Overview of GLAST physics

Transcription

1 Overview of GLAST physics Gamma-ray Large Area Space Telescope Nicola Giglietto Politecnico di Bari and INFN-Bari New Worlds in Astroparticle Physics-Faro, January 8,2005

2 The GLAST observatory Gamma Ray Burst Monitor (GBM) Large Area Telescope (LAT) Spacecraft Launch Vehicle Delta II H Launch Location Kennedy Space Center Orbit Altitude 575 Km Orbit Inclination 28.5 degrees Orbit Period 95 Minutes Orientation +X to the Sun Launch Date May 2007 Payload LAT mass 3000Kg LAT power 650W Talk overview mission motivation instrument design the LAT Tracker science goals conclusions

3 Need for a high energy -ray detector AMS AGIL E GLA ST MEGA SuperAGI LE

4 Covering the Gamma-Ray Spectrum Broad spectral coverage is crucial for studying and understanding most astrophysical sources. The GLAST observatory and ground- based experiments cover complimentary energy ranges and performances (wide FOV and alert capabilites for GLAST, large effetive area and energy reach for ground- based) The improved sensitivity of GLAST is necessary for matching the sensitivity of the next generation of ground- based detectors. GLAST goes a long ways toward Predicted sensitivities to a point source. EGRET, GLAST, and Milagro: 1-yr survey. Cherenkov telescopes: 50 hours on source. (Weekes et al., 1996, with GLAST added)

5 Overview of the LAT detector Precision Si-strip Tracker (TKR) 18 XY tracking planes Single-sided silicon strip detectors 228 m pitch, channels Measure the photon direction Segmented Anticoincidence Detector (ACD) 89 plastic scintillator tiles surrounding the TKR towers Reject background of charged cosmic rays Removes self-veto effects at high energy LAT: 4 x 4 modular array 3000 kg, 650 W HEP and astrophysics partenrship USA: US Dept. Of Energy, SU- SLAC, NASA GSFC, NRL Italy: INFN, ASI, Inst. CR Res (IFC) Japan: Univ. Tokyo, Univ. Hiroshima, Inst. Space Science, Inst. CR Res. (ICCR) France: CEA, CNES, IN2P3 Sweden: Royal Inst. Tech., Univ. Stockolm Electronics & Flying Software Data Acquisition System e + e - GRID Mechanical backbone Hodoscopic CsI Calorimeter(CAL) Array of 1536 CsI(Tl) crystals in 8 layers channels Measure the photon energy,image the shower

6 Experimental Technique Instrument must measure the direction, energy, and arrival time of high energy photons (from approximately 20 MeV to greater than 300 GeV): - photon interactions with matter in GLAST energy range dominated by pair conversion: determine photon direction clear signature for background rejection Energy loss mechanisms: Pair-Conversion Telescope anticoincidence shield conversion foil particle tracking detectors e + e calorimeter (energy measurement) must detect -rays with high efficiency and reject the much larger (~10 4 :1) flux of background cosmic-rays, etc.; energy resolution requires calorimeter of sufficient depth to measure buildup of the EM shower. Segmentation useful for resolution and background rejection.

7 Science Drivers on Instrument Design Effective area and PSF requirements drive the converter thicknesses and layout. PSF requirements also drive the sensor performance, layer spacings, and the design of the mechanical supports. ACD TRACKER Background rejection requirements drive the ACD design (and influence the calorimeter and tracker layouts). 0,9997 EFFICIENCY SEGMENTED,REDUNDANT Field of view sets the aspect ratio (height/width) FRONT 3 %X o BACK 18 % X o PITCH 228 m Energy range and energy resolution requirements bound the thickness and layout of calorimeter e + e Electronics CAL TKR CAL TKR CAL Time accuracy provided by electronics and intrinsic resolution of the sensors. NO DEAD _TIME FR0M SILICON SENSORS 8.5 X o HODOSCOPIC, GRANULAR On-board transient detection requirements, and on-board background rejection to meet telemetry requirements, are relevant to the electronics, processing, flight software, and trigger design. Instrument life has an impact on detector technology choices (NO CONSUMABLES). Derived requirements (source location determination and point source sensitivity) are a result of the overall system performance.

