Fast X-ray/IR observations of the black hole transient Swift J1753.5–0127: From an IR lead to a very long jet lag

¹ INAF - IASF Palermo, Via Ugo La Malfa, 153, I-90146 Palermo, Italy
² Università degli Studi di Palermo, Dipartimento di Fisica e Chimica, Via Archirafi 36, I-90123 Palermo, Italy
³ Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife, Spain
⁴ Departamento de Astrofísica, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Spain
⁵ INAF – Osservatorio Astronomico di Roma, Via Frascati 33, I-00078 Monteporzio Catone, Italy
⁶ Department of Physics and Astronomy, FI-20014 University of Turku, Finland
⁷ Nordita, Stockholm University and KTH Royal Institute of Technology, Hannes Alfvéns väg 12, SE-10691 Stockholm, Sweden
⁸ Department of Physics & Astronomy, Texas Tech University, Box 41051 Lubbock, TX 79409-1051, USA
⁹ Center for Astrophysics and Space Science (CASS), New York University Abu Dhabi, P.O. Box 129188 Abu Dhabi, UAE
¹⁰ Anton Pannekoek Institute, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
¹¹ INAF, Osservatorio Astronomico di Brera, Via E. Bianchi 46, I-23807 Merate (LC), Italy
¹² Dipartimento di Fisica, Universita degli Studi di Roma “Tor Vergata”, Via della Ricerca Scientifica 1, I-00133 Rome, Italy
¹³ University of Oxford, Department of Physics, Astrophysics, Denys Wilkinson Building, Keble Road, OX1 3RH Oxford, UK
¹⁴ Centre for Advanced Instrumentation, Department of Physics, Durham University, Durham, UK
¹⁵ Dipartimento di Fisica, Università degli Studi di Cagliari, SP Monserrato-Sestu km 0.7, 09042 Monserrato, Italy
¹⁶ School of Physics and Astronomy, University of Southampton, Southampton, Hampshire SO17 1BJ, UK
¹⁷ Department of Physics and Astronomy, Wheaton College, Norton, MA 02766, USA
¹⁸ IRAP, Université de Toulouse, CNRS, UPS, CNES, Toulouse, France

Received: 29 April 2024
Accepted: 28 June 2024

Abstract

We report two epochs of simultaneous near-infrared (IR) and X-ray observations of the low-mass X-ray binary black hole candidate Swift J1753.5–0127 with a subsecond time resolution during its long 2005–2016 outburst. Data were collected strictly simultaneously with VLT/ISAAC (K_S band, 2.2 μm) and RXTE (2–15 keV) or XMM-Newton (0.7–10 keV). A clear correlation between the X-ray and the IR variable emission is found during both epochs but with very different properties. In the first epoch, the near-IR variability leads the X-ray by ∼130 ms, which is the opposite of what is usually observed in similar systems. The correlation is more complex in the second epoch, with both anti-correlation and correlations at negative and positive lags. Frequency-resolved Fourier analysis allows us to identify two main components in the complex structure of the phase lags: the first component, characterised by a near-IR lag of a few seconds at low frequencies, is consistent with a combination of disc reprocessing and a magnetised hot flow; the second component is identified at high frequencies by a near-IR lag of ≈0.7 s. Given the similarities of this second component with the well-known constant optical/near-IR jet lag observed in other black hole transients, we tentatively interpret this feature as a signature of a longer-than-usual jet lag. We discuss the possible implications of measuring such a long jet lag in a radio-quiet black hole transient.