Anders W. Borgland. On behalf of the Fermi/LAT Collaboration. Fermi LAT ISOC/SLAC

Transcription

1 Fermi Status And Prospects Fermi LAT ISOC/SLAC On behalf of the Fermi/LAT Collaboration 1

2 A Broad Overview Of The Fermi Mission From GLAST To Fermi The Fermi Mission LAT Instrument Science Operations Center Detector Characteristics And Science Capabilities LAT On-Orbit Performance First Physics Results And Prospects 2

3 From GLAST To Fermi GLAST was renamed the Fermi Gamma-Ray Space Telescope on August 26,

4 Why Gamma-Rays... In Space? The most violent phenomena in the Universe produce gamma-rays! Non-thermal production Particle acceleration Gamma-rays can be produced by multiple mechanisms: Hadronic: Hadrons ---> πº ---> Gamma-rays Leptonic: Bremsstrahlung, Inverse Compton, synchrotron emission... Gamma-rays: Advantages: Point straight back to the production sources Photon energy related to the original energy Identify the original production mechanism Disadvantage: Can not penetrate the Earth atmosphere Earth based Atmospheric Cherenkov Telescopes: Use the Earth atmosphere as the detector Difficult to go below ~100 GeV Spaceborne gamma-ray experiments are filling a critical energy gap! 4

5 The Fermi Mission Two instruments covering the energy range from 8 kev to >300 GeV: Large Area Telescope (LAT) Gamma-Ray Burst Monitor (GBM) LAT: Unprecedented view of the gamma-ray sky: 30x improvement in sensitivity! Covering largely unexplored GeV domain GBM: Sees all of the un-occulted sky Hard x-rays and soft gamma-rays 5 year lifespan (design): Goal is 10 years Launched: 09:05 PDT June 11, days Commissioning phase nomsciops: Fermi is now calibrated. Taking data in nominal Science Configuration! Fermi data will be publicly available through NASA after the first year! 5

6 Fermi In Space - Circular orbit with a 94 minute period - Altitude: 565 km, Inclination: 25.5 degrees SAA South Atlantic Anomaly: - Area of high particle background - mostly low energy protons. - PMT HV in LAT ACD ramps down and the LAT stops data taking. - We spend about 15% of the time in the SAA. - Boundary optimized in the Commissioning phase. 6

7 All Sky Survey Mode LAT sees 20% of the sky at any moment: Covers the whole sky every 3h! Every point in the sky receives ~30 minutes of exposure every 3h. Rocking: Space craft rocks LAT ±35 degrees about the zenith direction every orbit. Uniform exposure: Achieved within a day! Less need for Pointed Observations: Can be done for interesting targets LAT source sensitivities for exposures of 100 seconds, one orbit, one day and one year: 7

8 Fermi LAT Collaboration United States California State University at Sonoma University of California at Santa Cruz - Santa Cruz Institute of Particle Physics Goddard Space Flight Center Laboratory for High Energy Astrophysics Naval Research Laboratory Ohio State University Stanford University (SLAC and HEPL/Physics) University of Washington University of Denver Purdue University France IN2P3, CEA/Saclay Italy INFN, ASI Japan Hiroshima University ISAS/JAXA, RIKEN Tokyo Inst of Technology Spain ICREA and Inst de Ciencies de l Espi PI: Peter Michelson (Stanford & SLAC) ~270 Members (including ~90 Affiliated Scientists, plus 37 Postdocs, and 48 Graduate Students) Cooperation between NASA and DOE, with key international contributions from France, Italy, Japan and Sweden. Managed at SLAC National Accelerator Laboratory. Germany MPE Sweden Royal Institute of Technology (KTH) Stockholm University 8

9 GLAST MISSION ELEMENTS GPS µsec Large Area Telescope & GBM DELTA 7920H - Telemetry 1 kbps Fermi Spacecraft TDRSS SN S & Ku S - GN Schedules Mission Operations Center (MOC) GRB Coordinates Network Fermi Science Support Center Schedules Alerts LAT Instrument Science Operations Center (SLAC) White Sands HEASARC GBM Instrument Operations Center Data, Command Loads 9

