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Constraints on cyclotron features and accretion regime in the high-mass X-ray binary 4U 1700–37 from NuSTAR
No full textInternational audience4U 1700–37 is a wind-fed high-mass X-ray binary comprising a compact object, most likely a neutron star, accreting from the O6.5 Iaf+ supergiant HD 153919. Coherent pulsations have not been firmly detected and the magnetic field strength remains uncertain, with previous NuSTAR studies reporting only marginal candidate cyclotron resonant scattering features (CRSFs). We analyses all available NuSTAR observations of 4U 1700–37 to characterize its hard X-ray timing and broadband spectral properties, test the robustness of candidate CRSFs against different continuum models and epochs, and constrain the magnetic field and accretion regime of the compact object. We perform a homogeneous timing and spectral analysis of two NuSTAR observations, modeling time-averaged and intensity-resolved spectra with several continua commonly used for accreting pulsars, and use spectral simulations to quantify the significance and model dependence of putative CRSFs. No coherent pulsations are detected and we constrain the pulsed fraction to be 12 G and a quasi-spherical subsonic accretion regime with an equilibrium spin period Peq ∼ 1.9 ks. Even without a secure CRSF detection, the homogeneous multi-epoch analysis provides quantitative constraints on the magnetic field and accretion physics of 4U 1700–37 and helps reconcile previously discrepant line-energy measurements
JWST Observations of Cosmic-Ray-excited H in Barnard 68: Spatial Variations and Constraints on Cosmic-Ray Attenuation
No full textInternational audienceWe present James Webb Space Telescope (JWST) NIRSpec observations of the starless dark cloud Barnard 68 (B68) that reveal the spatially resolved signature of cosmic-ray-excited molecular hydrogen (CRXH) emissions for the first time. Following up on our initial detection of CRXH emissions from B68, we now exploit JWST’s sensitivity and spatial multiplexing to map CRXH rovibrational lines across 16 sight lines through the cloud. By disentangling the CRXH and UV-pumped H components, we isolate the para-H-dominated spectrum attributable to cosmic-ray (CR) excitation. We find that there are significant spatial variations in the ratio of the CRXH line intensity to the line-of-sight H column density; these cannot be accounted for by dust extinction alone and demonstrate a clear attenuation of the CR flux with increasing shielding column. Modeling B68 as a Bonnor–Ebert sphere, we constrain both the unshielded CR ionization rate, ζH2, and how it decreases with shielding column. At a reference depth of N(H) = 3 × 10 cm, we infer ζH2≈1.4×10−16s, a factor of ≈3 higher than the average value derived from H3+absorption studies. These results provide the most direct probe to date of CR penetration into cold, dense gas, offering new constraints on both the microphysics of CR–H interactions and the attenuation of low-energy CRs in molecular clouds. Our findings establish CRXH emission as a powerful new diagnostic of the CR environment in interstellar space
JWST imaging of the Pleiades: anisotropy of turbulence in the cold neutral medium
No full textInternational audienceInterstellar medium studies rely on magnetohydrodynamic (MHD) turbulence as a framework for interpretation. In this context, the statistical characterization of interstellar observations is of prime importance. We open a new perspective on diffuse interstellar matter by analyzing James Webb Space Telescope (JWST) observations of the Pleiades nebula with NIRCam. These observations are remarkable in that they provide a microscope view at the cold neutral medium (CNM) with a spatial resolution of 0.2 mpc (40 au). A two-dimensional Fourier analysis is used to characterize the structure of PAH emission in regions near and far from the Pleiades star Merope. To produce maps of the interstellar emission, stars and galaxies are filtered out. The final step in the data cleaning involves subtracting a component, in Fourier space, which we infer to be a residual of the near-infrared cosmic background. The PAH emission power spectra are highly anisotropic. They are well fitted with a break-free power-law, suggesting that we do not observe a specific scale for energy dissipation. Power-law indices are -3.5 near Merope and -3 in the more distant field. The magnetic field orientation, as derived from the Planck dust polarization data, aligns with the PAH anisotropy. The power anisotropy is constant across scales. These findings are discussed in relation to interstellar turbulence that may be driven by the Pleiades stars. The JWST observations of the Pleiades offer a new viewpoint for comparing observations and theoretical models, as they examine physical scales at which turbulence in the CNM is subsonic and decoupled from the thermal instability. The observations may indicate that the turbulent energy cascade in the CNM is anisotropic
