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 1.

Results of the best-fit continuum modelling of the persistent emission with the TBabs*(diskbb+powerlaw) model in XSPEC.

ObsID	Date	Rate	Nh	kT_in	Norm	Γ	Norm	L_X	C-STAT (dev)
1050300108	2017-08-29	1799.4	$0 . 22_{- 0.01}^{+ 0.01}$ $0.22^{+0.01}_{-0.01}$	$0 . 91_{- 0.04}^{+ 0.04}$ $0.91^{+0.04}_{-0.04}$	$0 . 11_{- 0.02}^{+ 0.02}$ $0.11^{+0.02}_{-0.02}$	$1 . 46_{- 0.05}^{+ 0.05}$ $1.46^{+0.05}_{-0.05}$	$0 . 59_{- 0.05}^{+ 0.05}$ $0.59^{+0.05}_{-0.05}$	7.32 ± 0.08	393.5 (2.7)
1050300108	2017-08-29	1780.5	$0 . 22_{- 0.01}^{+ 0.01}$ $0.22^{+0.01}_{-0.01}$	$0 . 86_{- 0.03}^{+ 0.03}$ $0.86^{+0.03}_{-0.03}$	$0 . 13_{- 0.02}^{+ 0.02}$ $0.13^{+0.02}_{-0.02}$	$1 . 48_{- 0.04}^{+ 0.04}$ $1.48^{+0.04}_{-0.04}$	$0 . 60_{- 0.04}^{+ 0.04}$ $0.60^{+0.04}_{-0.04}$	7.24 ± 0.06	408.7 (3.3)
1050300109	2017-08-30	1459.7	$0 . 21_{- 0.01}^{+ 0.01}$ $0.21^{+0.01}_{-0.01}$	$0 . 63_{- 0.01}^{+ 0.01}$ $0.63^{+0.01}_{-0.01}$	$0 . 40_{- 0.04}^{+ 0.04}$ $0.40^{+0.04}_{-0.04}$	$1 . 45_{- 0.05}^{+ 0.05}$ $1.45^{+0.05}_{-0.05}$	$0 . 44_{- 0.04}^{+ 0.04}$ $0.44^{+0.04}_{-0.04}$	5.64 ± 0.04	342.4 (0.7)
1050300109	2017-08-30	1577.5	$0 . 21_{- 0.01}^{+ 0.01}$ $0.21^{+0.01}_{-0.01}$	$0 . 69_{- 0.02}^{+ 0.02}$ $0.69^{+0.02}_{-0.02}$	$0 . 29_{- 0.03}^{+ 0.03}$ $0.29^{+0.03}_{-0.03}$	$1 . 44_{- 0.05}^{+ 0.05}$ $1.44^{+0.05}_{-0.05}$	$0 . 48_{- 0.04}^{+ 0.04}$ $0.48^{+0.04}_{-0.04}$	6.25 ± 0.05	364.4 (1.6)
1050300109	2017-08-30	1682.4	$0 . 22_{- 0.01}^{+ 0.01}$ $0.22^{+0.01}_{-0.01}$	$0 . 74_{- 0.02}^{+ 0.02}$ $0.74^{+0.02}_{-0.02}$	$0 . 22_{- 0.03}^{+ 0.03}$ $0.22^{+0.03}_{-0.03}$	$1 . 44_{- 0.05}^{+ 0.04}$ $1.44^{+0.04}_{-0.05}$	$0 . 53_{- 0.04}^{+ 0.04}$ $0.53^{+0.04}_{-0.04}$	6.84 ± 0.05	395.6 (2.8)
2050300104	2019-06-07	999.2	$0 . 21_{- 0.01}^{+ 0.01}$ $0.21^{+0.01}_{-0.01}$	$0 . 44_{- 0.02}^{+ 0.02}$ $0.44^{+0.02}_{-0.02}$	$0 . 92_{- 0.10}^{+ 0.11}$ $0.92^{+0.11}_{-0.10}$	$1 . 50_{- 0.05}^{+ 0.05}$ $1.50^{+0.05}_{-0.05}$	$0 . 34_{- 0.02}^{+ 0.03}$ $0.34^{+0.03}_{-0.02}$	3.86 ± 0.04	303.5 (-0.9)
2050300108	2019-06-12	607.7	$0 . 22_{- 0.01}^{+ 0.01}$ $0.22^{+0.01}_{-0.01}$	$0 . 22_{- 0.02}^{+ 0.02}$ $0.22^{+0.02}_{-0.02}$	$7 . 5_{- 2.3}^{+ 3.5}$ $7.5^{+3.5}_{-2.3}$	$1 . 54_{- 0.03}^{+ 0.03}$ $1.54^{+0.03}_{-0.03}$	$0 . 26_{- 0.01}^{+ 0.01}$ $0.26^{+0.01}_{-0.01}$	2.67 ± 0.03	325.9 (-0.1)
2050300110	2019-06-14	643.0	$0 . 20_{- 0.01}^{+ 0.01}$ $0.20^{+0.01}_{-0.01}$	$0 . 28_{- 0.02}^{+ 0.02}$ $0.28^{+0.02}_{-0.02}$	$2 . 8_{- 0.7}^{+ 1.0}$ $2.8^{+1.0}_{-0.7}$	$1 . 50_{- 0.03}^{+ 0.03}$ $1.50^{+0.03}_{-0.03}$	$0 . 26_{- 0.01}^{+ 0.01}$ $0.26^{+0.01}_{-0.01}$	2.76 ± 0.02	376.5 (1.9)
