The nature of the X-ray binary transient MAXI J1834–021: Clues from its first observed outburst

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Volume 699 (July 2025)

A&A, 699 (2025) A114

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Table 1.

Best-fit values of the NICER + NuSTAR broadband spectrum.

Component	Parameter	Model 1B	Model 2	Model 3
`TBabs`	N_H (× 10²² cm⁻²)	0.84 $_{- 0.03}^{+ 0.03}$ ${}^{+0.03}_{-0.03}$	0.84 $_{- 0.02}^{+ 0.02}$ ${}^{+0.02}_{-0.02}$	0.90 $_{- 0.01}^{+ 0.04}$ ${}^{+0.04}_{-0.01}$

`gabs`	E (keV)	0.97^⋆	0.97^⋆	0.97^⋆
	σ (keV)	0.06 $_{- 0.04}^{+ 0.03}$ ${}^{+0.03}_{-0.04}$	0.05 $_{- 0.04}^{+ 0.04}$ ${}^{+0.04}_{-0.04}$	0.07 $_{- 0.04}^{+ 0.04}$ ${}^{+0.04}_{-0.04}$
	Strength (keV)	0.015 $_{- 0.007}^{+ 0.009}$ ${}^{+0.009}_{-0.007}$	0.015 $_{- 0.007}^{+ 0.008}$ ${}^{+0.008}_{-0.007}$	0.021 $_{- 0.009}^{+ 0.011}$ ${}^{+0.011}_{-0.009}$

`diskbb`	kT_disc (keV)	0.38 $_{- 0.03}^{+ 0.03}$ ${}^{+0.03}_{-0.03}$	0.37 $_{- 0.02}^{+ 0.02}$ ${}^{+0.02}_{-0.02}$	0.34 $_{- 0.04}^{+ 0.03}$ ${}^{+0.03}_{-0.04}$
`diskbb`	K_disc	163 $_{- 37}^{+ 66}$ ${}^{+66}_{-37}$	345 $_{- 80}^{+ 122}$ ${}^{+122}_{-80}$	177 $_{- 59}^{+ 226}$ ${}^{+226}_{-59}$

`nthComp`	Γ	1.79 $_{- 0.01}^{+ 0.01}$ ${}^{+0.01}_{-0.01}$	–	–

`simpl`	Scattered frac.	–	$0 . 45_{- 0.06}^{+ 0.02}$ $0.45^{+0.02}_{-0.06}$	–
`simpl`	Γ	–	1.79 $_{- 0.02}^{+ 0.01}$ ${}^{+0.01}_{-0.02}$	–

`smedge`	E_edge (keV)	7.5 $_{- 0.5}^{+ 0.5}$ ${}^{+0.5}_{-0.5}$	≲7.8	–
`smedge`	Absorption depth	0.26 $_{- 0.04}^{+ 0.04}$ ${}^{+0.04}_{-0.04}$	0.25 $_{- 0.04}^{+ 0.04}$ ${}^{+0.04}_{-0.04}$	–
	Index for photo-electric cross-section	–2.67^⋆	–2.67^⋆	–
	Smearing width (keV)	2^⋆	2^⋆	–

`relxillcp`	Γ	–	–	1.72 $_{- 0.01}^{+ 0.01}$ ${}^{+0.01}_{-0.01}$
	R_in (R_g)	–	–	<11.4
	A_Fe (A_⊙)	–	–	1^⋆
	log X_i	–	–	3.69 $_{- 0.02}^{+ 0.03}$ ${}^{+0.03}_{-0.02}$
	log (n_e/cm⁻³)	–	–	19^⋆
	Refl. frac.	–	–	>3

Observed Flux (× 10⁻¹⁰ erg cm⁻² s⁻¹)		3.29 $_{- 0.03}^{+ 0.13}$ ${}^{+0.13}_{-0.03}$	3.31 $_{- 0.34}^{+ 0.14}$ ${}^{+0.14}_{-0.34}$	3.21 $_{- 0.28}^{+ 0.05}$ ${}^{+0.05}_{-0.28}$
Unabsorbed Flux (× 10⁻¹⁰ erg cm⁻² s⁻¹)		3.78 $_{- 0.21}^{+ 0.28}$ ${}^{+0.28}_{-0.21}$	4.10 $_{- 0.11}^{+ 0.13}$ ${}^{+0.13}_{-0.11}$	4.06 $_{- 0.04}^{+ 0.05}$ ${}^{+0.05}_{-0.04}$
χ² (d.o.f.)		435.02(405)	426.71(405)	442.69(404)

Notes. Fluxes are calculated in the 0.5–60 keV energy band. Models used are: Model 1B: TBabs × gabs × smedge(nthComp + diskbb), Model 2:TBabs × gabs × smedge × simpl × diskbb, Model 3: TBabs × gabs(diskbb + relxillCp).

^⋆

Fixed parameter in the fit.

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