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Exploring the Extreme Exploring the Extreme Universe with Fermi Universe with Fermi Gamma-ray Space Gamma-ray Space Telescope (formerly Telescope (formerly called GLAST)called GLAST)

Dave ThompsonDave ThompsonNASA GSFC NASA GSFC Deputy Project Scientist, Fermi Mission Deputy Project Scientist, Fermi Mission

TeamTeam

• Why? • How? • What?

Rittenhouse Astronomical Society January 14, 2009

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What supposedly first turned David Banner into the Hulk?

Gamma Rays!

Because gamma rays are powerful

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What is a Gamma Ray?One of The Many Forms of 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.

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But what if you had gamma-ray vision?

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Fermi Gamma-ray SpaceTelescopeFermi Gamma-ray SpaceTelescope

Large Area Telescope

LAT

GLAST Burst Monitor

GBM

Successors to EGRET and BATSE on the Compton Gamma Ray Observatory

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How does a high-energy gamma-ray How does a high-energy gamma-ray telescope work?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.

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e+ e– Calorimeter (energy measurement)

Particle Tracking Detectors

Conversion Foil

AnticoincidenceDetector (background rejection)

Pair-Conversion Telescope

Fermi Large Area Telescope (LAT)Fermi Large Area Telescope (LAT)

• 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.

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LAT Gamma Candidate EventsLAT 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.  

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The ObservatoryThe Observatory

Gamma-ray Burst Monitor - GBM

Large Area Telescope -LAT

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Launch!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

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GN

HEASARC

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DELTA7920H •

White Sands

TDRSS SNS & Ku

LAT Instrument Science

Operations Center

GBM Instrument Operations Center

GRB Coordination

Network (GCN)

• Telemetry 1 kbps•

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S

Alerts

Data, Command Loads

Schedules

Schedules

Mission Operations Center (MOC)

Science Support Center

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Fermi Spacecraft

Large Area Telescope& GBMGPS

MISSION ELEMENTS

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About that NameAbout 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

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What is Fermi seeing?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!

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Large Area Telescope First Light!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.

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Milky Way – Gamma rays from powerful cosmic ray particles smashing into the tenuous gas between

the stars.

What is going on in the gamma-ray sky?

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Three months of LAT scanning data

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205 Preliminary LAT Bright Sources

Crosses mark source locations, in Galactic coordinates.

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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.

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The Pulsing SkyThe Pulsing Sky

Pulses attenth truerate

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LAT discovers a radio-quiet pulsar!LAT discovers a radio-quiet pulsar!

P ~ 317 msPdot ~ 3.6E-13Characteristic age ~ 10,000 yrs

Location of EGRET source 3EG J0010+7309, the Fermi-LAT source, and the central X-ray source RX J0007.0+7303

13 pulsars have now been found in blind searches of LAT data.

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THEORY: PARTICLE ACCELERATION LOCATIONS

Figure by Dany Page

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Gamma-only Pulsars: BeamshapeGamma-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.

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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

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How are the jets produced?

What keeps them tightly collimated over hundreds of thousands of light-years?

Radio image of Cygnus A

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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

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Blazars – supermassive black holes with huge jets of particles and radiation pointed right at Earth.

Gamma rays from blazars

3C454.3 - LAT saw it flare up 5 times brighter than EGRET ever measured.

PKS 1502+106 - 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.

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Flaring sourcesFlaring 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 1502+106, PKS 1454-354

– Flares from known gamma-ray blazars: 3C454.3, PKS 1510-089,3C273, AO 0235+164, PSK 0208-512, 3C66A, PKS 0537-441, 3C279

– Galactic plane transients: J0910-5041, 3EG J0903-3531

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The LAT Sky, August – OctoberThe LAT Sky, August – October

FSRQ Other AGNBL Lac

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How to learn about jets? VariabilityHow to learn about jets? Variability

Bonning et al. 2008

Correlated variability helps us learn how jets work.

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Two ATels - Astronomer’s TelegramsTwo ATels - Astronomer’s Telegramswww.astronomerstelegram.org

These announcements encourage cooperation from other telescopes, like Swift, to help understand how these powerful jet sources work.

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Gamma-Ray Bursts (GRBs): the most Gamma-Ray Bursts (GRBs): the most powerful explosions since the Big Bangpowerful 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.

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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.

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• The bulk of the emission of the 2nd peak is moving toward later times as the energy increases

• Clear signature of spectral evolution

Multiple detector light curveMultiple detector light curve

PRELIMINARY!

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What Next for Fermi?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.

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Photon Archaeology

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.

ussource

E lower

ussource

E higher

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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.

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

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

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Dark-matter particles annihilate with one another,

leading to gamma raysLight dark-matter particles produce 511 keV (low-energy) gamma rays

WIMP dark-matter particles (neutralinos) produce 30 MeV to 10 GeV (medium-energy) gamma rays

Heavy dark-matter particles produce 300 to 600 GeV (high-energy) gamma rays

Illustrations by Gregg Dinderman/Sky & Telescope

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A Long Shot: the decay of primordial black holes into

Hawking radiation

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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 http://www.nasa.gov/fermi

The MySpace site is http://www.myspace.com/GLAST

All the Fermi data will become public starting this Fall. Join the fun!