the gamma ray sky seen by the fermi large area...
TRANSCRIPT
The Gamma‐ray sky seen by the Fermi Large Area
Telescope.
F.Longo
INFN Trieste, CIFS Torinoon behalf of the Fermi‐LAT collaboration
7th AGILE Workshop
Frascati, 29 settembre 2009
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Outline
Introduction to the Fermi Gamma-ray Space TelescopeThe Large Area Telescope Astrophysical results– Solar System sources– PSR and Galactic Diffuse emission– Active Galactic Nuclei – Gamma-ray Bursts
The “electron” spectrum – Interpretations
Conclusions
The Observatory (GLAST)
• Large AreaTelescope (LAT) – 20 MeV ‐ >300 GeV
• Gamma‐ray Burst Monitor (GBM) – NaI and BGO Detectors
– 8 keV ‐ 30 MeV
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Operating modes
• Primary observing mode is Sky Survey
• Full sky every 2 orbits (3 hours)• Uniform exposure, with each
region viewed for ~30 minutes every 2 orbits
• Best serves majority of science, facilitates multi‐wavelength observation planning
• Exposure intervals commensurate with typical instrument integration times for sources
• EGRET sensitivity reached in days
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• Pointed observations when appropriate (selected by peer review in later years) with automatic earth avoidance selectable. Target of Opportunity pointing.
• Autonomous repoints for onboard GRB detections in any mode.
F. Longo – 7th AGILE Workshop, Frascati 2009
Fermi Science
A very broad menu that includes:• Systems with supermassive black holes (Active Galactic Nuclei)• Gamma‐ray bursts (GRBs)• Pulsars• Supernova remnants (SNRs)• PWNe• Origin of Cosmic Rays• Diffuse emissions• Solar physics• Probing the era of galaxy formation, optical‐UV background light• Solving the mystery of the high‐energy unidentified sources• Discovery! New source classes. Particle Dark Matter? Other
relics from the Big Bang? Other fundamental physics checks.
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Huge increment in capabilitiesDraws the interest of both the High Energy Particle Physics and
High Energy Astrophysics communities.
F. Longo – 7th AGILE Workshop, Frascati 2009
Overview of the Large Area Telescope (LAT)
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The LAT is a γ‐ray Telescope based on the conversionof gamma‐rays into electron‐positron pairs andis arranged in a 4×4 array of 16 identical towers.
Tracker/Converter (TKR):Si‐strip detectors∼ 80 m2 of siliconW conversion foils1.5 X0 on‐axis18 X‐Y planes ∼ 106 channelsHighly granularHigh precision trackingAverage plane PHA
Calorimeter (CAL):1536 CsI(Tl) crystals8.6 X0 on‐axis2 PIN‐PD per Xtal endlarge dynamic range per Xtal (2MeV‐60GeV)Hodoscopic (8 layers with 12 xtals)Shower profile reconEM vsHAD separation
Anti‐Coincidence (ACD):Segmented (89 tiles)Self‐veto @ high energy limited0.9997 detection efficiency
F. Longo – 7th AGILE Workshop, Frascati 2009
LAT Instrument Response Functions
on‐axis60° off‐axis
60° off‐axis
on‐axis
transient classsource classdiffuse class
Effective area
(cm
2 )En
ergy dispe
rsion
68% con
t
The Large Area Telescope on the Fermi Gamma‐ray Space TelescopeAtwood, W. B. et al. 2009, ApJ, 697, 1071
~EGRET
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Gamma‐ray Burst Monitor (GBM)
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Bismuth Germanate (BGO)Scintillation Detector
– spectral coverage: 150 keV – 40 MeV
LAT
(12) Sodium Iodide (NaI)Scintillation Detectors
– spectral coverage: 8 keV – 1 MeV
MSFC, MPE, Los Alamos collaboration PI: W. Paciesas co‐PI: J. Greiner
F. Longo – 7th AGILE Workshop, Frascati 2009
Launch June 11, 2008
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… few weeks later: First Light!
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August 26, 2008NASA Renames Observatory for Fermi, Reveals Entire Gamma‐Ray SkyGLAST has been renamed the Fermi Gamma‐ray Space Telescope. The new name honors Prof. Enrico Fermi (1901 ‐ 1954), a pioneer in high‐energy physics.
Four days of all-sky survey engineering data.
