Uncovering the invisible: A study of Gaia18ajz, a candidate black hole revealed by microlensing

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Table 4.

Optimal parameter values for fitting Gaia18ajz using both Gaia and ground-based follow-up photometric data.

Parameter	GG0	GG+	GG−
t_0, par − 2450000 [days]	–	8231
t₀ [days]	$8262 . 0_{- 1.4}^{+ 1.4}$ $8262.0^{+1.4}_{-1.4}$	$8230 . 8_{- 1.0}^{+ 1.0}$ $8230.8^{+1.0}_{-1.0}$	$8231 . 4_{- 1.6}^{+ 1.6}$ $8231.4^{+1.6}_{-1.6}$
u₀	$0 . 2476_{- 0.0094}^{+ 0.0093}$ $0.2476^{+0.0093}_{-0.0094}$	$0 . 204_{- 0.021}^{+ 0.023}$ $0.204^{+0.023}_{-0.021}$	$- 0 . 223_{- 0.012}^{+ 0.015}$ $-0.223^{+0.015}_{-0.012}$
t_E [days]	$345_{- 12}^{+ 12}$ $345^{+12}_{-12}$	$299_{- 22}^{+ 25}$ $299^{+25}_{-22}$	$336_{- 13}^{+ 18}$ $336^{+18}_{-13}$
π_EN	–	$0 . 159_{- 0.023}^{+ 0.020}$ $0.159^{+0.020}_{-0.023}$	$- 0 . 024_{- 0.006}^{+ 0.006}$ $-0.024^{+0.006}_{-0.006}$
π_EE	–	$0 . 063_{- 0.008}^{+ 0.011}$ $0.063^{+0.011}_{-0.008}$	$0 . 0929_{- 0.0056}^{+ 0.0058}$ $0.0929^{+0.0058}_{-0.0056}$
G₀(Gaia) [mag]	$19 . 3260_{- 0.0053}^{+ 0.0053}$ $19.3260^{+0.0053}_{-0.0053}$	$19 . 2427_{- 0.0060}^{+ 0.0061}$ $19.2427^{+0.0061}_{-0.0060}$	$19 . 2447_{- 0.0050}^{+ 0.0051}$ $19.2447^{+0.0051}_{-0.0050}$
f_s, G(Gaia)	$1 . 173_{- 0.053}^{+ 0.054}$ $1.173^{+0.054}_{-0.053}$	$0 . 83_{- 0.10}^{+ 0.11}$ $0.83^{+0.11}_{-0.10}$	$0 . 99_{- 0.07}^{+ 0.06}$ $0.99^{+0.06}_{-0.07}$
I₀(GaiaSP) [mag]	$18 . 080_{- 0.019}^{+ 0.020}$ $18.080^{+0.020}_{-0.019}$	$17 . 783_{- 0.012}^{+ 0.013}$ $17.783^{+0.013}_{-0.012}$	$17 . 812_{- 0.011}^{+ 0.012}$ $17.812^{+0.012}_{-0.011}$
f_{s, I(GaiaSP)}	$1 . 528_{- 0.056}^{+ 0.056}$ $1.528^{+0.056}_{-0.056}$	$0 . 82_{- 0.09}^{+ 0.11}$ $0.82^{+0.11}_{-0.09}$	$1 . 018_{- 0.072}^{+ 0.059}$ $1.018^{+0.059}_{-0.072}$
V₀(GaiaSP) [mag]	$21 . 741_{- 0.013}^{+ 0.013}$ $21.741^{+0.013}_{-0.013}$	$21 . 7264_{- 0.0050}^{+ 0.0053}$ $21.7264^{+0.0053}_{-0.0050}$	$21 . 7359_{- 0.0046}^{+ 0.0047}$ $21.7359^{+0.0047}_{-0.0046}$
f_{s, V(GaiaSP)}	$0 . 454_{- 0.005}^{+ 0.005}$ $0.454^{+0.005}_{-0.005}$	$0 . 315_{- 0.037}^{+ 0.043}$ $0.315^{+0.043}_{-0.037}$	$0 . 382_{- 0.028}^{+ 0.023}$ $0.382^{+0.023}_{-0.028}$
r₀(ZTF) [mag]	$20 . 2112_{- 0.0036}^{+ 0.0048}$ $20.2112^{+0.0048}_{-0.0036}$	$20 . 1697_{- 0.0035}^{+ 0.0040}$ $20.1697^{+0.0040}_{-0.0035}$	$20 . 1732_{- 0.0026}^{+ 0.0029}$ $20.1732^{+0.0029}_{-0.0026}$
f_s, r(ZTF)	$0 . 875_{- 0.039}^{+ 0.039}$ $0.875^{+0.039}_{-0.039}$	$0 . 656_{- 0.078}^{+ 0.090}$ $0.656^{+0.090}_{-0.078}$	$0 . 788_{- 0.059}^{+ 0.049}$ $0.788^{+0.049}_{-0.059}$
I₀(OGLE) [mag]	$17 . 928_{- 0.012}^{+ 0.012}$ $17.928^{+0.012}_{-0.012}$	$17 . 810_{- 0.010}^{+ 0.012}$ $17.810^{+0.012}_{-0.010}$	$17 . 8185_{- 0.0078}^{+ 0.0085}$ $17.8185^{+0.0085}_{-0.0078}$
f_s, I(OGLE)	$1 . 239_{- 0.050}^{+ 0.051}$ $1.239^{+0.051}_{-0.050}$	$0 . 86_{- 0.10}^{+ 0.11}$ $0.86^{+0.11}_{-0.10}$	$1 . 042_{- 0.074}^{+ 0.061}$ $1.042^{+0.061}_{-0.074}$
χ²/d.o.f.	1.38	0.97	0.98

Notes. The model GG0 represents a point-source–point-lens configuration that does not take into account the microlensing parallax effect. On the other hand, models GG+ and GG− incorporate the microlensing parallax effect into the point-source–point-lens configuration. In the case of GG0, the model with u₀ > 0 was selected, as the posterior distribution for u₀ is symmetrical.

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