10 LAT Instrument Science Operations Center The LAT Instrument Science Operations Center is located at SLAC. ISOC is responsible for: LAT Mission Planning LAT Flight Software LAT Science Data Processing and Science Data Monitoring Provide Analysis products to end users: Export final products to Fermi Science Support Center at Goddard Space Flight Center Automated Science Processing: Provide automated analyses with rapid turn-around:» Flaring sources» Refinement of and blind search for Gamma-ray bursts Light curves for pre-selected list of sources Some of this will be released to the general public even before the first year! About 6h-8h after we have taken the data in space the end users have the final analysis products on their laptops! 10

11 Fermi Science Support Center At GSFC Public gateway to Fermi Data: Fermi Science Support Center at Goddard Space Flight Center: Publicly available data products LAT monitored sources 11

12 Multiwavelength Campaigns Combining data sets from different experiments in particle physics: Gain is only increased statistics Astrophysics: Any single detector only looks in a specific wavelength range! Objects radiate in many different wavelenghts. Need to combine data sets from many different Observatories to get a complete picture: Gamma-ray, x-ray, visible,... Leads naturally to: Cooperation! Multiwavelength Campaigns! LAT's excellent angular resolution improves source localization and is crucial for Multiwavelength campaigns! 12

13 Fermi Observatory Two instruments integrated into one Observatory: Large Area Telescope (LAT): 20 MeV >300 GeV Gamma-Ray Burst Monitor (GBM): 8 kev 30 MeV LAT LAT is here shown without the ACD. LAT Power: 650 W and Weight: 2789 kg GBM NaI (x12) 8 kev 1 MeV - Burst triggering and localization - Spectroscopy GBM BGO (x2) 150 kev 30 MeV - Spectroscopy 13

14 LAT: A Particle Physics Detector In Space LAT is a pair-producing telescope: - A 4x4 grid with 16 identical towers for a high degree of redundancy. Each tower: - TKR + CAL+ Electronics box Trackers are covered by the Anti-Coincidence Detector. Single sided Silicon strip detector: - 36 alternating x and y layers: strips/layer µm pitch - Tungsten converters: - 12x(3%X0) + 4x(18%X0) - Optimized for Multiple scattering and effective area. Time-Over-Threshold: - For particle identication purposes. Total of >80m² of Si and 864k channels! CsI (TI) Calorimeter: radiation lenghts for normal incidence Total per tower: 10.1 X0 Finely segmented hodoscopic array: - 8 layers with 12 crystals per layer Detailed shower development profil: - Can estimate the leaked energy - Compensates for limited depth LAT: - Redundant readout capabilities built into all subsystems - No consumables Anti-Coincidence Detector: - 89 plastic tiles and 8 ribbons covering the trackers Crucial for rejecting the charged particle background: - Requirement: 99.97% efficiency Finely segmented: - Avoid self-veto effect 14

15 LAT Trigger And Software Filters LAT 'L1' Trigger: - Hardware based Workhorse trigger: - TKR 3 consecutive x-y layer pairs (six planes) - Very robust and with a high level of redundancy Additional triggers: - CAL: >100 MeV or >1 GeV in a single crystal - CNO: Large energy deposit in an ACD tile - ROI: - Minimum Ionizing Particle (MIP) in ACD tiles - Used for background rejection LAT 'L3 Trigger': - Software filters running on two Event Processing Units on the LAT Filters: - Gamma-filter for background rejection - Diagnostic filter - Heavy Ionizing Particle and Minimum Ionizing Particle filters for calibration purposes Rate reduction: - From 2.5 khz to 450 Hz: <2 Hz are photons - Main background rejection is done on the ground - Written to a Solid State Recorder on the Space Craft - Downlinked through TDRSS every 3h Allowed bandwidth: Mb/s LAT Gamma-Ray Burst algorithm: - GRB finding algorithm running on the LAT Complements the GBM: - Improved localization - Different energy range Autonomous Repoint Request can be sent to the space craft from both the LAT and the GBM. 15

