arXiv subjects

D. F. Torres

Publications and source records attributed to D. F. Torres.

At least 19 recordsLinked to original sources

arXiv2026

The Array Control and Data Acquisition software of the Cherenkov Telescope Array Observatory

The Cherenkov Telescope Array Observatory (CTAO) aims to advance knowledge of the gamma-ray sky as the largest gamma-ray observatory ever built. The CTAO will be deployed at two sites, one in the Northern Hemisphere and the other in the Southern Hemisphere, containing telescopes of three sizes to cover different energy domains. Commissioning of the prototype CTAO Large-Sized Telescope (LST-1) is being finalized at the northern site, while three additional LSTs are under construction. Additional calibration and environmental monitoring instruments, such as laser imaging detection and ranging (LIDAR) systems and weather stations, will support telescope operations. The Array Control and Data Acquisition (ACADA) system serves as the central element for on-site CTAO operations. ACADA controls, supervises, and handles the data generated by the telescopes and the auxiliary instruments. It drives the efficient planning and execution of observations while managing the multi-gigabit-per-second data streams produced by each CTAO telescope. The ACADA system contains the CTAO Science Alert Generation Pipeline - a real-time data processing and analysis pipeline, dedicated to automatically generating science alert candidates as data are acquired. These science alerts, along with external alerts received from other scientific instruments, are managed by the Transients Handler (TH) component. The TH informs ACADA's Short-Term Scheduler (STS) about relevant science alerts, enabling modification of ongoing observations on sub-minute timescales. This capability for rapid response, combined with the fast slewing of CTAO telescopes, makes the Observatory an excellent instrument for studying high-impact astronomical transients.

astro-ph.IM↗

arXiv2026

Population synthesis of Galactic middle-aged pulsar wind nebulae II. Observational signatures of superefficiency

Pulsar wind nebulae (PWNe) interacting with the host supernova remnants (SNRs) can enter the reverberation phase in which reverse-shock-driven compression amplifies the magnetic field and rapidly reprocesses particles, sometimes producing "superefficiency", where the radiative output in a given frequency band exceeds the pulsar's instantaneous spin-down power. We investigate the prevalence of this phenomenon in the Galactic population by modeling PWNe with the hybrid TIDE+L framework, which self-consistently follows dynamical evolution, particle spectra, and emission from radio to PeV energies. We track superefficiency across frequency bands and evolutionary stages, analyzing both individual objects and ensemble properties, including compression-resolved samples and population spectral energy distributions. Superefficiency is most common in the far-infrared, but emerges across frequencies and evolutionary phases. It is enhanced in systems where accumulated low-energy electrons radiate in magnetically amplified nebulae. We predict substantially more superefficient sources than a purely thin-shell model would, with differences ranging from factors of a few in FIR and GeV bands to more than an order of magnitude in several optical/UV/X-ray bands.

astro-ph.HE↗

arXiv2026

Population synthesis of Galactic middle-aged pulsar wind nebulae I. Detection prospects for current and future instruments

Pulsar wind nebulae (PWNe) constitute the largest population of Galactic very-high-energy (VHE; $E > 100$ GeV) $\gamma$-ray sources and are key laboratories for studying particle acceleration and pulsar--supernova remnant (SNR) interactions. However, realistic population-level predictions have so far lacked any detailed treatment of the reverberation phase, when the nebula is compressed by the SNR reverse shock, significantly altering its dynamics and radiative spectrum. We employ the hybrid \texttt{TIDE+L} framework, which combines a thin-shell dynamical model with a Lagrangian treatment of the SNR structure during reverberation, allowing self-consistent evolution of thousands of PWNe across all stages up to $10^5$ yr. Each source is evolved under distributions of pulsar spin-down, SNR, and environmental properties, and the resulting $\gamma$-ray fluxes are used to estimate the detectability by current and next-generation $\gamma$-ray observatories while accounting for their sensitivity and sky coverage. The model predicts that the upcoming Cherenkov Telescope Array Observatory (CTAO) will detect an order of magnitude more PWNe than those firmly detected in the TeV range, confirming its dominant contribution to the forthcoming TeV population census. Our results demonstrate that realistic modeling of reverberation is important for predicting the Galactic TeV PWNe population.

