TY - JOUR
T1 - No time for dead time
T2 - Timing analysis of bright black hole binaries with NuSTAR
AU - Bachetti, Matteo
AU - Harrison, Fiona A.
AU - Cook, Rick
AU - Tomsick, John
AU - Schmid, Christian
AU - Grefenstette, Brian W.
AU - Barret, Didier
AU - Boggs, Steven E.
AU - Christensen, Finn E.
AU - Craig, William W.
AU - Fabian, Andrew C.
AU - Fürst, Felix
AU - Gandhi, Poshak
AU - Hailey, Charles J.
AU - Kara, Erin
AU - Maccarone, Thomas J.
AU - Miller, Jon M.
AU - Pottschmidt, Katja
AU - Stern, Daniel
AU - Uttley, Phil
AU - Walton, Dominic J.
AU - Wilms, Jörn
AU - Zhang, William W.
N1 - Publisher Copyright:
© 2015. The American Astronomical Society. All rights reserved.
PY - 2015/2/20
Y1 - 2015/2/20
N2 - 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.
AB - 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.
KW - X-rays: stars
KW - accretion, accretion disks
KW - black hole physics
KW - methods: data analysis
KW - methods: statistical
UR - http://www.scopus.com/inward/record.url?scp=84924243705&partnerID=8YFLogxK
U2 - 10.1088/0004-637X/800/2/109
DO - 10.1088/0004-637X/800/2/109
M3 - Article
AN - SCOPUS:84924243705
VL - 800
JO - Astrophysical Journal
JF - Astrophysical Journal
SN - 0004-637X
IS - 2
M1 - 109
ER -