Transcript The GLAST Mission Omar Tibolla Padova University International School of Cosmic Ray
Gamma-ray Large Area Space Telescope
The GLAST Mission Omar Tibolla Padova University
International School of Cosmic Ray Astrophysics, Erice (Italy) 20 - 27 June 2006
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006
Large Area Telescope (LAT) Gamma-ray Large Area Space Telescope -France -Germany -Italy -Japan -Sweden -USA Energy Range 10 keV-300 GeV.
GLAST
:
GLAST Burst Monitor (GBM)
- An imaging gamma-ray telescope (
LAT
) - A second instrument for the study of Gamma Ray Bursts (
GBM
).
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006 The main instrument of GLAST is the
Large Area Telescope
(
LAT
): a pair conversion telescope:
Anticoincidence Shield
(
ACD
) made of plastic scintillator (Bicron-408) sensitive to charged particles; ACD is segmented to avoid self veto from Calorimeter backsplash and also for micrometeorites.
ACD contains 16 towers and each tower is divided in two parts:
TRACKER
-the
TRACKER
(
TKR
): 18 layers in each tower -Tungsten converters -2 orthogonal SSD planes of silicon microstrip sensors for detecting the electromagnetic shower (1.5 χ 0 including silicon and other materials) -a
CALORIMETER
(
CAL
) of CsI crystals dopped by Tl; so the energy deposited by the EM shower is converted in light signal. CAL is characterized by fast decaying fluorescent light (~ns) and a long decaying afterglow (~ms).
SHIELD e ANTICOINCIDENCE + e – CALORIMETER
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006
LAT Specifications and Performance Compared with EGRET
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006 <0.15
o (>10 GeV)
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006
Improvements from EGRET
to GLAST:
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006 The
Glast Burst Monitor
(
GBM
) will include two sets of detectors: -12 sodium iodide (NaI) scintillators -2 cylindrical bismuth germanate (BGO) scintillators The NaI detectors are sensitive in the lower end of the energy range, from a few keV to about 1 MeV and provide burst triggers and locations.
The BGO detectors cover the energy range ~150 keV to ~ 30 MeV, providing a good overlap with the NaI at the lower end and with the LAT at the higher end.
Schematic layout of the 12 NaI and two BGO detectors on the GLAST spacecraft
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006
GBM Specifications and Performance Compared with BATSE Quantity BATSE GBM (Minimum Spec.)
Energy Range Field of View Energy Resolution Deadtime per Event Burst Sensitivity GRB Alert Location GRB Final Location 25 keV - 10 MeV 4π sr < 10% 0.2 cm -2 s -1 ~ 25 ° 1.7
° < 10 keV - > 25 MeV all sky not occulted by the Earth < 10% < 15 μs < 0.5 cm -2 s -1 < 15 ° < 1.5
°
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006
Scientific purposes
PULSARS GAMMA-RAY BURSTS EXTRAGALACTIC BACKGROUND LIGHT NEW PARTICLE PHYSICS COSMIC RAYS AND INTERSTELLAR EMISSION UNIDENTIFIED EGRET SOURCES SOLAR FLARES AGN/BLAZARS
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006
AGN /BLAZARs
EGRET discovered that blazar-class active galactic nuclei are bright and variable sources of high energy gamma rays.
The emission is believed to be powered by accretion onto Supermassive Black Holes at core of distant galaxies.
GLAST will increase the number of known AGN gamma-ray sources from about 100 to thousands.
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006
Unidentified EGRET Sources
More than 60% of EGRET sources are Unidentified!
GLAST should be able to identify them!
Considering their distribution in the sky, almost one third of these are extragalactic (=Blazars).
Some should be Radio-quiet Pulsars.
Recent works speak about Galactic Micro Quasar, or also that these objects could be associated with the nearby Gould Belt of star forming regions that surrounds solar neighborhood.
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006
New Physics
SUSY theories (in particular Minimal Super-Simmetrical Model: MSSM) state the existence of the Lightest Super-Simmetrical Particle: neutralino.
The theories predict that annihilation of neutralino and anti-neutralino should give us a
signal
( cc 2 or cc Z ).
In last years they expect to be able to see this kind of signal from Galactic Center: (GLAST Scientific Brochure, 2001) (Cesarini et al., astro-ph/0305075 v2, 2004)
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006
New Physics (2)
mini-spikes (=clumps around intermediate Black Holes: 10 2 .
signal better from DM M O < M BH <10 6 M .
O ) in Galactic Halo (Bertone, Zentner and Silk, PhyRev D72, 103517) .
