First spectropolarimetric observation of the neutron star low-mass X-ray binary GX 3+1

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Volume 692 (December 2024)

A&A, 692 (2024) A123

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Table 2.

Best-fitting model parameters of the fits to GX 3+1 IXPE+NuSTAR+NICER spectra.

	Parameter	LB	UB
`TBabs`	N_H (10²² cm⁻²)	2.41 $_{- 0.02}^{+ 0.02}$ $^{+0.02}_{-0.02}$
`diskbb`	kT_in (keV)	0.94 $_{- 0.04}^{+ 0.05}$ $^{+0.05}_{-0.04}$	1.11 $_{- 0.03}^{+ 0.04}$ $^{+0.04}_{-0.03}$
	$R_{} in \sqrt{cos i}$ $R_\text{ in} \sqrt{\cos i}$ (km)	11.4 $_{- 1.5}^{+ 1.7}$ $^{+1.7}_{-1.5}$	9.3 $_{- 1.5}^{+ 1.6}$ $^{+1.6}_{-1.5}$
`thcomp`	τ	7.7 $_{- 0.2}^{+ 0.2}$ $^{+0.2}_{-0.2}$	7.9 $_{- 2.1}^{+ 1.9}$ $^{+1.9}_{-2.1}$
	kT_e (keV)	2.8 $_{- 0.1}^{+ 0.1}$ $^{+0.1}_{-0.1}$	2.7 $_{- 0.2}^{+ 0.2}$ $^{+0.2}_{-0.2}$
`bbodyrad`	kT (keV)	1.39 $_{- 0.04}^{+ 0.04}$ $^{+0.04}_{-0.04}$	1.65 $_{- 0.12}^{+ 0.11}$ $^{+0.11}_{-0.12}$
	R_bb (km)	7.9 $_{- 0.7}^{+ 0.7}$ $^{+0.7}_{-0.7}$	5.6 $_{- 0.7}^{+ 1.7}$ $^{+1.7}_{-0.7}$
`relxillNS`	q_em	[2.8]
	a	[0.1]
	i (deg)	36.1 $_{- 1.9}^{+ 1.1}$ $^{+1.1}_{-1.9}$
	R_in (ISCO)	< 1.5
	kT_bb (keV)	= kT	= kT
	log ξ	2.8 $_{- 0.1}^{+ 0.1}$ $^{+0.1}_{-0.1}$
	A_Fe	1.7 $_{- 0.1}^{+ 0.1}$ $^{+0.1}_{-0.1}$
	log n_e	[16.5]
	N_r (10⁻³)	4.2 $_{- 0.5}^{+ 0.5}$ $^{+0.5}_{-0.5}$	3.0 $_{- 0.3}^{+ 0.4}$ $^{+0.4}_{-0.3}$

Cross-calibration
𝒞_DU1/FPMA		0.864 $_{- 0.003}^{+ 0.003}$ $^{+0.003}_{-0.003}$	0.843 $_{- 0.006}^{+ 0.006}$ $^{+0.006}_{-0.006}$
𝒞_DU2/FPMA		0.869 $_{- 0.003}^{+ 0.003}$ $^{+0.003}_{-0.003}$	0.848 $_{- 0.006}^{+ 0.006}$ $^{+0.006}_{-0.006}$
𝒞_DU3/FPMA		0.849 $_{- 0.003}^{+ 0.003}$ $^{+0.003}_{-0.003}$	0.827 $_{- 0.006}^{+ 0.006}$ $^{+0.006}_{-0.006}$
𝒞_FPMB/FPMA		0.982 $_{- 0.002}^{+ 0.002}$ $^{+0.002}_{-0.002}$	0.978 $_{- 0.002}^{+ 0.002}$ $^{+0.002}_{-0.002}$
𝒞_XTI/FPMA		0.933 $_{- 0.003}^{+ 0.002}$ $^{+0.002}_{-0.003}$	0.861 $_{- 0.003}^{+ 0.003}$ $^{+0.003}_{-0.003}$

χ²/d.o.f.		880.9/817	812.3/800

Photon flux ratios (2–8 keV)

F_diskbb/F_Tot		34.3%	40.1%
F_{thcomp*bbodyrad}/F_Tot		47.9%	47.8%
F_relxillNS/F_Tot		16.8%	12.1%
Energy Flux (2–8 keV)
F_Tot (10⁻⁹ erg s⁻¹ cm⁻²)		7.03	7.05

Notes. Uncertainties are at the 90% confidence level for a single parameter. Parameters in common between the two columns were linked during the two spectral states, while those in square brackets were frozen during the fit. The normalizations of diskbb and bbodyrad are computed assuming a source distance of 6.5 kpc (Galloway et al. 2008). The cross-calibration constant are reported with respect to that of the NuSTAR FPMA detector.

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