GWTC-4.0: Updating the Gravitational-Wave Transient Catalog with Observations from the First Part of the Fourth LIGO-Virgo-KAGRA Observing Run
No full textInternational audienceVersion 4.0 of the Gravitational-Wave Transient Catalog (GWTC-4.0) adds new candidates detected by the LIGO, Virgo, and KAGRA observatories through the first part of the fourth observing run (O4a: 2023 May 24 15:00:00 to 2024 January 16 16:00:00 UTC) and a preceding engineering run. In this new data, we find 128 new compact binary coalescence candidates that are identified by at least one of our search algorithms with a probability of astrophysical origin and that are not vetoed during event validation. We also provide detailed source property measurements for 86 of these that have a false alarm rate < 1 \rm{yr}^{-1}. Based on the inferred component masses, these new candidates are consistent with signals from binary black holes and neutron star-black hole binaries (GW230518_125908 and GW230529_181500). Median inferred component masses of binary black holes in the catalog now range from (GW230627_015337) to (GW231123_135430), while GW231123_135430 was probably produced by the most massive binary observed in the catalog. For the first time we have discovered binary black hole signals with network signal-to-noise ratio exceeding 30, GW230814_230901 and GW231226_01520, enabling high-fidelity studies of the waveforms and astrophysical properties of these systems. Combined with the 90 candidates included in GWTC-3.0, the catalog now contains 218 candidates with and not otherwise vetoed, doubling the size of the catalog and further opening our view of the gravitational-wave Universe
Jet launching from the Kerr black hole magnetosphere: An electrogeodesic approach
No full textInternational audienceThe launch of relativistic jets of plasma on astrophysical to cosmological scales are observed in a variety of astrophysical sources, from active galactic nuclei to X-rays binaries. While these jets can be reproduced by the general relativistic magneto-hydrodynamic (GRMHD) and particle-in-cells (GRPIC) simulations of the dynamical Kerr magnetosphere, the development of analytic models to describe the physics of the jets has remained limited. A key challenge is to analytically describe the individual trajectories of accelerated charged particles which ultimately build up the jet and emit radiation. In this work, we provide a first simple but fully analytical model of jet launching from the Kerr magnetosphere based on the motion of charged particles. To that end, we use the integrability of electrogeodesic motion in the Kerr monopole magnetosphere to study the ejection of charged particles near the poles. This enables us to derive (i) a criterion for the rotation axis to constitute a stable latitunal equilibrium position, thereby representing an idealized jet, (ii) the expression for the magnetic frame-dragging effect, and (iii) the condition for an asymptotic observer to measure blueshifted particles emanating from the black hole surroundings. Our study reveals that particles can be accelerated only in a specific region whose maximal radius depends on the spin and magnetization of the black hole. Alongside these results, we provide a detailed review of the construction of test magnetospheres from (explicit and hidden) symmetries of the Kerr geometry and the condition for the separability of the electrogeodesic motion in a test magnetosphere, which serves as a basis for the model we study in this work
A sub-ppm upper limit on the cosmological variations of the fine structure constant alpha
No full textInternational audienceAbsorption spectroscopy toward high-redshift quasars provides strong constraints on the putative variation of fundamental constants of physics on cosmological time scales. The submillimeter ground-state transitions of methylidyne (CH) and water (H2O), both molecules widespread and coeval in the interstellar medium, provide a sensitive test for variations of alpha, the fine structure constant, and mu, the proton-to-electron mass ratio, taking advantage of the unmatched spectral resolution and frequency reliability of radio techniques. We used ALMA simultaneous observations of the two species to constrain any velocity offset between their absorption profiles toward the radio-bright lensed quasars PKS1830-211 (z_abs=0.88582) and B0218+357 (z_abs=0.68466). Our observational setup minimizes instrumental errors and known sources of systematics, such as time variability of the absorption profile and frequency-dependent morphology of the background quasar. The excellent correlation between CH and H2O opacities, the large number of individual narrow velocity components, and