astro-ph.HE↗

arXiv2026

Classical, large scale 3D MHD simulations of interacting pulsar wind nebulae

Magnetized rotating neutron stars, or pulsars, are a possible end product of massive star evolution. Their relativistic wind successively interacts with the supernova ejecta of their defunct progenitor, then with the circumstellar medium of the progenitor, and eventually with the interstellar medium. If a massive star is static with respect to its ambient medium, then its resulting circumstellar medium is elongated along the direction of the local magnetic field, and its supernova remnant transiently appears as a rectangle. The pulsar wind nebula forming in it is, in its turn, elongated, as long as the pulsar axis of rotation matches the direction of the local magnetization. In this work, we explore how the angle between the direction of the local magnetic field of the interstellar medium and the pulsar axis of rotation influences the shaping of its pulsar wind nebula with 3D MHD simulations are carried out with the PLUTO. We use those models to perform radiative transfer calculations to derive non-thermal radio emission maps of the pulsar wind nebulae. When the polar elongation of the pulsar develop, they bend in opposite directions under the effects of the cavity carved by the stellar wind and already filled by supernova ejecta. This induces a complex distribution of magnetized supernova ejecta and pulsar wind, resulting in various observable structures, appearing as rectangles, circles, or irregular oblong shapes, in the radio waveband. The angle between the direction of the pulsar rotation axis and that of the local ambient magnetization is a governing parameter for the shaping and non-thermal radio properties of the pulsar wind nebulae of static massive stars; however, the mixing of material, once the pulsar wind nebula is old (50 to 80 kyr), is not strongly affected by that factor.

astro-ph.HE↗

arXiv2025

Combined dark matter search towards dwarf spheroidal galaxies with Fermi-LAT, HAWC, H.E.S.S., MAGIC, and VERITAS

Dwarf spheroidal galaxies (dSphs) are excellent targets for indirect dark matter (DM) searches using gamma-ray telescopes because they are thought to have high DM content and a low astrophysical background. The sensitivity of these searches is improved by combining the observations of dSphs made by different gamma-ray telescopes. We present the results of a combined search by the most sensitive currently operating gamma-ray telescopes, namely: the satellite-borne Fermi-LAT telescope; the ground-based imaging atmospheric Cherenkov telescope arrays H.E.S.S., MAGIC, and VERITAS; and the HAWC water Cherenkov detector. Individual datasets were analyzed using a common statistical approach. Results were subsequently combined via a global joint likelihood analysis. We obtain constraints on the velocity-weighted cross section $\langle \sigma \mathit{v} \rangle$ for DM self-annihilation as a function of the DM particle mass. This five-instrument combination allows the derivation of up to 2-3 times more constraining upper limits on $\langle \sigma \mathit{v} \rangle$ than the individual results over a wide mass range spanning from 5 GeV to 100 TeV. Depending on the DM content modeling, the 95% confidence level observed limits reach $1.5\times$10$^{-24}$ cm$^3$s$^{-1}$ and $3.2\times$10$^{-25}$ cm$^3$s$^{-1}$, respectively, in the $\tau^+\tau^-$ annihilation channel for a DM mass of 2 TeV.

astro-ph.HE↗

arXiv2025

Puzzling Variation of Gamma Rays from the Sun over the Solar Cycle Revealed with Fermi-LAT

