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arXiv · 1906.06519

X-ray dips and a complex UV/X-ray cross-correlation function in the black hole candidate MAXI J1820+070

J. J. E. Kajava·S. E. Motta·A. Sanna·A. Veledina·M. Del Santo·A. Segreto
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Abstract

MAXI J1820+070, a black hole candidate first detected in early March 2018, was observed by XMM-Newton during the outburst rise. In this letter we report on the spectral and timing analysis of the XMM-Newton X-ray and UV data, as well as contemporaneous X-ray data from the Swift satellite. The X-ray spectrum is well described by a hard thermal Comptonization continuum. The XMM-Newton X-ray light curve shows a pronounced dipping interval, and spectral analysis indicates that it is caused by a moderately ionized partial covering absorber. The XMM-Newton/OM U-filter data does not reveal any signs of the 17 hr orbital modulation that was seen later on during the outburst decay. The UV/X-ray cross correlation function shows a complex shape, with a peak at positive lags of about 4 seconds and a pre-cognition dip at negative lags, which is absent during the X-ray dipping episode. Such shape could arise if the UV emission comes partially from synchrotron self-Compton emission near the black hole, as well as from reprocessing of the X-rays in the colder accretion disc further out.

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J. J. E. Kajava, S. E. Motta, A. Sanna, A. Veledina, M. Del Santo, A. Segreto. 2019-06-15. X-ray dips and a complex UV/X-ray cross-correlation function in the black hole candidate MAXI J1820+070. https://doi.org/10.1093/mnrasl%2Fslz089

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