* Astronomy

Title: Discovery of an unidentified Fermi object as a black widow-like millisecond pulsar
Authors: A. K. H. Kong, R. H. H. Huang, K. S. Cheng, J. Takata, Y. Yatsu, C. C. Cheung, D. Donato, L. C. C. Lin, J. Kataoka, Y. Takahashi, K. Maeda, C. Y. Hui, P. H. T. Tam

The Fermi Gamma-ray Space Telescope has revolutionised our knowledge of the gamma-ray pulsar population, leading to the discovery of almost 100 gamma-ray pulsars and dozens of gamma-ray millisecond pulsars (MSPs). Although the outer-gap model predicts different sites of emission for the radio and gamma-ray pulsars, until now all of the known gamma-ray MSPs have been visible in the radio. Here we report the discovery of a "radio-quiet" gamma-ray emitting MSP candidate by using Fermi, Chandra, Swift, and optical observations. The X-ray and gamma-ray properties of the source are consistent with known gamma-ray pulsars. We also found a 4.63-hr orbital period in optical and X-ray data. We suggest that the source is a black widow-like MSP with a ~0.1 solar-mass late-type companion star. Based on the profile of the optical and X-ray light-curves, the companion star is believed to be heated by the pulsar while the X-ray emissions originate from pulsar magnetosphere and/or from intra-binary shock. No radio detection of the source has been reported yet and although no gamma-ray/radio pulsation has been found, we estimated that the spin period of the MSP is ~3-5 ms based on the inferred gamma-ray luminosity.

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