aa r X i v : . [ a s t r o - ph ] J a n Mem. S.A.It. Vol. 0, 0 c (cid:13) SAIt 2004
Memorie della
The Seyfert galaxies in the lo al Universe: from
Be p poS AX to S imbol - X Mauro Dadina , INAF / IASF-Bo, via Gobetti 101, 40129 Bologna, Italy Dipartimento di Astronomia dell’Universit`a degli Studi di Bologna, via Ranzani 1, 40127Bologna, ItalyReceived date / Accepted date
Abstract.
The operational conditions found by
BeppoS AX in observing nearby (z ≤ S imbol - X in order to simulate a realistic final database of themission. The results indicate that, even in the worst conditions, the S imbol - X archive ofpointings will allow to fully characterize the high-energy spectrum of nearby Seyferts and,most importantly, to obtain solid results on R and Ec (fundamental to model the cosmic X-Ray background, CXB). The measurement of the inclination angle of the accretion disk willbe possible for ∼
15 objects allowing to directly test the unified models for AGN. Finally,the time-dependent characteristics of the reflected component will be studied in at least ∼ Key words.
X-rays: galaxies – galaxies: Seyfert: – galaxies: active
1. Introduction
In X-ray astronomy each mission has been animportant step forward in the comprehensionof the physics of known sources and in theopening of new interesting fields of research.This is expected to happen also for
S imbol - X (see, for instance the presentations by Fiore inthese proceedings) thanks to its unprecedentedsensitivity above 10 keV ( ∼ S imbol - X will also work as an ob-servatory that will leave a rich but, as usual, in-homogeneous archive of data. As such,tryingto estimate on how many objects deep spec-tral or timing studies will be performed, so asto fully exploit the astrophysical potentials ofthe new instruments, is not trivial. To make anattempt of tackling this issue for S imbol - X , it has been chosen to test the new mission re-producing the observational conditions (essen-tially the flux of the sources and the used ex-posure) really found by the only past missioncomparable with S imbol - X : BeppoS AX . Theastrophysical field inspected here is the oneconcerning the nearby (z ≤ BeppoS AX obtained importantresults on the X-rays emission mechanism, onthe geometry of the reflector and on the geom-etry of the cold absorber (Perola et al. 2002,Risaliti et al. 1999). These results were ob-tained investigating the properties of the high-energy cut-o ff (Ec), and of the reflection com-ponent (R) which study is possible only us-ing broad-band observatories. These quantitiesare hardly measurable and they are known onlyfor few bright objects. They were mainly mea- auro Dadina: The nearby Seyfert: from BeppoS AX to S imbol - X Table 1.
Grid of possible values for the inter-esting parameters of the simulated
S imbol - X spectra. N aH Γ R Ec b F c − keV Exp. d f a in units of 10 cm − ; b in units of keV; c in unitsof 10 − erg s − cm − ; d in units of ks; f fixed sured from BeppoS AX which operated above10 keV with a smaller ( ∼ S imbol - X butwith a broader band ( ∼ ∼ S imbol - X will observe in this detail.
2. Methods
The observational conditions (exposure timeend fluxes of the sources) found by
BeppoS AX were grossly reproduced in order to simulatethe results that would have been obtained if thenearby Seyferts were observed with
S imbol - X instead of BeppoS AX . To do that, the parame-ter F defined as follows, has been used:F = (F − keV × p T exp ) (1)where F − keV is the 2-10 keV flux in unitsof 10 − erg s − cm − and T exp is the expo-sure time in units of ks. Thus, the F param-eter define how “deep” an observation waswith BeppoS AX and may be used to quantifythe expected improvements achievable with thenew instruments. The distribution of F ob-tained for
BeppoS AX is presented in figure 1(note that Log(F) = Fig. 1.
