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Abstract:

Accurately localizing fast radio bursts (FRBs) is essential for understanding their birth environments and for their use as cosmological probes. Recent advances in radio interferometry, particularly with MeerKAT, have enabled the localization of individual bursts with arcsecond precision. In this work, we present the localization of 15 apparently non-repeating FRBs detected with MeerKAT. Two of the FRBs, discovered in 2022, were localized in 8 s images from the projects that MeerTRAP was commensal to, while eight were localized using the transient buffer (TB) pipeline, and another one through SeeKAT, all with arcsecond precision. Four additional FRBs lacked TB triggers and sufficient signal, limiting their localization only to arcminute precision. For eight of the FRBs in our sample, we identify host galaxies with greater than 90 per cent confidence, and one with 80 per cent confidence, while two FRBs have ambiguous associations. We measured spectroscopic redshifts for six host galaxies, ranging from 0.33 to 0.85, demonstrating MeerKAT’s sensitivity to high-redshift FRBs. We modelled the spectral energy distributions of host galaxies with sufficient photometric coverage to derive their stellar population and star formation properties. This work represents one of the largest uniform samples of well-localized distant FRBs to date, laying the groundwork for using MeerKAT FRBs as cosmological probes and understand how FRB hosts evolve at high redshift.

Abstract:

Context. Jets from accreting black-hole (BH) X-ray binary (XRB) systems are powerful outflows that release a large fraction of the accretion energy to the surrounding environment, providing a feedback mechanism that may alter the properties of the interstellar medium (ISM). Studying accretion processes alongside their feedback on the environment may enable one to estimate the matter and energy input and output around accreting BHs. Aims. We aim to study the extended jet structures around the BH XRB GRS 1758–258. First observed in VLA data, these parsec-scale jet structures originate from jet-ISM interaction, and are characterised by a peculiar Z-shape morphology. Methods. Using the MeerKAT radio telescope we observed GRS 1758–258 in the L band for a total exposure of 7 hr. Following a calorimetry-based method originally proposed for active galactic nuclei (AGN) and later applied to X-ray binaries, we estimated the properties of the jets and of the surrounding ISM. Results. We detect a jet and a counter-jet terminating in bow-shock structures induced by their interaction with the ISM. We identified both synchrotron and bremsstrahlung emitting regions within the northern lobe, while the southern lobe is dominated by thermal emission. We measured an ISM particle density of between 10 and 40 cm −3 across both the northern and southern jets, slightly lower in the northern region. The estimated ages of the two jet sides range from 6 to 51 kyr, with the northern jet seemingly younger than the southern one. The time-averaged transferred jet energy for both jets falls between 4.4 × 10 33 and 3.3 × 10 36 erg s −1 , with slight differences between the northern and southern jets ascribed to different local environmental conditions. Comparing the new MeerKAT with archival VLA observations, we measured a proper motion of a portion of the northern jet of ∼130 mas/year. Conclusions. Jet-ISM interaction structures on both sides of GRS 1758–258 reveal different local ISM properties. The comparison between the morphology of these structures and those from other XRBs indicates that the lobes in GRS 1758–258 may be younger and may result from a number of jet activity phases. The estimated time-averaged energy transferred to the environment is slightly lower than, but comparable to, that observed in other XRBs, consistent with the younger age of the lobes in GRS 1758–258 relative to those of other systems.

Abstract:

