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

D. L. Kaplan, University of Wisconsin-Milwaukee
K. Stovall, University of Texas at Brownsville and Texas Southmost College
S. M. Ransom, National Radio Astronomy Observatory
M. S.E. Roberts, Eureka Scientific, Inc.
R. Kotulla, University of Wisconsin-Milwaukee
A. M. Archibald, Université McGill
C. M. Biwer, University of Wisconsin-Milwaukee
J. Boyles, West Virginia University
L. Dartez, University of Texas at Brownsville and Texas Southmost College
D. F. Day, University of Wisconsin-Milwaukee
A. J. Ford, University of Texas at Brownsville and Texas Southmost College
A. Garcia, University of Texas at Brownsville and Texas Southmost College
J. W.T. Hessels, Netherlands Foundation for Research in Astronomy
F. A. Jenet, University of Texas at Brownsville and Texas Southmost College
C. Karako, Université McGill
V. M. Kaspi, Université McGill
V. I. Kondratiev, Netherlands Foundation for Research in Astronomy
D. R. Lorimer, West Virginia University
R. S. Lynch, Université McGill
M. A. McLaughlin, West Virginia University
M. D.W. Rohr, University of Wisconsin-Milwaukee
X. Siemens, University of Wisconsin-Milwaukee
I. H. Stairs, The University of British Columbia
J. Van Leeuwen, Netherlands Foundation for Research in Astronomy

Abstract

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. © 2012. The American Astronomical Society. All rights reserved.. ⊙