F. Longo – 7th AGILE Workshop, Frascati 2009
… and Pulsars using early engineering data
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Geminga: P=237 ms
Crab: P =33 msVela: P=89.3 ms
F. Longo – 7th AGILE Workshop, Frascati 2009
LAUNCH L+60 daysweek week week week month 12 m o n t h s
spacecraftturn‐on checkout
LAT, GBMturn‐on check out
“first light”whole sky
pointed + sky survey tuning
Start Year 1 Science Ops
Start Year 2 Science Ops
initial tuning/calibrations in‐depth instrument studies
sky survey + ~weekly GRB repoints + extraordinary TOOs
25 august 2009continuous
release of newphoton data
Observatoryrenaming
Release Flaring and Monitored Source Info
GBM and LAT GRB Alerts
LAT 6‐monthhigh‐confidencesource releaseGSSC science tools advance release
LAT Year 1 photondata release PLUSDiffuse Model
2ndSymposiumJune 11, 2008
August 12, 2009
1st LAT Catalog
Operations Timeline Overview
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LAT High Confidence Bright Source list
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3 months LAT data – 206 sources with > 10 σ significance only 60 associated with EGRET sources – variability!
F. Longo – 7th AGILE Workshop, Frascati 2009Abdo et al. 2009, ApJS, 183, 46
A sample of sources
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5 top sources within our Galaxy • the quiet sun (moving in the map)• LSI +61 303 ‐ a high‐mass X‐ray binary• PSR J1836+5925 – a gamma‐ray‐only pulsar• 47 Tucanae – a globular cluster of stars • unidentified, new and variable, 0FGL J1813.5‐1248
5 top sources beyond our Galaxy • NGC 1275 – the Perseus A galaxy• 3C 454.3 – a wildly flaring blazar• PKS 1502+106 – a flaring 10.1 billion ly away blazar• PKS 0727‐115 – a quasar• unidentified known, 0FGL J0614.3‐3330
11‐3‐20096 month sky
F. Longo – 7th AGILE Workshop, Frascati 2009
NASA's Fermi Telescope Probes Dozens of Pulsars
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Science, 322, 1218, 2008 – CTA1 the first γ‐ray only pulsar Science Vol 325, 840 (2009) – 16 γ‐ray only pulsarScience Vol 325, 848 (2009) – A population of ms γ‐ray pulsarsSeveral ApJ papers on specific meaningful pulsars (Vela, J20210, J1028 ….)Pulsar catalog submitted
F. Longo – 7th AGILE Workshop, Frascati 2009
Gamma ray burst LAT+GBM
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• 1 year from GBM turn on: 252 GRBs, 138 in the LAT FoV• 10 GRB detection at high energy so far (9 in the first year)• 090926
F. Longo – 7th AGILE Workshop, Frascati 2009
Example of a long burst: GRB 080916C
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• First high‐energy GRB (>100 MeV) with known redshift
• Sample >100 MeV – 14 events >1 GeV– Highest energy photon
(E = 13.2 GeV after 16.5 s)from GRB with z
– Apparent isotropic energy release is 8.8×1054 ergs, ~5 M(collimation very likely)
– Science 323, 1688 (2009)
T0
F. Longo – 7th AGILE Workshop, Frascati 2009
GRB 080916C
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• Region ±30° aroundGRB 080916C
– Observed at ~50˚ angle
• RGB= <100 MeV,100 MeV ‐ 1 GeV,>1 GeV
• Starts at T0‐200 s• 5 s between pictures
Dark zone = outside LAT field of view
GROND position
Photometric redshift of z=4.35 +/‐ 0.15
F. Longo – 7th AGILE Workshop, Frascati 2009
GRB 090902B: the brightest one
• 11:05:15 UT – GBM GCN alert notice – LAT ARR triggered• 21:19:03 UT – 1st GBM circular (GCN 9866) • 22:48:18 UT – 1st LAT circular (GCN 9867) • 03:00:57 UT – Swift/XRT afterglow candidate (GCN
9868) • 04:57:44 UT – Swift/UVOT observations, no afterglow
confirmation (GCN 9869) • 04:57:44 UT – enhanced Swift/XRT position (GCN 9871) • 07:36:42 UT – Fermi LAT and GBM refined analysis (GCN
9872) • 08:23:17 UT – Gemini‐N absorption redshift (GCN 8973)
z=1.822 (GMOS spectrograph)
• LAT pointing in celestial coordinates from ‐120 s to 2000 s
– Red cross = GRB 090902B
– Dark region = occulted by Earth
– White line = LAT FoV
– Blue lines = 20° (Earth avoidance angle) / 50°above horizon
– White points = LAT transient events (no cut on zenith angle)
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GRB 090902B light curves
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• Rdshift = 1.822• Sample >100 MeV
– 39 events >1 GeV– Highest energy photon
E = 33.4 GeV after 82 s– Apparent isotropic energy release
is 3.63×1054 ergs, ~2.5 M(collimation very likely)
– arXiv: 0909.2470 (Submitted to ApJL)
F. Longo – 7th AGILE Workshop, Frascati 2009
Galactic sources
• 6 EGRET pulsars 46 Fermi pulsars– 16 gamma‐ray only PSR – 8 ms PSR
• Globular clusters
• Pulsar Wind Nebula
• Supernova remnants
• X‐ray binaries
• So far, EGRET unidentified are pulsars.21
« Pulsar Wind Nebula = PWN »Chandra X‐ray imagePulsar in the middle
Crab supernova remnant (optical, Hubble) Supernova seen in 1054
F. Longo – 7th AGILE Workshop, Frascati 2009
Discovery of First Gamma‐ray‐only Pulsar
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A radio-quiet, gamma-ray only pulsar, in Supernova Remnant CTA1
Age ~(0.5 – 1)x104 yearsDistance ~ 1.4 kpcDiameter ~ 1.5°
P ~ 317 msPdot ~ 3.6E‐13
• Spin‐down luminosity ~1036 erg s‐1, sufficient to supply the PWN with magnetic fields and energetic electrons.
