Timing and Scintillation Studies of PSR J1439-5501

PSR J1439$-$5501 is a mildly recycled pulsar in a 2.12-day circular orbit around a heavy white dwarf. A white dwarf cooling model has estimated the companion mass to be between 1--1.3 M$_ odot $ and the inclination angle to be greater than 55degree . Such high mass and inclination are expected to induce a Shapiro delay, namely, a relativistic time delay in the signal propagation caused by the curved space-time induced by the companion. Until now, however, no Shapiro delay has been measured in this system. Our aim is to detect the Shapiro delay and, thus, to independently measure the mass and inclination of PSR J1439$-$5501 by using data from the Parkes and MeerKAT radio telescopes. The Shapiro delay parameters were measured through pulsar timing, which coherently accounts for every rotation of the pulsar. These measurements were then used to estimate the masses of the component stars and the inclination angle of the binary. A scintillation analysis was additionally performed by investigating the secondary spectra, which are the Fourier-transformed observed scintillation patterns. The obtained secondary spectral variations were analyzed in terms of the orbital motion and annual variation to estimate the ascending nodes, distance, and the location of the screen. We obtained a highly significant measurement of the Shapiro delay, which allows estimates of the pulsar mass ($1.57^ $ M$_ odot $), the white dwarf (WD) companion mass ($1.27^ $ M$_ odot $), and inclination angle, ($75(1) or $105(1) These estimates assume that the companion mass cannot exceed the Chandrasekhar mass limit (1.48 $ odot $), along with a lower limit of $1.17 \ odot $ for NS masses. These results are consistent with previous studies, but the precision of the component masses has been improved significantly. The orbital and spin parameters and the large WD mass make this system very similar to that of PSR J2222$-$0137 and PSR J1528$-$3146, thereby suggesting a common evolutionary mechanism. The scintillation analysis suggests that the longitude of the ascending node is $16(7) or $-20(6) depending on the sense of the inclination angle. The screen distance is 260 pm 100 pc, potentially associated with the edge of the Local Bubble.