8 Sensitivity and Sky Map EGRET ( ) - map based on 5 years data Integral Flux (E>100 MeV) cm -2 s -1 GLAST one year sky-survey - based on the extrapolation of the number of sources versus sensitivity of EGRET

9 LAT Sensitivity During All-sky Scan Mode 100 sec 1 orbit* EGRET Fluxes - GRB (100sec) - PKS flare - 3C279 flare - Vela Pulsar During the all-sky survey, LAT will have sufficient sensitivity after one day to detect (5) the weakest EGRET sources. - Crab Pulsar - 3EG (SNR Cygni?) 1 day^ - 3EG C279 lowest 5 detection - 3EG (AGN) - Mrk Weakest 5 EGRET source *zenith-pointed ^ rocking all-sky scan: alternating orbits point above/below the orbit plane

10 Glast Physics Sources identification and diffuse emission pulsar AGN GRB sky map SNR and CR acceleration solar flares dark matter 28/12/2004 N.Giglietto- FARO Jan,10th

11 GLAST science - the sky above 100 MeV sky map unidentified sources pulsar GRB solar flares AGN map SNR and CR acceleration dark matter 0.01 GeV 0.1 GeV 1 GeV 10 GeV 100 GeV 1 TeV

12 Identifying Sources 170/271 3 rd EGRET catalog still unidentified GLAST 95% C.L. radius on a 5 source, compared with a similar EGRET observation of 3EG Counting stats not included. GLAST high resolution and sensitivity will resolve gamma-ray point sources at arc-minute level detect typical signatures (e.g. spectra, flares, pulsation) for identification with known source types Cygnus region (15 0 x 15 0 ), Eg > 1 GeV

13 Active Galactic Nuclei AGN signature vast amounts of energy (10 49 erg/s) from a very compact central volume large luminosity fluctuations in fractions of a day energetic (multi-tev), highly-collimated, relativistic particle jets Prevailing idea: accretion onto super-massive black holes ( solar masses) AGN physics to-do list catalogue AGN classes with a large data sample (~>3000 new AGNs) identify contributions from leptonic (SSC/ESC) and/or hadronic ( 0 decay) emissions in the spectra multiwavelength campaigns resolve diffuse background and study redshift dependence of cut-off to probe EBL track flares ( ~ minutes)

14 AGN Multiwavelength Variety Science Topics Location and nature of particle acceleration and interaction in jets. Confirmation of unified models. Cosmological probes using high-energy cutoff due to absorption by Extragalactic Background Light. Contribution to the diffuse background. Due to variability on short time scales, AGN require simultaneous multiwavelength observations for maximum scientific return.

15 AGN &EBL Studies Photons with E>10 GeV are attenuated by the diffuse field of UV- Optical-IR extragalactic background light (EBL) opaque Opacity (Salamon & Stecker, 1998) only e - of the original source flux reaches us EBL over cosmological distances is probed by gammas in the GeV range. Important science for GLAST! In contrast, the TeV-IR attenuation results in a flux that may be limited to more local (or much brighter) sources. A dominant factor in EBL models is the time of galaxy formation -- attenuation measurements can help distinguish models. No significant attenuation below ~10 GeV.

