Triple trouble with PSR J1618-3921: Mass measurements and orbital dynamics of an eccentric millisecond pulsar

Abstract

PSR J1618-3921 is one of five known millisecond pulsars (MSPs) in eccentric orbits (eMPSs) located in the Galactic plane, whose formation is poorly understood. Earlier studies of these objects revealed significant discrepancies between observation and predictions from standard binary evolution scenarios of pulsar-Helium white dwarf binaries. We conducted observations with the L-band receiver of the MeerKAT radio telescope and the UWL receiver of the Parkes Murriyang radio telescope between 2019 and 2021. These data were added to archival observations. We perform an analysis of this joint 23-year-dataset. We use the recent observations to give a brief account of the emission properties of J1618-3921, including a Rotating Vector model fit of the linear polarisation position angle of the pulsar. The long timing baseline allowed for a highly significant measurement of the rate of advance of periastron of $\dot{\omega }$. We can only report a low significance detection of the orthometric Shapiro delay parameters $h_3$ and $\varsigma$, leading to mass estimates of the total and individual binary masses. We detect an unexpected change in the orbital period of, which is an order of magnitude larger and carries an opposite sign to what is expected from Galactic acceleration and the Shklovskii effect. We also detect a significant second derivative of the spin frequency. Furthermore, we report an unexpected, abrupt change of the mean pulse profile in June 2021 with unknown origin. We propose that the anomalous $\dot{P_b}$ and $\ddot{f}$ indicate an additional varying acceleration due to a nearby mass, i.e., the J1618-3921 binary system is likely part of a hierarchical triple. This finding suggests that at least some eMSPs might have formed in triple star systems. Although the uncertainties are large, the binary companion mass is consistent with the $P_b$ - $M_{WD}$ relation.

17 pages, 11 figures, 3 tables

References in corpus (17)

• Gaia Data Release 3: Summary of the content and survey properties
• TEMPO2, a new pulsar timing package. I: Overview
• PSRCHIVE and PSRFITS An Open Approach to Radio Pulsar Data Storage and Analysis
• Formation of Double Neutron Star Systems
• An Eccentric Binary Millisecond Pulsar in the Galactic Plane
• PARSEC V2.0: Stellar tracks and isochrones of low and intermediate mass stars with rotation
• High-fidelity radio astronomical polarimetry using a millisecond pulsar as a polarized reference source
• The MeerTime Pulsar Timing Array -- A Census of Emission Properties and Timing Potential
• A Massive Millisecond Pulsar in an Eccentric Binary
• On the beam properties of radio pulsars with interpulse emission
• The disturbance of a millisecond pulsar magnetosphere
• The Relativistic Binary Programme on MeerKAT: Science objectives and first results
• The Thousand-Pulsar-Array programme on MeerKAT IV: Polarisation properties of young, energetic pulsars
• The eccentric millisecond pulsar, PSR J0955$-$6150 I: Pulse profile analysis, mass measurements and constraints on binary evolution
• Gravitational signal propagation in the Double Pulsar studied with the MeerKAT telescope
• Artefacts of circumpolar cartography in radio pulsar polarization
• Profile changes associated with DM events in PSR J1713+0747

Cited by in corpus (1)

• Explanation of the exceptionally strong timing noise of PSR J0337+1715 by a circum-ternary planet and consequences for gravity tests