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

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Table 3.

Best-fit parameters of the EPIC spectra H and S of 4U 0728-25, in the case of the four best-fitting continuum models.

Parameter	Spectrum H	Spectrum S
TBPCF × PL
TBABS N_H(×10²¹ cm⁻²)	7.3 ± 0.4	7.8 ± 0.4
TBPCF N_H(×10²² cm⁻²)	6.3 ± 1.1	6.8 $_{- 1.3}^{+ 1.4}$ ${}^{+1.4}_{-1.3}$
TBPCF Covering Fraction	0.51 $_{- 0.06}^{+ 0.05}$ ${}^{+0.05}_{-0.06}$	0.46 $_{- 0.07}^{+ 0.06}$ ${}^{+0.06}_{-0.07}$
Γ	1.70 $_{- 0.08}^{+ 0.09}$ ${}^{+0.09}_{-0.08}$	1.83 $_{- 0.10}^{+ 0.09}$ ${}^{+0.09}_{-0.10}$
Flux_PL (0.2–12 keV) ^(a)	3.4 $_{- 0.3}^{+ 0.8}$ ${}^{+0.8}_{-0.3}$	2.7 $_{- 0.3}^{+ 0.4}$ ${}^{+0.4}_{-0.3}$
Luminosity (0.2–12 keV) ^(b)	2.2 $_{- 0.2}^{+ 0.3}$ ${}^{+0.3}_{-0.2}$	1.8 ± 0.2
$χ_{ν}^{2}$ $\chi ^{2}_{\nu }$ /d.o.f.	1.047/1615	0.974/1527

CUTOFFPL
TBABS N_H(×10²¹ cm⁻²)	4.9 $_{- 0.3}^{+ 0.4}$ ${}^{+0.4}_{-0.3}$	5.8 $_{- 0.4}^{+ 0.3}$ ${}^{+0.3}_{-0.4}$
Γ	0.65 $_{- 0.10}^{+ 0.11}$ ${}^{+0.11}_{-0.10}$	1.0 ± 0.1
E_cut (keV)	6.6 $_{- 0.9}^{+ 1.4}$ ${}^{+1.4}_{-0.9}$	9 ± 2
Flux_CPL (0.2–12 keV) ^(a)	2.10 ± 0.06	1.61 ± 0.05
Luminosity (0.2–12 keV) ^(b)	1.37 ± 0.04	1.05 ± 0.03
$χ_{ν}^{2}$ $\chi ^{2}_{\nu }$ /d.o.f.	1.048/1616	0.980/1528

PL + BB
TBABS N_H(×10²¹ cm⁻²)	5.9 ± 0.4	6.8 ± 0.4
Γ	1.33 $_{- 0.08}^{+ 0.11}$ ${}^{+0.11}_{-0.08}$	1.6 ± 0.1
Flux_PL (0.2–12 keV) ^(a)	1.8 $_{- 0.2}^{+ 0.1}$ ${}^{+0.1}_{-0.2}$	1.41 $_{- 0.09}^{+ 0.10}$ ${}^{+0.10}_{-0.09}$
kT_BB (keV)	1.4 $_{- 0.2}^{+ 0.1}$ ${}^{+0.1}_{-0.2}$	1.5 $_{- 0.2}^{+ 0.1}$ ${}^{+0.1}_{-0.2}$
R_BB (m) ^(c)	270 ± 40	200 ± 30
Flux_BB (0.2–12 keV) ^(d)	5 ± 1	3 ± 1
Flux_BB/Flux_TOT (0.2–12 keV)	20.6%	19.0%
Flux_BB/Flux_TOT (0.01–100 keV)	5.7%	7.6%
Unabsorbed flux (0.2–12 keV) ^(a)	2.23 ± 0.05	1.74 $_{- 0.05}^{+ 0.07}$ ${}^{+0.07}_{-0.05}$
Luminosity (0.2–12 keV) ^(b)	1.46 ± 0.03	1.14 $_{- 0.03}^{+ 0.05}$ ${}^{+0.05}_{-0.03}$
$χ_{ν}^{2}$ $\chi ^{2}_{\nu }$ /d.o.f.	1.044/1615	0.975/1527

CPL + APEC
TBABS N_H(×10²² cm⁻²)	4.9 $_{- 0.3}^{+ 0.4}$ ${}^{+0.4}_{-0.3}$	5.8 $_{- 0.4}^{+ 0.8}$ ${}^{+0.8}_{-0.4}$
Γ	0.6 ± 0.1	0.9 ± 0.1
E_cut (keV)	6 $_{- 1}^{+ 2}$ ${}^{+2}_{-1}$	8 ± 2
Flux_CPL (0.2–12 keV) ^(a)	2.06 $_{- 1.4}^{+ 0.08}$ ${}^{+0.08}_{-1.4}$	1.58 $_{- 0.13}^{+ 0.07}$ ${}^{+0.07}_{-0.13}$
kT_APEC (keV)	2.2 ± 1.7	1.4 $_{- 1.0}^{+ 1.5}$ ${}^{+1.5}_{-1.0}$
N_APEC (cm⁻⁵)	<8×10⁻⁴	1.2 $_{- 1.1}^{+ 3.1}$ ${}^{+3.1}_{-1.1}$
Flux_APEC (0.2–12 keV) ^(e)	–	1.8 $_{- 0.9}^{+ 4.4}$ ${}^{+4.4}_{-0.9}$
Flux_APEC/Flux_TOT (0.2–12 keV)	–	1.1%
Flux_APEC/Flux_TOT (0.01–100 keV)	–	1.1%
Unabsorbed flux (0.2–12 keV) ^(a)	2.09 $_{- 0.05}^{+ 0.06}$ ${}^{+0.06}_{-0.05}$	1.60 $_{- 0.05}^{+ 0.07}$ ${}^{+0.07}_{-0.05}$
Luminosity (0.5–10 keV) ^(b)	1.36 $_{- 0.03}^{+ 0.04}$ ${}^{+0.04}_{-0.03}$	1.04 $_{- 0.03}^{+ 0.05}$ ${}^{+0.05}_{-0.03}$
$χ_{ν}^{2}$ $\chi ^{2}_{\nu }$ /d.o.f.	1.048/1614	0.979/1526

Notes.

^(a)

Corrected for absorption, ×10⁻¹¹ erg cm⁻² s⁻¹;

^(b)

×10³⁵ erg s⁻¹, assuming a source distance d = 7.6 kpc;

^(c)

Assuming a source distance d = 7.6 kpc;

^(d)

Corrected for absorption, ×10⁻¹² erg cm⁻² s⁻¹;

^(e)

Corrected for absorption, ×10⁻¹³ erg cm⁻² s⁻¹.

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