The Gamma ray sky seen by the Fermi Large Area...

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

2

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

3F. Longo – 7th AGILE Workshop, Frascati 2009

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

4

• 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.

5

Huge increment in capabilitiesDraws the interest of both the High Energy Particle Physics and

High Energy Astrophysics communities.


Overview of the Large Area Telescope (LAT)

6

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


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


Gamma‐ray Burst Monitor (GBM)

8

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


Launch June 11, 2008


… few weeks later: First Light!

10

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.


… and Pulsars using early engineering data

11

Geminga: P=237 ms

Crab: P =33 msVela: P=89.3 ms


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


LAT High Confidence Bright Source list

13

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

14

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


NASA's Fermi Telescope Probes Dozens of Pulsars

15

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


Gamma ray burst LAT+GBM

16

• 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


Example of a long burst: GRB 080916C

17

• 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


GRB 080916C

18

• 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


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)


GRB 090902B light curves

20

• 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)


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


Discovery of First Gamma‐ray‐only Pulsar

22

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)


The Pulsing sky

Vela Pulsar – Phase‐averaged SED

24

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 = −

−= ±


Abdo, A. A. et al. 2009, ApJ, 696, 1084

Crab pulsar

25

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.


Abdo, A. A. et al. 2009, ApJ submitted

Crab

26

Off‐pulse (nebula)

Synchrotron and Inverse Compton components

ON‐pulse (pulsar)


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.

27

LAT spectra for PSR J2021+3651Abdo, A. A. et al. 2009, ApJ, 700, 1059


Blind search pulsars: the link to SNRs and PWNe

28

Science, 325, 14th August, 840


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


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


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


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


LAT Bright AGN Sample (LBAS)

34

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)


Deviation from simple power law from an AGNAbdo, A. A. et al. 2009, ApJ, arXiv: 0904.4280

3C454.3

35

3C454.3Super‐massive black hole8 billion light‐years from us


http://www.arxiv.org/abs/0904.4280

Blazar: Spectral Energy Distribution

36

3C454.3 (FSRQ)


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%


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)

38

~140

~60

~50

~40

~25


• 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.

39

LAT


The LAT as CR telescope

Event Topology

40

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


41

Total statistics collected for 6 months of Fermi LAT observations4 million electrons above 20 GeV> 400 electrons in last energy bin (770‐1000 GeV)


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

42

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)


Fermi symposium

44

2009 Fermi Symposium2‐5 November 2009Hyatt Regency Washington, Capitol Hill

October 1 ‐ Early registration and abstract deadline.


Scineghe 2009


http://glastweb.pg.infn.it/scineghe2009/

The Gamma ray sky seen by the Fermi Large Area...

Documents

Transcript of The Gamma ray sky seen by the Fermi Large Area...