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Table 4

Characteristics of the power spectral densities of PKS 2155−304 at different energies and timescales.

Energy Instrument Range of Method β Goodness Ref.
range log 10(f/ d-1) of fit
> 200 GeV H.E.S.S. [−4.0,−0.3] LSP, FF no break (fixed) 56%
> 200 GeV H.E.S.S. [−3.5,0.0] SF, FF no break (fixed) 48%
> 200 GeV H.E.S.S. [−3.5,0.0] MFVF, FF no break (fixed) 11%
> 200 GeV H.E.S.S. [−4.0,−0.3] LSP, FF 51%
> 200 GeV H.E.S.S. [−3.5,0.0] SF, FF 43%
> 200 GeV H.E.S.S. [− 3.5,0.0] MFVF, FF 10%
0.1–300 GeV Fermi-LAT [− 4.0,−1.3] LSP, FF no break (fixed) 6.3%
0.1–300 GeV Fermi-LAT [−3.3,−1.0] SF, FF no break (fixed) 46%
0.1–300 GeV Fermi-LAT [−3.3,−1.0] MFVF, FF no break (fixed) 40 %
0.1–300 GeV Fermi-LAT [−4.0,−1.3] LSP, FF 2.4%
0.1–300 GeV Fermi-LAT [− 3.3,−1.0] SF, FF 33%
0.1–300 GeV Fermi-LAT [− 3.3,−1.0] MFVF, FF 30%
> 200 GeV H.E.S.S. a [0.9,2.6] SF, FF 2.06 ± 0.21 [0.1,0.9] − (1)
0.1−300 GeV Fermi-LAT b [−2.0,−0.9] PSD, fit 0.577 ± 0.332 − − (2)
0.1−300 GeV Fermi-LAT c [−3.2,−0.7] PSD, fit < −1.7 − (3)
2.5–20 keV RXTEd [−0.9,0.0] PSD, fit 1.46 ± 0.10 − − (4)
2.5–20 keV RXTEd [0.0,1.9] PSD, fit 2.23 ± 0.10 − − (4)
Optical Geneva [−1.2,2.0] SF, fit − − (5)
Optical ROTSE [− 4.4,−1.3] MFVF, FF − (6)
Optical SMARTS [−2.4,−0.9] PSD, fit − − (7)

Notes. Range of log 10(f/ d-1): the range over which the PSD is characterized. Method: the methods used for the analysis; forward folding method (FF), best fit of the slope by, e.g. a χ2-test (fit), Structure Function (SF), Lomb-Scargle Periodogram (LSP) and Multiple Fragments Variance Function (MFVF). Goodness of fit: the p-value obtained with simulated light curves. Upper part – results from this work. Lower part – results reported in the literature with superscripts referring to:

(a)

H.E.S.S. flaring state: a break was detected with a 95% confidence in the SF. It shall be noted that a break in the SF is at a ~3 times larger frequency than in the intrinsic PSD.

(b)

Based on aperture photometric Fermi-LAT light curves provided by the Fermi Science Support Center at http://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/.

(c)

Model results assuming a superposition of Ornstein-Uhlenbeck processes (OU) and using 4 yr of Fermi-LAT data. A slight preference for a single OU with different slope is reported.

(d)

Based on non-simultaneous data.

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