Fermi Large Area Telescope observations of the fast-dimming Crab Nebula in 60–600 MeV

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Volume 638 (June 2020)

A&A, 638 (2020) A147

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Table 2.

PDF models fit to the histogram of the flux measurements.

Model	Component	N₀^(a)	F_maxPD^(b)	σ_lnF^(c)	ΔTS ^(d)	Δdof ^(e)
		(%)	(10⁻⁶ cm⁻² s⁻¹)
Single log-normal	…	100	1.56 ± 0.06	0.94 ± 0.03	0	0

Double log-normal	A ^(f)	5.6 ± 1.0	0.066 (fixed)	0.51 (fixed)	180.4	1
	B	94.4 ± 1.0	1.82 ± 0.05	0.67 ± 0.02

Triple log-normal	X ^(f)	3.3 ± 1.0	0.066 (fixed)	0.51 (fixed)	233.6	4
	Y	31.2 ± 13.0	1.14 ± 0.33	1.07 ± 0.18
	Z	65.5 ± 13.9	2.10 ± 0.08	0.45 ± 0.06

Notes.

^(a)

The normalization for scaling a component. In each model, the sum of normalizations of all components must be 1.

^(b)

The flux corresponding to the maximum probability density. It is mathematically equivalent to the exponential of the mean of the flux’s natural logarithm.

^(c)

The standard deviation of the flux’s natural logarithm.

^(d)

The natural logarithm of the square of the likelihood ratio of a model compared to the single log-normal. The likelihood function is for a Poisson distribution.

^(e)

The number of additional parameters (the extra degrees of freedom) of a model compared to the single log-normal.

^(f)

Components which model the shot-noise fluctuations of the extrapolated IC flux. All of their parameters except normalizations are fixed at values estimated from the photon statistics.

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