Discovery of an ultracompact gamma-ray millisecond pulsar binary candidate

Albert K.H. Kong, Ruolan Jin, T. C. Yen, C. P. Hu, C. Y. Hui, P. H.T. Tam, J. Takata, L. C.C. Lin, K. S. Cheng, S. M. Park, C. L. Kim

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22 Scopus citations


We report multi-wavelength observations of the unidentified Fermi object 2FGL J1653.6-0159. With the help of high-resolution X-ray observations, we have identified an X-ray and optical counterpart to 2FGL J1653.6-0159. The source exhibits a periodic modulation of 75 minutes in the optical and possibly also in the X-ray. We suggest that 2FGL J1653.6-0159 is a compact binary system with an orbital period of 75 minutes. Combining the gamma-ray and X-ray properties, 2FGL J1653.6-0159 is potentially a black-widow-/redback-type gamma-ray millisecond pulsar (MSP). The optical and X-ray light curve profiles show that the companion is mildly heated by the high-energy emission and that the X-rays are from intrabinary shock. Although no radio pulsation has yet been detected, we estimated that the spin period of the MSP is ∼ 2 ms based on a theoretical model. If pulsation can be confirmed in the future, 2FGL J1653.6-0159 will become the first ultracompact rotation-powered MSP.

Original languageEnglish
Article numberL22
JournalAstrophysical Journal Letters
Issue number2
StatePublished - 2014

Bibliographical note

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© 2014. The American Astronomical Society. All rights reserved.


  • binaries: close
  • gamma rays: stars
  • pulsars: general
  • X-rays: binaries


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