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

T. J. Johnson; P. S. Ray; J. Roy; C. C. Cheung; A. K. Harding; H. J. Pletsch; S. Fort; F. Camilo; J. Deneva; B. Bhattacharyya; B. W. Stappers; M. Kerr

doi:10.1088/0004-637x/806/1/91

arXiv · 1502.06862

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

T. J. Johnson·P. S. Ray·J. Roy·C. C. Cheung·A. K. Harding·H. J. Pletsch·S. Fort·F. Camilo·J. Deneva·B. Bhattacharyya·B. W. Stappers·M. Kerr

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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.

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T. J. Johnson, P. S. Ray, J. Roy, C. C. Cheung, A. K. Harding, H. J. Pletsch, S. Fort, F. Camilo, J. Deneva, B. Bhattacharyya, B. W. Stappers, M. Kerr. 2015-02-24. Discovery of Gamma-ray Pulsations from the Transitional Redback PSR J1227-4853. https://doi.org/10.1088/0004-637x/806/1/91

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