Multi-colour optical light curves of the companion star to the millisecond pulsar PSR J2051-0827

Abstract

We present simultaneous, multi-colour optical light curves of the companion star to the black-widow pulsar PSR J2051-0827, obtained approximately 10 years apart using ULTRACAM and HiPERCAM, respectively. The ULTRACAM light curves confirm the previously reported asymmetry in which the leading hemisphere of the companion star appears to be brighter than the trailing hemisphere. The HiPERCAM light curves, however, do not show this asymmetry, demonstrating that whatever mechanism is responsible for it varies on timescales of a decade or less. We fit the symmetrical HiPERCAM light curves with a direct-heating model to derive the system parameters, finding an orbital inclination of $55.9_{-4.1}^{+4.8}$ degrees, in good agreement with radio-eclipse constraints. We find that approximately half of the pulsar's spin-down energy is converted to optical luminosity, resulting in temperatures ranging from approximately $5150_{-190}^{+190}$ K on the day side to $2750_{-150}^{+130}$ K on the night side of the companion star. The companion star is close to filling its Roche lobe ($f_{\mathrm{RL}}=0.88_{-0.02}^{+0.02}$) and has a mass of $0.039_{-0.011}^{+0.010}$ M${}_{\odot }$, giving a mean density of $20.24_{-0.44}^{+0.59}$ g cm${}^{-3}$ and an apsidal motion constant in the range $0.0036<k_2<0.0047$. The companion mass and mean density values are consistent with those of brown dwarfs, but the apsidal motion constant implies a significantly more centrally-condensed internal structure than is typical for such objects.

10 pages, 4 figures, 3 tables, accepted for publication in Monthly Notices of the Royal Astronomical Society

References in corpus (20)

• A New Electron Density Model for Estimation of Pulsar and FRB Distances
• Incremental Fermi Large Area Telescope Fourth Source Catalog
• ULTRACAM: an ultra-fast, triple-beam CCD camera for high-speed astrophysics
• PSR J1810+1744: Companion Darkening and a Precise High Neutron Star Mass
• HiPERCAM: a quintuple-beam, high-speed optical imager on the 10.4-m Gran Telescopio Canarias
• Atmospheric Circulation on Black Widow Companions
• Discovery of a Gamma-ray Black Widow Pulsar by GPU-accelerated Einstein@Home
• Einstein@Home Discovery of the Gamma-ray Millisecond Pulsar PSR J2039-5617 Confirms Its Predicted Redback Nature
• A Spectroscopic Study of the Extreme Black Widow PSR J1311-3430
• Study of spider pulsar binary eclipses and discovery of an eclipse mechanism transition
• 21-year timing of the black-widow pulsar J2051-0827
• B-ducted Heating of Black Widow Companions
• An active, asynchronous companion to a redback millisecond pulsar
• Measuring the mass of the black widow PSR J1555-2908
• Identification of the Optical Counterpart of Fermi Black Widow Millisecond Pulsar PSR J1544+4937
• Discovery and modelling of broad-scale plasma lensing in black-widow pulsar J2051$-$0827
• Characterising eclipsing white dwarf M dwarf binaries from multi-band eclipse photometry
• Heated Poles on the Companion of Redback PSR J2339$-$0533
• Optical photometry of two transitional millisecond pulsars in the radio pulsar state
• First measurement of the total gravitational quadrupole moment of a black widow companion

Cited by in corpus (5)

• A New Flaring Black Widow Candidate and Demographics of Black Widow Millisecond Pulsars in the Galactic Field
• An Optical Study of the Black Widow Population
• A black widow population dissection through HiPERCAM multi-band light curve modelling
• The Green Bank North Celestial Cap Survey. VII. 12 New Pulsar Timing Solutions
• A census of galactic spider binary millisecond pulsars with the Nançay Radio Telescope