Line detections in photospheric radius expansion bursts from 4U 1820-303 - Confirmation of previous detections and their temporal evolution

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Volume 694 (February 2025)

A&A, 694 (2025) A266

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Table 3.

Results of the continuum modelling for all bursts with a bb+comt model in SPEX.

Fit parameter	Burst 1	Burst 2	Burst 3	Burst 4	Burst 5	Burst 6	Burst 7	Burst 8	Burst 9	Burst 10	Burst 11	Burst 12
n_H	1.63	1.63	1.63	1.63	1.63	1.63	1.63	1.63	1.63	1.63	1.63	1.63
L_X, bb	0.09 ± 0.03	0.05 ± $_{0.05}^{0.08}$ $_{0.05}^{0.08}$	0.06 ± $_{0.06}^{0.08}$ $_{0.06}^{0.08}$	0.25 ± 0.19	0.18 ± $_{0.08}^{0.28}$ $_{0.08}^{0.28}$	0.91 ± 0.06	0.76 ± 0.02	0.93 ± 0.04	0.86 ± 0.05	0.04 ± 0.11	0.68 ± 0.14	0.83 ± 0.09
L_X, comt	3.70 ± 0.17	4.05 ± 0.26	3.98 ± 0.25	3.78 ± 0.34	3.73 ± 0.22	2.63 ± 0.06	2.09 ± 0.05	1.27 ± 0.06	2.80 ± 0.06	3.78 ± 0.14	2.92 ± 0.46	3.04 ± 0.06
L_Bol, tot	3.82 ± 0.17	4.24 ± 0.26	4.16 ± 0.25	4.16 ± 0.34	4.00 ± 0.22	3.66 ± 0.06	2.97 ± 0.05	2.39 ± 0.06	3.82 ± 0.06	3.99 ± 0.14	3.72 ± 0.46	3.99 ± 0.06
kT_bb	0.13 ± 0.01	0.16 ± 0.01	0.13 ± 0.01	0.15 ± 0.02	0.13 ± 0.01	0.182 ± 0.004	0.175 ± 0.003	0.161 ± 0.004	0.161 ± 0.001	0.10 ± 0.01	0.16 ± 0.02	0.177 ± 0.002
kT_seed (coupled)	0.13	0.16	0.13	0.15	0.13	0.182	0.175	0.161	0.161	0.10	0.16	0.177
kT_e	0.88 ± 0.03	1.27 ± 0.08	0.83 ± 0.02	0.91 ± 0.05	0.97 ± 0.04	0.562 ± 0.005	0.505 ± 0.006	0.377 ± 0.004	0.480 ± 0.003	0.73 ± 0.02	0.64 ± 0.03	0.58 ± 0.01
τ	16.4 ± 0.07	13.33 ± 0.76	16.54 ± 0.74	16.5 ± 1.5	15.09 ± 0.07	100 ± $_{48.6}^{0}$ $_{48.6}^{0}$	100 ± $_{51.35}^{0}$ $_{51.35}^{0}$	100 ± $_{55.11}^{0}$ $_{55.11}^{0}$	100 ± $_{30.69}^{0}$ $_{30.69}^{0}$	18.15 ± 0.06	23.56 ± $_{3.52}^{7.80}$ $_{3.52}^{7.80}$	100 ± $_{55}^{0}$ $_{55}^{0}$
C_stat/d.o.f.	133/64	64/65	125/65	170/66	104/65	148/64	140/63	159/57	155/63	146/65	122/64	164/65

Notes. The column density of the cold interstellar gas, n_H, is fixed at 1.63 × 10²¹ cm⁻² for all bursts (Costantini et al. 2012). The luminosities L_X and L_Bol are calculated in the 0.3–10 keV and 0.1–20 keV band, respectively, and expressed in 10³⁸ erg s⁻¹ units. The temperatures kT are expressed in keV unit. τ is the optical depth of the Comptonisation component. For more information, see the SPEX manual.

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