Intermediate polars (IPs), a subclass of magnetic cataclysmic variables, often show discrepancies between white-dwarf (WD) mass measurements from X-ray spectral modeling and optical dynamical studies. We investigate the IP IGR J17014-4306. We performed a joint spectral analysis of NuSTAR observations combined with archival XMM-Newton and Swift data, modeling the broad-band X-ray spectrum with a multi-temperature cooling-flow model. Additionally, we obtained time-resolved optical spectroscopy with the SOAR telescope to measure the radial velocity of the donor star and constrain the system's orbital parameters. The X-ray spectral analysis reveals a very high post-shock plasma temperature of kT_max=50_-8^+11 keV, corresponding to a WD mass of M_WD=0.94_-0.07^+0.09 M_⊙. We also fitted the NuSTAR spectrum above 10 keV with the ipolar30KK model, obtaining M_WD=0.88_-0.12^+0.14 M_⊙. Our optical spectroscopy yields a radial-velocity semi-amplitude for the companion star of K_2=165±4 km s^-1 and an optical mass function of f(M)=0.249±0.018 M_⊙. Combined with the eclipse geometry and the WD mass estimate from the X-ray models, these results favor a high mass ratio, 0.76≲ q≲0.95, and a donor-star mass of approximately 0.67≲ M_2/M_⊙≲0.89. In the limiting case of q=1, the WD mass has an upper limit of 1.14 M_⊙. Together with the X-ray measurements, this indicates a relatively massive WD. The lack of an independent measurement of the WD dynamical mass leaves it unclear whether the dynamical mass is consistent with the X-ray measurements or whether the X-ray mass is underestimated, as has been found for other IPs. Thus, our constraints make IGR J17014-4306 an important system for improving our understanding of IPs.
We investigate rotating black holes surrounded by perfect-fluid dark matter (PFDM), described by the parameter k, and determine the Kerr-connected region of the (a/M, k/M) parameter space that contains an event horizon. The critical value kc(a), obtained from the degenerate-horizon conditions Δ(rc)=Δ′(rc)=0, defines the boundary between black-hole and horizonless configurations. We derive an exact parametric form of this extremal boundary and show that its near-Kerr behavior includes a logarithmic correction; therefore, kc/M≃2.8828(1−a/M)1.5377 is only an empirical fit over 0.90 ≤ a/M ≤ 0.999, not an asymptotic scaling law. For horizon-bearing solutions, we calculate unstable spherical photon orbits and the shadow’s mean radius, area, and distortion, finding that increasing k/M shifts the photon region inward and reduces the shadow size. Backward ray tracing through a phenomenological optically thin disk, tested on independent 412, 812, and 1612 image grids, confirms this trend: for a/M=0.9 and an inclination of 17∘, the 20 μas beam-convolved ridge diameter decreases from 42.47 to 37.88 μas as k/M increases from 0 to 0.08, with the two finest grids agreeing to within 0.5%. Thus, PFDM produces a consistent contraction from the horizon and photon region to the geometric shadow and image ridge, although these illustrative images do not provide an Event Horizon Telescope constraint because they lack a self-consistent emission model and interferometric likelihood analysis.
Variations in the shapes of individual pulses introduce a broadband noise component in pulsar times of arrival beyond what is expected from radiometer noise, referred to as the jitter noise. This noise limits the timing accuracy and, consequently, the sensitivity required for the detection of nanohertz gravitational waves using pulsar timing arrays. Accurate characterization of jitter noise, including its amplitude and frequency dependence, is therefore essential for each pulsar. In this work, we present the first detailed study of jitter noise in PSR J1744 - 1134 over the frequency range 300–500 MHz, using observations from the Indian Pulsar Timing Array experiment conducted with the upgraded Giant Metrewave Radio Telescope. We detect clear signatures of jitter in this pulsar through pulse-level analysis and Bayesian inference. Furthermore, we investigated the frequency dependence of the jitter noise and compared our results with earlier measurements at higher frequencies. The observed differences in jitter amplitude suggest a possible frequency evolution, highlighting the importance of low-frequency studies for improving pulsar timing precision and accuracy. We also investigated the effect of jitter on the high precision dispersion measure derived from our observations and found that jitter is not the limiting factor for DM precision achieved for this pulsar in the given observation timescale.
We investigate the long-term spin evolution of high-mass X-ray binary (HMXB) pulsars in the Small Magellanic Cloud (SMC) using archival measurements of spin periods and period derivatives from XMM-Newton, Chandra, and RXTE. In the P–|P˙| plane, the HMXB pulsars follow an approximately linear relation in log–log space with slope 1.02 ± 0.11, similar to the trend shown by the youngest isolated rotation-powered pulsars (RPPs) (e.g., Lorimer and Kramer, 2005; Manchester et al., 2005). For comparison, young RPPs from the ATNF Pulsar Catalogue give slopes that depend strongly on the characteristic-age cut (1.10 ± 0.16 for τc < 104 yr and 0.72 ± 0.08 for τc < 105 yr), whereas the full non-recycled population shows no significant correlation. The HMXB pulsars lie in the same range of τc ( ∼ 1–10 kyr) as the youngest RPPs, but at spin periods two to three orders of magnitude longer. Reference characteristic-age contours in the HMXB P–|P˙| plane are roughly parallel to this relation, consistent with a continuous evolutionary sequence.If the measured long-term spin-up rates were sustained, slowly rotating accreting pulsars would reach spin periods typical of isolated radio pulsars within only ∼ 102–104 yr; for example, SXP 101 (P ≈ 101 s, |P˙|≈1.9×10−9 s s−1) would reach P ∼ 1 s after ∼ 2 × 103 yr. Because these timescales are far shorter than the lifetimes of the Be donors, the spin at the end of the accretion phase is more likely set by torque equilibrium than by uninterrupted spin-up. We suggest that a subset of isolated neutron stars may descend from accretion-powered HMXB pulsars following binary disruption, most plausibly at the supernova of the donor star (e.g., Bhattacharya and van den Heuvel, 1991; Tauris and Takens, 1998), providing an observational link between accretion-powered and rotation-powered neutron-star populations.
In the present work, we investigate a bulk-viscous cosmological model in the framework of f(Q, Lm) gravity, where the non-metricity scalar (Q) is non-minimally coupled to the matter Lagrangian Lm. The free parameters of the model are constrained through Bayesian statistical analysis using Cosmic Chronometers (CC), Pantheon+SH0ES Type Ia supernovae, and DESI baryon acoustic oscillation datasets, both individually and jointly. The reconstructed Hubble evolution exhibits good agreement with observational data and provides insights into the ongoing Hubble tension. Furthermore, the cosmological dynamics are examined through the evolution of the effective equation of state parameter, deceleration parameter, and energy conditions. Overall, the proposed bulk-viscosity model in the f(Q, Lm) framework offers a viable modified-gravity scenario that successfully accounts for the late-time evolution of the Universe and sheds light on the Hubble tension.
