arXiv subjects

Michael Sarkis

Publications and source records attributed to Michael Sarkis.

7 recordsLinked to original sources

arXiv2026

The MeerKAT Thousand-Pulsar Polarisation Array II: Searches for Ultralight Axion-Like Dark Matter

We construct Pulsar Polarisation Arrays (PPA), using regular pulsars monitored in MeerKAT's Thousand Pulsar Array (TPA) Programme, to search for Axion-like Dark Matter (ALDM) within Milky Way. Specifically, from a catalogue of 1237 regular pulsars, we select the 50 ones with the highest signal-to-noise ratio and set upper limits on the ALDM Chern-Simons coupling. We find no signals with statistical significance over the mass range of $[10^{-23},10^{-20}]\,{\rm eV}$ in the six-year MeerKAT's data. By combining the high-quality TPA pulsars and the accurate ionospheric subtraction of spinifex, we establish the most sensitive upper limits to the date on the ALDM Chern-Simons coupling, namely $\lesssim 10^{-14} - 3\times 10^{-13}\,{\rm GeV}^{-1}$, for the mass range of $[10^{-23},10^{-21}]\,{\rm eV}$ except at $m_a \sim 1.3 \times 10^{-22}\,$eV. This study underscores the great potential of constructing regular-pulsar PPAs for scientific tasks.

astro-ph.HE↗

arXiv2026

The MeerKAT Thousand-Pulsar Polarization Array I: Properties of the Polarization and Rotation Measure Time Series Data

The polarimetry of recent pulsar observations has provided a wealth of observational data with which to test physical theories of emission mechanisms, radiative transfer and even theories that extend beyond the Standard Model. In this work, we have outlined the data analysis of the polarisation time series data of a population of 513 pulsars from the Thousand Pulsar Array observing programme, laying the foundation for building the MeerKAT Thousand-Pulsar Polarization Array as a probe for ultralight Axion-Like Dark Matter (ALDM). From this large dataset we have focused on the temporal trends in the observed polarisation angle (PA) through a measure we call the PA offset, and characterised the trends due to the effects of Faraday Rotation within the interstellar medium and the Earth's ionosphere, as well as generic white and red noise models that are estimated within a Bayesian MCMC analysis. Then, motivated by potential extra contributions to the rotation of the PA that may not be Faraday-like, arising from the proposed ALDM field, we have investigated a derived time dependence for the rotation measure (RM) required to explain the observed PA offset. Comparison of these estimates to RM values that are measured in typical pulsar studies, through a technique known as RM Synthesis, provides a probe of any wavelength-independent contribution to the rotation of the PA. Although we find no evidence for oscillatory behaviour within our dataset's observation timespan, we do find cases of deviation from the usual RM values in several `pulsars of interest', as well as long-term linear trends in the time evolution of Faraday rotation that have been presented in the literature before.

astro-ph.HE↗

arXiv2024

DarkMatters: A powerful tool for WIMPy analysis

We introduce a new software package, DarkMatters, which has been designed to facilitate the calculation of all aspects of indirect dark matter detection of WIMPs in astrophysical settings. Two primary features of this code are the improvement in performance compared to existing tools, and higher levels of accuracy when determining radio synchrotron emission associated with WIMP annihilations, both of which are enabled by the employment of a set of modern and novel numerical techniques. The code also includes functionality for a multi-wavelength set of output products including gamma-ray, radio and neutrino fluxes which can be saved in common formats used by the astronomical community, such as the FITS data file format. The calculations may be tailored to work with a wide range of astrophysical target structures, from dwarf galaxies to galaxy clusters, and the configuration of the underlying calculations is managed by a set of key-value dictionary entries that are easy to understand and use. The code base is publicly accessible through an online repository with a permissive MIT source code licence.

hep-ph↗

arXiv2024

A radio-frequency WIMP search with the MeerKAT Galaxy Cluster Legacy Survey

Radio-frequency, indirect dark matter searches have recently been gaining prevalence, due to the high sensitivity and resolution capabilities of the new generation of radio interferometers. MeerKAT is currently one of the most sensitive instruments of its kind, making it ideal for indirect dark matter searches. By making use of publicly available data from the MeerKAT Galaxy Cluster Legacy Survey we are able to use both the observed diffuse synchrotron emission and non-detections to constrain the WIMP dark matter parameter space. In addition to a subset of generic WIMP annihilation channels, we probe the dark matter candidate within the 2HDM+S particle physics model, which was developed as an explanation for anomalies observed in the Large Hadron Collider data from runs 1 and 2. By undertaking a statistical analysis of the radio flux densities within galaxy clusters we are able to exclude the thermal relic value for WIMP masses $< \, \sim 1000 $ GeV for annihilation into bottom quarks with our median case. This is competitive with the best constraints in the current literature.

astro-ph.CO↗

arXiv2023

A radio-frequency search for WIMPs in RXC J0225.1-2928

Recent studies focusing on the use of radio data in indirect dark matter detection have led to a set of highly competitive limits on the WIMP annihilation cross-section, especially in light of high-resolution data from instruments like ASKAP and MeerKAT. In this work we present an analysis of radio observations of the RXC J0225.1-2928 galaxy cluster, taken from the recent MeerKAT Galaxy Cluster Legacy Survey public data release. We adopt a robust morphological analysis of this source that allows us to derive a set of upper-limits on the annihilation cross-section, and in our most constraining scenario these results are comparable to the most stringent limits yet found in the literature.

astro-ph.HE↗

arXiv2023

Simulating the radio emissions of dark matter for new high-resolution observations with MeerKAT

Recent work has shown that searches for diffuse radio emission by MeerKAT - and eventually the SKA - are well suited to provide some of the strongest constraints yet on dark matter annihilations. To make full use of the observations by these facilities, accurate simulations of the expected dark matter abundance and diffusion mechanisms in these astrophysical objects are required. However, because of the computational costs involved, various mathematical and numerical techniques have been developed to perform the calculations in a feasible manner. Here we provide the first quantitative comparison between methods that are commonly used in the literature, and outline the applicability of each one in various simulation scenarios. These considerations are becoming ever more important as the hunt for dark matter continues into a new era of precision radio observations.

astro-ph.CO↗

arXiv2022

Galaxy clusters in high definition: a dark matter search

Recent radio-frequency probes, with the ATCA and ASKAP telescopes, have proven themselves to be at the forefront of placing indirect limits on the properties of dark matter. The latter being able to substantially exceed the constraining power of Fermi-LAT data. However, these observations were based only on dwarf galaxies, where magnetic field uncertainties are large. Here we re-examine the case for galaxy clusters, often ignored due to substantial diffuse radio backgrounds, by considering the extrapolation of known cluster surface brightness profiles down to scales observable with MeerKAT. Despite large baryonic backgrounds, we find that clusters can be competitive with dwarf galaxies. Extrapolated Coma data being able to rule out WIMPs of mass $< 700$ GeV annihilating via $b$-quarks. This is while having lesser uncertainties surrounding the magnetic field and diffusive environment. Such compelling results are possible due to a clash between the inner shape of the dark matter halo and the flat inner profile of radio halos which is most pronounced for NFW-like Einasto profiles, the presence of which having some supporting evidence in the literature.

astro-ph.CO↗