SwiftBAT Census of Black Holes

1
Swift/BAT Census of Black Holes
Preliminary results in Markwardt et al 2005
energy coded color
2
Why is the Swift/BAT census of Black Holes so
good?

• Hard X-rays are a unique signature of an
  accreting black hole

• The last all-sky hard X-ray survey was HEAO1 in
  1977BAT is 17 times more sensitive.
• detect rare sources
• high galactic latitudesfor optical follow-up

3
Burst Alert Telescope (BAT)
Coded Aperture Mask
BAT Detector Array

• BAT Characteristics
• hard X-ray energies similar to medical X-rays
• wide field of view (100X70) 1/8 of the
  whole sky
• resolution 22 arcmin 300000 independent
  pixels whole sky
• Location accuracy lt5 arcmin
• Spectroscopy (10)

4
Stacking of Images in Sky Coordinates
Single Snapshot (lt40 min)
5
Stacking of Images in Sky Coordinates
Ten Snapshots (5.5 hours)
6
Stacking of Images in Sky Coordinates
Anti-sun
Sun
One Calendar Day
7
9-month Survey Sky Coverage
8
9-month Sensitivity vs. Exposure

• extragalactic BAT sources are easily to identify
  at high latitudes
• very bright IR galaxy
• low redshift (zlt0.06)
• optical AGN
• high X-ray absorption (XRT)
• With time, the survey will keep detecting more
  sources.
• A longer survey also makes better spectra for the
  previously detected sources.

9
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.
10
BACKUP SLIDES
11
BAT GALAXY Identifications
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
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

12
Swift/BAT AGN
13
Swift/BAT survey a Census of AGN

• What do you need for an accurate census?
• It must be unbiased
• cover whole country
• must not discriminate against minorities
• It must be a statistically significant sample

14
BAT Time Histories
15
BAT Imaging
Aperture Pattern
Sky Image
batfftimage
DPI

• Cross correlate mask aperture pattern with
  detector image (search all possiblepoints on sky)

16
Astronomy Misconceptions of BAT imaging

• No focusing optics
• Each detector can be illuminated by many points
  on the sky andEach point on the sky illuminates
  many detectors
• Two distinct spaces
• Detector space
• Sky space
• Transform between two spaces with special
  cross-correlation software
• Normally background dominated
• 1 Crab 10 of background

Detector Space
Sky Space