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Dynamical confirmation of a black hole in MAXI J1820+070

Torres, M. A. P. and Casares, J. and Jiménez-Ibarra, F. and Muñoz-Darias, T. and Armas-Padilla, M. and Jonker, P. G. and Heida, M. (2019) Dynamical confirmation of a black hole in MAXI J1820+070. Astrophysical Journal Letters, 882 (2). Art. No. L21. ISSN 2041-8213. doi:10.3847/2041-8213/ab39df.

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We present time-resolved 10.4 m Gran Telescopio Canarias and 4.2 m William Herschel Telescope intermediate resolution spectroscopy of the X-ray transient MAXI J1820+070 (=ASASSN-18ey) obtained during its decline to the quiescent state. Cross-correlation of the 21 individual spectra against late-type templates reveals a sinusoidal velocity modulation with a period of 0.68549 ± 0.00001 day and semi-amplitude of 417.7 ± 3.9 km s^(−1). We derive a mass function f(M) = 5.18 ± 0.15 M⊙, dynamically confirming the black hole (BH) nature of the compact object. Our analysis of the stellar absorption features supports a K3-5 spectral classification for the donor star, which contributes ≈20% of the total flux at 5200–6800 Å. The photometric 0.703 ± 0.003 day periodicity observed during outburst is 2.6% longer than the orbital period supporting the presence of a superhump modulation in the outburst light curves. In line with this interpretation, we constrain the binary mass ratio to be q ≃ 0.12. In addition, we observe a sharp increase in the Hα emission line equivalent width during inferior conjunction of the donor star that we interpret as a grazing eclipse of the accretion disk and allows us to constrain the binary inclination to i ≳ 69°. On the other hand, the absence of X-ray eclipses during outburst imply i ≾ 77°. These inclination limits, together with our dynamical solution, lead to a BH mass in the range 7–8 M⊙. We also measure a systemic velocity γ = −21.6 ± 2.3 km s^(−1), which, combined with the Gaia second data release proper motion and parallax, implies a large peculiar velocity ~100 km s^(−1).

Item Type:Article
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URLURL TypeDescription Paper
Jonker, P. G.0000-0001-5679-0695
Heida, M.0000-0002-1082-7496
Additional Information:© 2019 The American Astronomical Society. Received 2019 July 8; revised 2019 July 25; accepted 2019 August 9; published 2019 September 6. We are grateful to the GTC and ING staff, in particular Antonio L. Cabera Lavers and Ian Skillen, for their help to implement the observations presented in this work. We thank the referee for useful comments. We acknowledge support by the Spanish MINECO under grant AYA2017-83216-P. T.M.D. and M.A.P.T. acknowledge support via Ramón y Cajal Fellowships RYC-2015-18148 and RYC-2015-17854. P.G.J. acknowledges funding from the European Research Council under ERC Consolidator grant agreement No. 647208. molly software developed by Tom Marsh is gratefully acknowledged. iraf is distributed by the National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. We dedicate this Letter to the memory of Jeff E. McClintock.
Group:Space Radiation Laboratory
Funding AgencyGrant Number
Ministerio de Economía, Industria y Competitividad (MINECO)AYA2017-83216-P
Ramón y Cajal FellowshipRYC-2015-18148
Ramón y Cajal FellowshipRYC-2015-17854
European Research Council (ERC)647208
Subject Keywords:Astrophysical black holes; Low-mass X-ray binary stars; Stellar accretion disks; X-ray binary stars
Issue or Number:2
Classification Code:Astrophysical black holes (98); Low-mass X-ray binary stars (939); Stellar accretion disks (1579); X-ray binary stars (1811)
Record Number:CaltechAUTHORS:20190812-160655506
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Official Citation:M. A. P. Torres et al 2019 ApJL 882 L21
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:97803
Deposited By: Tony Diaz
Deposited On:12 Aug 2019 23:27
Last Modified:16 Nov 2021 17:34

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