We present two Rossi Xray Timing Explorer ( RXTE ) PCA observations of the type 2 Seyfert galaxy NGC 4388 caught in an unusual low X-ray absorption state .
The observations were triggered by a detection in the 1.5-3 keV band of the RXTE All-Sky Monitor .
NGC 4388 was found at a somewhat high continuum level ( f ( 2-10 keV ) =8 \times 10 ^ { -11 } erg cm ^ { -2 } s ^ { -1 } ) and with a column density ( N _ { H } \sim 3 \times 10 ^ { 22 } cm ^ { -2 } ) , a factor \sim 10 lower than normal .
The second PCA observation , four hours later , gave N _ { H } < 2 \times 10 ^ { 21 } cm ^ { -2 } indicating , at the 3.1 \sigma level , variability so rapid puts the absorber on a few 100 Schwartzschild radii scale , similar to the Broad Emission Line Region , or smaller .
This small scale creates difficulties for the parsec-scale obscuring torus paradigm of Unified Schemes for type 1 and type 2 AGNs .