Browsing by Author "Serylak, M"

Now showing 1 - 4 of 4
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    Anomalous gas in ESO 149-G003: A MeerKAT-16 view
    (Oxford University Press, 2021) Jozsa, G.I.G; Thorat, K; Serylak, M
    ESO 149-G003 is a close-by, isolated dwarf irregular galaxy. Previous observations with the ATCA indicated the presence of anomalous neutral hydrogen (H I) deviating from the kinematics of a regularly rotating disc. We conducted follow-up observations with the MeerKAT radio telescope during the 16-dish Early Science programme as well as with the MeerLICHT optical telescope. Our more sensitive radio observations confirm the presence of anomalous gas in ESO 149-G003, and further confirm the formerly tentative detection of an extraplanar H I component in the galaxy. Employing a simple tilted-ring model, in which the kinematics is determined with only four parameters but including morphological asymmetries, we reproduce the galaxy's morphology, which shows a high degree of asymmetry. By comparing our model with the observed H I, we find that in our model, we cannot account for a significant (but not dominant) fraction of the gas. From the differences between our model and the observed data cube, we estimate that at least 7-8 per cent of the H I in the galaxy exhibits anomalous kinematics, while we estimate a minimum mass fraction of less than 1 per cent for the morphologically confirmed extraplanar component.
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    The impact of solar wind variability on pulsar timing
    (EDP Sciences, 2021) Serylak, M; Tiburzi, C; Shaifullah, G.M
    Context. High-precision pulsar timing requires accurate corrections for dispersive delays of radio waves, parametrized by the dispersion measure (DM), particularly if these delays are variable in time. In a previous paper, we studied the solar wind (SW) models used in pulsar timing to mitigate the excess of DM that is annually induced by the SW and found these to be insufficient for high-precision pulsar timing. Here we analyze additional pulsar datasets to further investigate which aspects of the SW models currently used in pulsar timing can be readily improved, and at what levels of timing precision SW mitigation is possible. Aims. Our goals are to verify: (a) whether the data are better described by a spherical model of the SW with a time-variable amplitude, rather than a time-invariant one as suggested in literature, and (b) whether a temporal trend of such a model's amplitudes can be detected. Methods.
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    PSRJ1910–5959A: A rare gravitational laboratory for testing white dwarf models
    (EDP Sciences, 2023) Corongiu, A; Venkatraman, Krishnan V; Freire, P C C; Kramer, M; Serylak, M
    Context. PSR J1910-5959A is a binary millisecond pulsar in a 0.837 day circular orbit around a helium white dwarf (HeWD) companion. The position of this pulsar is 6.3 arcmin (∼74 core radii) away from the optical centre of the globular cluster (GC) NGC 6752. Given the large offset, the association of the pulsar with the GC has been debated. Aims. We aim to obtain precise measurements of the masses of the stars in the system along with secular orbital parameters, which will help identify if the system belongs to the GC. Methods. We have made use of archival Parkes 64 m 'Murriyang'telescope data and carried out observations with the MeerKAT telescope with different backends and receivers over the last two decades. Pulse times of arrival were obtained from these using standard pulsar data reduction techniques and analysed using state-of-the-art Bayesian pulsar timing techniques. We also performed an analysis of the pulsar's total intensity and polarisation profile to understand the interstellar scattering along the line of sight, and we determined the pulsar's geometry by fitting the rotating vector model to the polarisation data. Results. We obtain precise measurements of several post-Keplerian parameters: the range, r = 0.202(6) TȮ, and shape, s = 0.999823(4), of the Shapiro delay, from which we infer: the orbital inclination to be 88.9-0.14+0.15 deg; the masses of the pulsar and the companion to be 1.55(7) MȮ and 0.202(6) MȮ, respectively; a secular change in the orbital period Pb = -53-6.0+7.4 × 10-15 s s-1 that proves the GC association; and a secular change in the projected semi-major axis of the pulsar, x = -40.7-8.2+7.3 × 10-16 s s-1, likely caused by the spin-orbit interaction from a misaligned HeWD spin, at odds with the likely isolated binary evolution of the system. We also discuss some theoretical models for the structure and evolution of white dwarfs in neutron star-white dwarf binaries, using PSR J1910-5959A's companion as a test bed. Conclusions. PSR J1910-5959A is a rare system for which several parameters of both the pulsar and the HeWD companion can be accurately measured. As such, it is a test bed for discriminating between alternative models of HeWD structure and cooling.
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    The thousand-Pulsar-Array programme on MeerKAT - VI. Pulse widths of a large and diverse sample of radio pulsars
    (Oxford, 2022) Posselt, B; Karastergiou, A; Serylak, M
    We present pulse width measurements for a sample of radio pulsars observed with the MeerKAT telescope as part of the Thousand-Pulsar-Array (TPA) programme in the MeerTime project. For a centre frequency of 1284 MHz, we obtain 762 W10 measurements across the total bandwidth of 775 MHz, where W10 is the width at the 10 per cent level of the pulse peak. We also measure about 400 W10 values in each of the four or eight frequency sub-bands. Assuming, the width is a function of the rotation period P, this relationship can be described with a power law with power law index μ = -0.29 ± 0.03. However, using orthogonal distance regression, we determine a steeper power law with μ = -0.63 ± 0.06. A density plot of the period-width data reveals such a fit to align well with the contours of highest density. Building on a previous population synthesis model, we obtain population-based estimates of the obliquity of the magnetic axis with respect to the rotation axis for our pulsars. Investigating the width changes over frequency, we unambiguously identify a group of pulsars that have width broadening at higher frequencies. The measured width changes show a monotonic behaviour with frequency for the whole TPA pulsar population, whether the pulses are becoming narrower or broader with increasing frequency. We exclude a sensitivity bias, scattering and noticeable differences in the pulse component numbers as explanations for these width changes, and attempt an explanation using a qualitative model of five contributing Gaussian pulse components with flux density spectra that depend on their rotational phase.