Leonard E Parker

Center for Gravitation, Cosmology & Astrophysics

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Leonard E Parker Center for Gravitation, Cosmology and Astrophysics

Discovery of the Optical/Ultraviolet/Gamma-Ray Counterpart to the Eclipsing Millisecond Pulsar J1816+4510

Discovery of the Optical/Ultraviolet/Gamma-Ray Counterpart to the Eclipsing Millisecond Pulsar J1816+4510 D.L. Kaplan et al., including UWM authors R. Kotulla, C.M. Biwer, D.F. Day, M.D.W. Rohr, X. Siemens (Paper)
Pulse Phase

The gamma-ray source 2FGL J1816.5+4511 nearly matches the sky position of pulsar J1816.4510 and is considered the pulsar's companion. The pulsed gamma-ray light curve (in blue) is repeated twice for clarity. The red line represents the radio pulse profile of the pulsar. Credit: Kaplan et al.

The recently-discovered 3.2-ms pulsar J1816+4510 is not alone. In their work, the authors report the discovery of the optical/ultraviolet companion to this pulsar; the pulsar and the companion orbit around each other every 8 hours, and are separated by about 2.5 times the radius of the Sun.

The pulsar, recently discovered during radio observations at the Green Bank Telescope, is approximately 2 kpc from Earth and has an orbital period of 8.7 hours around its companion. An energetic wind from the pulsar blows off the outer layers of the companion. Because of this blown-off gas, during approximately 10% of the orbit of J1816+4510 the pulsar is invisible as it is eclipsed by the gas.

A few other systems are known where the pulsars are slowly destroying their companions. Usually the companions are cool (cooler than the Sun), like a normal star. Kaplan and collaborators used archival ultraviolet data from the GALEX All-sky Imaging Survey, the Swift satellite's Ultraviolet and Optical Telescope (UVOT) to identify the companion, along with new optical data from the Wisconsin Indiana Yale NOAO (WIYN) telescope. The ultraviolet data allowed the authors to see that the companion was unusually hot, about 3 times hotter than other similar objects. It appears much more like a white dwarf than a normal star, but even so its is about twice as large as a white dwarf is expected to be.

Many questions remain about the nature of this system. Perhaps the hot temperature and large size are the result of a recent dramatic change in the system, where it lost most of its mass and is still cooling down. Further observations should resolve this issue. It is also exciting that the companion is one of the brightest pulsar companions known, so very high-quality data can be taken to measure the mass of the neutron star.


The spectral energy distribution of pulsar J1816+4510 from optical to gamma-rays. For the optical/UV region, the best-fit blackbody curve is shown. Since no x-rays were detected by Swift, the upper limit appears. The gamma-ray points are shown with two power-law models, represented by the red and blue lines (with dotted 1-σ uncertainties). Credit: Kaplan et al.

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