Context. The H I mass function (HIMF) is a crucial tool for understanding the evolution of the H I content in galaxies over cosmic time and, hence, to constraining both the baryon cycle in galaxy evolution and the reionization history of the Universe. Aims. We aim to derive semiempirical constraints at z ∼ 0.37 by combining literature results on the stellar mass function from optical surveys with recent findings on the M HI − M ⋆ scaling relation derived via spectral stacking analysis applied to 21 cm line interferometric data from the MIGHTEE and CHILES surveys, conducted with the MeerKAT and VLA radio telescopes, respectively. Methods. We drew synthetic stellar mass samples directly from the publicly available results underlying the analysis of the COSMOS2020 galaxy photometric sample. We then converted M ⋆ into M HI using analytical fitting functions to the data points from H I stacking. We next fit a Schechter function to the median HIMF from all the samples via Monte Carlo Markov chains. We finally derived the posterior distribution for Ω HI by integrating the models for the HIMF built from the posteriors samples of the Schechter parameters. Results. We find a deviation of the HIMF at z ∼ 0.37 from the results at z ∼ 0 from the ALFALFA survey and at z ∼ 1 from uGMRT data. Our results for Ω HI are in broad agreement with other literature results and follow the overall trend on Ω HI as a function of redshift. The derived value Ω HI = (7.02 +0.59 −0.52 ) × 10 −4 at z ∼ 0.37 from the combined analysis deviates by ∼2.9 σ from the ALFALFA result at z ∼ 0. Conclusions. Our findings regarding the HIMF and Ω HI derived from deep, state-of-the-art interferometric surveys differ from previous literature results at z ∼ 0 and z ∼ 1. We are unable to confirm at this stage whether these differences are due to cosmic evolution consistent with a smooth transition of the H I content of galaxies over the last 8 Gyr or due to selection biases and systematics.

Abstract:

We review the existing distance estimates to the black hole X-ray binary Swift J1727.8–1613, present new radio and near-UV spectra to update the distance constraints, and discuss the accuracies and caveats of the associated methodologies. We use line-of-sight H i absorption spectra captured using the MeerKAT radio telescope to estimate a maximum radial velocity with respect to the local standard of rest of 24.8 ± 2.8 km s−1 for Swift J1727.8−1613, which is significantly lower than that of a nearby extragalactic reference source. From this, we derive a near-kinematic distance of dnear = 3.6 ± 0.3 (stat) ± 2.3 (sys) kpc as a lower bound after accounting for additional uncertainties given its Galactic longitude and latitude, (l, b) ≈ (8.6°, 10.3°). Near-UV spectra from the Hubble Space Telescope’s Space Telescope Imaging Spectrograph allows us to constrain the line-of-sight color excess to E(B – V) = 0.37 ± 0.01 (stat) ± 0.025 (sys). We then implement this in Monte Carlo simulations and present a distance to Swift J1727.8−1613 of 5.5−1.1+1.4 kpc, under the assumption that the donor star is an unevolved, main-sequence K4(±1)V star. This distance implies a natal kick velocity of 190 ± 30 km s−1 and therefore an asymmetrical supernova explosion within the Galactic disk as the expected birth mechanism. A lower distance is implied if the donor star has instead lost significant mass during the binary evolution. Hence, more accurate measurements of the binary inclination angle or donor star rotational broadening from future observations would help to better constrain the distance.

Abstract:

Jets from stellar-mass and supermassive black holes provide the unique opportunity to study similar processes in two very different mass regimes. Historically, the apparent speeds of black hole X-ray binary (BHXRBs) jets have been observed to be lower than jet speeds from active galactic nuclei (AGNs) and specifically blazars. In this work, we show that selection effects could be the primary cause of the observed population differences. For the first time, it is possible to perform a statistical analysis of the underlying BHXRB jet Lorentz factor distribution. We use both the Anderson–Darling test and apply nested sampling to this problem. With Bayes factors, we confirm that the Lorentz factor distribution of BHXRBs is best described with a power law, the same model that has been applied to AGN jets. For a Lorentz factor distribution following we find a value for the exponent of . This exponent is consistent with values found in AGN population studies, within for Swift-BAT and Fermi-LAT selected AGNs. The best-fitting exponent for the radio selected MOJAVE sample is just above our limit. This is a remarkable agreement given the different scales at which the jets are observed. The observed slower apparent speeds in BHXRBs are largely due to the much larger inclinations in this sample. Furthermore, nested sampling confirms that is completely unconstrained using this method. Therefore, based on kinematics alone, BHXRB jets are broadly consistent with being just as relativistic as those from supermassive black holes.