Histogram of the real distributions ofthe F parameters (see text for details) obtainedfor the
BeppoS AX list of observations of thenearby Seyferts. The vertical line at F ∼ BeppoS AX in inspecting Rand Ec, while the one at F ∼ S imbol - X .tions of sources having F − keV = − erg s − cm − ). The BeppoS AX catalog used here is theone presented in Dadina (2007), which con-tains 163 observations of 105 objects (of which43 are type I and 62 are type II Seyferts).To produce the
S imbol - X fake spectra itwas assumed that the X-ray emission of thesources is described by an absorbed (by coldmatter) power-law with an Ec, plus a cold re-flection component and a narrow emission line.Each combination of the values presented inTable 1 has been used to simulate the fake S imbol - X spectra. When R and Ec were avail-able from BeppoS AX , the closest value be-tween the 3 reported in table 1 were usedfor fake data, otherwise it was set R = =
200 keV. The resulting grid of spectra havebeen fit with what presented in Dadina (2007)in order to reproduce for
S imbol - X the distri-bution of F presented in figure 1. Finally 90%cofidence levels have been obtained for eachinteresting parameters in the simulated spectra.The configuration assumed for S imbol - X ischaracterized by the following specifications: – Internal particle background for the low en-ergy detector MPD = × − cts / s / keV – Internal particle background for the highenergy detector CZT = × − cts / s / keV – MPD dead-time = S imbol - X simulations (Sauvageot, 2007). S imbol - X vs. BeppoS AX
The first remarkable results obtainable with
S imbol - X is that all the pointed nearby Seyfert Mauro Dadina: The nearby Seyfert: from
BeppoS AX to S imbol - X
10 10020 50 200 . . . k e V ( P ho t on s c m − s − k e V − ) Energy (keV)
Ec=150 keV
10 10020 50 200 . . . k e V ( P ho t on s c m − s − k e V − ) Energy (keV)
Ec=200 keV
10 10020 50 200 . . . k e V ( P ho t on s c m − s − k e V − ) Energy (keV)
Ec=250 keV
100 150 200 250 300 350 . . . . . P ho t on I nd e x Ec (keV)100 150 200 250 300 350 . . . . . P ho t on I nd e x Ec (keV)
Fig. 2.
Upper panel: 10-200 keV spectra forpower-law with Ec =
150 keV (lower curve),Ec =
200 keV (middle curve), and Ec =
250 keV(upper curve). It is worth noting that at 70keV the three line di ff er for ∼
10% each otherand that the di ff erence decreses as Ec = in-creases. Lower panel: Γ vs. Ec confidence con-tours for a F =
1, R = = =
200 keV (big-ger contours).galaxies observed with
BeppoS AX are ex-pected to be detected above 10 keV with re-spect ∼
80% detected by
BeppoS AX . At thesame time the range of F parameters availablefor the inspection of the properties of R and Ecincreases by ∼ BeppoS AX archive as the reference one. Most inter-estingly, a significant fraction of the “new”sources (26 out of 41) for which informationabout Ec and R will be for the first time achiev-able are type II objects. These were almost ex-cluded in the
BeppoS AX era since the spec-tral complexity due to the cold absorption. Thecoupling o ff ered by S imbol - X of a good sen-sitivity below 10 keV (comparable to the one −2.5 −2 −1.5 −1 −0.5 . . . P ho t on I nde x R−2.5 −2 −1.5 −1 −0.5 . . . P ho t on I nde x R−2.5 −2 −1.5 −1 −0.5 . . . P ho t on I nde x R −2.5 −2 −1.5 −1 −0.5 . . . . . P ho t on I nde x R Fig. 3.
Upper panel:confidence contours for Rgoing from 0.5 to 1.5 for a simulated type I ob-jects (F =
1, Ec =
200 keV). Lower panel: confi-dence contours for a simulated Seyfert II withR = =
1, Ec =
200 keV).of
XMM - Newton or S uzaku ) and the great im-provement ( ∼ two orders of magnitude if com-pared with BeppoS AX and
S uzaku ) between10-70 keV should at least partially disentanglethis degeneracy.
