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Published February 20, 2015 | Submitted + Published
Journal Article Open

No Time for Dead Time: Timing analysis of bright black hole binaries with NuSTAR


Timing of high-count rate sources with the NuSTAR Small Explorer Mission requires specialized analysis techniques. NuSTAR was primarily designed for spectroscopic observations of sources with relatively low count-rates rather than for timing analysis of bright objects. The instrumental dead time per event is relatively long (∼2.5 msec), and varies by a few percent event-to-event. The most obvious effect is a distortion of the white noise level in the power density spectrum (PDS) that cannot be modeled easily with the standard techniques due to the variable nature of the dead time. In this paper, we show that it is possible to exploit the presence of two completely independent focal planes and use the cross power density spectrum to obtain a good proxy of the white noise-subtracted PDS. Thereafter, one can use a Monte Carlo approach to estimate the remaining effects of dead time, namely a frequency-dependent modulation of the variance and a frequency-independent drop of the sensitivity to variability. In this way, most of the standard timing analysis can be performed, albeit with a sacrifice in signal to noise relative to what would be achieved using more standard techniques. We apply this technique to NuSTAR observations of the black hole binaries GX339−4, CygX-1 and GRS 1915+105.

Additional Information

© 2015 American Astronomical Society. Received 2014 September 9; accepted 2014 December 22; published 2015 February 18. MB and DB wish to acknowledge the support from the Centre National d'Études Spatiales (CNES) and the Centre National de la Recherche Scientifique (CNRS). CS acknowledges funding by the German BMWi under DLR grant numbers 50 QR 0801, 50 QR 0903, and 50 OO 1111. P.G. thanks STFC for support (grant reference ST/J003697/1). This work was supported under NASA Contract No. NNG08FD60C, and made use of data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration. We thank the NuSTAR Operations, Software and Calibration teams for support with the execution and analysis of these observations. This research has made use of the NuSTAR Data Analysis Software (NuSTARDAS) jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (USA). The timing analysis was executed with Matteo Bachetti's Libraries and Tools in Python for NuSTAR Timing (MaLTPyNT). This code is available upon request. Most of the plots were produced with the Veusz software by Jeremy Sanders. The authors wish to thank Chris Done, Denis Leahy and Tomaso Belloni for very insightful discussions.

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Published - 0004-637X_800_2_109.pdf

Submitted - 1409.3248v1.pdf


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August 20, 2023
October 18, 2023