# Presentation: 070480

## Swift/BAT Census of Black Holes

- Preliminary results in Markwardt et al 2005

- energy coded color

**Notes:**
we are reporting the results from the first 9 months of the Swift Burst alert telescope (BAT) census of black holes
The Swift instruments were designed for Gamma-ray bursts and BAT's job  is to detect the gamma-ray bursts position them accurately so the soft x-ray and UV telescopes be  pointed at them and see the afterglow from these bright explosions.The bursts have most of their flux at high energies and we do not know where they will happen so BAT must monitor a large part of the sky at all times. the front face of bat is the large flat panel on the top in this drawing.  Swift follows bursts all over the sky and BAT does not care where it is observing as there are bursts everywhere.
We have known from the start that in performing it  primary function BAT would also make a map of the whole hard x-ray sky. There hhas not been an all sky map since 1977 (HEAO1) and it detected ~10 extragalactic black holes. BAT's imaging can easily resolve sources that are half a degree apart over a huge field of view (top right) and BAT can make  a broad band x-ray spectrum for all the sources in the sky.  The BAT map  shows ~150 of these active galactic nuclei.
The the map, the size of each circle tells us the brightness and the color corresponds to the hard x-ray color blue is higher energy (hard) spectrum and red is lower energy (soft) In this map you can see the bright sourcesclustered near the galactic plane and  in our galaxy which tend to have softer spectra and the weak sources all over the sky which are gaint accretiing black holes at the en ter of other galaxies.

## 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 1977–BAT is 17 times more sensitive.
- detect rare sources
- high galactic latitudesfor optical follow-up

**Notes:**
The strong hard x-ray emission can only  come from black holes and an accreting black hole mush have this kind of emission
 We need a hard x-ray survey to find the active black holes because most of them are buried in material flowing into the black hole.  This is what makes them visible, but it can also cover them up.  If any primary radiation escapes from the black hole it it must include hard x-rays. At other wavelengths the radiation from the black hole may be absorbed or it may be covered by radiation from other sources.
BAT  survey covers the whole sky and it detects all the active black holes out to z=0.03 or ~130 Megaparsecs.  It detects the sources at high latitudes that are not obscured by the gas and dust in the galactic plane or confused with galactic sources.
But there  is more  too the Swift survey.  When the narrow field instruments do not have an afterglow to look at they are observing the BAT  source They provide contemporaneous soft x-ray spectra and UV optical colors for all thhe BAT survey sources, and the all is important.

## Burst Alert Telescope (BAT)

**BAT Detector Array**

**Coded Aperture Mask**

**BAT Characteristics**
- hard X-ray energies similar to medical X-rays
- wide field of view (100°X70°)    1/8 of the whole sky
-  resolution 22 arcmin  = 300000 independent pixels whole sky
- Location accuracy <5 arcmin
- Spectroscopy (~10%)

**Notes:**
Energy Range 14-200 keV
 (Moon=~30 arcmin)
32K CZT dets, 5200 cm2
the detector is made of 32000 detectors eah 4mm by 4 mm and 1/2 of the mask is covered with lead small lead tiles 5mm by 5mm.  the pattern of tiles is random but we know where every tile is.  when a source casts a shadow oon the array that shadow is unique to one place in the sky and we can deconvolve x-rays from  all the positions in the sky. BAT covers 1/8 of the sky at any time and it typically covers 70% of the sky on any day

## Stacking of Images in Sky Coordinates

- Single Snapshot (<40 min)

**Notes:**
this is the BAT image for one observation during an orbit.  Swift looks at several locations per orbit.

## Stacking of Images in Sky Coordinates

- Ten Snapshots (~5.5 hours)

**Notes:**
this is the coverage after ten observations

## Stacking of Images in Sky Coordinates

- One Calendar Day

- Sun

- Anti-sun

**Notes:**
this is the coverage at the end of a day.  There is a hole around the sun because the narrow field telescopes cannot look at the  sun and there is a whole in the other direction due to observing constraints.

## 9-month Survey Sky Coverage

**Notes:**
The is the all sky exposure map at 9 months BAT gets 1Ms for large parts of the sky and >500,000 nearly everywhere

## 9-month Sensitivity vs. Exposure

- extragalactic BAT sources are easily to identify at high latitudes
- very bright IR galaxy
- low redshift (z<0.06)
- 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.

**Notes:**
BAT survey is getting better with time
as BAT detects more sources but also better spectra for sources

## BAT Source Detections

- ---------------------
- 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 survey
- At 3 years expect 450 AGN.

**Notes:**
Unidentified sources are real but the type of source is undetermined.  Unidentified sources are expected, but they effect the results as we do not know where to put them in distributions.  6% is a low number, but we will make more intensive efforts to identify these sources as they are probably interesting.

clusters are for another time, but Rita sambruna is presenting beamed sources
Richard Mushotzky will now discuss the significance of our initial BAT results.

126 to 107
3 with no redshift - very far south
2 no rate - eyeball position
mention Volker's work with integral 
mention XSS 3-20 keV

## BACKUP SLIDES

## 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**

**Notes:**
Absorbed NH>10^22/cm^2
70% of the galaxies with no spectroscopic ID are heavily absorbed and have no spectroscopic lines.  Many are edge on spirals where optical absorption in the host galaxy prevents ID. 3 known galaxies with no spectroscopy and no redshift
3 high latitude unidentified sources SWIFT J0201.9-4513SWIFT J1328.4+6928SWIFT J1319.7-3350  not enough to effect errors

## Swift/BAT AGN

## 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

## BAT Time Histories

## BAT Imaging

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

- DPI

- Aperture Pattern

- batfftimage

- Sky Image

## 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