S imbol - X is expected to give a major con-tribute in the measurements of the reflectioncharacteristics in nearby Seyfert galaxies. Infact, the reflection hump peaks at 30-40 keV(Lightman & White 1987), i.e. just in the mid-dle of the working range of the CZT detector.Moreover, S imbol - X will permit to investigatethe time-dependent behavior of the reflection.In figure 3, the confidence contours are plot-ted for three di ff erent observations of a Seyfert1 (upper panel) with F = = = =
1, R =
1, Ec =
200 keV) is pre-sented and shows how the presence of the coldabsorption prevent this kind of studies.For very bright (F ≥
10) sources,
S imbol - X is expected to allow the study of the inclina-tion angle of the accretion disk (figure 4). Thiskind of studies will be permitted only in typeI sources since the spectral complexity intro-duced by the absorber at low energy will ham-per to constraint this parameter.
4. Summary and conclusions
This work is a first attempt to determine a real-istic number of nearby (z ≤ auro Dadina: The nearby Seyfert: from BeppoS AX to S imbol - X − . − − . R Cos( Θ ) Fig. 4.
Upper panel: Confidence contours forthe inclination angle ( Θ ) for a type I sourcewith F =
1, R = = S imbol - X will carry deep spec-tral and timing analysis. The basic assumptionhere are: 1) that these studies will be possiblewhen the measurements of R and Ec are pos-sible; 2) that Simbol-X will observe sourceswith a distribution of F similar to what doneby BeppoS AX . The last assumption is quitestrong and it is probable that the characteris-tics of Simbol-X will be used to inspect sourcesthat were barely detectable with
BepoS AX , asthe Compton-thick sourcces. Thus, what ob-tained here may be considered as lower limits.The results can be summarized as follows: i)the fraction of nearby Seyfert galaxies detectedabove 10 keV should be ∼ ∼ ∼ ∼
25 objects it will be possibleto perform meaningful time dependent studiesof R; v) for ∼
15 type I sources is will be pos-sible to study the inclination angle of the ac-cretion disk inspecting the properties of the re-flected components.These results, thus, indicate that
S imbol - X is expected to leave an archive of pointed ob-servations that will allow to fully characterizethe average spectrum of nearby Seyfert galax-ies on solid statistical basis (for instance, thedistribution of N H for the Seyfert galaxies in the local Universe was obtained with a sam-ple of 74 objects, Risaliti et al. 1999). Mostimportantly, it is expected to obtain solid de-scription of the distributions of R and Ec, fun-damental to synthesize the CXB. Moreover itwill be possible to test the UM for the bright-est Seyferts checking if the inclination angleof the system is in accordance with the opti-cal classification of the sources. Finally, the as-trophysics of the accretion will be studied us-ing timing techniques at the energies where thebulk of the reflection peaks. Some basic assumption and simplificationshave been made in this work and these mustbe kept in mind when evaluating the the op-portunities o ff ered by S imbol - X in the in-spected astrophysical field. The sample of ob-jects / observations used here have been accu-mulated in six years while S imbol - X is ex-pected to fly for 2-5 years (Ferrando et al.,2006). Nonetheless, the higher observationale ffi ciency (up to ∼ S imbol - X to observe the nearbySeyferts for ∼
10 Ms as BeppoSAX did. Thebaseline model assumed here does not includewarm absorber or ionized reflection, nor in-clude soft excess in type I sources. All thesecomponents introduce additional spectral com-plexities not accounted for. On the contrary, thecapabilities of
S imbol - X in measuring R andEc were here tested only on pure statistical ba-sis: i.e. no physical assumption were made dur-ing the fitting and the significance of the mea-surements of R and Ec were calculated leavingall the other parameters free to vary. Acknowledgements.
Financial support from ASIunder contract ASI / INAF I / / / References
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