on the reconstructed γ-ray spectra and variability of classical bright BL Lacertae objects, which were observed during the early commissioning phase of the instrument. LST-1 data from known bright γ-ray blazars ─ Markarian 421, Markarian 501, 1ES 1959+650, 1ES 0647+250, and PG 1553 + 113 ─ were collected between 2020 July 10, and 2022 May 23, covering a zenith angle range of 4∘ to 57∘. The reconstructed light curves were analysed using a Bayesian block algorithm to distinguish the different activity phases of each blazar. Simultaneous Fermi-LAT data were utilized to reconstruct the broad-band γ-ray spectra for the sources during each activity phase. High-level reconstructed data in a format compatible with gammapy are provided together with measured light curves and spectral energy distributions (SEDs) for several bright blazars and an interpretation of the observed variability in long and short time-scales. Simulations of historical flares are generated to evaluate the sensitivity of LST-1. This work represents the first milestone in monitoring bright BL Lacertae objects with a CTAO telescope.
Magnetar-like flares behind the high-energy emission in LS 5039
(EDP Sciences, 2025-11-26)
Context: LS 5039 is a system hosting a high-mass star and a compact object of unclear nature. There are hints that the system may host a strongly magnetized neutron star, a scenario that requires a mechanism to power its persistent and strong nonthermal emission. We investigate a mechanism in which the nonsteady interaction structure of the stellar and the compact object winds can regularly excite neutron star magnetospheric activity, which can release extra energy and fuel the source nonthermal emission. Methods: The neutron star wind shocked by the stellar wind can recurrently touch the neutron star magnetosphere, triggering magnetic instabilities whose growth can release extra energy into the neutron star wind in a cyclic manner. To illustrate and study the impact of these cycles on the two-wind interaction structure on different scales, we performed relativistic hydrodynamics simulations in two and three dimensions with periods of an enhanced power in the neutron star wind along the orbit. We also used analytical tools to characterize processes near the neutron star relevant for the nonthermal emission. Results: As the neutron star wind termination shock touches the magnetosphere energy dissipation occurs, but the whole shocked two-wind structure is eventually driven away, stopping the extra energy injection. However, due to the corresponding drop in the neutron star wind ram pressure, the termination shock propagates back toward the magnetosphere, resuming the process. These cycles of activity excite strong waves in the shocked flows, intensifying their mixing and the disruption of their spiral-like structure produced by orbital motion. Further downstream, the shocked winds can become a quasi-stable, relatively smooth flow. Conclusions: The recurrent interaction between the neutron star magnetosphere and a shocked wind can fuel a relativistic outflow powerful enough to explain the nonthermal emission of LS 5039. A magnetospheric multipolar magnetic field much stronger than the dipolar one may provide the required energetics, and help to explain the lack of evidence of a recent supernova remnant.

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