The steady-state gamma-ray emission from the Sun is thought to consist of two emission components due to interactions with Galactic cosmic rays: (1) a hadronic disk component, and (2) a leptonic extended component peaking at the solar edge and extending into the heliosphere. The flux of these components is expected to vary with the 11-year solar cycle, being highest during solar minimum and lowest during solar maximum, as it varies with the cosmic-ray flux. No study has yet analyzed the flux variation of each component over solar cycles. In this work, we measure the temporal variations of the flux of each component over 15 years of Fermi Large Area Telescope observations and compare them with the sunspot number and Galactic cosmic-ray flux from AMS-02 near Earth. We find that the flux variation of the disk anticorrelates with the sunspot number and correlates with cosmic-ray protons, as expected, confirming its emission mechanism. In contrast, the extended component exhibits a more complex variation: despite an initial anticorrelation with the sunspot number, we find neither anticorrelation with the sunspot number nor correlation with cosmic-ray electrons over the full 15-year period. This most likely suggests that cosmic-ray transport and modulation in the inner heliosphere are unexpectedly complex and may differ for electrons and protons or, alternatively, that there is an additional, unknown component of gamma rays or cosmic rays. These findings impact space weather research and emphasize the need for close monitoring of Cycle 25 and the ongoing polarity reversal.

astro-ph.HE↗

arXiv2025

Polarized multiwavelength emission from pulsar wind - accretion disk interaction in a transitional millisecond pulsar

Transitional millisecond pulsars (tMSPs) bridge the evolutionary gap between accreting neutron stars in low-mass X-ray binaries and millisecond radio pulsars. These systems exhibit a unique subluminous X-ray state characterized by the presence of an accretion disk and rapid switches between high and low X-ray emission modes. The high mode features coherent millisecond pulsations spanning from the X-ray to the optical band. We present multiwavelength polarimetric observations of the tMSP PSR J1023+0038 aimed at conclusively identifying the physical mechanism powering its emission in the subluminous X-ray state. During the high mode, we detect polarized emission in the 2-6 keV energy range, with a polarization degree of 12% +/- 3% and a polarization angle of -2deg +/- 9deg (1sigma) measured counterclockwise from the North celestial pole towards East. At optical wavelengths, we find a polarization degree of 1.41% +/- 0.04% and a polarization angle aligned with that in the soft X-rays, suggesting a common physical mechanism operating across these bands. Remarkably, the polarized flux spectrum matches the pulsed emission spectrum from optical to X-rays. The polarization properties differ markedly from those observed in other accreting neutron stars and isolated rotation-powered pulsars and are also inconsistent with an origin in a compact jet. Our results provide direct evidence that the polarized and pulsed emissions both originate from synchrotron radiation at the shock formed where the pulsar wind interacts with the inner regions of the accretion disk.

astro-ph.HE↗

arXiv2025

3D MHD simulations of runaway pulsars in core collapse supernova remnants

Pulsars are one of the possible final stages in the evolution of massive stars. If a supernova explosion is anisotropic, it can give the pulsar a powerful kick, propelling it to supersonic speeds. The resulting pulsar wind nebula is significantly reshaped by its interaction with the surrounding medium as the pulsar moves through it. First, the pulsar crosses the supernova remnant, followed by the different layers of circumstellar medium formed during different stages of the progenitor star s evolution. We aim to investigate how the evolutionary history of massive stars shapes the bow shock nebulae of runaway kicked pulsars, and how these influences in turn affect the dynamics and non-thermal radio emission of the entire pulsar remnant. We perform three-dimensional magnetohydrodynamic simulations using the PLUTO code to model the pulsar wind nebula generated by a runaway pulsar in the supernova remnant of a red supergiant progenitor, and derive its non-thermal radio emission. The supernova remnant and the pre-supernova circumstellar medium of the progenitor strongly confine and reshape the pulsar wind nebula of the runaway pulsar, bending its two side jets inwards and giving the nebula an arched shape for an observer perpendicular to the jets and the propagation direction, as observed around PSR J1509 5850 and Gemina. We perform the first classical 3D model of a pulsar moving inward through its supernova ejecta and circumstellar medium, inducing a bending of its polar jet that turns into characteristic radio synchrotron signature. The circumstellar medium of young runaway pulsars has a significant influence on the morphology and emission of pulsar wind nebulae, whose comprehension requires a detailed understanding of the evolutionary history of the progenitor star.

