Santiago del Palacio

Forward shocks produced by interactions between a single ejected blob and the circumnuclear medium (CNM) around a supermassive black hole are widely invoked to explain radio emission from tidal disruption events (TDEs). However, recent observational evidence such as rapidly rising radio emission, double-peaked broadband spectral energy distributions, and declining shock energies at late times poses challenges to this picture. Alternative scenarios have therefore been proposed, including bow shocks arising from outflows colliding with dense clouds, the production of new ejecta at late times, and variations in microphysical parameters. To investigate the roles of these factors, we analyze the long-lived radio flare of the TDE candidate AT 2019avd, for which dust has been identified through mid-infrared observations, using a radio dataset spanning more than 5 yr. We find that a bow-shock scenario can account for the majority of the observed radio emission, while a forward shock, or an additional bow shock involving different clouds, may begin to dominate at late times. However, a forward-shock scenario remains viable when allowing for evolving microphysical parameters and more complex CNM structures. We discuss the remaining tensions in both the outflow–CNM and outflow–cloud interaction scenarios.

Context . Galaxy mergers drive intense radiation environments that fundamentally alter interstellar dust properties through photo-destruction and thermal processing. The luminous infrared galaxy II Zw 096 presents several distinctive regions, including starburst clumps and a proposed buried Active galactic nucleus (AGN) in region D1, making it an ideal laboratory for studying dust evolution under extreme conditions. Aims . This work aims to determine the carbonaceous dust properties across II Zw 096 by characterizing the spatial variations in carbonaceous feature ratios and to investigate how intense radiation fields process carbonaceous dust grains, using the relationship between dust processing signatures and traditional radiation field diagnostics. Methods . Using JWST NIRSpec IFU and MIRI MRS, carbonaceous features were observed and analyzed using the Continuum and Feature Extraction tool (CAFE) with 61 carbonaceous features from the PDRs4all project and new absorption features for ice and crystalline silicates. We analyze spatial variations in carbonaceous feature ratios at multiple resolutions (0.281″, 0.787″, and 0.961″) to trace dust composition and grain-size distribution. The 3.4/3.3 µm ratio probes aliphatic versus aromatic content, while the 11.3/3.3 µm ratio diagnoses grain-size distribution. Results . The 3.4/3.3 µm ratio spans between 0.056–0.148, with the lowest values near the proposed AGN (D1) and starburst clumps (C0, D0), indicating preferential destruction of C–H bonds connected to aliphatic structures in highly irradiated environments. The 11.3/3.3 µm ratio varies from 0.334 to ∼2.348 in D1. Both polycyclic aromatic hydrocarbon (PAH) ratios show no clear correlation with [Ne III]/[Ne II], suggesting ionization diagnostics break down either in extreme merger environments or as an effect of tracing different interstellar medium (ISM) phases and radiation-field regimes in this highly obscure merger environment. We detect water ice (3.1 µm), CO ₂ ice (4.27 µm), and crystalline silicates (11.1 µm) with spatial distributions anti-correlating with carbonaceous processing signatures. Conclusions . Spatial resolution critically affects dust diagnostics: the 3.4/3.3 µm dynamic range doubles when increasing the resolution from 0.961″ to 0.281″, demonstrating that apparent uniformity at low resolution masks significant variations in compact regions undergoing intense dust processing. Multiple coherent diagnostics point to intense dust processing, such as photo-destruction of the smallest nanograins and aromatisation, consistent with a buried AGN in D1, although definitive confirmation remains elusive.

