Cosmic X-ray Background with Swift/BAT: un update (and some new results)

1
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 ?

3
CXB Measurement via Occultation
On - Off ? ? ( CXB - Earth)
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 -gt spectral
templates assumed
5
Results CXB spectrum

• BAT CXB extends up to 200 keV
• BAT finds CXB is 8 larger than HEAO-1

6
Results 2nd measurement
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

8
BAT Clusters Poster H. 1
9
Open Question

• Radio Halos prove that relativistic electrons
  exist in the ICM (KempnerSarazin 01,Govoni et al
  01, Thierbach et al 03)
• EUV and soft excesses support this view (e.g.
  Bonamente 03-05-07, Nevalainen 03, Werner et al
  07)

Is there any non-thermal X-ray component?
Yes (e.g Fusco-Femiano et al 99-03-04,
Rephaeli 01-02, GruberRephaeli 02, Nevalainen et
al 01-04, Eckert et al 07, Lutovinov et al 08)
No (e.g MolendiDe Grandi, De GrandiMolendi 99,
Revnivtsev 04, RossettiMolendi 04-07, Ota
et al 08)
10
BAT sample Ajello, Rebusco, Cappelluti, ApJ
submitted, May 2nd (www.mpe.mpg.de/majello/ARC08.
pdf)

• 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 ? .

11
NT component, finally!
Perseus
Abell 0754
12
NT component, finally!
Too Early! Only AGN..
Perseus
Abell 0754
13
Indeed
Sy2 _at_ z0.3 Credits A. Rau
Henry04
14
The rest of the clusters

• Consistent with pure thermal emission
• Derive upper limit in the 50-100 keV band

15
Comparison with previous detections
CLUSTER Perseus A 3266 A 0754 A 3571 A 2029 A 2142 Triangulum A. Ophiucus A 2319 INSTRUMENT BeppoSAX -- BeppoSAX -- -- BeppoSAX -- INTEGRAL/BeppoSAX RXTE AGREE? AGN AGN!
16
Stacking analysis

• Average of 8 spectra
• Sensitivity pushed a factor 3 (10x exposure)
• Still no NT emission
• F50-100lt1.9 x 10-12 cgs

17
What do we learn ?

• Relativistic (GeV) e- can upscatter CMB photons
  via Inverse Compton (e.g. Rephaeli79,
  Sarazin99)
• At the current fluxes, very low B no
  equipartition (?)

(e.g. HarrisRomanishin 74)
18
First source count and luminosity function (gt15
keV)

• BAT Clusters contribute only 0.1 to the CXB,
  but they are 5 wrt AGN
• Good agreement with ROSAT (Jones98,
  Boehringer01)

• Good agreement with ROSAT (Boehringer02)

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.
  Okajima08)