In Padova, following this model we are trying to simulate these kind of scenarios; see the spectra by Riccardo Rando’s work (work in progress): for different masses and distance of the clumps.
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006
Extragalactic Background Light
The Diffuse EBL consists of the sum of the starlight emitted by Galaxies through the history of the Universe.
A way to study this extragalactic background is to measure the attenuation on -ray spectra of distant extragalactic objects by these EBL photons. (see the spectra by Luis Reyes’s work on DC2)
The sensitivity of GLAST at high energies will permit the measurement of AGN spectra at high energies and so the study of extragalactic background light
: thanks to the large number of AGNs that GLAST will discover, the intrinsic spectra of AGNs should be distinguishable from the effects of attenuation.
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006
Gamma Ray Bursts
GLAST will measure
spectra from keV to GeV energies
and tracking their
afterglows
.
With its
high-energy response
very short
deadtime
and (very important to confirm the Standard models) GLAST will give big improvements in GRBs study.
LAT and GBM will detect
almost 100 bursts
per year and will provide near real-time location information to other observatories for afterglow searches.
(Simulated light curve of a GRB detected by LAT and by GBM) (GLAST Scientific Brochure, 2001)
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006
PULSARS
GLAST will
discover many gamma-ray Pulsars, 250 or more
(considering that many radio-quiet, Geminga-like, Pulsars should be discovered and that GLAST will be able to precisely search for periodicities directly in EGRET Unidentified Sources) and will provide definitive
spectral measurements
(in order to distinguish between the two primary models: outer gap and polar cap models) (Geminga seen by EGRET) (Spectra of the 2 primary models, simulated for 1 year of survey observation)
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006
Cosmic Rays and Interstellar Emission
GLAST will
spatially resolve some Supernovae Remnants
and
precisely measure their spectra
(see the end of this talk); and it may determine whether SNRs are sources of cosmic rays.
RXJ1713.7-3946 and RXJ0852.0-4622 (Vela Junior) seen by H.E.S.S. array Spatial and spectral studies of this gamma-ray emission will permit to study separately the distributions of protons and electrons; so will test
cosmic-ray production and diffusion theories
.
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006
Solar Flares
GLAST should be able also to
study Solar Flares
.
In fact EGRET discovered that the Sun is a source of GeV gamma rays.
Thank to its Large Effective Area and its small deadtime, GLAST will be able to determine
where the acceleration takes place
and it should be able also to confirm (or not)
if the protons are accelerated along with electrons
.
Mandzhavidze and Ramaty (1992) modeled EGRET data using a composite spectrum of electron bremsstrahlung and pion decay
And other extremely important features are the
COMPLEMENTARITY WITH GROUND-BASED GAMMA-RAY TELESCOPES
and that GLAST will study the Universe in
UNEXPLORED REGIONS OF EM SPECTRUM
.
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006
GLAST CURRENT STATUS: Hardware
16 towers were assembled last year and now LAT final assembly is complete!
Delivery of LAT for integration with the spacecraft: May 2006 GBM instruments (NaI, BGO Detectors, Power Supply Box, etc.) are ready and they have just passed through EMI and thermal vacuum tests.
GLAST integration and testing: Summer 2006 through Summer 2007 Launch: Launch Date Launch Site Launch Vehicle Orbit Begin Science Mission Duration August 2007 Kennedy Space Center Delta 2920H-10 565 km Circular (i.e.; e<0.01), 28.5
° Inclination 1-2 months after launch 5 years (10 years Goal)
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006
GLAST CURRENT STATUS: Software
DC2 is closed the 2 nd of June 2006: http://www-glast.slac.stanford.edu/software/DataChallenges/DC2/JuneCloseout/default.html
Data challenges are full-sky simulations. They provide excellent testbeds for science analysis software.
•
Full observation, instrument, and data processing simulation. Team uses data and tools to find the science. “Truth” revealed at the end.
A progression of data challenges.
– – – DC1 in 2004. 1 simulated day all-sky survey simulation ( enlarged to a week of simulation.
• • find the sources, including GRBs a few physics surprises DC3 (?) in 2007. Support for flight science production.
3 rd EGRET Catalog), later DC2 NOW (kickoff 1-3 March). 55 simulated days all-sky survey.
