All Figures

Figure 1: XMM-Newton observation of the Ophiuchi cloud. The upper panel shows the tricolor image where EPIC MOS1, MOS2, and PN images are added together after vignetting correction. The image was smoothed with a 6 -FWHM Gaussian to increase the contrast. The red, green, and blue colors code X-ray events in the 0.5-1.0 keV, 1.0-2.4 keV, and 2.4-8.0 keV band, respectively. The lower panel shows the same area with the positions of the 87 X-ray sources detected by XMM-Newton labeled by ROXN numbers (Table 1). The dashed lines show the field of view of Chandra (Imanishi et al. 2001a, 2003). The background image is a combination between DSS2-red (black & white), ISOCAM LW2 6.7 m (blue), and LW3 14.3 m (red) filters.

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In the text

	Figure 2: A sample of X-ray background subtracted light curves of YSOs obtained with XMM-Newton showing variabilities. High background time intervals were suppressed (gaps in the light curve). We use an adaptive binning to keep a constant count number in each bin (see Table 3). X-ray light curves of the bona fide brown dwarfs GY310 and GY141 are shown in Fig. 9.
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In the text

	Figure 3: X-ray spectra of IRS44/YLW16A (Class I), EL29 (Class I), GY314 (Class II), and SR12A-B (Class III) in the quiescent state obtained with XMM-Newton. In each panel, the filled circles and open squares indicate PN and MOS1+MOS2 spectra. The solid lines show the best fit models whose spectral parameters are listed in Table 4.
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In the text

Figure 4: Comparison of source detection between XMM-Newton and Chandra (Imanishi et al. 2001a). The background image shows the XMM-Newton image in the 0.3-8 keV energy range smoothed with a 6 -FWHM Gaussian. The rectangle shows the field of view of Chandra. The triangles, circles, and crosses show the positions of the X-ray sources detected with only XMM-Newton, only Chandra, and both observatories, respectively.

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In the text

Figure 5: Comparison between XMM-Newton/EPIC and Chandra/ACIS-I count rates for X-ray sources in Chandra and XMM-Newton overlapping field-of-views. The continuous line shows the median of the count rate ratio for sources detected by both instruments. The dashed line is the median of the count rate upper limit for Chandra sources which are not detected during the 33 ks XMM-Newton observation. The dotted line shows the Chandra detection limit (6 counts) for a 33 ks observation.

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In the text

	Figure 6: Stellar luminosity vs. extinction for Class II (filled circles) and III (open circles) sources in the ISOCAM survey (Bontemps et al. 2001) and XMM-Newton overlapping area. The sources which have XMM-Newton counterparts are indicated by crosses. The new Class III candidates are indicated by asterisks and are labeled with ROXN numbers of Table 1 and 2.
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In the text

Figure 7: Color-color diagram of the XMM-Newton sources having 2MASS near-IR counterparts. The arrow shows an extinction of 10 mag (Cohen et al. 1981). The intrinsic colors of giants (dotted line) and A0-M6 dwarfs from Bessel & Brett (1988), adapted for the 2MASS photometric system using the 2MASS color transformation (Carpenter 2001; Cutri et al. 2003), are plotted for comparison. The dashed line shows the locus of the intrinsic color classical T Tauri stars (Meyer et al. 1997). Arrows indicate lower limits on J-H when J magnitude is not available.

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In the text

	Figure 8: Color-magnitude diagram of the XMM-Newton X-ray sources with 2MASS counterparts. The solid line shows the 1 Myr isochrone for solar metalicity low-mass stars from 0.02 to 1.00  (Baraffe et al. 1998), and 10 mag reddening vectors (Cohen et al. 1981). Symbols are the same as in Fig. 7. Arrows indicate lower limits on J-H and when J and H magnitudes are not available, respectively.
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In the text

	Figure 9: X-ray background subtracted light curves of the young bona fide brown dwarfs GY310 and GY141 obtained with XMM-Newton. High background time intervals were suppressed (gaps in the light curve). We use an adaptive binning to keep a constant count number in each bin (see Table 3).
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In the text

	Figure 10: X-ray spectra of the young bona fide brown dwarf GY310 during the flare state obtained with XMM-Newton. The filled circles and open squares indicate PN and MOS1+MOS2 spectra. The solid lines show the best fit models whose spectral parameters are listed in Table 4.
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In the text

Figure 11: X-ray luminosity, , vs. stellar luminosity, L*, plot for YSOs in the  Ophiuchi cloud core F. The open squares, stars, triangles, and diamonds indicate Class I, II, and III sources and brown dwarfs in the flare state, respectively, and the filled squares, stars, triangles, and circles indicate Class I, II, and III sources and new Class III candidates in the quiescent state, respectively. For Class I sources, the bolometric luminosities are plotted as the upper limits of stellar luminosities.

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In the text

	Figure 12: vs. kT plot of the X-ray sources listed in Table 4. The symbols are the same as in Fig. 11. For ROXN-27-28, ROXN-36, and ROXN-73 which need multi-temperature model for the spectral fitting, the average temperatures weighted by the emission measures are plotted. The errors show 90% confidence region.
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In the text

Figure B.1: Comparison of determinations from spectral fitting between Chandra and XMM-Newton. We plot for comparison the diagonal with a slope equal to 1. The symbols are the same as in Fig. 10. The errors show 90% confidence region. Chandra and XMM-Newton estimates of  are consistent taking account the error bars.


In the text