1. Rittenhouse Astronomical Society January 14, 2009
Exploring the Extreme Universe with Fermi Gamma-ray Space Telescope (formerly called GLAST)
Dave Thompson
NASA GSFC
Deputy Project Scientist, Fermi Mission Team
Why?
How?
What?

2. What supposedly first turned David Banner into the Hulk?
Gamma Rays!
Because gamma rays are powerful

3. Each type of light carries different information.
What is a Gamma Ray?
One of The Many Forms of Light
Two questions – what is there? How do they work? Can’t go; must learn from what comes to us. Mostly light.
Each type of light carries different information.
Gamma rays, the highest-energy type of light, tell us about the most energetic processes in the Universe.

4. But what if you had gamma-ray vision?
Imagine the night sky. Now imagine the gamma-ray sky. It is very different.
But what if you had gamma-ray vision?

5. Fermi Gamma-ray SpaceTelescope
Large Area Telescope
LAT
GLAST Burst Monitor
GBM
Successors to EGRET and BATSE on the Compton Gamma Ray Observatory

6. How does a high-energy gamma-ray telescope work?
The key is “high-energy”
A gamma ray is a packet of energy – lots of energy.
Who do we call for help?
Prof. Einstein, what do we do with something that is just a large amount of energy?
Energy? That’s E, and E = mc2
Convert the energy to mass.

7. Fermi Large Area Telescope (LAT) e+ e–
Calorimeter
(energy measurement)
Particle Tracking Detectors
Conversion Foil
Anticoincidence
Detector (background rejection)
Pair-Conversion Telescope
Gamma rays interact by pair production, the conversion of the gamma-ray energy into two particles – an electron and a positron (really an antiparticle); LAT is a particle detector.

8. LAT Gamma Candidate Events
The green crosses show the detected positions of the charged particles, the blue lines show the reconstructed track trajectories, and the yellow line shows the candidate gamma-ray estimated direction.  The red crosses show the detected energy depositions in the calorimeter.   8

9. The Observatory Large Area Telescope -LAT
Gamma-ray Burst Monitor - GBM

11. Launch!
Launch from Cape Canaveral Air Station 11 June 2008 at 12:05PM EDT
Circular orbit, 565 km altitude (96 min period), 25.6 deg inclination.
Communications:
Science data link via TDRSS Ku-band, average data rate 1.2 Mbps.
S-band via TDRSS and ground stations

12. LAT Instrument Science Operations Center Coordination Network (GCN)
MISSION ELEMENTS • m
sec
Large Area Telescope
& GBM
GPS • •
Telemetry 1 kbps -
Fermi Spacecraft •
TDRSS SN
S & Ku
DELTA
7920H • • - S - • GN •
LAT Instrument Science Operations Center
White Sands
Schedules
Mission Operations
Center (MOC)
Science
Support Center
HEASARC
GRB
Coordination Network (GCN)
Schedules
GBM Instrument
Operations Center
Alerts
Data, Command Loads

13. About that Name
Enrico Fermi was an Italian physicist who immigrated to the United States before World War II. He was the first to suggest a viable way to produce high-energy particles in cosmic sources. Since gamma-rays are produced by interactions of such energetic particles, his work is the foundation for many of the studies being done with the Fermi Gamma-ray Space Telescope, formerly GLAST.
U. S. Postal Service

14. What is Fermi seeing?
A key point - because gamma rays are detected one at a time like particles, the Fermi telescopes do not have high angular resolution like radio, optical or X-ray telescopes. No pretty pictures of individual objects.
Instead, Fermi trades resolution for field of view. The LAT field of view is 2.4 steradians (about 20% of the sky), and the GBM field of view is over 8 steradians.
The Fermi satellite is operated in a scanning mode, always looking away from the Earth.
The combination of huge field of view and scanning means that the LAT and GBM view the entire sky every three hours!

15. Large Area Telescope First Light!
The full gamma-ray sky projected onto a surface - Galactic coordinates
The Fermi Large Area Telescope sees the whole gamma-ray sky every three hours. This is an important feature, because the high-energy sky is constantly changing. This image represents just four days of observations.

16. What is going on in the gamma-ray sky?
Milky Way – Gamma rays from powerful cosmic ray particles smashing into the tenuous gas between the stars.

17. Three months of LAT scanning data

18. 205 Preliminary LAT Bright Sources
Crosses mark source locations, in Galactic coordinates.

19. Pulsars - rapidly rotating neutron stars
Vela pulsar - brightest persistent source in the gamma-ray sky.
The actual rotation of the star takes less than 1/10 second.

20. The Pulsing Sky
Pulses at
tenth true
rate

21. LAT discovers a radio-quiet pulsar!
13 pulsars have now been found in blind searches of LAT data.
P ~ 317 ms
Pdot ~ 3.6E-13
Characteristic age ~ 10,000 yrs
Location of EGRET source 3EG J ,
the Fermi-LAT source, and the central X-ray
source RX J

22. THEORY: PARTICLE ACCELERATION LOCATIONS
Dipole magnetic field, offset from rotation axis. Goldreich-Julian found that magnetosphere is filled with charges, different signs in different regions. Forms a force-free region, so no particle acceleration. Some regions have to violate this in order to have particle acceleration we know must take place.
Figure by Dany Page

23. Gamma-only Pulsars: Beamshape
Traditional ‘Lighthouse’
Beam
Wide ‘Fan beam’
Gamma-ray-only pulsars open a new window on these exotic and powerful objects, helping us learn how they work and how they influence our Galaxy.