astro-ph.HE↗

arXiv2025

Identification and characterisation of the gamma-ray counterpart of the transitional pulsar candidate CXOU J110926.4-650224

Transitional millisecond pulsars (tMSPs) represent a crucial link between the rotation-powered and accretion-powered states of binary pulsars. During their active X-ray state, tMSPs are the only low-mass X-ray binary systems detected up to GeV energies by the Fermi Large Area Telescope (LAT). CXOU J110926.4-650224 is a newly discovered tMSP candidate in an active X-ray state, potentially spatially compatible with a faint gamma-ray source listed in the latest Fermi-LAT point-source catalogue as 4FGL J1110.3-6501. Confirming the association between CXOU J110926.4-650224 and the Fermi source is a key step toward validating its classification as a tMSP. In this study, we analyse Fermi-LAT data collected from August 2008 to June 2023 to achieve a more accurate localisation of the gamma-ray source, characterise its spectral properties, and investigate potential time variability. By thoroughly reconstructing the gamma-ray background around the source using a weighted likelihood model, we obtain a new localisation that aligns with the position of the X-ray source at the 95% confidence level, with a Test Statistic value of $\sim 42$. This establishes a spatial association between the gamma-ray source and CXOU J110926.4-650224. The gamma-ray emission is adequately described by a power-law model with a photon index of $Γ= 2.5 \pm 0.1$ and a corresponding flux of $(3.7\pm0.9) \times 10^{-12}$ erg cm$^{-2}$ s$^{-1}$ in the 0.1-300 GeV range.

astro-ph.HE↗

arXiv2025

Multi-band study of the flaring mode emission in the transitional millisecond pulsar PSR J1023+0038

We present a comprehensive study of the flaring mode of the transitional millisecond pulsar (tMSP) PSR J1023+0038 during its X-ray sub-luminous state, using strictly simultaneous X-ray, UV, optical, and radio observations. The X-ray flares exhibit UV and optical counterparts and coincide with the brightest radio flare observed in the past decade, reaching 1.2 mJy at 6 GHz and lasting ~1 hour. During the flare, the optical polarization drops from ~1.4% to ~0.5%, indicating the emergence of an unpolarized component. We propose that the thickening of the disc, which enlarges the shock region between the pulsar wind and the accretion flow and may drive the X-ray flaring observed in tMSPs, enhances the ionization level of the disc, thereby generating an increased number of free electrons. These electrons could then be channelled by magnetic field lines into the jet. This increased jet mass-loading could drive the associated radio and optical variability. The radio spectral evolution during flares is consistent with synchrotron self-absorption in jet ejecta or internal shocks within the compact jet. We infer radio polarization upper limits (<8.7%, <2.3%, and <8.2%, before, during, and after the radio flare) that further support a compact jet origin but do not rule out discrete ejections. Our findings suggest that tMSPs could serve as essential laboratories for investigating jet-launching mechanisms, mainly because they operate under very low mass accretion rates. This accretion regime has not been explored before in the context of the accretion-ejection coupling.

astro-ph.HE↗

arXiv2025

Periodic Gamma-ray Modulation of the blazar PG 1553+113 Confirmed by Fermi-LAT and Multi-wavelength Observations

