# Presentation: 224376

## The Fermi Gamma-ray Space Telescope     Bright Source List

**The Fermi Gamma-ray Space Telescope     Bright Source List**
**Dave Thompson, GSFC**
**Jean Ballet,**** ****SAp, CEA Saclay **
**On behalf of the **
**Fermi Large Area Telescope (LAT)**
**Collaboration**

## The LAT Bright Source List 

**The LAT Bright Source List**

- During the early part of the Fermi mission, the Large Area Telescope (LAT) team is optimizing calibrations, analysis methods, and background subtraction techniques.
- The brightest sources seen by LAT are less influenced by these ongoing improvements than are weaker sources.

- Releasing information about the brightest sources early has two principal goals:
- Provide opportunities for multiwavelength studies of these sources;
- Facilitate proposals for the second cycle of Fermi Guest Investigator proposals, due on March 6.

- The release date for the bright source list is February 6.
- This list is a first step toward the first LAT catalog, due in the Fall of this year.

## Exposure map

- Equivalent on-axis observing time, Galactic coordinates

- Ms

- Data used are the first three months of all-sky scanning data,  Aug. - Oct. 2008. Total live time is 7.53 Ms
- Scanning scheme makes exposure map very uniform (SAA creates North-South asymmetry)

*PRELIMINARY*

## Constructing the LAT Bright Source List 

**Constructing the LAT Bright Source List**

- 2.8 M events above 100 MeV with current cuts
- Maximum likelihood analysis was used to determine source significance, fluxes in two energy bands, locations, and variability information, all of which is included in the list.
- Only sources with confidence level greater than **10 ****** over 3 months were retained for the bright source list.

- The resulting bright source list is not a full catalog:
- Not complete - many more sources at lower significance
- Not flux limited - cut is on confidence level
- Not uniform - sources near the Galactic plane must be brighter because of the strong diffuse background.
- No detailed energy spectral information.

## Sensitivity map

**Sensitivity map**

- Structure is mostly that of the interstellar medium
- Below 10-7 ph/cm2/s over most of the extragalactic sky

- Flux > 100 MeV required to reach 10 σ for average E-2.2 spectrum

- 2
- 1.5
- 1
- 0.5

- 10-7 ph/cm2/s

*PRELIMINARY*

## 205 Preliminary LAT Bright Sources 

**205 Preliminary LAT Bright Sources**

- Crosses mark source locations, in Galactic coordinates

- Map above 300 MeV

## Source localization

**Source localization**

- Conservative error radii adjusted on known associations
- Conservative 0.04° absolute limit based on bright pulsars

*PRELIMINARY*

## Source variability

- Build light curves of all sources on one-week time scale
- Pulsars are stable within 3%
- Bright blazars are very clearly variable

- Geminga pulsar

- AO 0235+164 blazar

**Not at same scale!**

*PRELIMINARY*

## Source variability 2

- Many blazars are too faint (even at TS > 100) to be detected as variable even if they were
- Many fewer variable sources in the plane

*PRELIMINARY*

## 205 Preliminary LAT Bright Sources 

**Census of Associations (not Identifications)**

| Class | Number |
| --- | --- |
| Radio/X-ray pulsar | 15 |
| LAT pulsar | 14 |
| Globular cluster (pulsars?) | 1 |
| HMXB | 2 |
| LMC  | 1 |
| Flat Spectrum Radio Quasars | 62 |
| Bl Lac Objects | 46 |
| Blazar, uncertain type | 11 |
| Radio galaxies | 2 |
| Special cases (under study) | 14 |
| Unassociated | 37 |

## Source association

**Source association**

*PRELIMINARY*

- Mostly AGN outside the Galactic plane
- Not that many unassociated outside the plane

- Red - steeper spectra
- Blue - harder spectra

## Source association 2

**Source association 2**

- Most associated sources in the Galaxy are pulsars
- Many unassociated sources in the inner regions of the Galaxy

*PRELIMINARY*

## 205 Preliminary LAT Bright Sources 

**Conclusions**

**EGRET on the Compton Observatory found only 31 sources above 10 ******** in its lifetime. **
**Typical 95% error radius is less than 10 arcmin.  For the brightest sources, it is less than 3 arcmin.  Improvements are expected. **
**About 1/3 of the sources show definite evidence of variability. **

**29 pulsars in the list are identified by gamma-ray pulsations.**
**Over half the sources are associated positionally with blazars.  Some of these are firmly identified as blazars by correlated multiwavelength variability. **
**37 sources have no obvious associations with known gamma-ray emitting types of astrophysical objects. **