Discovery of Three New Millisecond Pulsars in Terzan 5

We report on the discovery of three new millisecond pulsars (MSPs; namely J1748-2446aj, J1748-2446ak, and J1748-2446al) in the inner regions of the dense stellar system Terzan 5. These pulsars have been discovered thanks to a method, alternative to the classical search routines, that exploited the large set of archival observations of Terzan 5 acquired with the Green Bank Telescope over five years (from 2010 to 2015). This technique allowed the analysis of stacked power spectra obtained by combining ∼206 hr of observation. J1748-2446aj has a spin period of ∼2.96 ms, J1748-2446ak of ∼1.89 ms (thus it is the fourth fastest pulsar in the cluster) and J1748-2446al of ∼5.95 ms. All three MSPs are isolated, and currently we have timing solutions only for J1748-2446aj and J1748-2446ak. For these two systems, we evaluated the contribution to the measured spin-down rate of the acceleration due to the cluster potential field, thus estimating the intrinsic spin-down rates, which are in agreement with those typically measured for MSPs in globular clusters (GCs). Our results increase the number of pulsars known in Terzan 5 to 37, which now hosts 25% of the entire pulsar population identified, so far, in GCs.