SwiftBAT Hard Xray Survey

1
Swift/BAT Hard X-ray Survey
Preliminary results in Markwardt et al 2005
energy coded color
2
BAT Instrument Parameters

• Energy Range 14 - 195 keV
• Area 5200 cm2 (x 50 open fraction)
• Field of View 2 Steradian, partially coded
• Background 10,000 ct/s (cosmic diffuse
  dominated)
• Spatial 21 sky pixel, centroided to
  lt1-3Resolution
• Spectral 6 keV FWHM _at_ 60 keV, average
  
  Resolution
• Sensitivity 0.2 photons/cm2/sec
• Timing Resolution 100 usec
• Observing Random (piggy-back
  SwiftStrategy GRB observing plan)

3
9-month Swift/BAT Survey
Sensitivity vs Time

• Exposure Map
• Covers whole sky, mostly gt1Ms
• deficit on Ecliptic Plane due to Sun avoidance
• Sensitivity improves as square root of time
  (1.2-2 X statistical) to 0.6 milliCrab in 3 years

4
BAT Source Detections

• Galactic b gt15 (74)
• ----------------------
• 159 sources
• 9 unidentified sources
• 29 galactic
• 2 galaxy clusters
• 121 AGN
• 15 beamed

• 9 months
• ---------------------
• 323 sources
• 39 unidentified sources
• 158 galactic
• 5 galaxy clusters
• 158 AGN
• 16 beamed

already the most sensitive all-sky hard x-ray
survey At 3 years expect 450 AGN.
5
BAT GALAXY Identifications
absorbed Log nH gt 22 Gal b gt15

• 70 of the galaxies with no Sy classification are
  absorbed.
• Most unknown galaxies are absorbed Sy2's or edge
  on spiral galaxies with no lines (3 with no
  spectroscopy)
• Sy2/Sy1 ratio is 1.2 (0.5 Sy1.5/Sy1) and 52 of
  Seyfert galaxies are absorbed confirming
  Markwardt et al 2005 Much lower than 75
  predicted by the standard model for the CXB

6
Correlations of BAT Rate with other Bands

• no correlation between BAT and ROSAT count rates
• 44 BAT sources not detected by ROSAT

• no close correlation with total 2MASS J band
• soft x-ray and IR do not measure true AGN
  luminosity or complete populations

7

Heavily Absorbed and Complex Spectra Abound

• gt25 of BAT sources have weak soft X-ray emission
• only a survey at gt20 keV is unbiased by absorption

• Many have extremely complex spectra with soft and
  hard components that seem unrelated
• Simultaneous X-ray and hard X-ray spectra are
  required to understand AGN

8
LogN/LogS and Luminosity Function

• errors 25 in normalization, 10 in slopes and
  lt1 in break luminosity
• New, much tighter constraints will test CXB models

• Treister, Urry, and Lira standard unified AGN
  model 2500 AGN, LBATgt10-11ergs cm-2 s-1
• BAT measures 1100 AGN, LBATgt10-11ergs cm-2 s-1
• Pashak Ghandi800 AGN, LBATgt10-11ergs cm-2 s-1

9
Average BAT AGN Spectrum

• no evidence for a break below 200 keV
• same with brightest 36 AGN removed
• Same for luminosity lt1044 or gt1044
• Contrast with strong break at 40 keV in CXB
• spectrum is much flatter than CXB (slope 2.75)
  above the break

Crab Normalized Response
10
Background vs BAT AGN Spectrum

• BAT AGN spectrum is a bad fit to CXB for Egt40 keV
• Soft x-ray surveys put source of CXB at Z0.7
• to fit the CXB the BAT AGN must be at Z gt 1 or
  show strong spectral evolution

11
What is the Blazar Contribution to the CXB?

• BAT beamed sum spectrum is 10-16 AGN sum
• In 3 years, BAT will detect gt40 beamed sources.

• BAT survey can answer this question.

12
Conclusions

• The first complete AGN survey is answering many
  of the old questions about AGN and their
  contribution to the CXB.
• What are the numbers of hard x-ray AGN?
• 1100 AGN, LBATgt10-11ergs cm-2 s-1 14-200 keV
• Are the hard x-ray AGN and CXB spectra the same?
  No
• Does the standard unified model explain all? No
• How many of the AGN are absorbed? 0.6 not 3/4
• What is the blazar contribution to CXB? 10-15
• Follow up of the BAT selected AGN offers many
  exciting new opportunities. We are just getting
  started!

13
BACKUP SLIDES
14
BAT Survey Characteristics

• survey sensitivity is still improving as the
  square root of time
• a longer survey detects more sources but it also
  makes better spectra for the previous sources
• 4 energy bands will be expanded to 8 bands soon
• extragalactic BAT sources are easily to identify
  at high latitudes
• very bright IR galaxy
• low redshift (zlt0.06)
• optical AGN or high absorption
• XRT positions and joint XRT/BAT spectra make ID's
  unambiguous

Sensitivity vs. Exposure
15
Tests of the Standard Model

• With ltEgt50 kev BAT measures the true nature of
  the continuum relatively unaffected by absorption
  or scattering
• BAT selected Sy1's have softer spectra than Sy2's
  (5.7?)

• BAT selected Sy1's have higher luminosity than
  Sy2's (3.6?)
• differences are small, so no selection effect for
  BAT

16
Absorption's Effect on Luminosity Function

• more high luminosity with NHlt22 and more low
  luminosity NHgt22
• more statistics required
• the Swift/BAT survey will get there

17
Swift/BAT and Integral luminosity functions

• the INTEGRAL and Swift/BAT luminosity functions
  are in rough agreement
• The Sazanov data seems to be systematically
  higher