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

Amruta D Jaodand,Slavko Bogdanov,Sotiris Sanidas,James C A Miller-Jones,Alessandro Patruno,Rudy Wijnands,Anne M Archibald,Cees Bassa,Adam T Deller,Jason W T Hessels,Nina Gusinskaia

doi:10.3847/1538-4357/ac1ff7

Abstract

Abstract 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 μJy down to ≲15 μJy (3σ upper limit) at four epochs spanning three weeks. At the brightest epoch, the radio luminosity is L 5 GHz = (2.17 ± 0.17) × 1027 erg s−1 for a quasi-simultaneous X-ray luminosity L 2–10 keV = (4.32 ± 0.23) × 1033 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.

Highlights

Transitional millisecond pulsars are a recently discovered type of binary system that transitions between rotation-powered radio millisecond pulsar (RMSP) and accretion-powered low-mass X-ray binary (LMXB) states (e.g., Archibald et al 2009; Papitto et al 2013; Bassa et al 2014; Stappers et al 2014; Roy et al 2015)
The Swift X-Ray Telescope (XRT) flux measurements from MJD 53,983 −57,254 (2006 Sep to 2015 Aug) are consistent with 3FGL J1544.6−1125 being in the LMXB state for this entire
It is clear that the source was in the LMXB state during our 2015 May to June Very Large Array (VLA) campaign: we find an average X-ray luminosity of (4.32 ± 0.23) × 1033 erg s−1 at this time, which we use as the point of reference for our radio measurements

Summary

Introduction

Transitional millisecond pulsars (tMSPs) are a recently discovered type of binary system that transitions between rotation-powered radio millisecond pulsar (RMSP) and accretion-powered low-mass X-ray binary (LMXB) states (e.g., Archibald et al 2009; Papitto et al 2013; Bassa et al 2014; Stappers et al 2014; Roy et al 2015). The tMSPs provide a rich observational phenomenology that helps build such a connection (see Table 2), with the caveat that there are only three such systems currently known and perhaps a larger sample will display a larger diversity. In their LMXB11 state, tMSPs show distinct X-ray luminosity modes. PSR J1023+0038 switches within 10 s between “high” (L2–10 keV ∼ 1033 erg s−1, present ∼80% of the time) and “low” (L2–10 keV ∼ 1032 erg s−1, present ∼20% of the time) X-ray luminosity modes (Archibald et al 2015; Bogdanov et al 2015; Jaodand et al 2016) These modes last typically for minutes up to an hour. A very similar variability pattern was observed in XSS J12270−4859, prior to its 2012 transformation to an RMSP (de Martino et al 2013), whereas IGR J18245−2452’s moding behavior differs as it shows longer-lasting modes (several hours’ duration; see Linares et al 2014)

Objectives

Results

Conclusion