Context. Multimessenger observations of the Seyfert-starburst composite galaxies NGC 1068 and NGC 7469 indicate a characteristic feature in the radio band (the so-called millimeter bump) as well as indication of high-energy neutrinos by the active galactic nucleus (AGN) corona. Moreover, the starburst ring of these sources is bright in the radio, and hence a potential source of γ -rays and neutrinos. Aims. We aim to explain the nonthermal features of these two sources with our homogeneous steady-state Seyfert-starburst composite model, which we refined in this work. Hereby, we account for stochastic diffuse acceleration and energy losses within the corona and γγ -pair attenuation of the escaping γ -rays. Methods. Since the nonthermal features of these Seyfert sources make a minor contribution in the electromagnetic spectrum, we are left with just a few data points that can be attributed to the starburst ring or the AGN corona. Hence, a proper inclusion of the prior information on the physical parameters is needed and subsequently used in the context of a Markov chain Monte Carlo approach to avoid overfitting. Results. Based on this Bayesian parameter study, we show that the nonthermal features of NGC 1068 can be explained well. Still a more detailed treatment of the spatial inhomogeneities in the central region of the AGN could further improve the fit results. This manifests itself even more clearly in the case of NGC 7469, where the millimeter bump needs to emerge from a coronal size of R _c > 100 ℛ _s (with the Schwarzschild radius ℛ _s ), whereas (tera-electronvolt–peta-electronvolt)-neutrino emission requires R _c < 10 ℛ _s . Conclusions. Similar to what has previously been shown in other wave bands, our analysis highlights that the spatial extension of the so-called AGN corona depends on the considered energy of the messenger. Hence, it seems that there is not a unique edge of the corona and substantial progress in the understanding of these phenomena is expected if future analysis is to account for these spatial inhomogeneities.

Rotating nonaxisymmetric neutron stars (NSs) are promising sources for continuous gravitational waves (CWs). CWs may, if detected, inform us about the internal structure and equation of state of NSs. Here, we present a narrowband search for CWs from known pulsars, for which a matched-filter search can be applied. Narrowband searches are robust to mismatches between electromagnetic (EM) and gravitational emissions, in contrast to fully targeted searches where they are assumed to be phase-locked. In this work, we search for the CW counterparts emitted by 34 pulsars using data from the first and second parts of the fourth LIGO–Virgo–KAGRA observing run. We use the 5n-vector narrowband pipeline, which applies frequency-domain matched filtering. In previous searches, it covered a narrow range in the frequency—frequency time derivative ( f — f ̇ ) space. Here, we also explore a range in the second time derivative of the frequency f ̈ around the EM observations. Additionally, for the first time, we target sources in a binary system with this kind of search. We find no evidence for CWs and therefore set upper limits on the strain amplitude emitted by each pulsar. For 20 analyses, we report an upper limit below the theoretical spin-down limit. The tightest constraint is for pulsar PSR J0534+2200 (the Crab pulsar), for which our strain upper limit on the CW amplitude corresponds to ≤0.04% of the spin-down power being radiated in the CW channel.

A tight correlation between nuclear millimeter and X-ray emission has recently been found in nearby ( z < 0.01) and low-Eddington ratio ( λ _Edd < 0.1) radio-quiet active galactic nuclei (AGNs), suggesting a common origin in the hot X-ray corona. We test this relation in nine more distant AGNs ( z ∼ 0.06–0.16) with higher bolometric luminosities ( log ( L bol / erg s − 1 ) = 45.3 –46.3), Eddington ratios ( λ _Edd = 0.19–0.85), and X-ray bolometric corrections ( κ = 29–194), selected from the Burst Alert Telescope (BAT) survey. We obtained observations with Swift at 2–10 keV and quasi-simultaneous observations with the Atacama Large Millimeter/submillimeter Array at 100 GHz with high angular resolution ( . ″ 14 arcsec). We find that these high-luminosity AGNs lie above the millimeter/X-ray correlation defined by lower-luminosity sources. A joint fit to both samples yields a second-degree polynomial with an intrinsic scatter of 0.32 dex. Furthermore, the millimeter emission correlates linearly with both the UV disk luminosity and L _bol , with intrinsic scatters of 0.45 and 0.35 dex, respectively. We propose that the deviation from the linear millimeter/X-ray relation arises from a two-component coronal electron population: thermal electrons that produce X-rays, but become less efficient at higher luminosities, and nonthermal electrons that produce millimeter emission and remain tied to L _bol . Additional millimeter emission from outflow-driven shocks may also contribute, though spectral energy distribution modeling and spectral index studies favor a coronal origin.

