Space based and X-Ray telescopes
Alexander Sellerholm
2006-06-01
Outline
● Gamma rays
● Astrophysical Sources
● Space based telescopes – Past to Future
● Observatories GLAST
Chandra
● Data Challenge II
Gamma rays
Typicaly:
E > 0.1 Mev > 10 18 Hz < 10 -11 m
Due to the their small wave length, gammas do not scatter of atoms, rather the atom is mostly empty space and the gammas scatter inelasticaly against the nucleus
and the electrons. Therefore no gamma-ray mirrors!
Production of gammas I
Thermal production
Blackbody radiation:
Wien's law:
I = 8 h c
3⋅ e
h/ kT1 −1
0.2898 [cm K ]= max ⋅T ⇒ 1 MeV
T =2⋅10 9 K
NOT very common!
Production of gammas II
Nonthermal processes:
Cosmic gamma-ray sources
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Firebals: thermal, optically thick such as the Big Bang and possibly Super Novae and gamma-ray bursts, collisons of bare compact objects.
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Explosive events: extreme energy density, sucha as Super Novae and Gamma-ray bursts.
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Energetic collisions: particle jet sources (microquasars, active galactic nuclei), in vicinity of accreting compact objects (Black Holes, neutron stars),
cosmic ray collisions with matter or in solar flares.
●
Charged particle beams: from gravittional or magnetic sources such as in the vicinity of compact objects, quasars and active galactic nucleai. Up to 10 TeV gammas detected.
GLAST simulation of the gamma-ray sky.
Dark Matter annihilation
Simulated detection of a neutralino annihilation line from the Galactic center.
Extra galactic gamma-ray flux for two sample thermal relics in the MSSM
or Z with energies E =M and E=M(1-m
z2/4M
2)
The neutralino makes a viable DM candidate in models with masses in the interval:
30 GeV < M < 10 TeV
Vela: U.S. army
discovered GRBs 1967.
Uhuru: First dedicated satelite observetary 1972
CGRO: NASAs second Great Observatorie.
Carried BATSE, OSSE and EGRET. 1991-2000.
BeppoSAX: Italian-Dutch program, first to locate GRB and follow the glow.
1996-2002.
Some Active missions
X-Ray: Chandra, XMM-Newton, Suzaku
-Ray: HETE-2, Integral, Swift
Future
Constellation-X : four X-Ray telescopes will for instance be able to capture ”slow-motion movies”
of hot gas falling onto Black Holes.
Part of The Beyond Einstein program together
with LISA.
Gamma Ray Large Area Telescope GLAST
Scientific goals
● Blazars and Active Galactic Nuclei
● Unidentified sources
● Indirect detection of Dark Matter
● Extragalactic Background Light
● Gamma-Ray Bursts
● Pulsars
● Cosmic Rays and Interstellar Emission
● Solar Flares
Specs
Mass: 4277 kg
Dimensions: 2.8 x 2.5 m Instruments: LAT & GBM
Energy range: 15 keV- 300 GeV
Launch: August 2007, on a Delta 2920H-10
Orbit: 565 km @ 28.5
○inclination
Large Area Telescope
-rays detection by pair conversion: →e + e -
Event characterized by:
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No signal in anticoincidence shield.
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More than one tracks from the same point.
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E-M shower in the calorimeter.
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Anticoincidence shield rejects charged background whose flux is 10
5times higher.
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The pair production is induced in the field of heavy nucleous.
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The tracker gives a X-Y coordinate in each of the 18 ”trays”.
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Energy deposited in the calorimeter.
Better protection against self-veto with a
segmented anticoincidence shield.
LAT VS. EGRET
EGRET map of VIRGO compared to a
simulation of 1 yr data from GLAST > 1 GeV.
Quantity LAT (Minimim Spec.) EGRET
Energy Range 20 MeV - 300 GeV 20 MeV - 30 GeV
Peak Effective Area > 8000 cm
21500 cm
2Field of View > 2 sr (> 100
○) 0.5 sr Angular Resolution < 3.5° (100 MeV) 5.8° (100 MeV)
< 0.15° (>10 GeV)
Energy Resolution < 10% 10%
Deadtime per Event < 100 μs 100 ms
Source Location Determination< 0.5' 15'
Point Source Sensitivity < 6 x 10
-9cm
-2s
-1~ 10
-7cm
-2s
-1EGRET data of a 80x80 degree map of the Galactic Anticenter
compared to a simulated 1-yr all-sky survey with GLAST.
Semiconductor Detectors
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P-n-junction, usually with silicon as bulk n material.
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Intrinsic energy resolution ~ 3.6 eV to produce electron- hole pair.
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Possistion localization accuracy ~ 5 μm.
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Excellent responstime (ns).
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No consumables.
Principle:
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Ionizing particle creates electron-hole pairs.
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External fields seperates the pair before they recombine.
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The collected charge is a measure of the energy deposited and the strip involved in detection gives the location.
Problems:
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Detectros must be thin to avoid multiple scattering.
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Signal amplitude proportional to thicknes ->
low signal-to-noise ratio.
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Sensitive to radiational damages.
Read out strips
Glast Burst Monitor GBM
2 x BGO scintilators ~150 keV-30 MeV
12.7 cm thick
12.7 cm diameter 2 PMTs
12 x NaI scintillators ~1 keV-1 MeV 1.27 cm thick
12.7 cm diameter 1 PMT
Large field of view without blocking the LAT.
Will cover low energy spectra of GRBs
and provide a fast GRB alert for LAT.
Chandra
NASAs third Great Observatory
Launched July 1999 (designed for 5 years) Covers 0.1 – 10 kev, X-Rays
1 X-Ray telescope 2 cameras
2 spectrometers
Starburst galaxy M82
As seen by Chandra, HST
and Spitzer
X-Ray Telescope
Visible light is reflected of mirrors,
X-Rays goes through unless very
large inclination angle.
Data Challenge II
The second of three packages of simulated data for GLAST to let astronomers test their skills.
Contains
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55 day simulation of high energy gamma-ray sky.
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Full and realistic simulation of the detector, including imperfections and dead-time etc.
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Detailed modeling of astrophysical sources and background.
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Rich description of gamma-ray sources, including variable sources, pulsars and GRBs.
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Enhanced event classification and background rejection analysis.
DCII sky in galactic coordinates
The Crab pulsar in gamma-rays
Histogram of photons centered around the
Crab pulsar.
The Galactic Center and the Anti Galactic Center
100 degree view of the galactic and anti galactic center.
Spectra of GC and Anti GC
Spectra of radiation from the galactic center (black) and the anti galactic center (red dotted)
from a 100 degree and a 3 degree view.
Galactic center compared to 70 degrees
perpendicular to the galactic plane.
Another possibility...
Also from DCII data:
A 3 degree view of the GC compared with the whole sky.
Taken from Jan Conrad
Conclusion
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Looking at high energy photons has opend up new fields of astrophysics.
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X and Ray telescopes will continue to be a gerat resource of information abot astrophysical phenomena.
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Uniqe way of probing truly high energy phenomena.
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