Constraining the geometry of the dipping atoll 4U 1624–49 with X-ray spectroscopy and polarimetry

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Volume 690 (October 2024)

A&A, 690 (2024) A230

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Table 3.

Best-fit spectral parameters for the Western model obtained for 4U 1624–49 with IXPE+NuSTAR+NICER spectra.

Western model	Parameter	Nondip	Dip
`TBabs`	N_H (10²² cm⁻²)	10.3 $_{- 0.1}^{+ 0.2}$ $^{+0.2}_{-0.1}$	[10.3]
`edge`	E_c (keV)	[1.839]	[1.839]
	D	0.31 $_{- 0.07}^{+ 0.07}$ $^{+0.07}_{-0.07}$	0.28 $_{- 0.05}^{+ 0.04}$ $^{+0.04}_{-0.05}$
`CLOUDY`	log ξ	4.7 $_{- 0.3}^{+ 0.3}$ $^{+0.3}_{-0.3}$	4.2 $_{- 0.1}^{+ 0.1}$ $^{+0.1}_{-0.1}$
	log N_Heq	22.8 $_{- 0.2}^{+ 0.3}$ $^{+0.3}_{-0.2}$	23.2 $_{- 0.1}^{+ 0.1}$ $^{+0.1}_{-0.1}$
`thcomp`	τ	15.8 $_{- 2.2}^{+ 2.1}$ $^{+2.1}_{-2.2}$	[15.8]
	kT_e (keV)	2.6 $_{- 0.1}^{+ 0.1}$ $^{+0.1}_{-0.1}$	[2.6]
`diskbb`	kT_in (keV)	[0.6]	[0.6]
	R_in (km)	18.9 $_{- 2.9}^{+ 2.8}$ $^{+2.8}_{-2.9}$	16.9 $_{- 1.2}^{+ 1.2}$ $^{+1.2}_{-1.2}$
`bbodyrad`	kT (keV)	1.26 $_{- 0.02}^{+ 0.02}$ $^{+0.02}_{-0.02}$	[1.26]
	R_bb (km)	8.4 $_{- 1.7}^{+ 1.6}$ $^{+1.6}_{-1.7}$	7.2 $_{- 0.7}^{+ 0.8}$ $^{+0.8}_{-0.7}$
`relxillNS`	q_em	[1.8]	[1.8]
	a	[0.1]	[0.1]
	i (deg)	64 $_{- 22}^{+ 18}$ $^{+18}_{-22}$	[64]
	R_in (ISCO)	[1.5]	[1.5]
	kT_bb (keV)	= kT	= kT
	log ξ	2.93 $_{- 0.33}^{+ 0.34}$ $^{+0.34}_{-0.33}$	[2.93]
	A_Fe	[1]	[1]
	log n_e	[16]	[16]
	N_r (10⁻⁴)	8.2 $_{- 3.4}^{+ 4.5}$ $^{+4.5}_{-3.4}$	10.8 $_{- 1.8}^{+ 1.9}$ $^{+1.9}_{-1.8}$

χ²/d.o.f.		716.5/675	683.5/646
F_Comp/F_Tot (2–8 keV) ^(a)		46.6%	44.3%
F_bb/F_Tot (2–8 keV) ^(b)		39.8%	33.6%
F_Refl/F_Tot (2–8 keV) ^(c)		13.6%	22.1%
F_X (10⁻⁹ erg s⁻¹ cm⁻²) ^(d)		1.45	1.17

Notes. The errors are at the 90% confidence level for a single parameter. Parameters in square brackets were frozen during the fit. A 15 kpc distance is assumed to compute the inner radius R_in and R_bb from the diskbb and bbodyrad normalizations.

^(a)

Percentage of Comptonized photon flux in the 2–8 keV range.

^(b)

Percentage of blackbody photon flux in the 2–8 keV range.

^(c)

Percentage of reflected photon flux in the 2–8 keV range.

^(d)

Model flux in the energy range 0.1–20 keV.

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