X-ray spectropolarimetry of the bright atoll Serpens X-1

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Volume 690 (October 2024)

A&A, 690 (2024) A200

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Table 3.

Best-fitting model parameters of the fits to the NuSTAR and NuSTAR+IXPE data.

Parameter
`diskbb`
kT_in (keV)	$0 . 93_{- 0.03}^{+ 0.01}$ $0.93^{+0.01}_{-0.03}$
$R_{in} \sqrt{cos i}$ $R_{\mathrm{in}} \sqrt{\cos i}$ (km)	$13 . 1_{- 0.4}^{+ 0.2}$ $13.1^{+0.2}_{-0.4}$

`bbodyrad`
kT_bb (keV)	$1 . 38_{- 0.05}^{+ 0.02}$ $1.38^{+0.02}_{-0.05}$
R_bb (km)	$7 . 7_{- 0.5}^{+ 0.2}$ $7.7^{+0.2}_{-0.5}$

`thcomp`
τ	$8 . 1_{- 0.2}^{+ 0.3}$ $8.1^{+0.3}_{-0.2}$
kT_e (keV)	$2 . 92_{- 0.04}^{+ 0.03}$ $2.92^{+0.03}_{-0.04}$

`relxillns`
q_em	2.26 ± 0.09
a	[0.2]
incl (deg)	$25 . 1_{- 1.5}^{+ 1.3}$ $25.1^{+1.3}_{-1.5}$
R_in (units of R_ISCO)	$1 . 6_{- 0.5}^{+ 0.3}$ $1.6^{+0.3}_{-0.5}$
kT_bb (keV)	[=kT_{bb, bbodyrad}]
log(ξ/erg cm s⁻¹)	2.88 ± 0.07
A_Fe	$5 . 0_{- 0.3}^{+ 1.1}$ $5.0^{+1.1}_{-0.3}$
log n_e	[18]
N_r (10⁻³)	$1 . 37_{- 0.08}^{+ 0.09}$ $1.37^{+0.09}_{-0.08}$

Cross-calibration
C_{DU1 − FPMA}	$0 . 881_{- 0.007}^{+ 0.005}$ $0.881^{+0.005}_{-0.007}$
C_{DU2 − FPMA}	$0 . 880_{- 0.005}^{+ 0.006}$ $0.880^{+0.006}_{-0.005}$
C_{DU3 − FPMA}	$0 . 861_{- 0.006}^{+ 0.005}$ $0.861^{+0.005}_{-0.006}$
C_{FPMB − FPMA}	0.987 ± 0.001
C_{XTI − FPMA}	0.929 ± 0.001
Gain shift
α_DU1	$1 . 013_{- 0.003}^{+ 0.002}$ $1.013^{+0.002}_{-0.003}$
β_DU1 (eV)	$- 53_{- 10}^{+ 12}$ $-53^{+12}_{-10}$
α_DU2	$1 . 008_{- 0.003}^{+ 0.002}$ $1.008^{+0.002}_{-0.003}$
β_DU2 (eV)	$- 30_{- 11}^{+ 12}$ $-30^{+12}_{-11}$
α_DU3	$1 . 007_{- 0.003}^{+ 0.002}$ $1.007^{+0.002}_{-0.003}$
β_DU3 (eV)	$- 33_{- 11}^{+ 12}$ $-33^{+12}_{-11}$
α_XTI	1.032 ± 0.001
β_XTI (eV)	$- 65_{- 3}^{+ 2}$ $-65^{+2}_{-3}$

χ²/d.o.f.	1031/962

Photon flux ratios ^(a)
2–8 keV
F_diskbb/F_tot	0.44
F_bbodyrad/F_tot	0.47
F_relxillns/F_tot	0.09
2–4 keV
F_diskbb/F_tot	0.58
F_bbodyrad/F_tot	0.35
F_relxillns/F_tot	0.07
4–8 keV
F_diskbb/F_tot	0.19
F_bbodyrad/F_tot	0.69
F_relxillns/F_tot	0.12
Energy flux (2–8 keV)
F_tot (erg s⁻¹ cm⁻²)	5.1 × 10⁻⁹

Notes. Uncertainties are given at the 68% confidence level for one parameter of interest. Parameters in square brackets were kept frozen during the fit. The normalizations of diskbb and bbodyrad are computed assuming a source distance of 7.7 kpc.

^(a)

The photon fluxes are in units of photon cm⁻² s⁻¹.

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