Discovery of a 0.8-mHz quasi-periodic oscillation in the transient X-ray pulsar SXP31.0 and associated timing transitions

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Volume 705 (January 2026)

A&A, 705 (2026) A141

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Table 4.

Spectral parameters for the best-fit model of SXP31.0 based on data from epochs 1–5.

Parameter	`cutoffpl+bbodyrad+bbodyrad+gauss`

	Epoch 1	Epoch 2	Epoch 3	Epoch 4	Epoch 5
const_FPMA	1.000 (frozen)		1.000 (frozen)
const_FPMB	1.017 ± 0.003		1.028 ± 0.003
const_{ART − XC}	0.925 ± 0.003	1.000 (frozen)		1.000 (frozen)	1.000 (frozen)
const_{XRT, PC}	$0 . 949_{- 0.066}^{+ 0.069}$ $0.949^{+0.069}_{-0.066}$
const_{XRT, WT}	1.059 ± 0.038	$0 . 924_{- 0.023}^{+ 0.017}$ $0.924^{+0.017}_{-0.023}$	1.067 ± 0.020	$0 . 896_{- 0.016}^{+ 0.015}$ $0.896^{+0.015}_{-0.016}$	$0 . 976_{- 0.021}^{+ 0.019}$ $0.976^{+0.019}_{-0.021}$
N_H, 10²² cm⁻²	0.18 (frozen)	0.18 (frozen)	0.18 (frozen)	0.18 (frozen)	0.18 (frozen)
Photon index (Γ)	−0.55 ± 0.04	$- 0 . 7_{- 0.2}^{+ 0.3}$ $-0.7^{+0.3}_{-0.2}$	$- 0 . 33_{- 0.04}^{+ 0.03}$ $-0.33_{-0.04}^{+0.03}$	−0.1 ± 0.1	−0.2 ± 0.1
E_fold, keV	8.6 ± 0.1	$8 . 3_{- 0.8}^{+ 1.6}$ $8.3^{+1.6}_{-0.8}$	$9 . 4_{- 0.1}^{+ 0.2}$ $9.4^{+0.2}_{-0.1}$	12 ± 1	10 ± 1
T_bb, keV	1.29 ± 0.03	$1 . 35_{- 0.06}^{+ 0.04}$ $1.35^{+0.04}_{-0.06}$	1.1 ± 0.4	1.29 ± 0.03	$1 . 24_{- 0.04}^{+ 0.03}$ $1.24^{+0.03}_{-0.04}$
R_bb, km	7.4 ± 0.2	$9 . 8_{- 0.3}^{+ 0.2}$ $9.8^{+0.2}_{-0.3}$	$10 . 2_{- 0.5}^{+ 0.6}$ $10.2^{+0.6}_{-0.5}$	7.6 ± 0.4	7.3 ± 0.3
T_excess, keV	0.22 ± 0.02	0.22 (frozen)	0.22 (frozen)	0.22 (frozen)	0.22 (frozen)
R_excess, km	$164_{- 30}^{+ 38}$ $164^{+38}_{-30}$	$163_{- 17}^{+ 18}$ $163^{+18}_{-17}$	167 ± 4	161 ± 4	$141_{- 5}^{+ 4}$ $141^{+4}_{-5}$
E_iron, keV	6.4 (frozen)	6.4 (frozen)	6.4 (frozen)	6.4 (frozen)	6.4 (frozen)
σ_iron, keV	0.35 ± 0.07	0.1 (frozen)	0.5 ± 0.1	0.1 (frozen)	0.1 (frozen)
EW_iron, keV	0.08 ± 0.01	0.05 ± 0.01	0.11 ± 0.01	0.01 ± 0.01	0.05 ± 0.01
Flux ^a	5.35 ± 0.02	$7 . 8_{- 0.2}^{+ 0.3}$ $7.8^{+0.3}_{-0.2}$	5.96 ± 0.03	5.7 ± 0.1	4.5 ± 0.1
Luminosity^b	2.50 ± 0.01	3.6 ± 0.1	2.78 ± 0.01	2.7 ± 0.1	2.1 ± 0.1
W-statistic/d.o.f.	3725/3654	875/819	3387/3451	1029/903	941/849

Notes.

Unabsorbed flux in the 0.1–100 keV range in units 10⁻¹⁰ erg s⁻¹ cm⁻².

Unabsorbed luminosity in the 0.1–100 keV range in units 10³⁸ erg s⁻¹.

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