Bibcode
Malzac, J.; Maitra, D.; Fender, R. P.; Altamirano, D.; Shahbaz, T.; Sanna, A.; O'Brien, K.; Melandri, A.; Motta, S. E.; Baglio, M. C.; Imbrogno, M.; Ambrosino, F.; Uttley, P.; Maccarone, T. J.; Russell, D. M.; Casella, P.; Veledina, A.; Vincentelli, F. M.; Ulgiati, A.
Bibliographical reference
Astronomy and Astrophysics
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10
2024
Journal
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Description
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 (KS 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.
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