The persistent nature of the Be X-ray binary pulsar 4U 0728-25

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Table 4.

Best–fit values for the BB and PL parameters, when the two spectra H and S are fitted simultaneously with common values of N_H, Γ, and kT_BB (Case 1) or with common values of N_H, kT_BB, and R_BB (Case 2).

Phase	Case 1		Case 2
interval	H	S	H	S
N_H ^(a)	6.7 $_{- 0.3}^{+ 0.2}$ ${}^{+0.2}_{-0.3}$	6.7 $_{- 0.3}^{+ 0.2}$ ${}^{+0.2}_{-0.3}$	6.4 ± 0.3	6.4 ± 0.3

Γ	1.55 $_{- 0.07}^{+ 0.08}$ ${}^{+0.08}_{-0.07}$	1.55 $_{- 0.07}^{+ 0.08}$ ${}^{+0.08}_{-0.07}$	1.34 $_{- 0.05}^{+ 0.06}$ ${}^{+0.06}_{-0.05}$	1.55 ± 0.08
f_PL ^(b)	1.58 $_{- 0.08}^{+ 0.09}$ ${}^{+0.09}_{-0.08}$	1.45 ± 0.08	1.92 ± 0.08	1.34 ± 0.07

kT_BB	1.56 ± 0.09	1.56 ± 0.09	1.4 ± 0.1	1.4 ± 0.1
R_BB	250 ± 20	170 ± 20	230 $_{- 30}^{+ 20}$ ${}^{+20}_{-30}$	230 $_{- 30}^{+ 20}$ ${}^{+20}_{-30}$
f_BB ^(b)	0.68 ± 0.09	0.31 ± 0.08	0.36 $_{- 0.07}^{+ 0.08}$ ${}^{+0.08}_{-0.07}$	0.36 $_{- 0.07}^{+ 0.08}$ ${}^{+0.08}_{-0.07}$

f_TOT ^(b)	2.26 ± 0.05	1.76 ± 0.03	2.28 $_{- 0.04}^{+ 0.05}$ ${}^{+0.05}_{-0.04}$	1.70 ± 0.04
f_PL/f_TOT	69.9%	82.4%	84.2%	78.8%
f_BB/f_TOT	30.1%	17.6%	15.8%	21.1%

$χ_{ν}^{2}$ $\chi ^{2}_{\nu }$	1.015		1.014
d.o.f.	3147		3147
NHP ^(c)	0.28		0.29

Notes.

^(a)

×10²¹ cm⁻²;

^(b)

Unabsorbed flux in the energy range 0.2–12 keV, in units of 10⁻¹¹ erg s⁻¹;

^(c)

Null hypothesis probability.

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