Among known neutron stars, the Vela pulsar is one of the best targets for gravitational-wave searches. It is also one of the most prolific in terms of glitches, which are sudden frequency changes in a pulsar’s rotation. Such glitches could cause a variety of transient gravitational-wave signals. Here, we search for signals associated with a Vela glitch on 2024 April 29 in data of the two LIGO detectors from the fourth LIGO–Virgo–KAGRA observing run. We search both for seconds-scale burst-like emission, primarily from fundamental ( f -)mode oscillations, and for longer quasi-monochromatic transients up to 4 months in duration, primarily from quasi-static quadrupolar deformations. We find no significant detection candidates, but for the first time we set direct observational upper limits on gravitational strain amplitude that are stricter than what can be indirectly inferred from the overall glitch energy scale. We discuss the short- and long-duration observational constraints in the context of specific emission models. These results demonstrate the potential of gravitational-wave probes of glitching pulsars as detector sensitivity continues to improve.

Context . Particle-accelerating colliding-wind binaries (PACWBs) are multiple systems of massive stars in which strong stellar winds collide, accelerating particles to relativistic energies. This population of relativistic particles emits NT radiation, including synchrotron radiation in the radio domain. This emission is expected to be linearly polarized, but the polarization signature has not yet been detected for a PACWB. Aims . Our objective is to quantify the linear polarization of synchrotron radiation in two well-known PACWBs and to interpret our measurements within the framework of the physics of these specific NT emitters. Methods . We observed the PACWBs WR 147 and HD 167971 with the Very Large Array (VLA) radio interferometer in the frequency bands L and C (1–2 and 4–8 GHz, respectively), where synchrotron emission is expected to be more prominent. We performed polarization calibration and analyzed the resulting Stokes maps. Results . We did not detect any polarization signature for either of the two targets in either of the two bands, even when considering narrower bands to mitigate the effect of bandpass depolarization. The most conservative upper limit on the polarization degree is on the order of 1% for both targets. Conclusions . The lack of linear polarization for the two targets is likely attributable to a combination of effects, including the turbulent nature of the magnetic field in the synchrotron-emitting region, and depolarization processes based on Faraday rotation that are certainly active in these sources. Their complex geometry, unresolved by the VLA at these frequencies, is most likely to lead to beam depolarization. We emphasize that, in contrast to other canonical synchrotron sources, PACWBs are also subject to thermal dilution. This is especially relevant for systems with stars whose winds are strong enough to contribute copiously to thermal emission, such as those harboring a Wolf-Rayet component.

Context. XTE J1810−197 is one of the six magnetars that exhibit radio emission, sometimes visible only during periods of increased activity or outbursts. XTE J1810−197 underwent its latest outburst in December 2018. Aims. We analyzed the population of single pulses of XTE J1810−197 in radio, characterized its timing properties, and explored the potential connection between magnetars and fast radio bursts (FRBs). Methods. We observed XTE J1810−197 between 29 September 2022 and 14 July 2023 with the radio telescopes at the Argentine Institute of Radioastronomy (IAR). We searched for single pulses in time series at a dispersion measure (DM) range of 100–400 pc cm ⁻³ , with a signal-to-noise ratio (S/N) threshold of 8. We folded each observation to obtain an integrated pulse profile. We also analyzed archival X-ray observations of the MAXI instrument from the same period, and studied the flux evolution and the magnetar’s activity. Results. We found 249 giant pulses (GPs) at a DM mean value of 178.8 ± 0.1 pc cm ⁻³ . We measured peak flux densities up to 119 Jy, and fluences up to 58 Jy ms. We fitted a power-law distribution to the flux density, obtaining an index of −4.0 ± 0.3. We observed a maximum rate of approximately 15 pulses per hour on 20 February 2023, followed by an abrupt disappearance of transient radio emission, indicating a transition to a less active state. The brightest single pulses are limited to ∼2% of the rotational phase and have similar fluence values to the reported intermediate FRB-like bursts of SGR 1935+2154. No significant X-ray activity in the MAXI data was detected during the radio observing period. Conclusions. This is the first study of single radio pulses of a magnetar using IAR data, showing the potential of the upgraded telescopes for investigating the transient radio sky. The properties of the single pulses detected here show the magnetar transient nature and capability to emit high-luminosity pulses. We compared the detected emission to FRB-like bursts and single pulses emitted by SGR 1935+2154. Even though the mechanism producing all the events should be coherent, the luminosity of the events, features on the dynamic spectra, and the difference between being phase confined or not, indicate that XTE J1810−197 presents GP emission, while SGR 1935+2154 only shows normal single pulses or FRB bursts. This could indicate that the conditions for producing each type of event differ.