Rouhin Nag

Context . Globular clusters are efficient factories of recycled pulsars, but searches towards high dispersion-measure (DM) clusters can be strongly limited around 1 GHz – which is where most pulsar surveys are typically conducted – due to dispersive smearing and interstellar scattering. Observations at higher radio frequencies provide a complementary route to mitigate these effects and improve sensitivity. Aims . We present the first results from a MeerKAT S-band ( ν ≃ 2.4 GHz) pulsar survey of 14 globular clusters. Our aims were to discover new pulsars, re-detect known pulsars with a uniform high-frequency dataset, and assess practical S-band sensitivity and DM-search requirements for future globular cluster pulsar surveys. Methods . High time and frequency resolution S-band observations were searched in the Fourier domain using segmented acceleration and jerk techniques to maintain sensitivity to pulsars in compact binaries, followed by candidate identification and folding. For selected detections and non-detections, we additionally folded the S-band data together with archival MeerKAT L-band observations using available timing ephemerides to derive flux-density measurements and spectral-index constraints. Results . We re-detected 39 previously known pulsars across 14 clusters and discovered four new millisecond pulsars in Glimpse-C01 (J1848–0129C, D, E, and F). Multi-epoch follow-up enabled preliminary Keplerian orbital fits for two of the new systems based on their observed barycentric spin-period modulation. J1848–0129C is an eclipsing millisecond pulsar with P _b ∼ 5 d, placing it among the long-period eclipsing systems known as ‘huntsman’ binaries. J1848–0129D is in a P _b ∼ 3.4 d nearly circular orbit with a ∼1 M _⊙ massive white dwarf companion. Two Glimpse-C01 pulsars exhibit substantial DM offsets relative to the average cluster value. Comparison with other Galactic globular clusters showed that large intracluster DM spreads become increasingly common at high foreground DMs, implying that searches confined to narrow DM windows may be sub-optimal for high-DM clusters. From detections and non-detections, we inferred a practical single-epoch S-band tied-array detectability scale of ∼10–20 μJy, which serves as an operational benchmark rather than a strict completeness limit. Conclusions . MeerKAT S-band observations are highly effective for probing globular clusters affected by strong dispersion and scattering, enabling both reliable re-detections and the discovery of new millisecond pulsars in high-DM environments such as Glimpse-C01. The results of our work highlight the importance of high-frequency surveys for expanding the known pulsar population in obscured clusters.

We report on the identification of the optical counterpart to the recently discovered millisecond pulsar (MSP) NGC 362D in the Galactic globular cluster NGC 362 based on deep, multi-band, and multi-epoch Hubble Space Telescope observations. Our analysis robustly shows that this object is a very low-mass (∼0.18 M _⊙ ) He white dwarf (WD) still in the pre-cooling phase. Interestingly, a detailed comparison with updated binary evolution models indicates that this object completed the mass-transfer phase only recently (∼0.6 Gyr ago), thus strongly suggesting that COM-NGC 362D is the youngest WD companion to a MSP identified to date. Remarkably, in this respect, the photometric properties of NGC 362D show, for the first time in this class of objects, significant wavelength-dependent variations that are consistent with the presence of residual circumstellar material. This system therefore provides a valuable test case to directly probe the immediate aftermath of the MSP recycling process and to constrain the early evolutionary stages of proto-WD companions and their radio and optical properties. Our results suggest that residual material can produce radio and optical signatures that mimic those of systems with non-degenerate companions, potentially leading to the misclassification of young MSPs.

In this paper we present PSR J0024−7204ai, a 13.026-ms binary pulsar recently discovered in the globular cluster 47 Tucanae by the MeerKAT radio telescope. This is the slowest-spinning pulsar known in this globular cluster. It has a ∼1.67-day orbit with an eccentricity of e ≈ 0.18. Although it is not yet possible to derive an unambiguous phase-connected timing solution, by combining detections obtained from MeerKAT and archival Parkes data, we were able to measure the rate of advance of periastron to a high significance: ω ˙ = 0.1601 ± 0.0046 deg yr ⁻¹ . This value implies a total system mass of 2.41 ± 0.11 M _⊙ (68.3% C.L.), which, when combined with the binary mass function, gives a maximum pulsar mass of ∼1.7 M _⊙ and a minimum companion mass of ∼0.7 M _⊙ . Apart from being the slowest pulsar in 47 Tucanae, its orbit is by far the most eccentric, and its companion is the most massive among all known binary pulsars in this globular cluster. It is possible that the system is an old millisecond pulsar–carbon-oxygen white dwarf binary whose orbit was perturbed by stellar dynamical interactions in the cluster core. Further follow-up observations of this system will be essential to obtaining a more detailed characterisation of this system and its evolution.