TY - JOUR

T1 - Multicolour optical light curves of the companion star to the millisecond pulsar PSR J2051-0827

AU - Dhillon, V. S.

AU - Kennedy, M. R.

AU - Breton, R. P.

AU - Clark, C. J.

AU - Sanchez, D. Mata

AU - Voisin, G.

AU - Breedt, E.

AU - Brown, A. J.

AU - Dyer, M. J.

AU - Green, M. J.

AU - Kerry, P.

AU - Littlefair, S. P.

AU - Marsh, T. R.

AU - Parsons, S. G.

AU - Pelisoli, I

AU - Sahman I, D.

AU - Wild, J. F.

AU - van Kerkwijk, M. H.

AU - Stappers, B. W.

N1 - We thank the anonymous referee for their comments on the manuscript. The design and construction of HiPERCAM was funded by the European Research Council (ERC) under the European Union’s Seventh Framework Programme (FP/2007-2013) under ERC-2013-ADG Grant Agreement no. 340040 (HiPERCAM). VSD, ULTRACAM, and HiPERCAM operations are funded by the UK's Science and Technology Facilities Council (STFC), grant ST/V000853/1. RPB, CJC, DMS, MRK, and GV acknowledge support from the ERC under the European Union’s Horizon 2020 research and innovation programme under Grant Agreement No. 715051 (Spiders). MRK acknowledges support from the Irish Research Council in the form of a Government of Ireland Postdoctoral Fellowship (GOIPD/2021/670: Invisible Monsters). DMS acknowledges the Fondo Europeo de Desarrollo Regional (FEDER) and the Canary Islands government for the financial support received in the form of grant number PROID2020010104. SGP acknowledges the support of an STFC Ernest Rutherford Fellowship. IP and TRM acknowledge support from the STFC, grant ST/T000406/1. The GTC is installed at the Spanish Observatorio del Roque de los Muchachos (ORM) of the Instituto de Astrofísica de Canarias (IAC), on the island of La Palma. The WHT is operated on La Palma by the Isaac Newton Group (ING) in the Spanish ORM of the IAC. For the purpose of open access, the author has applied a Creative Commons Attribution (CC BY) licence to any Author Accepted Manuscript version arising.

PY - 2022/9/13

Y1 - 2022/9/13

N2 - We present simultaneous, multicolour optical light curves of the companion star to the black-widow pulsar PSR J2051-0827, obtained approximately 10 yr 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 time-scales 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(RL)= 0.88(-0.02)(+0.02)) and has a mass of 0.039(-0.011)(+0.010)M(circle dot), 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.

AB - We present simultaneous, multicolour optical light curves of the companion star to the black-widow pulsar PSR J2051-0827, obtained approximately 10 yr 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 time-scales 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(RL)= 0.88(-0.02)(+0.02)) and has a mass of 0.039(-0.011)(+0.010)M(circle dot), 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.

KW - stars: neutron

KW - pulsars: individual: PSR J2051-0827

UR - http://www.scopus.com/inward/record.url?scp=85145569988&partnerID=8YFLogxK

U2 - 10.48550/arXiv.2208.09249

DO - 10.48550/arXiv.2208.09249

M3 - Article

VL - 516

SP - 2792

EP - 2800

JO - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

SN - 0035-8711

IS - 2

ER -