Identification of three new ultraluminous X-ray sources in NGC 4631 and NGC 1097: Evidence for stellar-mass black holes

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Table 2.

X-ray spectral parameters of NGC 4631 in the Chandra and XMM–Newton observations.

Data label	Net Rate	N_H	Γ/T_in	Cstat/dof	F_x	L_x
	(10⁻³ counts/s)	(10²² cm⁻²)	(/keV)		(10⁻¹³ erg cm⁻² s⁻¹)	(10³⁹ erg s⁻¹)

tbabstbabsdiskbb
C1	> 0.20
C2	6.56 ± 0.48	$1 . 25_{- 0.19}^{+ 0.20}$ $Mathematical equation: $ 1.25^{+0.20}_{-0.19} $$	$0 . 60_{- 0.01}^{+ 0.01}$ $Mathematical equation: $ 0.60^{+0.01}_{-0.01} $$	34.08/30	$0 . 88_{- 0.11}^{+ 0.13}$ $Mathematical equation: $ 0.88^{+0.13}_{-0.11} $$	$1 . 78_{- 0.21}^{+ 0.22}$ $Mathematical equation: $ 1.78^{+0.22}_{-0.21} $$
C3	7.72 ± 0.58	$0 . 66_{- 0.19}^{+ 0.21}$ $Mathematical equation: $ 0.66^{+0.21}_{-0.19} $$	$0 . 95_{- 0.03}^{+ 0.03}$ $Mathematical equation: $ 0.95^{+0.03}_{-0.03} $$	14.69/27	$1 . 09_{- 0.16}^{+ 0.22}$ $Mathematical equation: $ 1.09^{+0.22}_{-0.16} $$	$1 . 16_{- 0.14}^{+ 0.15}$ $Mathematical equation: $ 1.16^{+0.15}_{-0.14} $$
C4	6.19 ± 0.58	$0 . 17_{- 0.17}^{+ 0.20}$ $Mathematical equation: $ 0.17^{+0.20}_{-0.17} $$	$0 . 87_{- 0.03}^{+ 0.03}$ $Mathematical equation: $ 0.87^{+0.03}_{-0.03} $$	10.10/18	$0 . 93_{- 0.22}^{+ 0.30}$ $Mathematical equation: $ 0.93^{+0.30}_{-0.22} $$	$0 . 75_{- 0.11}^{+ 0.12}$ $Mathematical equation: $ 0.75^{+0.12}_{-0.11} $$
C5	8.55 ± 0.64	$0 . 91_{- 0.18}^{+ 0.20}$ $Mathematical equation: $ 0.91^{+0.20}_{-0.18} $$	$0 . 69_{- 0.02}^{+ 0.02}$ $Mathematical equation: $ 0.69^{+0.02}_{-0.02} $$	26.59/28	$1 . 01_{- 0.14}^{+ 0.17}$ $Mathematical equation: $ 1.01^{+0.17}_{-0.14} $$	$1 . 61_{- 0.19}^{+ 0.21}$ $Mathematical equation: $ 1.61^{+0.21}_{-0.19} $$
C6	7.75 ± 0.72	$0 . 14_{- 0.14}^{+ 0.23}$ $Mathematical equation: $ 0.14^{+0.23}_{-0.14} $$	$0 . 78_{- 0.03}^{+ 0.03}$ $Mathematical equation: $ 0.78^{+0.03}_{-0.03} $$	12.44/17	$1 . 05_{- 0.29}^{+ 0.32}$ $Mathematical equation: $ 1.05^{+0.32}_{-0.29} $$	$0 . 96_{- 0.14}^{+ 0.16}$ $Mathematical equation: $ 0.96^{+0.16}_{-0.14} $$
C7	6.44 ± 0.66	$0 . 92_{- 0.25}^{+ 0.27}$ $Mathematical equation: $ 0.92^{+0.27}_{-0.25} $$	$0 . 55_{- 0.02}^{+ 0.02}$ $Mathematical equation: $ 0.55^{+0.02}_{-0.02} $$	12.38/15	$0 . 70_{- 0.15}^{+ 0.28}$ $Mathematical equation: $ 0.70^{+0.28}_{-0.15} $$	$1 . 46_{- 0.24}^{+ 0.26}$ $Mathematical equation: $ 1.46^{+0.26}_{-0.24} $$
C_combine	7.68 ± 0.29	$0 . 67_{- 0.08}^{+ 0.09}$ $Mathematical equation: $ 0.67^{+0.09}_{-0.08} $$	$0 . 73_{- 0.01}^{+ 0.01}$ $Mathematical equation: $ 0.73^{+0.01}_{-0.01} $$	90.12/99	$0 . 95_{- 0.07}^{+ 0.07}$ $Mathematical equation: $ 0.95^{+0.07}_{-0.07} $$	$1 . 20_{- 0.07}^{+ 0.08}$ $Mathematical equation: $ 1.20^{+0.08}_{-0.07} $$
C8	< 0.49
C9	< 0.97
C10	< 0.29
C11	< 0.23
C12	< 0.53

XM1	< 0.83
XM2	8.18 ± 0.78	$0 . 20_{- 0.06}^{+ 0.07}$ $Mathematical equation: $ 0.20^{+0.07}_{-0.06} $$	$0 . 94_{- 0.32}^{+ 0.30}$ $Mathematical equation: $ 0.94^{+0.30}_{-0.32} $$	19.30/20	$0 . 82_{- 0.06}^{+ 0.04}$ $Mathematical equation: $ 0.82^{+0.04}_{-0.06} $$	$0 . 50_{- 0.09}^{+ 0.06}$ $Mathematical equation: $ 0.50^{+0.06}_{-0.09} $$
XM3	< 0.55

Notes. The $N_{H}$ $Mathematical equation: $ N_\mathrm{H} $$ of one tbabs component was fixed to the line-of-sight value of 0.013 × 10²² cm⁻², while the intrinsic $N_{H}$ $Mathematical equation: $ N_\mathrm{H} $$ (second tbabs component) was left to free to vary. C_combine corresponds to combined observations C3–C7. Absorbed fluxes were calculated in the 0.5–8 keV energy range, while unabsorbed luminosities were derived assuming a distance of 7.6 Mpc. Quoted uncertainties correspond to the 90% confidence level for each parameter.

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