We report on our analysis of XMM-Newton observations of the Seyfert 2 galaxy ESO 138-G1(z = 0.0091). These data reveal a complex spectrum in both its soft and hard portions. The 0.5-2 keV band is characterized by a strong "soft-excess" component with several emission lines, as commonly observed in other narrow-line AGN. Above 3 keV, a power-law fit yields a very flat slope (Gamma similar to 0.35), along with the presence of a prominent line-like emission feature around similar to 6.4 keV. This indicates heavy obscuration along the line of sight to the nucleus. We find an excellent fit to the 3-10 keV continuum with a pure reflection model, which provides strong evidence of a Compton-thick screen, preventing direct detection of the intrinsic nuclear X-ray emission. Although a model consisting of a power law transmitted through an absorber with N(H) similar to 2.5 x 10(23) cm(-2) also provides a reasonable fit to the hard X-ray data, the equivalent width (EW) value of similar to 800 eV measured for the FeK alpha emission line is inconsistent with a primary continuum obscured by a Compton-thin column density. Furthermore, the ratio of 2-10 keV to de-reddened [OIII] fluxes for ESO 138-G1 agrees with the typical values reported for well-studied Compton-thick Seyfert galaxies. Finally, we also note that the upper limits to the 15-150 keV flux provided by Swift/BAT and INTEGRAL/IBIS seem to rule out the presence of a transmitted component of the nuclear continuum even in this very hard X-ray band, hence imply that the column density of the absorber could be as high as 10(25) cm(-2). This makes ESO 138-G1 a very interesting, heavy Compton-thick AGN candidate for the next X-ray missions with spectroscopic and imaging capabilities above 10 keV.
Piconcelli, E., Bianchi, S., Vignali, C., Jimenez Bailon, E., Fiore, F. (2011). X-ray spectroscopy of the Compton-thick Seyfert 2 ESO 138-G1 RID B-4804-2010. ASTRONOMY & ASTROPHYSICS, 534 [10.1051/0004-6361/201117462].
X-ray spectroscopy of the Compton-thick Seyfert 2 ESO 138-G1 RID B-4804-2010
BIANCHI, STEFANO;
2011-01-01
Abstract
We report on our analysis of XMM-Newton observations of the Seyfert 2 galaxy ESO 138-G1(z = 0.0091). These data reveal a complex spectrum in both its soft and hard portions. The 0.5-2 keV band is characterized by a strong "soft-excess" component with several emission lines, as commonly observed in other narrow-line AGN. Above 3 keV, a power-law fit yields a very flat slope (Gamma similar to 0.35), along with the presence of a prominent line-like emission feature around similar to 6.4 keV. This indicates heavy obscuration along the line of sight to the nucleus. We find an excellent fit to the 3-10 keV continuum with a pure reflection model, which provides strong evidence of a Compton-thick screen, preventing direct detection of the intrinsic nuclear X-ray emission. Although a model consisting of a power law transmitted through an absorber with N(H) similar to 2.5 x 10(23) cm(-2) also provides a reasonable fit to the hard X-ray data, the equivalent width (EW) value of similar to 800 eV measured for the FeK alpha emission line is inconsistent with a primary continuum obscured by a Compton-thin column density. Furthermore, the ratio of 2-10 keV to de-reddened [OIII] fluxes for ESO 138-G1 agrees with the typical values reported for well-studied Compton-thick Seyfert galaxies. Finally, we also note that the upper limits to the 15-150 keV flux provided by Swift/BAT and INTEGRAL/IBIS seem to rule out the presence of a transmitted component of the nuclear continuum even in this very hard X-ray band, hence imply that the column density of the absorber could be as high as 10(25) cm(-2). This makes ESO 138-G1 a very interesting, heavy Compton-thick AGN candidate for the next X-ray missions with spectroscopic and imaging capabilities above 10 keV.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
