BeppoSAX observed the Seyfert 1.9 galaxy NGC4258 on December 1998 , when its 2-10 keV luminosity was about 10 ^ { 41 } erg s ^ { -1 } .
Large amplitude ( 100 \% ) variability is observed in the 3-10 keV band on timescales of a few tens of thousands seconds while variability of \sim 20 \% is observed on timescales as short as one hour .
The nuclear component is visible above 2 keV only , being obscured by a column density of ( 9.5 \pm 1.2 ) \times 10 ^ { 22 } cm ^ { -2 } ; this component is detected up to 70 keV with a signal to noise { { } _ { > } \atop { } ^ { \sim } } 3 , and with the steep power law energy spectral index of \alpha _ { E } = 1.11 \pm 0.14 .
Bremsstrahlung emission for the 2-70 keV X-ray luminosity , as expected in Advection Dominated Accretion Flow ( ADAF ) models with strong winds , is ruled out by the data .
The ratio between the nuclear radio ( 22 GHz ) luminosity and the X-ray ( 5 keV ) luminosity is { { } _ { < } \atop { } ^ { \sim } } 10 ^ { -5 } , similar to that of radio-quiet quasars and Seyfert galaxies .
X-ray variability and spectral shape , radio-to-X-ray and near infrared-to-X-ray luminosity ratios suggest that the nucleus of NGC4258 could be a scaled-down version of a Seyfert nucleus , and that the X-ray nuclear luminosity can be explained in terms of Comptonization in a hot corona .

The soft ( E { { } _ { < } \atop { } ^ { \sim } } 2 keV ) X-ray emission is complex .
There are at least two thermal-like components with temperatures of 0.6 \pm 0.1 keV and { { } _ { > } \atop { } ^ { \sim } } 1.3 keV .
The cooler ( L _ { 0.1 - 2.4 keV } \sim 10 ^ { 40 } erg s ^ { -1 } ) component is probably associated with the jet , resolved in X-rays by the ROSAT HRI ( Cecil et al .
1994 ) .
The luminosity of the second component , which can be modeled equally well by an unobscured power law model with \alpha _ { E } = 0.2 ^ { +0.8 } _ { -0.2 } , is L _ { 0.1 - 2.4 keV } \sim 7 \times 10 ^ { 39 } erg s ^ { -1 } , consistent with that expected from discrete X-ray sources ( binaries and SN remnants ) in the host galaxy .

Observations of NGC4258 and other maser AGNs show strong nuclear X-ray absorption .
We propose that this large column of gas might be responsible for shielding the regions of water maser emission from X-ray illumination .
So a large column density absorbing gas may be a necessary property of masing AGNs .