16 LAT studies EBL cutoff Probe history of star formation to z ~4 by determining spectral cutoff in AGN due to EBL

17 CR production and SNR widely believed to be the source of CR proton acceleration after shell interaction with interstellar medium 0 bump in the galactic spectrum detected by EGRET acceleration in SNR GLAST will locate SNR resolve SNR shells at 10 level measure SNR spectra E (MeV) GLAST simulations showing SNR -Cygni spatially and spectrally resolved from the compact inner gamma-ray pulsar a clear 0 decay signature from the shell would indicate SNR as a source of proton CR

18 Dark Matter a short review Evidence: Rapidly moving galaxies in clusters Rotation curves of galaxies Hot gas in galaxy clusters Gravitational lensing Stability of rotating spiral galaxies Types: Baryonic vs. non-baryonic Cold vs. Hot Hot gas in Galaxy Cluster

19 Searching for dark matter The lightest supersymmetric particle is a leading candidate for non-baryonic CDM It is neutral (hence neutralino) and stable if R- parity is not violated It self-annihilates in two ways: where E = M c 2 where EMc 2 M z 4M 2 Gamma-ray lines possible: 30 GeV - 10 TeV

20 Gamma Ray Flux From WIMPS The flux of gamma rays from WIMP annihilation has many terms: Cesarini et al, astro-ph/ ( E, ) v 4 Annihilation Cross Section & Thermal Velocity : Angle away from Galactic Center l.o.s : Line-of-Sight in direction f dn de f B f l. o. s. Branching Fraction & Photon Spectrum dl( ) 1 2 ( l) M 2 2 WIMP Number Density (governed by the Halo distribution)

21 Road Map for Photons from Dark Matter Type Line XX, Z 0 (Small Br, Line Spectra) Particle Source SUSY X: 0 (LSP - many models parameter space large) Where Galactic Center Known Location Intensity Dependence Diffuse Character Inclusive XX + Anything (Large Br, Continuum Spectra) LIMP X: Heavy R (Signal to weak too be observed by GLAST) Extra Galactic Associated with AGN Point Like Character Galactic Center Extra Galactic Line Inclusive Strongest Location & Energy Focus Difficult on Galactic to disentangle Center Bkg model dependent Weak Energy smeared by red-shift Very Hard

22 GLAST WIMP Search Regions Galactic center Galactic satellites Galactic halo Extra-galactic

23 Diffuse emission from Relic decay Set limits on relic mass, density and lifetime GLAST EGRET Unresolved AGNs WIMPs Total

24 WIMP line detectability line line Supersymmetry model calculations by Bergstrom, Ullio and Buckley 1998 assume enhanced density near Galactic Center (Navarro, Frenk and White 1996)

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26 Pulsar physics with GLAST known gamma-ray pulsars direct pulsation search in the -ray band high time resolution detect new gamma-ray pulsars (~250) precise test of polar cap vs outer gap emission models large effective area

27 Gamma-Ray Bursts and GLAST spectral studies for non-thermal emission model (synchrotron, ICS) fireball baryon fraction high energy resolution observed ~ (0.1-10) x 10-6 erg/cm 2 () little data > 50MeV isotropic distribution in the sky cosmological origin from afterglow redshift spectacular energies ~ erg (!) large effective area, high angular resolution transient signal, ~ 100 µs time scale light curves vs energy time structure and burst geometry fast response/ short dead time

28 Gamma-Ray Bursts GLAST LAT will be best suited to studying the GeV tail of the gamma-ray burst spectrum. A separate instrument (GBM) on the spacecraft will cover the energy range 10 KeV 25 MeV and will provide a hard X-ray trigger for GRB. GLAST should detect 200 GRB per year with E>100 MeV, with a third of them localized to better than 10, in real time. Excellent wide field monitor for GRB. Nearly real-time trigger for other wavelength bands, often with sufficient localization for optical follow-up. With a 10s dead time, GLAST will see nearly all of the high-e photons. Simulated one-year GLAST scan, assuming a various spectral indexes. GBM LAT 1- localization accuracy (arc min.) vs nb photons more straight tracks from higher energy g allow more precise localization LAT GBM complimentarity

