Abstract
ABSTRACT We present the results regarding the analysis of the fast X-ray/infrared (IR) variability of the black hole transient MAXI J1535−571. The data studied in this work consist of two strictly simultaneous observations performed with XMM–Newton (X-rays: 0.7–10 keV), VLT/HAWK-I (Ks band, 2.2 μm) and VLT/VISIR (M and PAH2_2 bands, 4.85 and 11.88 μm, respectively). The cross-correlation function between the X-ray and near-IR light curves shows a strong asymmetric anticorrelation dip at positive lags. We detect a near-IR QPO (2.5σ) at 2.07 ± 0.09 Hz simultaneously with an X-ray QPO at approximately the same frequency (f0 = 2.25 ± 0.05). From the cross-spectral analysis, a lag consistent with zero was measured between the two oscillations. We also measure a significant correlation between the average near-IR and mid-IR fluxes during the second night, but find no correlation on short time-scales. We discuss these results in terms of the two main scenarios for fast IR variability (hot inflow and jet powered by internal shocks). In both cases, our preliminary modelling suggests the presence of a misalignment between the disc and jet.
Highlights
Black hole low mass X-ray binaries (BH LMXB) have been historically studied mainly in X-rays, where, depending on the accretion regime, great part of the dissipated gravitational energy is radiated away by either a geometrically-thin, optically-thick accretion disc (Shakura & Sunyaev 1973) or a geometrically-thick, optically-thin inflow (Esin et al 1997; Poutanen et al 1997)
A detailed modelling of this source showed that the observed Cross-Correlation Function (CCF) could be reproduced by assuming that the optical emission originates from both reprocessed and synchrotron radiation coming from a hot, magnetised inflow, while the X-rays are generated from the Comptonization of the synchrotron radiation (Veledina et al 2011)
Superimposed on the strong broadband noise, a ∼ 2.1 Hz quasi-periodic oscillations (QPO) is simultaneously detected both in the X-rays and in the near-IR power spectral densities (PSDs), which we identify as a type-C QPO
Summary
Black hole low mass X-ray binaries (BH LMXB) have been historically studied mainly in X-rays, where, depending on the accretion regime, great part of the dissipated gravitational energy is radiated away by either a geometrically-thin, optically-thick accretion disc (Shakura & Sunyaev 1973) or a geometrically-thick, optically-thin inflow (Esin et al 1997; Poutanen et al 1997). Further fast O-IR photometry observations led to the discovery of a 0.1-second O-IR lag with respect to the X-ray variability (Gandhi et al 2008; Casella et al 2010) This behaviour was attributed to the jet and was well reproduced by the so called “internal shock model" (Kobayashi et al 1997; Spada et al 2001; Jamil et al 2010) when linking the shells’ velocities to the variations observed in X-rays (Malzac 2013, 2014). There is growing evidence that the O-IR jet emitting region is extended and probably stratified (Vincentelli et al 2018; Vincentelli & Casella 2019; Paice et al 2019); Malzac et al (2018) recently showed that Doppler boosting modulation can lead to an anti-correlation with X-rays on long timescales Another important feature which gave new insight to the geometry of these systems are the quasi-periodic oscillations (QPO). We find that the properties of fast near-IR variability put tight constraints on the current jet and accretion flow models
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