Four pulsar discoveries in NGC 6624 by TRAPUM using MeerKAT

Abstract

We report 4 new pulsars discovered in the core-collapsed globular cluster (GC) NGC 6624 by the TRAPUM Large Survey Project with the MeerKAT telescope. All of the new pulsars found are isolated. PSR J1823−3021I and PSR J1823−3021K are millisecond pulsars with period of respectively 4.319 ms and 2.768 ms. PSR J1823−3021J is mildly recycled with a period of 20.899 ms, and PSR J1823−3022 is a long period pulsar with a period of 2.497 s. The pulsars J1823−3021I, J1823−3021J, and J1823−3021K have position and dispersion measure (DM) compatible with being members of the GC and are therefore associated with NGC 6624. Pulsar J1823−3022 is the only pulsar bright enough to be re-detected in archival observations of the cluster. This allowed the determination of a timing solution that spans over two decades. It is not possible at the moment to claim the association of pulsar J1823−3022 with the GC given the long period and large offset in position (∼3 arcminutes) and DM (with a fractional difference of 11 percent compared the average of the pulsars in NGC 6624). The discoveries made use of the beamforming capability of the TRAPUM backend to generate multiple beams in the same field of view which allows sensitive searches to be performed over a few half-light radii from the cluster center and can simultaneously localise the discoveries. The discoveries reflect the properties expected for pulsars in core-collapsed GCs.

Likely Detection of γ-Ray Pulsations of PSR J1717+4308A in NGC 6341 and Implication of the γ-Ray Millisecond Pulsars in Globular Clusters

“…From fitting the off-pulse spectra, the numbers of other MSPs in NGC 6624 and NGC 6626 are constrained to be 1-5 and 1-6, respectively (Figure 8). The numbers well match those of the known radio pulsars (see Figure 10; Abbate et al 2022;Douglas et al 2022;and references therein), while it should be noted that several pulsars in the two GCs do not have the spindown rate information 7 (i.e., not shown in Figure 10). Further, there is a caveat that the off-pulse emissions are assumed not to contain any of the two MSPs, which may not be true and possibly lead to overestimates of the numbers of other MSPs in the two GCs.…”

“…We might extend this thinking to all the GCs: that the pulsars found in them are close to being complete, given the particular effort that has been made toward finding GC pulsars in the past with different facilities (e.g., Pan et al 2021;Abbate et al 2022;Douglas et al 2022;Gautam et al 2022). Then according to Figure 10, for which a companion table (Table 5) is made to provide more detailed information, we should make an effort to search for γ-ray MSPs in Terzan 5, NGC 6266, NGC 6440, 47 Tuc, and probably NGC 5904 and NGC 6752 as well; the latter two contain known MSPs with  E similar to that of PSR J1717+4308A.…”

“…(Abbate et al 2022;Douglas et al 2022; and references therein), and 2) the γ-ray luminosity of each 12 GCs (in which no γ-ray pulsars are identified) as that of each of their radio pulsars (where the values are from Wu et al 2022). In NGC 6652, PSR J1835−3259B is the only pulsar with  E (DeCesar et al 2015; Gautam et al 2022).…”

Missing for 20 yr: MeerKAT Redetects the Elusive Binary Pulsar M30B

“…Unlike MSPs, such mildly recycled pulsars spin down fast, which means that their LMXB disruption must be recent. This explains why slow, apparently young pulsars in GCs are overwhelmingly found in high-γ GCs and lie below the pulsar spin-up line (Verbunt & Freire 2014;Abbate et al 2022), although in this regard we must keep in mind that there are alternative explanations for the formation of apparently young pulsars in GCs (e.g., Ivanova et al 2008).…”

MeerKAT discovery of 13 new pulsars in Omega Centauri

“…About one-third of these (e.g. Ridolfi et al 2021;Douglas et al 2022;Ridolfi et al 2022;Vleeschower et al 2022;Abbate et al 2022), are found in various GCs, including 47 Tucanae (Chen et al, in prep. ), a cluster that has been searched for over 20 years.…”