Table 9: Intrinsic X-ray fluxes and luminosity in the 0.35-7.5 keV band ( $f_{\rm X}$ and $L_{\rm X}$ ) as derived from the EPIC pn spectral fits for the X-ray-bright PMS detected in L1551. Also given is the probability of constancy from the Kolmogorov-Smirnov (K-S) test for the XMM-Newton EPIC-pn light curves (shown in Fig. 3). The average flux level of the sources during the XMM-Newton, ROSAT and ASCA observations (when available) in the same bands as used by Carkner et al. (1996) is also reported. Carkner et al. provide ROSAT and ASCA fluxes over different energy ranges for each source; we report these energy ranges in the columns " $\Delta E_{\rm ROSAT}$ '' and " $\Delta E_{\rm ASCA}$ '' and provide the source flux over the same ranges derived from the fits to XMM-Newton spectral data. Energy ranges are in keV, flux units are 10^-13 erg cm^-2 s^-1 and X-ray luminosity is in units of 10²⁸ erg s^-1.
Source Name $f_{\rm X}$ $L_{\rm X}$ K-S $\Delta E_{\rm ROSAT}$ $F_{\rm X}$ XMM F_xROSAT $\Delta E_{\rm ASCA}$ $F_{\rm X}$ XMM $F_{\rm X}$ ASCA

S2 MHO 5 0.66 15.6 0.79 0.2-2.0 0.34 $\la$ 0.4 0.5-3.0 0.33 -

S3 V826 Tau 23.0 534 $0.13\times10^{-4}$ 0.2-2.0 12.9 15.0 0.5-3.0 13.4 15.8^a

S6 V827 Tau 4.0 93.8 $0.37\times10^{-1}$ 0.2-2.0 1.9 13.0 0.8-3.5 1.5 4.5

S7 V1075 Tau 8.5 199 $0.2\times10^{-25}$ 0.1-2.0 4.1 5.3 0.5-2.5 4.1 4.9

S14 V710 Tau 5.5 131 0.35 0.2-2.0 2.2 6.9^c 0.5-3.0 2.5 -

S18 XZ Tau 55.3 1300 <10^-38 0.5-2.0 2.9 $\sim$ 1.0 0.5-2.0 2.9 15.0

S19 HL Tau 10.0 235 $0.74\times10^{-1}$ 1.0-2.0^f 0.4 ^d 1.0-3.0 1.4 ^d

S23 MHO 4 0.31 7.34 0.54 0.2-2.0 0.2 0.4^c 0.5-3.0 0.2 -

S25 MHO 9 0.24 5.55 0.59 0.2-2.0 0.2 $\la$ 0.4^e 0.5-3.0 0.2 -

^a Average flux, the source underwent a large flare during ASCA observations.
^c Computed using the approximate relation of Carkner et al. (1996) 1 cts ${\rm (ks)^{-1}} \simeq 3 \times 10^{28}~{\rm ergs~s^{-1}}$ .
^d Unresolved from XZ Tau.
^e As minimum flux level detectable by ROSAT we took the flux level of the weakest source detected by Carkner et al. (1996), MHO 4.
^f In our data HL Tau was clearly visible in the image only for energies $\Delta E > 1.0$ keV (see text).

**Table 9:** Intrinsic X-ray fluxes and luminosity in the 0.35-7.5 keV band ( $f_{\rm X}$ and $L_{\rm X}$ ) as derived from the EPIC pn spectral fits for the X-ray-bright PMS detected in L1551. Also given is the probability of constancy from the Kolmogorov-Smirnov (K-S) test for the XMM-*Newton* EPIC-pn light curves (shown in Fig. 3). The average flux level of the sources during the XMM-*Newton*, ROSAT and ASCA observations (when available) in the same bands as used by Carkner et al. (1996) is also reported. Carkner et al. provide ROSAT and ASCA fluxes over different energy ranges for each source; we report these energy ranges in the columns " $\Delta E_{\rm ROSAT}$ '' and " $\Delta E_{\rm ASCA}$ '' and provide the source flux over the same ranges derived from the fits to XMM-*Newton* spectral data. Energy ranges are in keV, flux units are 10^-13 erg cm^-2 s^-1 and X-ray luminosity is in units of 10²⁸ erg s^-1.
Source	Name	$f_{\rm X}$	$L_{\rm X}$	K-S	$\Delta E_{\rm ROSAT}$	$F_{\rm X}$ XMM	F_xROSAT	$\Delta E_{\rm ASCA}$	$F_{\rm X}$ XMM	$F_{\rm X}$ ASCA
S2	MHO 5	0.66	15.6	0.79	0.2-2.0	0.34	$\la$ 0.4	0.5-3.0	0.33	-
S3	V826 Tau	23.0	534	$0.13\times10^{-4}$	0.2-2.0	12.9	15.0	0.5-3.0	13.4	15.8^a
S6	V827 Tau	4.0	93.8	$0.37\times10^{-1}$	0.2-2.0	1.9	13.0	0.8-3.5	1.5	4.5
S7	V1075 Tau	8.5	199	$0.2\times10^{-25}$	0.1-2.0	4.1	5.3	0.5-2.5	4.1	4.9
S14	V710 Tau	5.5	131	0.35	0.2-2.0	2.2	6.9^c	0.5-3.0	2.5	-
S18	XZ Tau	55.3	1300	<10^-38	0.5-2.0	2.9	$\sim$ 1.0	0.5-2.0	2.9	15.0
S19	HL Tau	10.0	235	$0.74\times10^{-1}$	1.0-2.0^f	0.4	^d	1.0-3.0	1.4	^d
S23	MHO 4	0.31	7.34	0.54	0.2-2.0	0.2	0.4^c	0.5-3.0	0.2	-
S25	MHO 9	0.24	5.55	0.59	0.2-2.0	0.2	$\la$ 0.4^e	0.5-3.0	0.2	-

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