The NuSTAR view of the changing look AGN ESO 323-G77
Journal
Date Issued
2023
Author(s)
•
•
Reeves, James N.
•
•
•
•
Turner, Tracey Jane
Abstract
The presence of an obscuring torus at pc-scale distances from the central
black hole is the main ingredient for the Unified Model of Active Galactic
Nuclei (AGN), as obscured sources are thought to be seen through this
structure. However, the Unified Model fails to describe a class of sources that
undergo dramatic spectral changes, transitioning from obscured to unobscured
and vice-versa through time. The variability in such sources, so-called
Changing Look AGN (CLAGN), is thought to be produced by a clumpy medium at much
smaller distances than the conventional obscuring torus. ESO 323-G77 is a CLAGN
that was observed in various states through the years with Chandra, Suzaku,
Swift-XRT and XMM-Newton, from unobscured ($N_{\rm H}<3\times10^{22}$
cm$^{-2}$) to Compton-thin ($N_{\rm H}\sim1-6\times10^{23}$ cm$^{-2}$) and even
Compton-thick ($N_{\rm H}>1\times10^{24}$ cm$^{-2}$), with timescales as short
as one month. We present the analysis of the first NuSTAR monitoring of ESO
323-G77, consisting of 5 observations taken at different timescales (1, 2, 4
and 8 weeks from the first one) in 2016-2017, in which the AGN was caught in a
persistent Compton-thin obscured state ($N_{\rm H}\sim2-4\times10^{23}$
cm$^{-2}$). We find that a Compton-thick reflector is present ($N_{\rm
H,refl}=5\times10^{24}$ cm$^{-2}$), most likely associated with the presence of
the putative torus. Two ionized absorbers are unequivocally present, located
within maximum radii of $r_{\rm max,1}=1.5$ pc and $r_{\rm max,2}=0.01$ pc. In
one of the observations, the inner ionized absorber is blueshifted, indicating
the presence of a possible faster ($v_{\rm out}=0.2c$) ionized absorber,
marginally detected at $3\sigma$. Finally, we are able to constrain the coronal
temperature and the optical depth of ESO 323-G77, obtaining $kT_e=38$ keV or
$kT_e=36$ keV, and $\tau=1.4$ or $\tau=2.8$, depending on the coronal geometry
assumed.
Volume
672
Start page
A10
Issn Identifier
0004-6361
Rights
open.access
File(s)![Thumbnail Image]()
Loading...
Name
aa45224-22.pdf
Description
Pdf editoriale
Size
596.95 KB
Format
Adobe PDF
Checksum (MD5)
200dbaabb36a745e99d3aff0cddf4e2e