Discovery of Gamma-ray Pulsations from the Transitional Redback PSR J1227-4853

Abstract

The 1.69 ms spin period of PSR J1227-4853 was recently discovered in radio observations of the low-mass X-ray binary XSS J12270-4859 following the announcement of a possible transition to a rotation-powered millisecond pulsar state, inferred from decreases in optical, X-ray, and gamma-ray flux from the source. We report the detection of significant (5$\sigma$) gamma-ray pulsations after the transition, at the known spin period, using ~1 year of data from the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. The gamma-ray light curve of PSR J1227-4853 can be fit by one broad peak, which occurs at nearly the same phase as the main peak in the 1.4 GHz radio profile. The partial alignment of light-curve peaks in different wavebands suggests that at least some of the radio emission may originate at high altitude in the pulsar magnetosphere, in extended regions co-located with the gamma-ray emission site. We folded the LAT data at the orbital period, both pre- and post-transition, but find no evidence for significant modulation of the gamma-ray flux. Analysis of the gamma-ray flux over the mission suggests an approximate transition time of 2012 November 30. Continued study of the pulsed emission and monitoring of PSR J1227-4853, and other known redback systems, for subsequent flux changes will increase our knowledge of the pulsar emission mechanism and transitioning systems.

5 figures, 1 table, accepted for publication in ApJ, updated to reflect accepted version and add additional coauthor

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• An image-based search for pulsars among Fermi unassociated LAT sources
• Search for transitions between states in redbacks and black widows using seven years of Fermi-LAT observations
• Orbital Dynamics of Candidate Transitional Millisecond Pulsar 3FGL J1544.6-1125: An unusually face-on system
• 2FGL J0846.0+2820: A new neutron star binary with a giant secondary and variable $\gamma$-ray emission
• The Flare-Dominated Accretion Mode of a Radio-Bright Candidate Transitional Millisecond Pulsar
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• NuSTAR and Parkes observations of the transitional millisecond pulsar binary XSS J12270-4859 in the rotation-powered state
• Multiwavelength evidence for a new flare-mode transitional millisecond pulsar
• Search for gamma rays from SNe with a variable-size sliding-time-window analysis of the Fermi-LAT data
• Quasi-Simultaneous Radio/X-ray Observations of the Candidate Transitional Millisecond Pulsar 3FGL J1544.6-1125 During its Low-Luminosity Accretion-Disc State
• A 350-MHz Green Bank Telescope Survey of Unassociated Fermi LAT Sources: Discovery and Timing of Ten Millisecond Pulsars
• Gamma-ray orbital modulation of the transitioning millisecond pulsar binary XSS J12270-4859
• X-ray study of high-and-low luminosity modes and peculiar low-soft-and-hard activity in the transitional pulsar XSS J12270-4859
• Characterizing the Gamma-ray Emission Properties of the Globular Cluster M5 with the Fermi-LAT
• Gamma-ray Pulsar Emission is Mostly Stable on Timescales from Minutes to Years
• Recurrent Instability in LMXB Accretion Disks: How Strange is GRS 1915+105?