A 2.1-year periodic oscillation of the gamma-ray flux from the blazar PG 1553+113 has previously been tentatively identified in almost 7 year of data from the Fermi Large Area Telescope. After 15 years of Fermi sky-survey observations, doubling the total time range, we report >7 cycle gamma-ray modulation with an estimated significance of 4 sigma against stochastic red noise. Independent determinations of oscillation period and phase in the earlier and the new data are in close agreement (chance probability <0.01). Pulse timing over the full light curve is also consistent with a coherent periodicity. Multiwavelength new data from Swift X-Ray Telescope, Burst Alert Telescope, and UVOT, and from KAIT, Catalina Sky Survey, All-Sky Automated Survey for Supernovae, and Owens Valley Radio Observatory ground-based observatories as well as archival Rossi X-Ray Timing Explorer satellite-All Sky Monitor data, published optical data of Tuorla, and optical historical Harvard plates data are included in our work. Optical and radio light curves show clear correlations with the gamma-ray modulation, possibly with a nonconstant time lag for the radio flux. We interpret the gamma-ray periodicity as possibly arising from a pulsational accretion flow in a sub-parsec binary supermassive black hole system of elevated mass ratio, with orbital modulation of the supplied material and energy in the jet. Other astrophysical scenarios introduced include instabilities, disk and jet precession, rotation or nutation, and perturbations by massive stars or intermediate-mass black holes in polar orbit.

astro-ph.HE↗

arXiv2024

Material mixing in pulsar wind nebulae of massive runaway stars

In this study we quantitatively examine the manner pulsar wind, supernova ejecta and defunct stellar wind materials distribute and melt together into plerions. We performed 2.5D MHD simulations of the entire evolution of their stellar surroundings and different scenarios are explored, whether the star dies as a red supergiant and Wolf Rayet supernova progenitors, and whether it moved with velocity 20 km/s or 40 km/s through the ISM. Within the post explosion, early 10 kyr, the H burning products rich red supergiant wind only mixes by <= 20 per cent, due to its dense circumstellar medium filling the progenitor bow shock trail, still unaffected by the supernova blastwave. Wolf Rayet materials, enhanced in C, N, O elements, distribute circularly for the 35 Mo star moving at 20 km/s and oblongly at higher velocities, mixing efficiently up to 80 per cent. Supernova ejecta, filled with Mg, Si, Ca, Ti and Fe, remain spherical for longer times at 20 km/s but form complex patterns at higher progenitor speeds due to earlier interaction with the bow shock, in which they mix more efficiently. The pulsar wind mixing is more efficient for Wolf Rayet (25 per cent) than red supergiant progenitors (20 per cent). This work reveals that the past evolution of massive stars and their circumstellar environments critically shapes the internal distribution of chemical elements on plerionic supernova remnants, and, therefore, governs the origin of the various emission mechanisms at work therein. This is essential for interpreting multi-frequency observations of atomic and molecular spectral lines, such as in optical, infrared, and soft X rays.

astro-ph.SR↗

arXiv2024

Millisecond pulsars phenomenology under the light of graph theory

We compute and apply the minimum spanning tree (MST) of the binary millisecond pulsar population, and discuss aspects of the known phenomenology of these systems in this context. We find that the MST effectively separates different classes of spider pulsars, eclipsing radio pulsars in tight binary systems either with a companion with a mass in the range of approximately 0.1-0.8 solar masses (redbacks) or with a companion of less than or approximately 0.06 solar masses (black widows), into distinct branches. The MST also separates black widows located in globular clusters from those found in the field and groups other pulsar classes of interest, including transitional millisecond pulsars. Using the MST and a defined ranking for similarity, we identify possible candidates likely to belong to these pulsar classes. In particular, based on this approach, we propose the black widows' classification of J1300+1240, J1630+3550, J1317-0157, J1221-0633, J1627+3219, J1737-0314A, and J1701-3006F, discuss that of J1908+2105, and analyze J1723-2837, J1431-4715, and J1902-5105 as possible transitional systems. We introduce an algorithm that quickly locates where new pulsars fall within the MST and use this to examine the positions of the transitional millisecond pulsar IGR J18245-2452 (PSR J1824-2452I), the transitional millisecond pulsar candidate 3FGL J1544.6-1125, and the accreting millisecond X-ray pulsar SAX J1808.4-3658. Assessing the positions of these sources in the MST assuming a range for their unknown variables (e.g., the spin period derivative of PSR J1824-2452I) we can effectively narrow down the parameter space necessary for searching and determining key pulsar parameters through targeted observations.

