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Chandra Was Launched Aboard Space Shuttle Columbia on July 23, 1999!!! Crew Lost During Re-Entry Modern X-Ray Telescopes and Detectors

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Chandra Was Launched Aboard Space Shuttle Columbia on July 23, 1999!!! Crew Lost During Re-Entry Modern X-Ray Telescopes and Detectors Chandra was launched aboard Space Shuttle Columbia on July 23, 1999!!! Crew Lost During Re-Entry Modern X-ray Telescopes and Detectors •X-ray Telescopes •X-ray Instruments •Some early highlights •Observations •Data characteristics •Calibration •Analysis X-ray Telescope: The advantages • Achieve 2-D imaging – Separate sources – Study morphology of extended sources – Simultaneously measure both source and local background • Reduce the background Æ increase the source 1/2 detection sensitivity: S/N ~ Fs t/(Fst+ ASbt) –t –exposure time –Fs – source count flux –A –source detection area –Sb – background surface brightness: Detector + sky background • Facilitate high-resolution dispersive spectrometers X-ray Telescope: Focusing mechanism External reflection at small grazing angles - an analogy of skipping stones on water •Snell’s law: sinφr=sinφi/n, where the index of refraction n=1-δ+iβ • External reflection occurs with sinφr > 1 Æ 1/2 The critical grazing angle θ = π/2- φi ~ (2δ) 1/2 (δ ∝ ne /E << 1) Focusing mechanism (cont.) • The critical angle (effective collecting area) decreases with increasing photon energy • High Z materials allow for reflecting high energy photon with the same grazing angle X-ray Telescope: Hans Wolter Configuraions • A Paraboloid gives a perfect image for on-axis rays. But it gives a coma blur of equivalent image size proportional to the off-axis angle. • Wolter showed that two reflections were needed to eliminate the coma. • A Paraboloid-Hyperboloid combination proves to be the most useful in X-ray astronomy. X-ray Telescopes • First used to observe the Solar corona • Then transferred to general astronomy with HEAO-2 (Einstein Observatory), launched in 1978: – imaged X-rays in 0.5-4.0 keV. – the first X-ray astronomy mission with a guest observer program and a “public archive” (which I used for my PhD thesis). • Followed by ROSAT (Germany-US-UK), – performed an all-sky imaging survey in the 0.2-2.5 keV range – followed by longer pointed observations at specific targets. – generated a vast public database (which still has lots of potential) - and is a fertile source of targets for Chandra and XMM-Newton. Einstein X-ray Observatory Einstein Imaging of the LMC Wang et al. 1991 Recent X-ray Observatories Observatory ROSAT ASCA Chandra XMM/Newton PSPC HRI Service 90 - Feb. 99 93 -July 00 July 99- Dec. 1999- Energy Coverage (keV) 0.1-2.4 0.4-12 0.3-10 0.2-15 Spatial Res. (") ~30 ~6 ~60 ~0.5 ~6 Spectral Res. (E/∆E) ~2 - ~30 ~30 ~30 Field of View 2° 30’ 30’ 16’ 30’ Effective Area (cm2) ~210 ~80 ~230 ~620 ~1200 XMM-Newton Chandra vs. XMM-Newton • Chandra is best for… – Anything requiring better than 5” spatial resolution. – High resolution spectroscopy for energies < 0.5 or > 2 keV. • XMM-Newton is best for… – Imaging or imaging-spectroscopy which does not require a resolution of 5 arcseconds or better. – High resolution spectroscopy for energies 0.5 < E < 2 keV. – High resolution spectroscopy on extended objects that are larger than 10” and smaller than 1’. Chandra X-ray Observatory before the launch 45 feet tall Inertial Upper Stage boosted Chandra from shuttle orbit to transfer orbit Payload doors open 1.5 hrs after launch Propulsion system fired to reach final orbit of 10,000 x 140,000 km (1/3 way to moon) Propulsion system fired to reach final orbit of 10,000 x 140,000 km (1/3 way to moon) Orbital period is 64 hrs From above, with radiation belts & Moon Side view, showing radiation belts Chandra: illustration • Nested mirrors increase collecting area • Coated with iridium - highly reflective to X-rays •Largest mirror diameter = 1.2m (2x Einstein) •Nested mirrors for increasing collecting area •Coated with iridium - highly reflective to X-rays Chandra Scientific Instruments • 2 Imaging Focal Plane Science Instruments – ACIS (Advanced CCD Imaging Spectrometer) – HRC (High Resolution Camera) • 2 Objective Transmission Gratings for Dispersive Spectra – LETG (Low-Energy Transmission Grating) – HETG (High-Energy Transmission Grating) CCD imaging spectrometer • Semi-conductor (Si) requires small amount of energy to generate a free electron • Photoelectric interaction of a single X-ray photon Æ a measurable number of free electrons 27 < Ne < 2700 for 0.1 < E < 10 keV) • The number is good measurement of E • Spectral resolution depends on – Good charge collection and trasfer efficiencies – Low readout and dark-current noise –High readout rate ACIS and HRC in Focal Plane ACIS •Two types of CCDs: FI and BI • CCD size: 1024 x1024 each • Readout area •Aiming point •CCD gaps Transmission Grating Spectrometers Gratings Detector Characteristics Detector Spatial Pixel Size Spectral Timing Resolution Resolution Resolution ACIS ~1 arcsec 0.492 ~100-200 3.2 s (full arcsec eV frame) HRC 0.4 arcsec 0.132 ~1 keV 16 µs arcsec HETG ~1-2 eV LETG ~5 eV Chandra X-ray Observatory Spacecraft Schematic CXC Chandra X-ray Observatory CXC Chandra X-ray Observatory CXC Crab Nebula, Rosat Crab Nebula, Chandra Eta Cari HST optical image Chandra X-ray image Chandra survey of the Galactic ridge Wang et al. (2002) X-ray Flare from Sgr A* Peak L(2-10 keV) ∼1035 erg s-1 Lasted for about 3 hrs Variability timescale ~ a few minut The most compelling evidence yet Baganoff et al. (2001) that matter falling toward the black hole is fuelling energetic activity. The Coma Cluster of galaxies Optical, Kitt Peak Chandra-Data, A.Vikhlinin et al. ⇒ Galaxies swim in a sea of hot gas Images Taken in Chandra’s First Two Years http://asc.harvard.edu http://chandra.harvard.edu.
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