29 GRB and new Physics GRB can be used to probe new physics: for example theory models involving an energy dependent speed of light can be verified by the observation of a delayed high energy photon in GRBs A large sample of observed GRBs can help to discriminate different theory models

30 Conclusions The large statistics collected by GLAST also in the first year of operations will address many important questions: - origin of CRs - AGN and EBL studies - Dark Matter - GRB - study of unidentified EGRET sources Importance of multiwavelength observations

31 Backup material

32 Expanded view of converter-tracker: Tracker/Converter Issues Some lessons learned from simulations X Y X Y At 100 MeV, opening angle ~ 20 mrad At low energy, direction measurement is dominated by planes closest to conversion point due to multiple scattering Low energy PSF completely dominated by multiple scattering effects: 0 ~ 2.9 mrad / E[GeV] (scales as (x 0 ) ½ ) High energy PSF set by hit resolution/lever arm X Y PSF ~1/E Roll-over and asymptote ( 0 and D ) depend on design At higher energies, more planes contribute information: Energy # significant planes 100 MeV 2 1 GeV ~5 10 GeV >10 E

33 Instrument Triggering and Level 1 Trigger hardware trigger single tower initiates readout Function: did anything happen? Onboard Data Flow On-board Processing full instrument information available to processors. Function: reduce data to fit within downlink Hierarchical filter process: first make the simple selections that require little CPU and data unpacking. x x x TKR 3 x y pair planes in a row workhorse trigger OR CAL: LO independent check on TKR trigger. HI indicates high energy event disengage use of ACD. Upon a L1T, all towers are read out within 20s Instrument Total L1T Rate: <4 khz>* * peak ~12 khz (down to 3.8 khz with throttle) * possible because of no consumables, little dead-time, fast CPUs subset of full background rejection analysis, with loose cuts only use quantities that are simple and robust do not require application of sensor calibration constants On-board science analysis: transient detection (AGN flares, bursts) complete event information signal/bkgd tunable, depending on analysis cuts: cosmic-rays~ 1:~few Total L3T Rate: <25-30 Hz> (average event size: ~8-10 kbits) Spacecraft

34 Gamma Ray Flux From WIMPS The flux of gamma rays from WIMP annihilation has many terms: Cesarini et al, astro-ph/ ( E, ) v 4 Annihilation Cross Section & Thermal Velocity : Angle away from Galactic Center : Line-of-Sight in direction l.o.s ( E, ) f ( 10 dn de f B f l. o. s. Branching Fraction & Photon Spectrum 26 v cm 3 s 1 50GeV )( M Units: cm -2 s -1 GeV -1 sr -1 1 ( l) 2 J ( ) ( ) dl( ) 3 8.5kpc.3GeVcm l. o. s With: dl( ) Recasting & Scaling in terms of nominal values ) 2 f 1 2 ( l) M 2 2 WIMP Number Density (governed by the Halo distribution) dn de f B f J ( )

35 Largest Uncertainty in Predicted Rate WIMP Density Parameterization c ( r) ( ) / ( r / a) ( r) (1 ( r / a) Density Models a = core halo radius / pwr. law break pt. ~ 3 kpc = Cusp. parm. (0= no cusp.) Isothermal profile Navarro-Frenk-White Moore et al Kravtsov et al.(a) Kravtsov et al.(b) ) r a r a / c r a Orders of Magnitude Uncertainty in J() GLAST Angular Resolution per Photon ~.1 o above ~ 10 GeV Navarro-Frenk-White Kravtsov et al. Isothermal GOOD NEWS! Recent evidence from analysis of INTEGRAL data suggests.4 < <.8 r a Boehm et al, astro-ph/ Phys.Rev.Lett. 92 (2004)

36 The Anti-Coincidence Tile Shell Assembly Segmented with optmized layout to minimize backsplash self-veto probability with minimum nb tiles Detector Proto-tile Assemblies High light yeild for high MIP detection efficiency 89 tiles 1 cm thick (8.6 m 2 total) 2 phototubes per tile Waveshifting fiber embedded White Tetratec wrapping Charged particle efficiency > Power < 31 W total Mockup of Cable Layout Base Electronics Assembly (BEA)

