1. M. Ajello (MPE-Garching)
Cosmic X-ray Background with Swift/BAT: un update (and some new results)
M. Ajello (MPE-Garching)
with
G.Sato, J. Greiner, G. Hasinger, G. Kanbach, A. Strong, N. Gehrels, J. Tueller, C. Markwardt
Submitted on Apr. 2nd

2. CXB problem HEAO-1 CXB: wrong in normalization, in shape or in both ?
Gilli et al. 2007
M. Ajello

3. CXB Measurement via Occultation
OFF
On - Off   ( CXB - Earth)
ON-OFF
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4. The ON-OFF ‘difference’ spectrum
BAT detects modulation up to 200 keV at high significance
Earth albedo dominates above 100 keV
Method: fit in Xspec with CXB -albedo -> spectral templates assumed
M. Ajello

5. Results: CXB spectrum BAT CXB extends up to 200 keV
BAT finds CXB is 8% larger than HEAO-1
M. Ajello

6. Results 2nd measurement
Occultation
Background fitting
M. Ajello

7. New Results from Swift/XRT!!
XRT measurement uses:
GRB follow-up observation
1 month of closed-camera data
Several Crab observations to assess stray light
Moretti et al. in preparation
Stray-light well assessed
M. Ajello

8. BAT Clusters : Poster H. 1
M. Ajello

9. Is there any non-thermal X-ray component?
Open Question
Radio Halos prove that relativistic electrons exist in the ICM (Kempner&Sarazin 01,Govoni et al 01, Thierbach et al 03)
EUV and soft excesses support this view (e.g. Bonamente , Nevalainen 03, Werner et al 07)
Is there any non-thermal X-ray component?
Yes: (e.g Fusco-Femiano et al , Rephaeli 01-02, Gruber&Rephaeli 02, Nevalainen et al 01-04, Eckert et al 07, Lutovinov et al 08)
No: (e.g Molendi&De Grandi, De Grandi&Molendi 99, Revnivtsev 04, Rossetti&Molendi 04-07, Ota et al 08)
M. Ajello

10. BAT sample Ajello, Rebusco, Cappelluti, ApJ submitted, May 2nd (www
BAT sample Ajello, Rebusco, Cappelluti, ApJ submitted, May 2nd (
10 Clusters detected above 15 keV (all sky, out of 450 sources)
BAT does not provide spatial information (i.e. all clusters are point-like ….)
Use Chandra/XMM/XRT data in order to constrain non-thermal processes
What do we find ? ….
M. Ajello

11. NT component, finally!
Perseus
Abell 0754
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12. NT component, finally! Too Early! Only AGN….. Perseus Abell 0754
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13. Indeed…
z=0.3
Credits : A. Rau
Henry+04
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14. The rest of the clusters
Consistent with pure thermal emission
Derive upper limit in the keV band
Abell 2319
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15. Comparison with previous detections
CLUSTER
Perseus
A 3266
A 0754
A 3571
A 2029
A 2142
Triangulum A.
Ophiucus
A 2319
INSTRUMENT
BeppoSAX --
INTEGRAL/BeppoSAX
RXTE
AGREE?
AGN
AGN!
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16. Stacking analysis Average of 8 spectra
Sensitivity pushed a factor 3 (10x exposure)
Still no NT emission
F50-100<1.9 x cgs
M. Ajello

17. What do we learn ?
Relativistic (GeV) e- can upscatter CMB photons via Inverse Compton (e.g. Rephaeli+79, Sarazin+99)
At the current fluxes, very low B : no equipartition (?)
BAT
BAT +
XMM
XRT
Chandra
(e.g. Harris&Romanishin 74)
M. Ajello

18. First source count and luminosity function (>15 keV)
N S-1.4
BAT Clusters contribute only ~0.1% to the CXB, but they are ~5% wrt AGN
Good agreement with ROSAT (Jones+98, Boehringer+01)
Good agreement with ROSAT (Boehringer+02)
M. Ajello

19. Conclusions
BAT is a fantastic surveying instrument
Many exciting results on AGN, Clusters, etc.
Swift (BAT and XRT) show HEAO-1 CXB wrong in shape (?!) Good agreement with INTEGRAL
BAT clusters show no non-thermal components (agreement with independent analysis of T. Okajima+08)
M. Ajello