• The γ‐ray flux from the CTA 1 pulsar corresponds to about 1‐10% of Erot (depending on beam geometry)
• Science, 322, 1218, 2008
Quick discovery enabled by• large leap in key capabilities• new analysis technique (Atwood et al)
F. Longo – 7th AGILE Workshop, Frascati 2009
The Pulsing sky
Vela Pulsar – Phase‐averaged SED
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bcEEeENEN )/(
0)( −Γ= Consistent with b=1 (simple exponential)
b=2 (super‐exponential) rejected at 16.5σ
No evidence for magnetic pair attenuation:Near-surface emission ruled out
0.051.51
0.042.9 0.1 GeVcE
+Γ = −
−= ±
F. Longo – 7th AGILE Workshop, Frascati 2009
Abdo, A. A. et al. 2009, ApJ, 696, 1084
Crab pulsar
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P = 33 ms
>100 MeV (Fermi)Phase 0.002 per bin(66 μs per bin)
1.4 GHz radio(Nançay & Jodrell Bank)
Unprecedented timing accuracy.
F. Longo – 7th AGILE Workshop, Frascati 2009
Abdo, A. A. et al. 2009, ApJ submitted
Crab
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Off‐pulse (nebula)
Synchrotron and Inverse Compton components
ON‐pulse (pulsar)
F. Longo – 7th AGILE Workshop, Frascati 2009
Abdo, A. A. et al. 2009, ApJ submitted
About the LAT pulsars
• Generally (but not always), two peaks separated by ½ rotations.
• Generally (but not always), gamma peak offset from radio.
• Exponential cut‐offs at few GeV.• Favors outer magnetosphere emission.
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LAT spectra for PSR J2021+3651Abdo, A. A. et al. 2009, ApJ, 700, 1059
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Blind search pulsars: the link to SNRs and PWNe
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Science, 325, 14th August, 840
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The flaring and variable sky
• ~45 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
• Galactic plane transients: – J0910‐5041, 3EG J0903‐
3531, J1057‐6027
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Animation of 3 months data set
• 87 days starting with August 4 ‐ 1 frame per day
• Northern (left) and Southern (right) hemispheres in orthographic proj.
Gammas from earth limb – pole pointing obs
Credit: J. Ballet30
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Sun and Moon
Active Galactic Nuclei (AGN)
• Almost all galaxies contain a massive black hole
– 99% of them are (almost) silent (e.g. our Galaxy)– 1% is active (mostly radio-quiet AGNs)
• BH+disk: most of the emission in the UV-X-ray band– 0.1% is radio loud: jets mostly visible in the radio
• Active galactic nuclei (AGN) are galaxies with extraordinarily luminous cores powered by super massive black holes
• In the most luminous AGN, the visible light exceeds the combined output of an entire galaxy's worth of stars, even though the light‐emitting area is only about the size of our solar system.
