The Gamma ray sky seen by. Telescope. F.Longo INFN Trieste, CIFS Torino. on behalf of the Fermi LAT collaboration

Transcription

1 The Gamma ray sky seen by the Fermi Large Area Telescope. F.Longo INFN Trieste, CIFS Torino on behalf of the Fermi LAT collaboration 7 th AGILE Workshop Frascati, 29 settembre 2009

2 Outline Introduction to the Fermi Gamma-ray Space Telescope The Large Area Telescope Astrophysical results Solar System sources PSR and Galactic Diffuse emission Active Galactic Nuclei Gamma-ray Bursts The electron spectrum Interpretations Conclusions 2

3 The Observatory (GLAST) Large AreaTelescope (LAT) 20 MeV >300 GeV Gamma ray Burst Monitor (GBM) NaI and BGO Detectors 8 kev 30 MeV 3

4 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 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. 4

5 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. Huge increment in capabilities Draws the interest of both the High Energy Particle Physics and High Energy Astrophysics communities. 5

6 Overview of the Large Area Telescope (LAT) The LAT is a γ ray Telescope based on the conversion of gamma rays into electron positron pairs and is arranged in a 4 4 array of 16 identical towers. Tracker/Converter (TKR): Si strip detectors 80 m 2 of silicon W conversion foils 1.5 X0 on axis 18 X Y planes 10 6 channels Highly granular High precision tracking Average plane PHA Anti Coincidence (ACD): Segmented (89 tiles) Self high energy limited detection efficiency Calorimeter (CAL): 1536 CsI(Tl) crystals 8.6 X0 on axis 2 PIN PD per Xtal end large dynamic range per Xtal (2MeV 60GeV) Hodoscopic (8 layers with 12 xtals) Shower profile recon EM vshad separation 6

7 LAT Instrument Response Functions Effective area (cm 2 ) transient class source class diffuse class ~EGRET 60 off axis on axis Energy dispersion 68% cont on axis 60 off axis The Large Area Telescope on the Fermi Gamma ray Space Telescope Atwood, W. B. et al. 2009, ApJ, 697,

8 Gamma ray Burst Monitor (GBM) MSFC, MPE, Los Alamos collaboration PI: W. Paciesas co PI: J. Greiner Bismuth Germanate (BGO) Scintillation Detector LAT spectral coverage: 150 kev 40 MeV (12) Sodium Iodide (NaI) Scintillation Detectors spectral coverage: 8 kev 1 MeV 8

9 Launch June 11,

10 few weeks later: First Light! Four days of all-sky survey engineering data. August 26, 2008 NASA Renames Observatory for Fermi, Reveals Entire Gamma Ray Sky GLAST has been renamed the Fermi Gamma ray Space Telescope. The new name honors Prof. Enrico Fermi ( ), a pioneer in high energy physics. 10

11 and Pulsars using early engineering data Geminga: P=237 ms Vela: P=89.3 ms Crab: P =33 ms 11

12 Operations Timeline Overview spacecraft turn on checkout LAT, GBM turn on check out first light whole sky Observatory renaming pointed + sky survey tuning Start Year 1 Science Ops sky survey + ~weekly GRB repoints + extraordinary TOOs August 12, 2009 Start Year 2 Science Ops week week week week month 12 m o n t h s LAUNCH June 11, 2008 L+60 days initial tuning/calibrations in depth instrument studies 2nd Symposium 1 st LAT Catalog Release Flaring and Monitored Source Info GBM and LAT GRB Alerts 25 august 2009 continuous release of new photon data LAT 6 month high confidence source release GSSC science tools advance release LAT Year 1 photon data release PLUS Diffuse Model 12

13 LAT High Confidence Bright Source list 3 months LAT data 206 sources with > 10 σ significance only 60 associated with EGRET sources variability! Abdo et al. 2009, ApJS, 183, 46 13

14 A sample of sources 6 month sky top sources within our Galaxy the quiet sun (moving in the map) LSI a high mass X ray binary PSR J a gamma ray only pulsar 47 Tucanae a globular cluster of stars unidentified, new and variable, 0FGL J top sources beyond our Galaxy NGC 1275 the Perseus A galaxy 3C a wildly flaring blazar PKS a flaring 10.1 billion ly away blazar PKS a quasar unidentified known, 0FGL J

15 NASA's Fermi Telescope Probes Dozens of Pulsars Science, 322, 1218, 2008 CTA1 the first γ ray only pulsar Science Vol 325, 840 (2009) 16 γ ray only pulsar Science Vol 325, 848 (2009) A population of ms γ ray pulsars Several ApJ papers on specific meaningful pulsars (Vela, J20210, J1028.) Pulsar catalog submitted 15

16 Gamma ray burst LAT+GBM 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)

17 Example of a long burst: GRB C 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 ergs, ~5 M (collimation very likely) Science 323, 1688 (2009) T 0 17