the number of independent spectra obtained due to the intrinsic time variability of the absorption profiles ensure that even the chemical segregation bias is minimized. We obtained bulk velocity shifts delta_v = -0.048 pm 0.028 km/s and -0.13 pm 0.14 km/s (1 sigma confidence level) between CH and H2O in the direction of PKS1830-211(NE) and B0218+357(SW), respectively. These values convert into the 3sigma upper limits |Delta_alpha/alpha| < 0.55 ppm and 1.5 ppm, respectively, taking into account the independent upper limits on |Delta_mu/mu| previously obtained for these systems. These constraints on |Delta_alpha/alpha|, at look-back times of about half the present age of the Universe, are two to four times deeper than previous constraints on any other single high-z system
HALO I: Photometric continuum reverberation mapping of Fairall 9
No full textInternational audienceWe investigate the origin of inter-band continuum time delays in active galactic nuclei (AGNs) to study the structure and properties of their accretion disks. We aim to measure the inter-band continuum time delays through photometric monitoring of Seyfert galaxy Fairall 9 to construct the lag-spectrum. Additionally, we explain the observed features in the Fairall 9 lag-spectrum and discuss the potential drivers behind them, based on our newly collected data from the Obserwatorium Cerro Murphy (OCM) telescope. We initiated a long-term, continuous AGN photometric monitoring program in 2024, titled 'Hubble constant constraints through AGN Light curve Observations' (HALO) using intermediate and broad band filters. Here, we present the first results from HALO, focusing on photometric light curves and continuum time-delay measurements for Fairall 9. To complement these observations and extend the wavelength coverage of the lag-spectrum, we also reanalyzed archival Swift light curves and spectroscopic data available in the literature. Using HALO and Swift light curves, we measured inter-band continuum delays to construct the lag-spectrum of Fairall 9. Excess lags appear in the and bands (Balmer continuum contamination) and in the band (Paschen jump/dust emission from the torus). Overall, the lag-spectrum deviates significantly from standard disk model predictions. We find that inter-band delays deviate from the power-law, due to BLR scattering, reprocessing, and dust contributions at longer wavelengths. Power-law fits are therefore not well suited for characterizing the nature of the time delays
A glitch in the millisecond pulsar J09003144
No full textInternational audienceWe report the detection of a glitch in the millisecond pulsar (MSP) PSR J09003144, which is included in the European, MeerKAT and Parkes pulsar timing array experiments. The dataset combines observations from the MeerKAT, Nançay, Lovell, and Murriyang telescopes, spanning a total baseline of approximately 14 years. The glitch occurred on MJD~59942(17), with a measured fractional spin frequency step of . This event represents the third glitch detected in a MSP, following those in PSRs B182124A and J06130200. Although smaller in amplitude than the previous two, the glitch in PSR J09003144 is of a comparable order of magnitude. The updated MSP glitch rate is glitches per pulsar per year, which suggests it is likely current PTAs will detect another MSP glitch within five years. Using simulations, we demonstrate that such small glitches can go undetected, especially in short datasets such as those from new PTAs, and can bias the inferred achromatic noise model parameters, potentially leading to the down-weighting of the pulsar in gravitational wave background searches
Leptonic and Hadronic Models of High-energy Nebula Around V4641 Sgr
No full textInternational audienceA prominent, 200-pc-scale high-energy nebula surrounding the microquasar V4641~Sgr is the brightest known gamma-ray source in the Southern sky at . In this paper, we develop self-consistent leptonic, hadronic, and leptohadronic models that reproduce both the observed spectrum and morphology of the source. Purely leptonic models are energetically more favorable yet they require rather specific morphological assumptions. The gamma-ray morphology of the source can be better explained within a hadronic scenario based on the identification of cold gas structures spatially correlated with the observed gamma-ray emission. However, a purely hadronic model for the source emission requires a substantial energy reservoir in protons and fails to reproduce the extended X-ray emission recently detected by XRISM. We show that emission including a combination of leptonic and hadronic components can reproduce both the spectral and morphological properties of the source. We provide predictions for the X-ray and neutrino spectra of~the~nebula that can discriminate the hadronic and leptonic contributions to the overall source signal