16 Analysis Method e+e- combined into a gamma, projected back into the ACD Photon converts to e+e- in the Tungsten converter 60 cm e+ and e- tracked through the tracker: - Small opening angle - No magnetic field Energy measured in the calorimeter. Final information used for analysis (FITS format): - Photon direction in the sky - Photon energy All the photon data - Photon arrival time fits on a laptop! - Instrument livetime - Instrument Response Functions 21 cm Detailed detector information for all events are in a traditional particle physics Root format and does not fit on a laptop! 16

17 LAT Performance Energy Resolution: ~10% PSF (68%) at 100 MeV: ~3.5 degrees PSF (68%) at 10 GeV: ~0.1 degree Field of view: 2.4 Sr PSF: Point Spread Function i.e. angular resolution 17

18 Success Is Not A Coincidence LAT completed an extensive testing program before launch: Thermal-vacuum, vibration, acoustic,... Each component tested individually: Then tested at each step of integration: LAT integration and Observatory integration Alltogether, we had >3 years of cosmic ray data taking with the LAT: Data quality for every single run was: Formally reviewed, investigated if necessary, signed off! One hardware failure during Integration & Test: Lost redundant readout capability in one TKR layer One out of 576 layers! No subsequent hardware failures: During launch or on orbit! Validation of the LAT MC: Beam tests at CERN and GSI in 2006 with real flight-spare towers Successful combination of two cultures! We put a particle physics detector... in space! NASA End-To-End tests Particle Physics Data Challenges 18

19 Standing On The Shoulders Of EGRET Fermi is the successor experiment to the: Energetic Gamma Ray Experiment Telescope (EGRET), rd EGRET Catalog: data First all-sky survey above 50 MeV Part of the Compton Gamma-Ray Observatory (CGRO) EGRET Data (5 years) 19

20 LAT Performance - I Huge field of view: See 20% of the sky at any given time Scan the complete sky every 3h Excellent Angular Resolution (PSF): 170/271 of EGRET sources not firmly identified Huge effective area! >9000 cm² Four orders of magnitude in energy: 20 MeV - >300 GeV EGRET could not go much beyond 10 GeV: Self-Veto effect monolithic ACD GeV range largely unexplored! >x4 better than EGRET >x3 better than EGRET >5x larger than EGRET Factor 30 improvement in sensitivity! Factor >100 above 10 GeV! LAT is a qualitative leap forward that will open up new directions in gamma-ray physics! 20

21 LAT Performance - II Low readout deadtime: x4000 smaller than EGRET 26.5 µs Essential for rapid transients like Gamma-Ray Bursts: Thousands of photons arriving within a few seconds LAT can read them out without significant deadtime! Excellent absolute time precision: Better than 10 µs: LAT uses a GPS based timing system Essential for Pulsar studies: Enables LAT to study pulsars for (sub)structures EGRET: 5 years of data LAT Simulations: 1 year 21

22 LAT Science Objectives - I Source catalog: LAT will find thousands of new gamma-ray sources: Population studies! Excellent angular resolution will help resolve the gamma-ray sky: Including the unidentified EGRET sources Essential for Multi-Wavelength campaigns! Diffuse emission: Improved source localization will improve the understanding of the origin of the background diffuse emission. Iterative process coupled to source detection Characterizing individual gamma-ray sources: Identify the particle acceleration mechanisms in celestial sources: Active Galactic Nuclei, Blazars,... Characterize transients and Gamma-Ray Bursts: The high energy behaviour and time development Pulsar studies: The unexplored GeV domain can be used to discriminate between different Pulsar emission models. 22

