Swift/BAT Hard X-ray Survey

Preliminary results in Markwardt et al 2005

35'

energy coded color

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 <1-3’

Resolution• Spectral 6 keV FWHM @ 60 keV, average

Resolution• Sensitivity 0.2 photons/cm2/sec• Timing Resolution 100 usec• Observing “Random” (piggy-back Swift

Strategy GRB observing plan)

9-month Swift/BAT Survey> 1.5 Ms

1-1.5 Ms

0.5-1 Ms

Eclip

tic P

lane

8.5 mCrab (T/20 ks)-0.5

Exposure Map• Covers whole sky, mostly >1Ms• 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

Sensitivityvs Time

9 months---------------------• 323 sources• 39 unidentified

sources• 158 galactic• 5 galaxy clusters• 158 AGN

• 16 beamed

|Galactic b| >15 (74%)----------------------• 159 sources• 9 unidentified sources• 29 galactic• 2 galaxy clusters• 121 AGN

• 15 beamed

already the most sensitive all-sky hard x-ray surveyAt 3 years expect 450 AGN.

BAT Source Detections

BAT GALAXY Identifications

• 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

absorbed Log nH > 22|Gal b| >15

abs unabs total

Sy1 3 31 34

Sy1.5 5 11 16

Sy2 36 3 40

no Sy ID 9 4 13

total 53 49 103

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

BATXMM peaks at

20 keV

• >25% of BAT sources

have weak soft X-ray emission

• only a survey at >20 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

Heavily Absorbed and Complex Spectra Abound

LogN/LogS and Luminosity Function• errors 25% in normalization,

~10% in slopes and <1% in break luminosity

• New, much tighter constraints will test CXB models

• Treister, Urry, and Lira: standard unified AGN model 2500 AGN, LBAT>10-11ergs cm-2 s-1

• BAT measures 1100 AGN, LBAT>10-11ergs cm-2 s-1

• Pashak Ghandi800 AGN, LBAT>10-11ergs cm-2 s-1

Average BAT AGN Spectrum

• no evidence for a break below 200 keV

• same with brightest 36 AGN removed

• Same for luminosity <1044 or >1044

• Contrast with strong break at 40 keV in CXB

• spectrum is much flatter than CXB (slope = 2.75) above the break

Crab NormalizedResponse

E-2

Background vs BAT AGN Spectrum• BAT AGN

spectrum is a bad fit to CXB for E>40 keV

• Soft x-ray surveys put source of CXB at Z=0.7

• to fit the CXB the BAT AGN must be at Z > 1 or show strong spectral evolution

150 keVBAT UL

What is the Blazar Contribution to the CXB?

• BAT beamed sum spectrum is 10-16% AGN sum

• In 3 years, BAT will detect >40 beamed sources.

• BAT survey can answer this question.

Beamed Sources

Beamed Fraction

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, LBAT>10-11ergs 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!

BACKUP SLIDES

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 (z<0.06)– optical AGN or high absorption

• XRT positions and joint XRT/BAT spectra make ID's unambiguous

8.5 mCrab (T/20 ks)-0.5

XRTUVOTBATjointspectra

BATXRT

Sensitivity vs. Exposure

Tests of the Standard Model

• BAT selected Sy1's have higher luminosity than Sy2's (3.6)

• differences are small, so no selection effect for BAT

With <E>~50 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)

Absorption's Effect on Luminosity Function• more high luminosity with

NH<22 and more low luminosity NH>22

• more statistics required• the Swift/BAT survey will

get there

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