2050300119	2019-06-26	968.1	$0 . 20_{- 0.01}^{+ 0.01}$ $0.20^{+0.01}_{-0.01}$	$0 . 43_{- 0.02}^{+ 0.01}$ $0.43^{+0.01}_{-0.02}$	$0 . 99_{- 0.10}^{+ 0.12}$ $0.99^{+0.12}_{-0.10}$	$1 . 44_{- 0.05}^{+ 0.05}$ $1.44^{+0.05}_{-0.05}$	$0 . 31_{- 0.02}^{+ 0.02}$ $0.31^{+0.02}_{-0.02}$	3.85 ± 0.04	392.4 (2.6)
2050300119	2019-06-26	1175.4	$0 . 21_{- 0.01}^{+ 0.01}$ $0.21^{+0.01}_{-0.01}$	$0 . 53_{- 0.01}^{+ 0.01}$ $0.53^{+0.01}_{-0.01}$	$0 . 60_{- 0.05}^{+ 0.06}$ $0.60^{+0.06}_{-0.05}$	$1 . 45_{- 0.05}^{+ 0.05}$ $1.45^{+0.05}_{-0.05}$	$0 . 35_{- 0.03}^{+ 0.03}$ $0.35^{+0.03}_{-0.03}$	4.52 ± 0.04	334.1 (0.3)
2050300124	2019-07-01	1095.7	$0 . 19_{- 0.01}^{+ 0.01}$ $0.19^{+0.01}_{-0.01}$	$0 . 51_{- 0.02}^{+ 0.02}$ $0.51^{+0.02}_{-0.02}$	$0 . 83_{- 0.07}^{+ 0.08}$ $0.83^{+0.08}_{-0.07}$	$1 . 21_{- 0.07}^{+ 0.07}$ $1.21^{+0.07}_{-0.07}$	$0 . 24_{- 0.03}^{+ 0.03}$ $0.24^{+0.03}_{-0.03}$	4.72 ± 0.08	341.7 (0.6)
4680010101	2021-05-02	971.2	$0 . 20_{- 0.01}^{+ 0.01}$ $0.20^{+0.01}_{-0.01}$	$0 . 41_{- 0.02}^{+ 0.02}$ $0.41^{+0.02}_{-0.02}$	$1 . 13_{- 0.13}^{+ 0.16}$ $1.13^{+0.16}_{-0.13}$	$1 . 49_{- 0.04}^{+ 0.04}$ $1.49^{+0.04}_{-0.04}$	$0 . 34_{- 0.02}^{+ 0.02}$ $0.34^{+0.02}_{-0.02}$	3.86 ± 0.03	319.0 (-0.3)

Notes. The best-fit spectral parameters of the persistent emission as recorded prior to the burst. The fit was performed between 0.3 and 10 keV. The integration time of the spectrum was 200 seconds, with the exception of observations 2 and 11, for which only ∼120 seconds were available prior to the burst. The spectra were grouped by three consecutive channels. For the C-STAT, the deviation of the best fit compared to the expected value expressed in σ and the number of degrees of freedom are given within the parentheses. The bolometric luminosity was computed to be between 0.2 and 20 keV, assuming a distance of 8 kpc (Baumgardt & Vasiliev 2021), and it is expressed in units of 10³⁷ erg s⁻¹. The normalisation parameter of the diskbb component is expressed in 10³ unit. The errors on the best-fit parameters are given at the 90% confidence levels. The error on the luminosity was derived from the standard deviation of fluxes computed from the multi-variate Gaussian distribution of the best-fit parameters, from which 40 parameter values were randomly drawn (using simpar command in XSPEC).

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