Detection of RS Oph with LST-1 and modelling of its HE/VHE gamma-ray emission

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Volume 695 (March 2025)

A&A, 695 (2025) A152

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Table 4.

Model-fit results without and with systematic uncertainties using the leptonic and hadronic modelling for observation days t − t₀ ∼ 1 d, 2 d, and 4 d.

Parameter	Best-fit value on observation day

	Day 1	Day 2	Day 4
Leptonic BPL model without systematics

Slope 1, Γ_e, 1	$0 . 0_{- 0.6}^{+ 0.8}$ $0.0^{+0.8}_{-0.6}$	$- 1 . 3_{- 0.5}^{+ 1.5}$ $-1.3^{+1.5}_{-0.5}$	$- 1 . 4_{- 0.7}^{+ 0.6}$ $-1.4^{+0.6}_{-0.7}$
Slope 2, Γ_e, 2	$- 3 . 79_{- 0.18}^{+ 0.17}$ $-3.79^{+0.17}_{-0.18}$	$- 3 . 57_{- 0.15}^{+ 0.11}$ $-3.57^{+0.11}_{-0.15}$	$- 3 . 52_{- 0.06}^{+ 0.05}$ $-3.52^{+0.05}_{-0.06}$
E_b, e [GeV]	$14_{- 3}^{+ 3}$ $14^{+3}_{-3}$	$17_{- 4}^{+ 8}$ $17^{+8}_{-4}$	$22_{- 6}^{+ 9}$ $22^{+9}_{-6}$
χ²/N_d.o.f	12.9/15	24.9/21	24.9/15
χ_red²	0.86	1.19	1.66
AIC_c	23.7	34.9	35.8

Hadronic ECPL model without systematics

Slope, Γ_p	$- 2 . 25_{- 0.13}^{+ 0.13}$ $-2.25^{+0.13}_{-0.13}$	$- 2 . 49_{- 0.07}^{+ 0.07}$ $-2.49^{+0.07}_{-0.07}$	$- 2 . 48_{- 0.08}^{+ 0.08}$ $-2.48^{+0.08}_{-0.08}$
E_c, p [TeV]	$0 . 26_{- 0.08}^{+ 0.08}$ $0.26^{+0.08}_{-0.08}$	$1 . 0_{- 0.3}^{+ 0.3}$ $1.0^{+0.3}_{-0.3}$	$1 . 6_{- 0.6}^{+ 0.6}$ $1.6^{+0.6}_{-0.6}$
χ²/N_d.o.f	21.5/16	24.9/22	26.5/16
χ_red²	1.34	1.13	1.66
AIC_c	29.1	32.0	34.1

Leptonic BPL model with systematics

Slope 1, Γ_e, 1	$0 . 4_{- 1.9}^{+ 1.9}$ $~~\,0.4^{+1.9}_{-1.9}$	$- 1 . 6_{- 0.3}^{+ 0.8}$ $-1.6^{+0.8}_{-0.3}$	$- 1 . 4_{- 0.7}^{+ 0.8}$ $-1.4^{+0.8}_{-0.7}$
Slope 2, Γ_e, 2	$- 3 . 70_{- 0.17}^{+ 0.17}$ $-3.70^{+0.17}_{-0.17}$	$- 3 . 6_{- 0.2}^{+ 0.2}$ $-3.6^{+0.2}_{-0.2}$	$- 3 . 75_{- 0.11}^{+ 0.13}$ $-3.75^{+0.13}_{-0.11}$
E_b, e [GeV]	$13_{- 3}^{+ 3}$ $13^{+3}_{-3}$	$20_{- 8}^{+ 9}$ $20^{+9}_{-8}$	$30_{- 10}^{+ 11}$ $30^{+11}_{-10}$
χ²/N_d.o.f	12.9/12	22.8/18	16.8/12
χ_red²	1.08	1.27	1.40
AIC_c	37.1	43.4	41.0

Hadronic ECPL model with systematics

Slope, Γ_p	$- 2 . 22_{- 0.10}^{+ 0.06}$ $-2.22^{+0.06}_{-0.10}$	$- 2 . 51_{- 0.05}^{+ 0.05}$ $-2.51^{+0.05}_{-0.05}$	$- 2 . 40_{- 0.15}^{+ 0.15}$ $-2.40^{+0.15}_{-0.15}$
E_c, p [TeV]	$0 . 23_{- 0.04}^{+ 0.06}$ $0.23^{+0.06}_{-0.04}$	$0 . 9_{- 0.2}^{+ 0.2}$ $0.9^{+0.2}_{-0.2}$	$1 . 0_{- 0.6}^{+ 0.6}$ $1.0^{+0.6}_{-0.6}$
χ²/N_d.o.f	21.1/13	20.4/19	19.9/13
χ_red²	1.62	1.07	1.53
AIC_c	40.1	37.1	38.9

Notes. For the leptonic modelling, Γ_e, 1 and Γ_e, 2 are the best-fit slopes below and above the best-fit energy break (E_b, e), respectively, of the electron energy distribution. For the hadronic case, Γ_p is the best-fit slope and E_c, p is the best-fit cutoff energy of the proton energy distribution. We provide the χ_red² fit statistics (χ_red² = χ²/N_d.o.f) and the daily AIC_c values (see text). The sum of the AIC_c values for all days for the leptonic model without and with systematics is 94.4 and 121.5, respectively, while for the hadronic model without and with systematics, it is 95.2 and 116.1, respectively. The error values correspond to the quadratic sum of 1σ fit and sampling errors (Appendix C). The units of E_c, p and E_b, e are in TeV and GeV, respectively.

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