@article{ee9c820f916e4abc92093cb9c499c472,
title = "A black hole X-ray binary at ∼100 Hz: Multiwavelength timing of MAXI J1820+070 with HiPERCAM and NICER",
abstract = "We report on simultaneous sub-second optical and X-ray timing observations of the low-mass X-ray binary black hole candidate MAXI J1820+070. The bright 2018 outburst rise allowed simultaneous photometry in five optical bands (ugrizs) with HiPERCAM/GTC (Optical) at frame rates over 100 Hz, together with NICER/ISS observations (X-rays). Intense (factor of 2) red flaring activity in the optical is seen over a broad range of time-scales down to ∼10 ms. Cross-correlating the bands reveals a prominent anticorrelation on time-scales of ∼seconds, and a narrow sub-second correlation at a lag of ≈ +165 ms (optical lagging X-rays). This lag increases with optical wavelength, and is approximately constant over Fourier frequencies of ∼0.3-10 Hz. These features are consistent with an origin in the inner accretion flow and jet base within ∼5000 Gravitational radii. An additional ∼+5 s lag feature may be ascribable to disc reprocessing. MAXI J1820+070 is the third black hole transient to display a clear ∼0.1 s optical lag, which may be common feature in such objects. The sub-second lag variation with wavelength is novel, and may allow constraints on internal shock jet stratification models.",
keywords = "X-rays: binaries, X-rays: individual: MAXI J1820+070, accretion, accretion discs",
author = "Paice, {J. A.} and P. Gandhi and T. Shahbaz and P. Uttley and Z. Arzoumanian and Charles, {P. A.} and Dhillon, {V. S.} and Gendreau, {K. C.} and Littlefair, {S. P.} and J. Malzac and S. Markoff and Marsh, {T. R.} and R. Misra and Russell, {D. M.} and A. Veledina",
note = "Funding Information: We acknowledge support from STFC and a UGC-UKIERI Thematic Partnership. JAP is part supported by a University of Southampton Central VC Scholarship, and thanks D Ashton for spectral timing help. Observations were made with the GTC telescope (Spanish Observatorio del Roque de los Muchachos, Instituto de Astrof{\'i}sica de Canarias), under Director{\textquoteright}s Discretionary Time. JM acknowleges financial support from PNHE in France, OCEVU Labex (ANR-11-LABX-0060), and the A∗MIDEX project (ANR-11-IDEX-0001-02) funded by the {\textquoteleft}Investissements d{\textquoteright}Avenir{\textquoteright} French government program managed by the ANR. TS thanks the Spanish Ministry of Economy and Competitiveness (MINECO; grant AYA2017-83216). AV acknowledges the Academy of Finland grant 309308. HiPERCAM and VSD funded by the European Research Council (FP/2007–2013) under ERC-2013-ADG grant agreement no. 340040. SMARTNet helped to coordinate observations. We also thank the referee for their valuable comments. We have made use of software and web tools from the High Energy Astrophysics Science Archive Research Center (HEASARC). Publisher Copyright: {\textcopyright} 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.",
year = "2019",
month = nov,
day = "1",
doi = "10.1093/mnrasl/slz148",
language = "English (US)",
volume = "490",
pages = "L62--L66",
journal = "Monthly Notices of the Royal Astronomical Society: Letters",
issn = "1745-3925",
publisher = "Oxford University Press",
number = "1",
}