Unprecedentedly bright X-ray flaring in Cygnus X-1 observed by INTEGRAL

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Table 1.

Best-fit parameters for the IBIS spectra of the time outside of the flares and the three flares.

	Non-Flare	Flare 1	Flare 2	Flare 3
T_exp	57 488	302	260	242

`cutoffpl`
Γ	$2 . 17_{- 0.20}^{+ 0.19}$ $2.17^{+0.19}_{-0.20}$	1.7 ± 0.4	1.5 ± 0.4	1.6 ± 0.4
E_fold	$190_{- 70}^{+ 170}$ $190^{+170}_{-70}$	$65_{- 17}^{+ 31}$ $65^{+31}_{-17}$	$47_{- 9}^{+ 13}$ $47^{+13}_{-9}$	$53_{- 12}^{+ 18}$ $53^{+18}_{-12}$
F_{40 − 80}	1.88 ± 0.04	14.2 ± 0.4	25.5 ± 0.6	33.3 ± 0.8
χ²/d.o.f.	46.2/59	55.7/59	71.4/59	63.4/59

`brokenpl`
Γ₁	$2 . 17_{- 0.43}^{+ 0.17}$ $2.17^{+0.17}_{-0.43}$	$2 . 13_{- 0.31}^{+ 0.23}$ $2.13^{+0.23}_{-0.31}$	$2 . 44_{- 0.23}^{+ 0.17}$ $2.44^{+0.17}_{-0.23}$	$2 . 21_{- 0.33}^{+ 0.25}$ $2.21^{+0.25}_{-0.33}$
E_break	55 ± 9	$55_{- 6}^{+ 7}$ $55^{+7}_{-6}$	64 ± 8	$57_{- 7}^{+ 11}$ $57^{+11}_{-7}$
Γ₂	2.70 ± 0.08	$3 . 06_{- 0.13}^{+ 0.15}$ $3.06^{+0.15}_{-0.13}$	$3 . 49_{- 0.17}^{+ 0.23}$ $3.49^{+0.23}_{-0.17}$	$3 . 21_{- 0.13}^{+ 0.20}$ $3.21^{+0.20}_{-0.13}$
F_{40 − 80}	1.92 ± 0.05	14.5 ± 0.4	25.7 ± 0.6	33.7 ± 0.9
χ²/d.o.f.	36.2/58	49.2/58	69.1/58	62.7/58

`compTT`
kT_e	$130_{- 70}^{+ 170}$ $130^{+170}_{-70}$	$33_{- 8}^{+ 22}$ $33^{+22}_{-8}$	$25_{- 4}^{+ 6}$ $25^{+6}_{-4}$	$28_{- 5}^{+ 8}$ $28^{+8}_{-5}$
τ	$0 . 10_{- 0.10}^{+ 0.28}$ $0.10^{+0.28}_{-0.10}$	$0 . 9_{- 0.5}^{+ 0.4}$ $0.9^{+0.4}_{-0.5}$	1.1 ± 0.4	1.1 ± 0.4
F_{40 − 80}	1.88 ± 0.04	14.1 ± 0.4	25.4 ± 0.6	33.1 ± 0.8
χ²/d.o.f.	46.2/59	57.5/59	74.8/59	65.9/59

Notes. Uncertainties are at the 90% level for one parameter of interest. Exposure time, T_exp, is given in seconds, while fluxes, F_{40 − 80}, are in units of 10⁻⁹ erg s⁻¹ cm⁻² for the 40–80 keV band. The break and folding energies, E_break and E_fold, as well as the temperature of the Comptonizing plasma, kT_e, are given in keV. The seed photon temperature for the comptt-model, assuming a disk geometry, was fixed at 200 eV.

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