Table 2: Best-fit parameters and results for the analysis of the nuclear spectra of NGC 6251. Model legenda: PL = power-law; TH = thermal component ( mekal implementation in X SPEC) with solar abundances; GA = Gaussian emission line; BKPL = broken power-law.
Model $N_{\rm H}$ $\Gamma$ kT1/ $\Gamma_{{\rm soft}}$ kT2/ $E_{{\rm break}}$ $E_{\rm c}$ $I_{\rm c}$ EW $\chi^2/$ d.o.f.
Mission (1021 cm-2)   (keV)/ (keV) (keV) (10-6 ph cm-2 s-1) (eV)  
BeppoSAX    
PL $0.8 \pm^{0.6}_{0.3}$ $1.79 \pm^{0.06}_{0.07}$ ... ... ... ... ... 96.7/92
PL+TH $1.0 \pm^{0.12}_{0.05}$ $1.70 \pm^{0.12}_{0.16}$ $1.4 \pm^{0.9}_{0.7}$ ... 6.4$^{\dag }$ <8.0 <160 92.3/90
        ... 6.59$^{\dag }$ <4.5 <80  
        ... 6.7$^{\dag }$ <3.0 <60  
        ... 6.96$^{\dag }$ <2.1 <50  
ASCA    
PL $0.9 \pm^{0.4}_{0.3}$ $2.06 \pm^{0.08}_{0.07}$ ... ... ... ... ... 259.7/225
PL+TH $1.6 \pm^{0.7}_{0.8}$ $2.00 \pm^{0.08}_{0.07}$ $0.85 \pm^{0.34}_{0.15}$ ... ... ... ... 240.6/223
PL+2$\times$TH $1.6 \pm^{2.1}_{0.8}$ $2.3 \pm 0.4$ $0.8 \pm^{0.3}_{0.2}$ $6 \pm^6_2$ ... ... ... 231.8/221
PL+TH+GA $1.7 \pm^{0.5}_{0.4}$ $2.05 \pm^{0.11}_{0.10}$ $0.84 \pm^{0.27}_{0.18}$   $6.59 \pm 0.16$ $8 \pm 4$ $500 \pm 200$ 228.1/221
BKPL+GA $4.0 \pm^{1.8}_{1.5}$ $2.28 \pm^{0.17}_{0.14}$ $3.7 \pm^{1.2}_{0.9}$ $1.38 \pm^{0.15}_{0.09}$ $6.62 \pm^{0.12}_{0.18}$ $10 \pm4 $ $800 \pm 300$ 245.0/226

$^{\dag }$ Gaussian emission profiles added to the best-fit continuum. Centroid energies $E_{\rm c}$ are fixed. Upper limits are at the 90% confidence level.

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