• first catalog • add source variability (AGN flares, pulsars) and extended sources (SNRs and Molecular Clouds); add GBM; add backgrounds (charged particles and albedo ) • closeout end of May (>100 participants)
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006
DATA CHALLENGE 2
(DC2 Sky) In DC2 there are simulated many Galactic sources: http://www-glast.slac.stanford.edu/software/DataChallenges/DC2/JuneCloseout/Presentations/Sky_model_Galactic_Digel_v3.ppt
And many Extragalactic sources: http://www-glast.slac.stanford.edu/software/DataChallenges/DC2/JuneCloseout/Presentations/dc2_truth_exgal_McEnery.ppt
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006
Galactic sources are summarized in this table: Simulated Extragalactic sources are: -Galaxies -Galaxy Clusters -AGNs -GRBs -Extragalactic Background Light
# sources Milky Way itself (=Diffuse Emission of MW) (1) Pulsars (414) Plerions (7) SNR (11) XRB (5) OB associations (4) Small molecular clouds (40) Dark matter (~2) ‘Other 3EG’ (120) Sun (1 flare) Moon (1) # gammas 1,704,807 140,596 9780 22,592 1491 295 1741 5158 112,386 4669 10,523
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006
SNRs simulations in DC2
During DC2 I essentially worked on SNRs: simulation and analysis.
About SNRs simulation, see again: http://www-glast.slac.stanford.edu/software/DataChallenges/DC2/JuneCloseout/Presentations/Sky_model_Galactic_Digel_v3.ppt
I implemented some HESS SNRs for GLAST software, including spectral extrapolation down to energy range of LAT; (sometimes, we used also Cangaroo ( I and II ) and EGRET results in order to do some tests on these SNRs) (SNRs in DC2 Sky)
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006
Simulated SNRs:
The full work was presented at Goddard Space Flight Center the 2 nd of June 2006:
http://www-glast.slac.stanford.edu/software/DataChallenges/DC2/JuneCloseout/Presentations/GSFC_simulation_Tibolla.ppt
-RXJ1713.7-3946 (astro-ph/0511678v2, 2005) -RXJ0852.0-4622 (A&A, 437, L7-L10, 2005) -HESS galactic survey (ApJ, 636, 777-797, 2006): -HESSJ1634-472 -HESSJ1640-465 -HESSJ1713-381 -HESSJ1813-178 -HESSJ1834-087
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006
RXJ1713.7-3946: spectrum
In DC2 RXJ1713-3946 is simulated using the Broken Power Law that H.E.S.S. used to fit their experimental data: The Break Energy is at 6.7 TeV, so for our model a single Power Law is perfectly fine and we used the lower energy part of the Broken Power Law: spectral index is 2.06 and the flux above 10 MeV integrates to 0.038 m -2 s -1 (a little smaller but very close to EGRET values).
Other test were made, using the Single Power Law spectrum proposed by Cangaroo ( I e II ), the Single Power Law spectrum proposed by H.E.S.S. in previous work and fluxes of the “Unidentified” EGRET source 3EG 1714-3857 (this source is very close to RXJ1713 3946, so the comparisons are immediate (see HESS paper); the total flux of 3EG 1714 3857 above 20 MeV is almost 0.03533 m-2 s-1 and it means a luminosity that is almost 1/5 of Crab luminosity, so we used this EGRET source as “the best case”) (the exempla, we will see, will follow the Cangaroo Single PL)
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006
RXJ1713.7-3946: spatial distribution
(starting from HESS Count Map) I constructed the “real physical SNRs”, using the spectral laws just seen in last slide.
(and HESS simple geometrical model)
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006 Using
gtobsim.exe
, a scientific tool that tell us if and how each photon from “real source” interact with our instrument, we can see for example the GLAST Count Maps of that gammas (1 month of observations in “survey mode”): (~2500 gammas, > 20 MeV) (~750 gammas, > 200 MeV) (33 gammas above 2 GeV) (Note: the different PSFs at different energies) (In reality in DC2 the things are a little bit different, because of new IRFs with harder cut for Background Rejection, but the procedure is exactly the same)
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006
RXJ0852.0-4622 (Vela Jr)
Almost the same thing was made for Vela Jr; as I did previously, I extrapolated the total flux we should have at LAT energies, using HESS Power Law:
E
20
MeV
20
MeV
1
TeV
E
1
TeV
2 .
1
0 .
0280295
m
Almost 1/5 - 1/6 of the luminosity of the Crab.
2
s
1
200
GeV
20
MeV
1
TeV
E
1
TeV
2 .
1
And with this flux, I constructed again the “real physical SNRs” starting from HESS Count map:
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006 Again, what we will see after one month of observations will be: (2285 gammas, > 20 MeV) (61 gammas above 2 GeV) (1080 gammas, > 200 MeV) So increasing the observation’s time up to 10 (5+5) years and giving a cut in energy at 2 GeV (in order to have a very small PSF) we obtain exactly the structure we had simulated before!
