A NuSTAR Observation of the Gamma-Ray-Emitting X-ray Binary and Transitional Millisecond Pulsar Candidate 1RXS J154439.4-112820

Abstract

I present a 40 kilosecond Nuclear Spectroscopic Telescope Array (NuSTAR) observation of the recently identified low-luminosity X-ray binary and transitional millisecond pulsar (tMSP) candidate 1RXS J154439.4-112820, which is associated with the high-energy gamma-ray source 3FGL J1544.6--1125. The system is detected up to ~30 keV with an extension of the same power-law spectrum and rapid large-amplitude variability between two flux levels observed in soft X-rays. These findings provide further evidence that 1RXS J154439.4-112820 belongs to the same class of objects as the nearby bona fide tMSPs PSR J1023+0038 and XSS J12270-4859 and therefore almost certainly hosts a millisecond pulsar accreting at low luminosities. I also examine the long-term accretion history of 1RXS J154439.4-112820 based on archival optical, ultraviolet, X-ray, and $\gamma$-ray light curves covering the past $\sim$decade. Throughout this period, the source has maintained similar flux levels at all wavelengths, which is an indication that it has not experienced prolonged episodes of a non-accreting radio pulsar state but may spontaneously undergo such a state transformation in the future.

6 pages, 4 figures; submitted to the Astrophysical Journal Letters

References in corpus (13)

• A state change in the low-mass X-ray binary XSS J12270-4859
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• A New Accretion Disk Around the Missing Link Binary System PSR J1023+0038
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• Multi-wavelength emissions from the millisecond pulsar binary PSR J1023+0038 during an accretion active state
• X-ray coherent pulsations during a sub-luminous accretion disk state of the transitional millisecond pulsar XSS J12270-4859
• Radio imaging observations of PSR J1023+0038 in an LMXB state
• The neutron star transient and millisecond pulsar in M28: from sub-luminous accretion to rotation-powered quiescence
• Identification of the High-Energy Gamma-Ray Source 3FGL J1544.6-1125 as a Transitional Millisecond Pulsar Binary in an Accreting State
• X-ray Observations of XSS J12270-4859 in a New Low State: A Transformation to a Disk-Free Rotation-Powered Pulsar Binary
• NuSTAR Observations of the State Transition of Millisecond Pulsar Binary PSR J1023+0038
• Engulfing a radio pulsar: the case of PSR J1023+0038
• Fermi Observation of the transitional pulsar binary XSS J12270-4859

Cited by in corpus (13)

• Optical spectroscopy and demographics of redback millisecond pulsar binaries
• Transitional millisecond pulsars
• Accreting pulsars: mixing-up accretion phases in transitional systems
• Search for transitions between states in redbacks and black widows using seven years of Fermi-LAT observations
• A multi-wavelength view of the neutron star binary 1FGL J1417.7--4402: A progenitor to canonical millisecond pulsars
• Orbital Dynamics of Candidate Transitional Millisecond Pulsar 3FGL J1544.6-1125: An unusually face-on system
• A New Candidate Transitional Millisecond Pulsar in the Sub-luminous Disk State: 4FGL J0407.7--5702
• The MAVERIC survey: A transitional millisecond pulsar candidate in Terzan 5
• Quasi-Simultaneous Radio/X-ray Observations of the Candidate Transitional Millisecond Pulsar 3FGL J1544.6-1125 During its Low-Luminosity Accretion-Disc State
• Multiwavelength Evidence for Two New Candidate Transitional Millisecond Pulsars in the Sub-luminous Disk State: 4FGL J0639.1--8009 and 4FGL J1824.2+1231
• Detection of low-luminosity X-ray pulsations from the accreting millisecond pulsar IGR J17511-3057: An ever-thinning thread between bright accretion and sub-luminous states
• Identification and characterisation of the gamma-ray counterpart of the transitional pulsar candidate CXOU J110926.4-650224
• Probing multi-band variability and mode switching in the candidate transitional millisecond pulsar 3FGL J1544.6-1125