We present a new Suzaku observation of the obscured active galactic nucleus in NGC 1365, revealing an unexpected excess of X-rays above 20 keV of at least a factor similar to 2 with respect to the extrapolation of the best-fitting 3-10 keV model. Additional Swift-BAT and Integral-IBIS observations show that the 20-100 keV is concentrated within similar to 1.5 arcmin from the center of the galaxy, and is not significantly variable on timescales from days to years. A comparison of this component with the 3-10 keV emission, which is characterized by a rapidly variable absorption, suggests a complex structure of the circumnuclear medium, consisting of at least two distinct components with rather different physical properties, one of which covers >80% of the source with a column density N(H) similar to 3-4x10(24) cm(-2). An alternative explanation is the presence of a double active nucleus in the center of NGC 1365.
Risaliti, G., Braito, V., Laparola, V., Bianchi, S., Elvis, M., Fabbiano, G., et al. (2009). A Strong Excess in the 20-100 keV Emission of NGC 1365. THE ASTROPHYSICAL JOURNAL, 705(1), L1-L5 [10.1088/0004-637X/705/1/L1].
A Strong Excess in the 20-100 keV Emission of NGC 1365
BIANCHI, STEFANO;MATT G;
2009-01-01
Abstract
We present a new Suzaku observation of the obscured active galactic nucleus in NGC 1365, revealing an unexpected excess of X-rays above 20 keV of at least a factor similar to 2 with respect to the extrapolation of the best-fitting 3-10 keV model. Additional Swift-BAT and Integral-IBIS observations show that the 20-100 keV is concentrated within similar to 1.5 arcmin from the center of the galaxy, and is not significantly variable on timescales from days to years. A comparison of this component with the 3-10 keV emission, which is characterized by a rapidly variable absorption, suggests a complex structure of the circumnuclear medium, consisting of at least two distinct components with rather different physical properties, one of which covers >80% of the source with a column density N(H) similar to 3-4x10(24) cm(-2). An alternative explanation is the presence of a double active nucleus in the center of NGC 1365.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
