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

We present results obtained from the time-resolved X-ray spectral analysis of the Narrow-Line-Seyfert 1 galaxy SWIFT J2127.4+5654 during a similar to 130 ks XMM-Newton observation. We reveal large spectral variations, especially during the first similar to 90 ks of the XMM-Newton exposure. The spectral variability can be attributed to a partial eclipse of the X-ray source by an intervening low-ionization/cold absorbing structure (cloud) with column density N-H = 2.0(-0.3)(+0.2) x 10(22) cm(-2) cm(-2) which gradually covers and then uncovers the X-ray emitting region with covering fraction ranging from zero to similar to 43 per cent. Our analysis enables us to constrain the size, number density and location of the absorbing cloud with good accuracy. We infer a cloud size (diameter) of D-c < 1.5 x 10(13) cm, corresponding to a density of n(c) >= 1.5 x 10(9) cm(-3) at a distance of R-c >= 4.3 x 10(16) cm from the central black hole. All of the inferred quantities concur to identify the absorbing structure with one single cloud associated with the broad line region of SWIFT J2127.4+5654. We are also able to constrain the X-ray emitting region size (diameter) to be D-s < 2.3 x 10(13) cm which, assuming the black hole mass estimated from single-epoch optical spectroscopy (1.5 x 10(7) M-circle dot), translates into D-s < 10.5 gravitational radii (r(g)) with larger sizes (in r(g)) being associated with smaller black hole masses, and vice versa. We also confirm the presence of a relativistically distorted reflection component off the inner accretion disc giving rise to a broad relativistic Fe K emission line and small soft excess (small because of the high Galactic column density), supporting the measurement of an intermediate black hole spin in SWIFT J2127.4+5654 that was obtained from a previous Suzaku observation.