24. Over half the bright sources seen with LAT appear to be associated with Active Galactic Nuclei (AGN)
Power comes from material falling toward a supermassive black hole
Some of this energy fuels a jet of high-energy particles that travel at nearly the speed of light

25. How are the jets produced?
What keeps them tightly collimated over hundreds of thousands of light-years?
Radio image of Cygnus A

26. AGN
Unified models of AGN suggest that different types of AGN are really defined by how we see them.
When such jets are pointed at Earth, we see what is called a blazar
Gamma rays are an important way to learn how these jets operate

27. Gamma rays from blazars
Blazars – supermassive black holes with huge jets of particles and radiation pointed right at Earth.
PKS a blazar 10 billion light years away, never detected by EGRET, flared up overnight to become one of the brightest things in the gamma-ray sky.
3C LAT saw it flare up 5 times brighter than EGRET ever measured.

28. Flaring sources
Automated search for flaring sources on 6 hour, 1 day and 1 week timescales.
13 Astronomers telegrams
Discovery of new gamma-ray blazars PKS , PKS
Flares from known gamma-ray blazars: 3C454.3, PKS ,3C273, AO , PSK , 3C66A, PKS , 3C279
Galactic plane transients: J , 3EG J

29. The LAT Sky, August – October
FSRQ
BL Lac
Other AGN

30. How to learn about jets? Variability
Bonning et al. 2008
Correlated variability helps us learn how jets work.

31. Two ATels - Astronomer’s Telegrams
These announcements encourage cooperation from other telescopes, like Swift, to help understand how these powerful jet sources work.

32. Gamma-Ray Bursts (GRBs): the most powerful explosions since the Big Bang
Originally discovered by military satellites, GRBs are flashes of gamma rays lasting a fraction of a second to a few minutes.
Optical afterglows reveal that many of these are at cosmological distances
The GBM and LAT extend the energy range for studies of gamma-ray bursts to higher energies, complementing Swift and other telescopes.
Fermi is helping learn how these tremendous explosions work.

33. Gamma-ray bursts come in at least three flavors
Collapsars: A rapidly spinning stellar core collapses and produces a supernova, along with relativistic jets that can produce long GRBs
Compact Mergers: Two neutron stars, or a neutron star and a black hole, collide and merge, producing a jet that gives rise to a short GRB
Magnetars: Neutron stars in our Galaxy or nearby galaxies with extremely strong magnetic fields can give off powerful bursts that resemble short GRBs
In both these cases, the burst probably produces a black hole.

34. Multiple detector light curve
PRELIMINARY!
The bulk of the emission of the 2nd peak is moving toward later times as the energy increases
Clear signature of spectral evolution

35. What Next for Fermi?
We have only scratched the surface of what the Fermi Gamma-ray Space Telescope can do.
The gamma-ray sky is changing every day, so there is always something new to learn about the extreme Universe.
Beyond pulsars, blazars, and gamma-ray bursts, other sources remain mysteries. Nearly 20% of the brightest sources do not seem to have obvious counterparts at other wavelengths.
There are also some other astrophysical problems that Fermi can address, shown in the next few slides. Credit: I borrowed most of these from Bob Naeye, who is now the editor of Sky and Telescope. Bob worked with us on Fermi for a while.

36. Photon Archaeology us Eg lower Eg higher
High-energy gamma-rays interacting with visible- and ultraviolet-light photons will produce electron-positron particle pairs.
Distant blazars will disappear from the LAT’s view as their gamma-ray photons are attenuated en route to Earth.
Provides a method to measure the light output of the early universe. us
source
Eg lower
Eg higher

37. Funky Physics?
At the smallest size scale, space itself may be distorted by effects of quantum gravity. These effects could cause the speed of light to differ from its constant value, depending on its wavelength. Distant blazars and gamma-ray bursts seen over the huge energy range of Fermi may be able to measure such changes.

38. A leading candidate for dark matter: Supersymmetry particles a. k. a
A leading candidate for dark matter: Supersymmetry particles a.k.a. “WIMPs” (weakly interacting massive particles)

39. A leading candidate for dark matter: Supersymmetry particles a. k. a
A leading candidate for dark matter: Supersymmetry particles a.k.a. “WIMPs” (weakly interacting massive particles)

40. Light dark-matter particles produce 511 keV (low-energy) gamma rays
Dark-matter particles annihilate with one another, leading to gamma rays
Light dark-matter particles produce 511 keV (low-energy) gamma rays
Heavy dark-matter particles produce 300 to 600 GeV (high-energy) gamma rays
WIMP dark-matter particles (neutralinos) produce 30 MeV to 10 GeV (medium-energy) gamma rays
Illustrations by Gregg Dinderman/Sky & Telescope

41. A Long Shot: the decay of primordial black holes into Hawking radiation

42. Summary - just the beginning
Gamma rays seen with the Fermi telescope are revealing aspects of the extreme universe - neutron stars, black holes, and exploding stars.
As the mission continues, Fermi scientists will be looking for even more exotic aspects of the Universe - such as quantum gravity, dark matter, and evaporating black holes.
The Fermi Web site is
The MySpace site is
All the Fermi data will become public starting this Fall. Join the fun!