astro-ph.HE↗

arXiv2024

Pulsar wind nebulae meeting the circumstellar medium of their progenitors

A significative fraction of high mass stars sail away through the interstellar medium of the galaxies. Once they evolved and died via a core collapse supernova, a magnetized, rotating neutron star (a pulsar) is usually their leftover. The immediate surroundings of the pulsar is the pulsar wind, which forms a nebula whose morphology is shaped by the supernova ejecta, channeled into the circumstellar medium of the progenitor star in the pre supernova time. Consequently, irregular pulsar wind nebulae display a large variety of radio appearances, screened by their interacting supernova blast wave or harboring asymmetric up down emission. Here, we present a series of 2.5 dimensional non relativistic magnetohydrodynamical simulations exploring the evolution of the pulsar wind nebulae (PWNe) generated by a red supergiant and a Wolf Rayet massive supernova progenitors, moving with Mach number M eq. to 1 and M eq. to 2 into the warm phase of the galactic plane. In such a simplified approach, the progenitors direction of motion, the local ambient medium magnetic field, the progenitor and pulsar axis of rotation, are all aligned, which restrict our study to peculiar pulsar wind nebula of high equatorial energy flux. We found that the reverberation of the termination shock of the pulsar wind nebulae, when sufficiently embedded into its dead stellar surroundings and interacting with the supernova ejecta, is asymmetric and differs greatly as a function of the past circumstellar evolution of its progenitor, which reflects into their projected radio synchrotron emission. This mechanism is particularly at work in the context of remnants involving slowly moving or very massive stars. We find that the mixing of material in plerionic core collapse supernova remnants is strongly affected by the asymmetric reverberation in their pulsar wind nebulae.

astro-ph.HE↗

arXiv2024

Short-term variability of the transitional pulsar candidate CXOU J110926.4-650224 from X-rays to infrared

CXOU J110926.4-650224 is a candidate transitional millisecond pulsar (tMSP) with X-ray and radio emission properties reminiscent of those observed in confirmed tMSPs in their X-ray 'subluminous' disc state. We present the results of observing campaigns that, for the first time, characterise the optical and near-infrared variability of this source and establish a connection with the mode-switching phenomenon observed in X-rays. The optical emission exhibited flickering activity, frequent dipping episodes where it appeared redder, and a multi-peaked flare where it was bluer. The variability pattern was strongly correlated with that of the X-ray emission. Each dip matched an X-ray low-mode episode, indicating that a significant portion of the optical emission originates from nearly the same region as the X-ray emission. The near-infrared emission also displayed remarkable variability, including a dip of 20 min in length during which it nearly vanished. Time-resolved optical spectroscopic observations reveal significant changes in the properties of emission lines from the disc and help infer the spectral type of the companion star to be between K0 and K5. We compare the properties of CXOU J110926.4-650224 with those of other tMSPs in the X-ray subluminous disc state and discuss our findings within the context of a recently proposed scenario that explains the phenomenology exhibited by the prototypical tMSP PSR J1023+0038.

