X-ray Study of Low-mass Young Stellar Objects in the ρ Ophiuchi ...

92 CHAPTER 6. INDIVIDUAL SOURCESFig. 6.26.— ACIS image around A-48 in 0.5–9.0 keVsmoothed with a Gaussian of σ = 6 pixels. Large andsmall circles represent the position of A-48 and a BD cGY84, respectively.6.6.3 A-75/BF-11 – LFAM21A-75 = BF-11 has no NIR counterpart but is spatially identified with the radio-bright sourceLFAM21, a candidate of a compact extragalactic AGN (Stine et al., 1988). Both X-ray spectra ofLFAM21 seem to be non-thermal typical of AGNs and show line-like structure at ∼5 keV (Figure6.27). We hence fit them by a (power-law + gaussian) model assuming the same absorption. Thebest-fit models and parameters are shown in Figure 6.27 and Table 6.8. The best-fit photon indexof 1.2–1.4 and N H of ∼6×10 22 cm −2 are reasonable to consider that the typical AGN spectrum isabsorbed at the ρ Oph cloud (Tachihara et al., 2000). The line center energy is 4.8–5.0 keV. If thisis a redshifted neutral iron (6.4 keV) frequently seen in the AGN spectra (Awaki et al., 1991), aredshift (z) of LFAM21 is estimated to be ∼ 0.3.Fig. 6.27.— X-ray spectra of LFAM21 in obs-A (A-75, left) and obs-BF (BF-11, right). The upperpanel shows data points (crosses) and the best-fit (power-law + gaussian) model (solid and dashedlines), while the lower panel shows residuals from the best-fit model.