Quasi-simultaneous Radio/X-Ray Observations of the Candidate Transitional Millisecond Pulsar 3FGL J1544.6−1125 during its Low-luminosity Accretion-disk State

• Published in: The Astrophysical journal 2021-12, Vol.923 (1), p.3
• Main Authors: Jaodand, Amruta D., Deller, Adam T., Gusinskaia, Nina, Hessels, Jason W. T., Miller-Jones, James C. A., Archibald, Anne M., Bogdanov, Slavko, Bassa, Cees, Wijnands, Rudy, Patruno, Alessandro, Sanidas, Sotiris
• Format: Article
• Language: English
• Subjects: Accretion; Accretion disks; Astrophysics; Binary pulsars; Binary stars; Continuum radiation; Emissions; Flux density; Gamma emission; Luminosity; Millisecond pulsars; Neutron stars; Neutrons; Phenomenology; Pulsars; Radio continuum emission; Radio emission; X-ray astronomy; X-rays
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ac1ff7

3FGL J1544.6−1125 is a candidate transitional millisecond pulsar (tMSP). Similar to the well-established tMSPs—PSR J1023+0038, IGR J18245−2452, and XSS J12270−4859—3FGL J1544.6−1125 shows γ -ray emission and discrete X-ray “low” and “high” modes during its low-luminosity accretion-disk state. Coordinated radio/X-ray observations of PSR J1023+0038 in its current low-luminosity accretion-disk state showed rapidly variable radio continuum emission—possibly originating from a compact, self-absorbed jet, the “propellering” of accretion material, and/or pulsar moding. 3FGL J1544.6−1125 is currently the only other (candidate) tMSP system in this state, and can be studied to see whether tMSPs are typically radio-loud compared to other neutron star binaries. In this work, we present a quasi-simultaneous Very Large Array and Swift radio/X-ray campaign on 3FGL J1544.6−1125. We detect 10 GHz radio emission varying in flux density from 47.7 ± 6.0 μ Jy down to ≲15 μ Jy (3 σ upper limit) at four epochs spanning three weeks. At the brightest epoch, the radio luminosity is L 5 GHz = (2.17 ± 0.17) × 10 27 erg s −1 for a quasi-simultaneous X-ray luminosity L 2–10 keV = (4.32 ± 0.23) × 10 33 erg s −1 (for an assumed distance of 3.8 kpc). These luminosities are close to those of PSR J1023+0038, and the results strengthen the case that 3FGL J1544.6−1125 is a tMSP showing similar phenomenology to PSR J1023+0038.