GLAST will be able to resolve spatially such SNRs!
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006
Other SNRs in inner Galaxy
HESSJ1834-087 HESSJ1813-178 HESSJ1713-381 HESSJ1634-472 HESSJ1640-465 http://www-glast.slac.stanford.edu/software/DataChallenges/DC2/JuneCloseout/Presentations/GSFC_simulation_Tibolla.ppt
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006
Analysis SNRs:
And what about analysis?
(also this work was presented at Goddard at same workshop, the 1 st of June 2006:
http://www-glast.slac.stanford.edu/software/DataChallenges/DC2/JuneCloseout/Presentations/GSFC_analysis_Tibolla.ppt
) Vela In order to see what we can do with analysis, we go on studying RXJ0852.0 4622, that in “real life” is one of the most “unlucky” object of the sky (Note: EGRET didn’t see it): PSR0904-5008 RXJ0852.0-4622
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006 First question should be: “Is it a source? Or is it only a feature of the Galaxy?” Using another GLAST tool (
gttsmap.exe
), we can to a statistical map of this region (we model the sky including backgrounds ( also the Galaxy) and all the known sources; so the tool, analyzing each single photon, give us the probability to have a point source(!!!) there).
And we obtained a big probability to have a source there: yes, it’s a source!
Is it extended? Using the same method we see that it seem to be also extended:
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006 We do another Statistical Map much more detailed (20-25 days of computations) and we can say that it surely extended: And we can also see something like a structure, a structure similar to the one we simulated!
Also in this “real” case GLAST will be able to solve spatially that SNR!
(Note: the “canonical” way to search this kind of structure should be: deconvolution + cuts in energy)
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006 And what about spectral analysis?
Doing spectral analysis on that source in principle is very difficult because of its “very noisy” neighbours.
We found that to study all the sources together was almost impossible. So we “isolated” and studied separately the sources; but in order to do it we had to use very small RoI, smaller than PSF ( cuts in energy).
Backgrounds
Extragalactic background (fixed): constant diffuse emission Pref = 1.6 ( x 10 -7 ) Sp. Index= -2.1
Galactic backgrounds: modeled with MapCube file GP_gamma.fits
The scale factor is almost 1 never change very much (up to 1.037..) Residual component: modeled with MapCube file residual.fits
The scale factor is more than 3 times grater than we was expecting... 3.309
Vela and PSR0904-5008
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006 PSR0904-5008 Vela Galactic backgrounds Residual components Extragalactic background Galactic backgrounds Residual components Extragalactic background Vela fits quite well with a Broken Power Law.
PSR0904-5008 with a single power law with an exponential cut-off.
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006 Putting all together we could analyze the SNR: Galactic backgrounds Vela Vela Jr RXJ0852.0-4622 seems to fit well with a single Power Law.
The work is still in progress but until now the values don’t differ too much; the extremes are: Prefactor 1 = 9769 + 982 ( x 10-9) Spectral Index 1 = -2.163 + 0.042
Prefactor 2 = 5180 + 797 ( x 10-9) Spectral Index 2 = -2.014 + 0.053
Residual components Extragalactic background Not very far from what we have simulated!
PSR0904-5008
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006
Conclusions
About GLAST, I think that, looking its scientific purposes, it doesn’t need other comments.
About SNRs, GLAST will
spatially resolve some Supernovae Remnants precisely measure their spectra
.
and About the other sources, I send you again to: http://www-glast.slac.stanford.edu/software/DataChallenges/DC2/JuneCloseout/default.html
Omar Tibolla. ISCRA.
Erice (Italy) 20 - 27 June 2006
Acknowledgements
In alphabetic order: - Giovanni Busetto; Padova University, Italy.
- Jim Chiang; GSSC/UMBC, USA.
- Valerie Connaughton; University of Alabama in Huntsville, USA.
- Bernard Degrange; Ecole Polytechnique, Palaiseau, France.
- Seth Digel; SLAC, Stanford, USA.
- Francesco Longo; Trieste University , Italy.
- Julie McEnery; GSFC, USA.
- Elisa Mosconi; Padova University, Italy.
- Riccardo Rando; Padova University, Italy.
- Luis Reyes; GSFC, USA.
- Steve Ritz; GSFC/UMD , USA.
- Antonio Saggion, Padova University, Italy.
- Francesca Maria Toma; Padova University, Italy.
- Tracy Usher; SLAC, Stanford, USA.
- John P. Wefel, Louisiana State University, Baton Rouge, USA.