Discovery of the optical/ultraviolet/gamma-ray counterpart to the eclipsing millisecond pulsar J1816+4510

D. L. Kaplan, K. Stovall, S. M. Ransom, M. S.E. Roberts, R. Kotulla, A. M. Archibald, C. M. Biwer, J. Boyles, L. Dartez, D. F. Day, A. J. Ford, A. Garcia, J. W.T. Hessels, F. A. Jenet, C. Karako, V. M. Kaspi, V. I. Kondratiev, D. R. Lorimer, R. S. Lynch, M. A. McLaughlinM. D.W. Rohr, X. Siemens, I. H. Stairs, J. Van Leeuwen

Research output: Contribution to journalReview articlepeer-review


The energetic, eclipsing millisecond pulsar J1816+4510 was recently discovered in a low-frequency radio survey with the Green Bank Telescope. With an orbital period of 8.7hr and a minimum companion mass of 0.16M , it appears to belong to an increasingly important class of pulsars that are ablating their low-mass companions. We report the discovery of the γ-ray counterpart to this pulsar and present a likely optical/ultraviolet counterpart as well. Using the radio ephemeris, we detect pulsations in the unclassified γ-ray source 2FGL J1816.5+4511, implying an efficiency of 25% in converting the pulsar's spin-down luminosity into γ-rays and adding PSR J1816+4510 to the large number of millisecond pulsars detected by Fermi. The likely optical/UV counterpart was identified through position coincidence (<01) and unusual colors. Assuming that it is the companion, with R = 18.27 ± 0.03mag and effective temperature ≳ 15,000K, it would be among the brightest and hottest of low-mass pulsar companions and appears qualitatively different from other eclipsing pulsar systems. In particular, current data suggest that it is a factor of two larger than most white dwarfs of its mass but a factor of four smaller than its Roche lobe. We discuss possible reasons for its high temperature and odd size, and suggest that it recently underwent a violent episode of mass loss. Regardless of origin, its brightness and the relative unimportance of irradiation make it an ideal target for a mass, and hence a neutron star mass, determination.

Original languageEnglish (US)
Article number174
JournalAstrophysical Journal
Issue number2
StatePublished - Jul 10 2012


  • binaries: eclipsing
  • gamma rays: stars
  • ultraviolet: stars
  • white dwarfs

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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