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We present results obtained from the time-resolved X-ray spectral analysis ofthe Narrow-Line-Seyfert 1 galaxy SWIFT J2127.4+5654 during a ~130 ks XMM-Newtonobservation. We reveal large spectral variations, especially during the first~90 ks of the XMM-Newton exposure. The spectral variability can be attributedto a partial eclipse of the X-ray source by an intervening low-ionization/coldabsorbing structure (cloud) with column density N_H = 2.0^{+0.2}_{-0.3}e22cm^-2 which gradually covers and then uncovers the X-ray emitting region withcovering fraction ranging from zero to ~43 per cent. Our analysis enables us toconstrain the size, number density, and location of the absorbing cloud withgood accuracy. We infer a cloud size (diameter) of $D_c < 1.5e13 cm,corresponding to a density of n_c > 1.5e9 cm^-3 at a distance of R_c > 4.3e16cm from the central black hole. All of the inferred quantities concur toidentify the absorbing structure with one single cloud associated with thebroad line region of SWIFT J2127.4+5654. We are also able to constrain theX-ray emitting region size (diameter) to be D_s < 2.3e13 cm which, assuming theblack hole mass estimated from single-epoch optical spectroscopy (1.5e7 M_sun),translates into D_s < 10.5 gravitational radii (r_g) with larger sizes (in r_g)being associated with smaller black hole masses, and viceversa. We also confirmthe presence of a relativistically distorted reflection component off the inneraccretion disc giving rise to a broad relativistic Fe K emission line and smallsoft excess (small because of the high Galactic column density), supporting themeasurement of an intermediate black hole spin in SWIFT J2127.4+5654 that wasobtained from a previous Suzaku observation.

The size of the X-ray emitting region in SWIFT J2127.4+5654 via a broad line region cloud X-ray eclipse