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No time for dead time: timing analysis of bright black hole binaries with NuSTAR

No time for dead time: timing analysis of bright black hole binaries with NuSTAR
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 event-to-event by a few percent. The most obvious effect is a distortion of the white noise level in the power density spectrum (PDS) that cannot be easily modeled with 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 cospectrum, the real part of the cross PDS, 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 ratio relative to what would be achieved using more standard techniques. We apply this technique to NuSTAR observations of the black hole binaries GX 339–4, Cyg X-1, and GRS 1915+105
accretion, accretion disks, black hole physics, methods: data analysis, methods: statistical, X-rays: stars
1538-4357
109
Bachetti, M.
fb499a38-fcff-4761-b0ad-8f03fd25dd5d
Gandhi, Poshak
5bc3b5af-42b0-4dd8-8f1f-f74048d4d4a9
Bachetti, M.
fb499a38-fcff-4761-b0ad-8f03fd25dd5d
Gandhi, Poshak
5bc3b5af-42b0-4dd8-8f1f-f74048d4d4a9

Bachetti, M. and Gandhi, Poshak (2015) No time for dead time: timing analysis of bright black hole binaries with NuSTAR. The Astrophysical Journal, 800 (2), 109. (doi:10.1088/0004-637X/800/2/109).

Record type: Article

Abstract

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 event-to-event by a few percent. The most obvious effect is a distortion of the white noise level in the power density spectrum (PDS) that cannot be easily modeled with 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 cospectrum, the real part of the cross PDS, 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 ratio relative to what would be achieved using more standard techniques. We apply this technique to NuSTAR observations of the black hole binaries GX 339–4, Cyg X-1, and GRS 1915+105

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More information

Accepted/In Press date: 22 December 2014
Published date: 18 February 2015
Keywords: accretion, accretion disks, black hole physics, methods: data analysis, methods: statistical, X-rays: stars
Organisations: Astronomy Group

Identifiers

Local EPrints ID: 400059
URI: https://eprints.soton.ac.uk/id/eprint/400059
ISSN: 1538-4357
PURE UUID: 87507766-3b47-4e38-903a-d5a2cf9e8fb2
ORCID for Poshak Gandhi: ORCID iD orcid.org/0000-0003-3105-2615

Catalogue record

Date deposited: 09 Sep 2016 08:45
Last modified: 06 Jun 2018 12:21

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