2013MNRAS.436.1588S

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 ∼ 130ks XMM-Newton observation. We reveal large spectral variations, especially during the first ∼ 90ks 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^+0.2_-0.3×10^22/cm2 which gradually covers and then uncovers the X-ray emitting region with covering fraction ranging from zero to ∼ 43 percent. 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 Dc ≤ 1.5x10¹³cm, corresponding to a density of nc ≥ 1.5x10⁹/cm3 at a distance of Rc ≥ 4.3x10¹⁶cm 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 Ds ≤ 2.3x10¹³cm which, assuming the black hole mass estimated from single-epoch optical spectroscopy (1.5x10⁷M_☉), translates into Ds ≤ 10.5 gravitational radii (rg) with larger sizes (in rg) 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.