18 GRB C Region ±30 around GRB C Observed at ~50 angle RGB= <100 MeV, 100 MeV 1 GeV, >1 GeV Starts at T s 5 s between pictures Dark zone = outside LAT field of view GROND position Photometric redshift of z=4.35 +/

19 GRB B: the brightest one 11:05:15 UT GBM GCN alert notice LAT ARR triggered 21:19:03 UT 1 st GBM circular (GCN 9866) 22:48:18 UT 1 st 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 B 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) 19

20 GRB B light curves Rdshift = Sample >100 MeV 39 events >1 GeV Highest energy photon E = 33.4 GeV after 82 s Apparent isotropic energy release is ergs, ~2.5 M (collimation very likely) arxiv: (Submitted to ApJL) 20

21 Galactic sources 6 EGRET pulsars 46 Fermi pulsars 16 gamma ray only PSR 8 ms PSR Globular clusters Pulsar Wind Nebula Crab supernova remnant (optical, Hubble) Supernova seen in 1054 Supernova remnants X ray binaries So far, EGRET unidentified are pulsars. «Pulsar Wind Nebula = PWN» Chandra X ray image Pulsar in the middle 21

22 Discovery of First Gamma ray only Pulsar A radio-quiet, gamma-ray only pulsar, in Supernova Remnant CTA1 Quick discovery enabled by large leap in key capabilities new analysis technique (Atwood et al) P ~ 317 ms Pdot ~ 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 Age ~(0.5 1)x10 4 years Distance ~ 1.4 kpc Diameter ~

23 The Pulsing sky

24 Vela Pulsar Phase averaged SED N ( E) = N 0 E Γ e ( E / E c ) b Consistent with b=1 (simple exponential) Γ= = 2.9 ± 0.1 GeV E c b=2 (super exponential) rejected at 16.5σ No evidence for magnetic pair attenuation: Near-surface emission ruled out Abdo, A. A. et al. 2009, ApJ, 696,

25 Crab pulsar P = 33 ms >100 MeV (Fermi) Phase per bin (66 μs per bin) 1.4 GHz radio (Nançay & Jodrell Bank) Unprecedented timing accuracy. Abdo, A. A. et al. 2009, ApJ submitted 25

26 Crab Abdo, A. A. et al. 2009, ApJ submitted Off pulse (nebula) Synchrotron and Inverse Compton components ON pulse (pulsar) 26

27 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. LAT spectra for PSR J Abdo, A. A. et al. 2009, ApJ, 700,

28 Blind search pulsars: the link to SNRs and PWNe Science, 325, 14 th August,

29 The flaring and variable sky ~45 Astronomers telegrams Discovery of new gamma ray blazars: PKS , PKS Flares from known gamma ray blazars: 3C454.3, PKS ,3C273, AO , PSK , 3C66A, PKS Galactic plane transients: J , 3EG J , J

30 Animation of 3 months data set Gammas from earth limb pole pointing obs 87 days starting with August 4 1 frame per day Northern (left) and Southern (right) hemispheres in orthographic proj. 30 Credit: J. Ballet

31 Sun and Moon

32 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 32

33 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 33

34 LAT Bright AGN Sample (LBAS) 106 AGN (LBAS): 2 Radio Galaxies Centaurus A NGC 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) 34

35 3C C454.3 Super massive black hole 8 billion light years from us Deviation from simple power law from an AGN Abdo, A. A. et al. 2009, ApJ, arxiv:

36 Blazar: Spectral Energy Distribution 3C454.3 (FSRQ) 36

37 The LAT view on diffuse gamma ray emission Abdo, A. A. et al. 2009, PRL submitted 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% Work to analyze and understand diffuse emission over the entire sky and broader energy range is in progress 37

38 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 C (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) ~140 ~60 ~50 ~40 ~25 38

39 The LAT as CR telescope 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. LAT 39

40 Event Topology Candidate electron 475 GeV raw energy, 834 GeV reconstructed Transverse shower size: 23.2 mm Fractional extra clusters: 1.48 Average ACD tile energy: 2.46 MeV Energy reconstruction quality: 0.73 Candidate hadron 823 GeV raw energy, 1 TeV reconstructed Transverse shower size: 34.4 mm Fractional extra clusters: 0.17 Average ACD tile energy: 10.2 MeV Energy reconstruction quality: 0.15 Well defined (not fully contained) symmetric shower in the calorimeter Clean 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 track Different ACD tile topology and large energy deposit per ACD tile 40

41 High electron/positron energy CR spectrum Total statistics collected for 6 months of Fermi LAT observations 4 million electrons above 20 GeV > 400 electrons in last energy bin ( GeV) 41

42 Some possible interpretations Several papers already published to explain electron spectrum Together with other observations (positron fraction, diffuse γ ray) Pulsars Dark Matter Grasso et al Secondary CR acc. Strumia et al Source stocasticity Blasi 2009 Grasso et al

43 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 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) 43

44 Fermi symposium 2009 Fermi Symposium 2 5 November 2009 Hyatt Regency Washington, Capitol Hill October 1 Early registration and abstract deadline. 44

45 Scineghe