37 The Calorimeter subsystem CsI Crystals Sweden (KTH) CDE Assembly NRL Mechanical Structure France (IN2P3/Ecole Polytechnique) 72 Front-End Electronics NRL, SLAC Optical Wrap PIN Diode (each end) Flex Cable CsI Crystal 1536 crystals (total) 2x2.7x33 cm 3 2 PIN diodes per end; 2 gain ranges each ~ 1500 kg Self-triggering 8.5 X 0 total Power < 91 W Module Assembly and Test, NRL+collab flight modules + 2 spares 18 PEM Assembly NRL

38 Calorimeter CsI Detector Module Endcap Endcap Foil of VM2000 CsI (Tl) PDA CDE consisting of : 1 crystal log of CsI doped with Thallium x 20 x 326 mm Provided and tested by Sweden 2 Photo Diode Assembly, one bonded to each end (DPD with wires), Wrapping consisting of 1 molded foil of VM Endcaps

39 Energy Resolution Energy corrections to the raw visible CAL energy are particularly important for depositions in the TKR at low photon energy (use TKR hits) leakage at high photon energy (use longitudinal profile) 18% >60 off-axis 300 GeV Normal-incidence (require <6%) 100 MeV (require <10%) 4.3% 9% uncorrected corrected E(MeV) corrected E(GeV)

40 Tracker detector - construction workflow Module Structure Components SLAC: Ti parts, thermal straps, fasteners. Italy (Plyform): Sidewalls SSD Procurement, Testing SLAC,Japan, Italy (HPK) SSD Ladder Assembly Italy (G&A, Mipot) 18 10,368 Tracker Module Assembly and Test Italy (Alenia Spazio) Tray Assembly and Test Italy (G&A) 342 Readout Cables UCSC, SLAC (Parlex) Electronics Fabrication, burn-in, & Test UCSC, SLAC (Teledyne) 648 Composite Panel, Converters, and Bias Circuits Italy (Plyform): fabrication SLAC: CC, bias circuits, thick W, Al cores

41 Silicon Sensor Devices Specifications Standard design Wafer size Sensor size (cmxcm) Thickness (m) Doping Implant Read-out Coupling Bias Strips Strip pitch (m) Implant width (m) X n-type p+ Single-sided AC Poly-Si Aggressive specs Bias voltage < 120V Breakdown < 175V Current(@150V) <500nA AND <200nA (averaged any 100 SSD) Bad strips rate 0.2 % Hamamatsu Photonics qualified producer 9500 INFN (enough for whole LAT) ~80% fully tested at INFN, ~0.6% rejected

42 Ladders assembly Large parts number (>2500) Delicate operations (handling, gluing, alingment, bonding, space-qualified production quality and yield Industrial approach 2 italian high-tech companies qualified Simple, reliable alignment and gluing using referencing jig Automatic wire bonding Dam&Fill encapsulation Electrical (global + single strips) and geometrical acceptance tests > 500 flight ladders produced 2% rejected (1% for mishandling) 0.03% bad strips rate Electrical properties and alignment in very good agremement with what expected from SSDs, thanks to high quality of SSDs and assembly (see F. Gargano talk for details)

43 Tray assembly All the assembly operations under C.M.M. Glue spots deposition with automatic dispenser Microbonding with automatic wedge bonder Ladder positioning Tray positioning 1 assembly chain ready 5 assembly chains in construction Max assembly rate : 15 trays/week Foreseen assembly rate: 10 trays/week Microbonding

44 Environmental test Vibrational tests Thermal cycles (-30 C +50 C) Z accelerometer response X accelerometer response Y accelerometer response L/L (m) Temperature ( C) TG07 Resonance search: 0 = 815 Hz, Q 51 T=25 C: L/L 100 T=-55 C: L/L (see S. Raino talk for details)

