We present evidence of flux variability, on bath short (hours) and long (months) time-scales, of the Seyfert 2 galaxy NGC 7172. These results are based on the ASCA observation of NGC 7172 performed in 1996 May. The source was detected at a rather low Aux level, about 3 times fainter than its usual state (including 1 yr before, when it was also observed by ASCA). The source also varied by about 30 per cent during the observation, confirming the presence of a type 1 nucleus in its centre. However, its spectrum appears to be flatter than the typical Seyfert 1 spectrum (in agreement with findings on other Seyfert 2s), posing problems for the unification model unless complex absorption is invoked.
Guainazzi, M., Matt, G., Antonelli, L.a., Fiore, F., Piro, L., Ueno, S. (1998). The X-ray spectrum and variability of the Seyfert 2 galaxy NGC 7172. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 298(3), 824-830 [10.1046/j.1365-8711.1998.01702.x].
The X-ray spectrum and variability of the Seyfert 2 galaxy NGC 7172
MATT, Giorgio;
1998-01-01
Abstract
We present evidence of flux variability, on bath short (hours) and long (months) time-scales, of the Seyfert 2 galaxy NGC 7172. These results are based on the ASCA observation of NGC 7172 performed in 1996 May. The source was detected at a rather low Aux level, about 3 times fainter than its usual state (including 1 yr before, when it was also observed by ASCA). The source also varied by about 30 per cent during the observation, confirming the presence of a type 1 nucleus in its centre. However, its spectrum appears to be flatter than the typical Seyfert 1 spectrum (in agreement with findings on other Seyfert 2s), posing problems for the unification model unless complex absorption is invoked.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
