1. Why is the BAT survey for AGN Important? All previous AGN surveys were biased- –Most AGN are ‘obscured’ in the UV/optical –IR properties show wide scatter wrt x- ray properties BAT survey should be unbiased wrt obscuration Much larger sample than best previous survey HEAO-1 (and Integral)-1st sensitive hard x-ray survey in 28 years ! Wide time coverage - good angular accuracy Spectra BAT data provides first large unbiased sample of host galaxy properties relation of optical spectral properties to intrinsic luminosity Direct comparison with z~1 Chandra and XMM surveys * Distribution of N(H) values * Luminosity function * Log N-Log S *necessary for modeling x-ray background

2. Intensity [nW m -2 sr -1 ] Frequency [Hz] Background Energy Distribution Hasinger 2006 H.E.S.S. upper limits ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ Spitzer / HST Spitzer AGN Treister et al.06 EGRET resolved ROSAT/XMM/ Chandra (Worsley et al.) ▲ RXTE (Revnivtsev et al.) Sy2 SED (Sturm et al. 06) AGN contribute ~4-15% of the 15  background -100%of XRB How much of the energy radiated in the universe comes from AGN When is it emitted ? In what form ? Which objects are responsible how do we find them?

3. Chandra/XMM Changed Everything Objects with broad optical lines (“optical AGN”) X-ray selected objects Steffen et al 2003 L(x)x10 40 ergs/sec Z=0.1-1 Chandra/XMM data: number of x-ray selected AGN exceeds optically selected ones by ~7:1 at a fixed optical flux X-ray selected objects have very different properties than “optically” selected AGN Most AGN are “invisible” to simple optical searches Luminosity function

4. BAT Follow-up Determines The Distribution of Obscuration Unified models of active galaxies try to account for the relative number of different types of AGN (so- called types I and II) Predict that the ratio of obscured to un- obscured objects in the local universe should be 4:1 (Antonnucci and Miller 1989, Treister et al 2006) BAT finds 2:1 - a serious discrepancy the models need to be changed Number of objects Obscured Not Obscured

5. Unified Model of AGN the unified model, says we observe "different" kinds of active galaxies because our angle of view changes. For example, we see two kinds of Seyfert galaxies because we are looking either edge on through the torus (Type II Seyferts) or at an inclined angle so there is a clear view of the nucleus (Type I Seyferts). High energy x-rays (BAT) can penetrate through the molecular torus Antonucci 1989 X-ray not obscured X-ray obscured Accretion disk

6. Tests of Unified Model The Unified model predicts that the obscuration is geometric and should not depend on the luminosity of the AGN BAT finds that the lower luminosity sources are much more likely to be obscured than the high luminosity sources A clear violation of the simple unified model Fraction of objects obscured

7. The soft X-ray and optical flux may not predict the hard flux at all x-ray deep surveys assumed spectra were simple - a 1 parameter family Follow-up observations of BAT sources shows this is not true, Most objects are complex HARD soft The largest x-ray survey of the sky was the Rosat all sky survey in the soft (0.2-2 keV) band ~ 100, 000 sources The Rosat and BAT fluxes are not correlated The follow-up to the BAT data shows us why: in many objects the soft and hard x-rays are due to different phenomena

8. Time Variability It has been known for 40 years that active galaxies are quite variable. However there never has been a long and continuous record of the intensity of any AGN The BAT data measure the intensity variability of more than 100 sources on time scales from days to years This may allow us to understand why these objects vary ( - e.g. is it due to a change in the accretion rate or something else ) Day of 2005 intensity

9. The X-ray Background (XRB) Allow first accurate synthesis models of E>10 kev x-ray background Basically before Integral and Swift there was little data above 10 keV- all extrapolation ! Chandra band BAT band The XRB is the sum of all radiation over cosmic time from active galaxies- its energy density peaks at 30 kev in the BAT band At E< 8 kev Chandra and XMM have determined the sources of the XRB Little is known about the nature of objects at E> 10 kev for models to synthesize the background before BAT and Integral Energy in x-ray background

10. Average BAT AGN Spectrum and the X-ray Background The BAT spectra of all the detected objects is a pure power law –slope is flatter than CXB above the break and steeper below Bat source Spectrum to fit the CXB the sources should be at z ≥ 1 so that the break does not fall in the BAT band CXB Spectrum

11. How do the sources differ? The spectral energy distribution (SED) of the absorbed and unabsorbed objects are very different and so is their ratio of x-ray to total luminosity This also changes with x-ray luminosity - lower luminosity sources are “redder” Using our AGN bolometric corrections and evolution absorbed objects contribute ~2/3 of today’s rest mass of black holes