45 TKR Construction and quality control Data storage, analysis, quality control and NCR through custom TKR Database Read-only web access at: Software tools: MS Access, Excel, VB

46 Control signal flow Tracker tower read-out low power: < ~ 190 W/channel Low noise occupancy: <10-4 ch/trigger redundant readout, control and power paths protection against power shorts Complete digital zero-suppression onboard data can shift left/right toward RC a single dead chip can be bypassed without losing data from any other chips trigger output = Fast-OR of all 1536 channels in a layer upon trigger (6-fold coincidence) data are latched into a 4-event-deep buffer in each front-end chip read command moves data into 1 of 2 GTRC buffers complete zero-suppression and formatting takes place in the controller chips token moves data from GTRCs to TEM for full LAT event processing (L2-3T) architecture channel amplifier-discriminator chips for each detector layer A22 GTRC GTRC GTRC TKR readout simplified block diagram Data flow GTFE Data flow to FPGA on DAQ TEM board. Control signal flow Nine detector layers are read out on each side of each tower. 2 readout controller chips for each layer GTFE GTRC GTRC GTRC Data flow to FPGA on DAQ TEM board channels CMOS VLSI (custom ASIC ) Front-End chips handle a single detector layer - 2 Read-out Controller (custom ASIC CMOS) complete zero-suppression and data formatting Control signal flow

47 Trays alignment on assembly jig EM Tower Assembly Full-size mechanical tower Cabling Geometrical tolerances well within limits (0.3 mm). Sidewalls in place with lifting tools

48 MiniTracker functional prototype First complete working prototype of flight-like hardware 6 Si-layers 5 trays minimal configuration for L1T check detector performance in terms of occupancy and efficiency specs integrate TKR and CAL take data with CR and 17.6 MeV from a Van de Graaff

49 MiniTracker performance Hit detection efficiency Strip noise occupancy 60% thr ~ ¼ MIP ½ MIP 1 MIP Layer noise occupancy Residual occupancy dominated by CR CR occupancy = CR accidental rate <ToT><cluster-size><CR trigger rate> = 10s x 2 x 30Hz ~105 m as expected ~ ¼ MIP

50 CR events from MiniTower

51 Off-line analysis Angular distribution of incoming CR Layer hitmap

52 EGRET All Sky Map (>1 GeV) 3EG J (Isolated Neutron Star?) 3C279 (blazar) Vela (radio pulsar) 3EG J (CTA 1 SNR?) Geminga (radioquiet pulsar) Crab (radio pulsar SNR) 3EG J (LSI +61 o 303 Binary System?) 3EG J ( Cygni SNR?) 3EG J (unidentified transient) 3EG J (Galactic Center?) Orion Cloud (Cosmic ray interactions with ISM) LMC (Cosmic ray interactions with ISM) PKS (blazar)

53 Unidentified Sources Science Topics Discovery science. New sources or new insight about known objects. Nature of non-blazar transients. Spectrum of 3EG J compared to that of Geminga, indicating a probable isolated neutron star (Halpern et al., Reimer et al. ) Spectrum of 3EG J /SNR RXJ With the limited multiwavelength coverage, no simple model explains the source (Reimer and Pohl). For transients or other variable unidentified gamma-ray sources, having simultaneous observations may be the only viable means of positive identification.

54 Transients (AGN Flares) PLAN FOR THE FIRST YEAR Most AGN science can be best addressed by the all-sky scan. Unusually large flares will be treated as Targets of Opportunity, and studied in a coordinated multiwavelength campaign, for those where a multiwavelength campaign is feasible. Thus, autonomous repointing of the spacecraft is not required for AGN science during the first year. This approach will be re-evaluated after the first year, as new knowledge about AGN might demand a new strategy.