astro-ph.HE↗

arXiv2024

X-ray and optical observations of the millisecond pulsar binary PSRJ1431-4715

We present the first X-ray observation of the energetic millisecond pulsar binary PSR J1431-4715, performed with XMM-Newton and complemented with fast optical multi-band photometry acquired with the ULTRACAM instrument at ESO-NTT. It is found as a faint X-ray source without a significant orbital modulation. This contrasts with the majority of systems that instead display substantial X- ray orbital variability. The X-ray spectrum is dominated by non-thermal emission and, due to the lack of orbital modulation, does not favour an origin in an intrabinary shock between the pulsar and companion star wind. While thermal emission from the neutron star polar cap cannot be excluded in the soft X-rays, the dominance of synchrotron emission favours an origin in the pulsar magnetosphere that we describe at both X-ray and gamma-ray energies with a synchro-curvature model. The optical multi-colour light curve folded at the 10.8h orbital period is double-humped, dominated by ellipsoidal effects, but also affected by irradiation. The ULTRACAM light curves are fit with several models encompassing direct heating and a cold spot, or heat redistribution after irradiation either through convection or convection plus diffusion. Despite the inability to constrain the best irradiation models, the fits provide consistent system parameters, giving an orbital inclination of 59$\pm$6deg and a distance of 3.1$\pm$0.3 kpc. The companion is found to be an F-type star, underfilling its Roche lobe ( f_RL = 73$\pm$4%), with a mass of 0.20$\pm$0.04 M_sun, confirming the redback status, although hotter than the majority of redbacks. The stellar dayside and nightside temperatures of 7500K and 7400K, respectively, indicate a weak irradiation effect on the companion, likely due to its high intrinsic luminosity. Although the pulsar mass cannot be precisely derived, a heavy (1.8-2.2 M_sun) neutron star is favoured

astro-ph.HE↗

arXiv2024

Characterizing the Gamma-ray Emission Properties of the Globular Cluster M5 with the Fermi-LAT

We analyzed the globular cluster M5 (NGC 5904) using 15 years of gamma-ray data from the Fermi Large Area Telescope (LAT). Using rotation ephemerides generated from Arecibo and FAST radio telescope observations, we searched for gamma-ray pulsations from the seven millisecond pulsars (MSPs) identified in M5. We detected no significant pulsations from any of the individual pulsars. Also, we searched for possible variations of the gamma-ray emission as a function of orbital phase for all the six MSPs in binary systems, but did not detect any significant modulations. The gamma-ray emission from the direction of M5 is well described by an exponentially cutoff power-law spectral model, although other models cannot be excluded. The phase-averaged emission is consistent with being steady on a time scale of a few months. We estimate the number of MSPs in M5 to be between 1 and 10, using the gamma-ray conversion efficiencies for well-characterized gamma-ray MSPs in the Third Fermi Large Area Telescope Catalog of Gamma-ray Pulsars, suggesting that the sample of known MSPs in M5 is (nearly) complete, even if it is not currently possible to rule out a diffuse component of the observed gamma rays from the cluster.

astro-ph.HE↗

arXiv2023

Matter ejections behind the highs and lows of the transitional millisecond pulsar PSR J1023+0038

Transitional millisecond pulsars are an emerging class of sources that link low-mass X-ray binaries to millisecond radio pulsars in binary systems. These pulsars alternate between a radio pulsar state and an active low-luminosity X-ray disc state. During the active state, these sources exhibit two distinct emission modes (high and low) that alternate unpredictably, abruptly, and incessantly. X-ray to optical pulsations are observed only during the high mode. The root cause of this puzzling behaviour remains elusive. This paper presents the results of the most extensive multi-wavelength campaign ever conducted on the transitional pulsar prototype, PSR J1023+0038, covering from the radio to X-rays. The campaign was carried out over two nights in June 2021 and involved 12 different telescopes and instruments, including XMM-Newton, HST, VLT/FORS2 (in polarimetric mode), ALMA, VLA, and FAST. By modelling the broadband spectral energy distributions in both emission modes, we show that the mode switches are caused by changes in the innermost region of the accretion disc. These changes trigger the emission of discrete mass ejections, which occur on top of a compact jet, as testified by the detection of at least one short-duration millimetre flare with ALMA at the high-to-low mode switch. The pulsar is subsequently re-enshrouded, completing our picture of the mode switches.

astro-ph.HE↗