23 Active Galactic Nuclei 23

24 LAT Science Objectives - II Probe the nature of Dark Matter and Dark Matter distribution in the galaxy. Weakly Interacting Massive Particle (WIMP): Two types of WIMP annihilation signals into gamma-rays. Continous flux below the mass of the WIMP: Decay of neutral pions from fragmentation of WIMP decay products Larger rate, but difficult to separate from other Galactic Diffuse foreground contributions GeV excess in the EGRET data: LAT's improved sensitivity will help confirm or refute this. Monoenergetic gamma-ray lines: From WIMP annihilation into two-body final states with two photons or Z and photon Smaller signal, but more easily distinguished LAT is an important piece of the Dark Matter puzzle: Combine information from accelerators, astrophysics and astroparticle-physics SLAC-KIPAC are well positioned for this: ATLAS, LSST, CDMS and Fermi 24

25 LAT On-Orbit Performance The LAT collects heavy ions during normal data taking: Calorimeter calibration MIPs are collected continously and in dedicated runs. Stable peaks: During the Commissioning phase the peak positions were found to be stable to within 1%. Results shown here are from 100h of data. Heavy Ions Carbon Peak C B Be O N Ne Mg Si Fe 25

26 On-Orbit Stability Of The CAL Thresholds Zero-suppression thresholds: 2 MeV See-Saw effect suspected due to rate dependence of the pedestals. Cal Low Trigger: >100 MeV in a crystal One-bit resolution in the trigger threshold ADC: 4 MeV Cal High Trigger: >1 GeV in a crystal 26

27 TKR Hit Efficiency Differences between ground and on-orbit efficiencies suspected due to accidentals. Hot strips: Increased from ~200 to ~280 during four months on orbit. Alignment: Stable through launch and on-orbit operations. 27

28 Point Spread Function Validation Using Vela Photons 28

29 LAT On-Orbit Rates Trigger rate: ~2.5 khz Downlinked rate: ~450 Hz Geomagnetic cut-off Photon rate after offline cuts: ~1 Hz - Earth albedo photon contamination 29

30 LAT First Light Presented at a NASA Press Conference on August 26, Based on 4 days of all sky survey data: Equivalent to EGRET one year source sensitivity! Geminga Pulsar Crab Pulsar Vela Pulsar 30

31 GRB080916C A Big Boom In The Sky! T-200, T-100 Gamma Ray Burst coincident with the first day of the first post-launch LAT Collaboration Meeting! T-95, T+5 Paper soon to come! T-75, T+25 T+50, T+150 GRB spectrum can be studied over 6 orders of magnitude in energy by Fermi! Includes the largely unexplored >10 GeV domain! 31

32 Gamma-Ray Burst Coordination Network Circulars For follow up by other observatories at different wavelenghts. One way for (young) people to get visibility! cf Tuesday's roundtable discussion. 32

33 PKS and 3C The sky is dynamic, Fermi is monitoring the sky, catching flaring sources over different time scales. ATEL #1628 (3C 454.3) and #1650 (PKS ) issued to announce these flares. ASP light curve for PKS : 33

34 The Astronomer's Telegram For follow up by other observatories at different wavelenghts. Another way for (young) people to get visibility! cf Tuesday's roundtable discussion. 34

35 Fermi Rapid Publications Fermi is already contributing to the Astrophysical Community! 35

36 Fermi's First Science Paper/Discovery to c O r e b,

37 Fermi's First Discovery A radio quiet, gamma-ray only pulsar, in Super Nova Remnant CTA1: First ever Fermi Science paper based on on-orbit data! Published in Science Express October 16, First gamma-ray only pulsar ever discovered! Results seem to favor slot-gap/outer-gap emission models. 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

38 Conclusions And Prospects Fermi has been successfully launched, the Comissioning Phase is over and we are now taking data in sky survey mode. The observatory and all ground elements are working flawlessly! Successful marriage of particle and astrophysics communities! First physics results are already coming out. Confirm the great discovery capabilities of Fermi! Concerning the GeV excess seen in the EGRET data: Work in progress. Stay tuned! The Dawn Of A New Era In Gamma-Ray Astrophysics! 38