Multiband Optical Light Curves of Black-widow Pulsars
Abstract
We collect new and archival optical observations of nine “black-widow” millisecond pulsar binaries. New measurements include direct imaging with the Keck, Gemini-S, MDM, and Las Cumbres Observatory 2 m telescopes. This is supplemented by synthesized colors from Keck long-slit spectra. Four black-widow optical companions are presented here for the first time. Together these data provide multicolor photometry covering a large fraction of the orbital phase. We fit these light curves with a direct (photon) heating model using a version of the ICARUS light-curve modeling code. The fits provide distance and fill-factor estimates, inclinations, and heating powers. We compare the heating powers with the observed GeV luminosities, noting that the ratio is sensitive to pulsar distance and to the gamma-ray beaming. We make a specific correction for “outer gap” model beams, but even then some sources are substantially discrepant, suggesting imperfect beaming corrections and/or errors in the fit distance. The fits prefer large metal abundance for half of the targets, a reasonable result for these wind-stripped secondaries. The companion radii indicate substantial Roche-lobe filling, f c ≈ 0.7-1 except for PSR J0952-0607, which with f c < 0.5 has a companion density ρ ≈ 10 g cm-3, suggesting unusual evolution. We note that the direct-heating fits imply large heating powers and rather small inclinations, and we speculate that unmodeled effects can introduce such bias.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- September 2019
- DOI:
- 10.3847/1538-4357/ab378b
- arXiv:
- arXiv:1908.00992
- Bibcode:
- 2019ApJ...883..108D
- Keywords:
-
- Pulsars;
- Close binary stars;
- Millisecond pulsars;
- 1306;
- 254;
- 1062;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- To appear in the Astrophysical Journal Revised version, fixed duplicate panel in Fig 6