Table 2: Characteristics of some telescope plus instrument combinations, and the resulting expected total number of pixel lensing events $\int N_{\rm det} {\rm d}\Omega$ over the full field of view with a total signal-to-noise ratio $Q\geq 5$ and the fraction $p(\delta w/w \leq 0.5)$ of these events with timescales measurable at a precision better than $50\%$ , when observing the central region of Maffei 1 in a 10 h program and assuming pre-existing reference images at the same noise level as the event images. More precisely, $p(\delta w/w\!\leq\!\varepsilon)\equiv \int \Delta N_{\rm det}(\delta w/w\!\leq\!\varepsilon){\rm d}\Omega/ \int N_{\rm det}{\rm d}\Omega$ . AO stands for instruments in adaptive optic mode. Z is the telescope zeropoint magnitude yielding 1 e $^-\!$ /s, and $S_{\!\rm sky}$ the background comprising the sky and any instrumental background not related to the observed galaxy. The adopted values refer to data found on the instrument web pages (except for Keck and WHT I-band backgrounds). The seeing $\theta _{\rm see}$ represents the full width at half maximum of the point spread function. For the HST, the value is taken from Buta & McCall 2003. With AO, the diffraction limit $\theta _{\rm see}\approx 1.22 \lambda /D$ , where D is the telescope diameter, is adopted, and otherwise the median site seeing $\theta_{\rm see}\approx 0.7''(\lambda /[0.5~\mu{\rm m}])^{-1/5}$ , valid for Mauna Kea and La Palma, is assumed.
Telescope/instrument Filter Z $S_{\!\rm sky}$ $\theta _{\rm see}$ Field of view $\int N_{\rm det} {\rm d}\Omega$ $p(\delta w/w \leq 0.5)$

(mag for 1 e $^-\!$ /s) [mag/arcsec²] [arcsec] [arcsec²] [%]

HST/ACS I 25.5 21.43 0.076 $202\times 202$ 5.11 3.9

Keck/LRIS I 28.0 19.5 0.63 $360\times 468$ 1.92 2.5

WHT/PFIP I 25.6 19.5 0.64 $972\times 972$ 0.46 0

Gemini/NIRI(AO) K 26.1 13.75 0.070 $51\times 51$ 6.32 8.7

Subaru/CISCO K 26.1 12.7 0.52 $108\times 108$ 1.54 6.1

CFHT/KIR(AO) K 24.0 11.6 0.154 $36\times 36$ 0.53 5.6

WHT/INGRID K 24.5 12.0 0.52 $244\times 244$ 0.76 3.9

**Table 2:** Characteristics of some telescope plus instrument combinations, and the resulting expected total number of pixel lensing events $\int N_{\rm det} {\rm d}\Omega$ over the full field of view with a total signal-to-noise ratio $Q\geq 5$ and the fraction $p(\delta w/w \leq 0.5)$ of these events with timescales measurable at a precision better than $50\%$ , when observing the central region of Maffei 1 in a 10 h program and assuming pre-existing reference images at the same noise level as the event images. More precisely, $p(\delta w/w\!\leq\!\varepsilon)\equiv \int \Delta N_{\rm det}(\delta w/w\!\leq\!\varepsilon){\rm d}\Omega/ \int N_{\rm det}{\rm d}\Omega$ . AO stands for instruments in adaptive optic mode. Z is the telescope zeropoint magnitude yielding 1 e $^-\!$ /s, and $S_{\!\rm sky}$ the background comprising the sky and any instrumental background not related to the observed galaxy. The adopted values refer to data found on the instrument web pages (except for Keck and WHT I-band backgrounds). The seeing $\theta _{\rm see}$ represents the full width at half maximum of the point spread function. For the HST, the value is taken from Buta & McCall 2003. With AO, the diffraction limit $\theta _{\rm see}\approx 1.22 \lambda /D$ , where D is the telescope diameter, is adopted, and otherwise the median site seeing $\theta_{\rm see}\approx 0.7''(\lambda /[0.5~\mu{\rm m}])^{-1/5}$ , valid for Mauna Kea and La Palma, is assumed.
Telescope/instrument	Filter	Z	$S_{\!\rm sky}$	$\theta _{\rm see}$	Field of view	$\int N_{\rm det} {\rm d}\Omega$	$p(\delta w/w \leq 0.5)$
		(mag for 1 e $^-\!$ /s)	[mag/arcsec²]	[arcsec]	[arcsec²]		[%]
HST/ACS	I	25.5	21.43	0.076	$202\times 202$	5.11	3.9
Keck/LRIS	I	28.0	19.5	0.63	$360\times 468$	1.92	2.5
WHT/PFIP	I	25.6	19.5	0.64	$972\times 972$	0.46	0
Gemini/NIRI(AO)	K	26.1	13.75	0.070	$51\times 51$	6.32	8.7
Subaru/CISCO	K	26.1	12.7	0.52	$108\times 108$	1.54	6.1
CFHT/KIR(AO)	K	24.0	11.6	0.154	$36\times 36$	0.53	5.6
WHT/INGRID	K	24.5	12.0	0.52	$244\times 244$	0.76	3.9

Source LaTeX | All tables | In the text

	1 Introduction
	2 The Maffei 1 galaxy
	3 Basic microlensing properties
	4 Luminosity function and fluctuation magnitude
	5 Detection rates
	6 Constraints from microlensing experiments
	7 Conclusion
	References