• In the standard model of AGN, cold material close to the central black hole forms an accretion disc
• At least some accretion discs produce jets, twin highly collimated and fast outflows that emerge in opposite directions from close to the disc
• Blazars are objects emitting non‐thermal radiation across the entire electromagnetic spectrum from a relativistic jet that is viewed closely along the line of sight
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Blazars
Blazar characteristics• Compact radio core, flat or
inverted spectrum• Extreme variability at all
frequencies• High optical and radio
polarization• FSRQs: bright broad (>2000
km/s) emission lines often evidences for the “blue bump” (acc. disc)
• BL Lac: weak (EW<5 Å) emission lines no signatures of accretion
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LAT Bright AGN Sample (LBAS)
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106 AGN (LBAS):2 Radio Galaxies
•Centaurus A•NGC 1275
104 Blazars:•58 FSRQ•42 BLLac• 4 Unknown
35 AGNs (both |b|>10° and |b|< 10°) sources in 3EG catalog with a comparable flux: 20 FSRQ, 11 BLLacs, 3 Unknown, 1 Radio galaxy (Cen A) + 2 AGNs at |b|<10°
4 NEW BLAZARS DISCOVERED on the basis of the LAT detections
(present in the CRATES catalog)
F. Longo – 7th AGILE Workshop, Frascati 2009
Deviation from simple power law from an AGNAbdo, A. A. et al. 2009, ApJ, arXiv: 0904.4280
3C454.3
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3C454.3Super‐massive black hole8 billion light‐years from us
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Blazar: Spectral Energy Distribution
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3C454.3 (FSRQ)
F. Longo – 7th AGILE Workshop, Frascati 2009
The LAT view on diffuse gamma‐ray emission
Work to analyze and understand diffuse emission over the entire sky and broader energy range is in progress
100 MeV – 10 GeV
Spectra shown for mid‐latitude range → EGRET GeV excess in this region of the sky is not confirmed
Sources are a minor component
LAT errors are systematic dominated and estimated ~10%
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Abdo, A. A. et al. 2009, PRL submitted
Science impact by citation
• “Measurement of the Cosmic Ray e++e‐ Spectrum from 20 GeV to 1 TeV with the Fermi Large Area Telescope” (05/2009)– Cited across a broad range ‐ cosmic‐ray, astronomy,
particle physics (D0, BABAR)• “Fermi/Large Area Telescope Bright Gamma‐Ray
Source List” (07/2009)• “Fermi Observations of High‐Energy Gamma‐Ray
Emission from GRB 080916C” (03/2009)• “Bright Active Galactic Nuclei Source List from the
First Three Months of the Fermi Large Area Telescope All‐Sky Survey” (07/2009)
• “The Fermi Gamma‐Ray Space Telescope Discovers the Pulsar in the Young Galactic Supernova Remnant CTA 1” (11/2008)
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~140
~60
~50
~40
~25
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• Gamma‐ray detection:– Look for an electromagnetic cascade. Reject charged primaries.
• Electron detection: – Also an electromagnetic cascade! (Loosen charge veto, tighten the
other cuts)– Fermi‐LAT does not distinguish between e‐ and e+, we use the term
electrons to refer to the sum of the two.
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LAT
F. Longo – 7th AGILE Workshop, Frascati 2009
The LAT as CR telescope
Event Topology
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Candidate electron 475 GeV raw energy, 834 GeV reconstructedTransverse shower size: 23.2 mmFractional extra clusters: 1.48Average ACD tile energy: 2.46 MeVEnergy reconstruction quality: 0.73
Candidate hadron823 GeV raw energy, 1 TeV reconstructed
Transverse shower size: 34.4 mmFractional extra clusters: 0.17Average ACD tile energy: 10.2 MeVEnergy reconstruction quality: 0.15
Well defined (not fully contained) symmetric shower in the calorimeterClean main track with extra clusters close to the track (note backsplash from the calorimeter)Relatively few ACD tile hits, mainly in conjunction with the track
Large and asymmetric shower profile in the calorimeter.Small number of extra clusters around main track, many clusters away from the trackDifferent ACD tile topology and large energy deposit per ACD tile
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Total statistics collected for 6 months of Fermi LAT observations4 million electrons above 20 GeV> 400 electrons in last energy bin (770‐1000 GeV)
F. Longo – 7th AGILE Workshop, Frascati 2009
High electron/positron energy CR spectrum
Some possible interpretations
• Several papers already published to explain electron spectrum
– Together with other observations (positron fraction, diffuse γ‐ray)
Source stocasticity
Grasso et al. 2009
Dark Matter
Strumia et al. 2009
Pulsars
Grasso et al. 2009
Secondary CR acc.
Blasi 2009
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Conclusions
• The Fermi Gamma‐Ray Space Telescope has been performing very well and stably for the first year of operations
• Photon data are public since August 25, 2009– Join the fun at http://fermi.gsfc.nasa.gov/ssc/
• Wealth of results in γ‐ray astrophysics– ~ 50 pulsars detected, many only in γ‐rays– many flaring active galaxies observed– 11 GRBs at high energy
• First high statistics measurement of CR electron spectrum (20 GeV – 1 TeV)
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Fermi symposium
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2009 Fermi Symposium2‐5 November 2009Hyatt Regency Washington, Capitol Hill
October 1 ‐ Early registration and abstract deadline.
F. Longo – 7th AGILE Workshop, Frascati 2009
Scineghe 2009
45F. Longo – 7th AGILE Workshop, Frascati 2009
http://glastweb.pg.infn.it/scineghe2009/