Chandra X-ray Observatory

Chandra X-ray Observatory

Annotated illustration of CXO
General information
NSSDC ID	1999-040B
Organization	NASA, SAO, CXC
Major contractors	TRW, Northrop Grumman
Launch date	23 July 1999
Launched from	Kennedy Space Center, USA
Launch vehicle	Space Shuttle Columbia STS-93
Mission length	planned: 5 years elapsed: 13 years, 10 months, and 27 days
Mass	4,790 kg (10,600 lb)
Orbit height	apogee 133,000 km (83,000 mi) perigee 16,000 km (9,900 mi)
Orbit period	64.2 hours
Wavelength	X-ray (0.1 - 10 keV)
Diameter	1.2 m (3.9 ft)
Collecting area	0.04 m2 (0.43 sq ft) at 1 keV
Focal length	10 m (33 ft)
Instruments
Website	chandra.harvard.edu

The Chandra X-ray Observatory is a space telescope launched on STS-93 by NASA on July 23, 1999. Chandra is sensitive to X-ray sources 100 times fainter than any previous X-ray telescope, enabled by the high angular resolution of its mirrors. Since the Earth's atmosphere absorbs the vast majority of X-rays, they are not detectable from Earth-based telescopes; therefore space-based telescopes are required to make these observations. Chandra is an Earth satellite in a 64 hour orbit, and its mission is ongoing as of 2013.

Chandra is one of the Great Observatories, along with the Hubble Space Telescope, Compton Gamma Ray Observatory (1991-2000), and the Spitzer Space Telescope. Chandra has been described as being as revolutionary to astronomy as Galileo's first telescope.

It was named in honor of the Nobel-prize winning Indian-American astrophysicist Subrahmanyan Chandrasekhar who worked for University of Chicago from 1937 until he died in 1995. He was known for determining the maximum mass for white dwarfs. "Chandra" means "moon" in Sanskrit. Before 1998, it was known as AXAF, the Advanced X-ray Astrophysics Facility. AXAF was assembled and tested by TRW (now Northrop Grumman Aerospace Systems) in Redondo Beach, California.

History

In 1976 the Chandra X-ray Observatory (called AXAF at the time) was proposed to NASA by Riccardo Giacconi and Harvey Tananbaum. Preliminary work began the following year at Marshall Space Flight Center (MSFC) and the Smithsonian Astrophysical Observatory (SAO). In the meantime, in 1978, NASA launched the first imaging X-ray telescope, Einstein (HEAO-2), into orbit. Work continued on the Chandra project through 1980s and 1990s. In 1992, to reduce costs, the spacecraft was redesigned. Four of the twelve planned mirrors were eliminated, as were two of the six scientific instruments. Chandra's planned orbit was changed to an elliptical one, reaching one third of the way to the Moon's at its farthest point. This eliminated the possibility of improvement or repair by the space shuttle but put the observatory above the Earth's radiation belts for most of its orbit.

AXAF was renamed Chandra in 1998 and launched in 1999 by the shuttle Columbia (STS-93). At 22,753 kg, it was the heaviest payload ever launched by the shuttle, a consequence of the two-stage Inertial Upper Stage booster rocket system needed to transport the spacecraft to its high orbit..

Crew of STS-93 with a scale model

STS-93 launches in 1999

Chandra has been returning data since the month after it launched. It is operated by the SAO at the Chandra X-ray Center in Cambridge, Massachusetts, with assistance from MIT and Northrop Grumman Space Technology. The ACIS CCDs suffered particle damage during early radiation belt passages. To prevent further damage, the instrument is now removed from the telescope's focal plane during passages.

Although Chandra was initially given an expected lifetime of 5 years, on 4 September 2001 NASA extended its lifetime to 10 years "based on the observatory's outstanding results." Physically Chandra could last much longer. A study performed at the Chandra X-ray Center indicated that the observatory could last at least 15 years. In July 2008, the International X-ray Observatory, a joint project between ESA, NASA and JAXA, was proposed as the next major X-ray observatory but was later cancelled. Its expected launch date would have been 2020.

Challenges

Chandra (AXAF) in the Shuttle bay

1976 saw Dr. Giacconi and Dr. Tananbaum's proposal to NASA. NASA accepted the proposal the next year, sending a 1.2 meter X-ray observatory into consideration, then let Marshall Space Flight Center (MSFC) and Harvard-Smithsonian take responsibility of this mission and fund the group for studying the feasibility of the project. They named the observatory as AXAF, because they hoped it wouldn't be taken as another Hubble Space Telescope (HST), an exorbitant instrument being built at that time.

After 3 years' concept design and preliminary analysis, AXAF didn't enter its designing and development phase, the most important phase called "new start", until 1991. There were mainly two reasons "contributing" to this long-lasting delay. First and foremost, almost everyone knew that HST cost a larger amount of money each year and often ran into problems. In that case, how would the Congress like to fund a project, which seems to be another HST? Second, it was the competition that came from many other instruments serving at other fields in astronomy. On the circumstances, administrators promoted the program by letting people with general or casual knowledge about astronomy know more about AXAF's value and significance and hence approved it. For example, they requested chief scientists in various disciplines to list top 10 interesting problems in their minds in astrophysics and corresponding solution-instruments. Then they extracted the 10 most frequent ones from all the problems and concluded 4 necessary instruments including AXAF and HST.

Scientists had been engaging themselves in selling AXAF till 1988. They were given the following three years and funds to build a pair of mirrors and prove its resolution to be 0.5 arc-second (the ability to discern words in newspapers about 2000 meters away). If they succeeded, AXAF would be funded, otherwise be canceled. That was called "Mirror Challenge". Although they overcame this challenge, because of retrenchment in funds, they had to adopt some reconstructions, such as some instruments' cancel, disconnection with astronauts, elevation of the orbit and so on. Faced with funding problem, scientists and engineers sometimes seemed pallid. What they could do at that time was set up new goals, and then spare no efforts to achieve them in order to make AXAF as powerful as possible.

Discoveries

Tycho Supernova remnant in x-ray light

SN 2006gy (upper right) and its parent galaxy NGC 1260 (lower left) in false color as observed through the Chandra X-Ray Observatory.

In this image of PSR B1509-58, the lowest energy X-rays that Chandra detects are red, the medium range is green, and the most energetic ones are colored blue.

X-rays from Jupiter.

The data gathered by Chandra have greatly advanced the field of X-ray astronomy.

• The first light image, of supernova remnant Cassiopeia A, gave astronomers their first glimpse of the compact object at the center of the remnant, probably a neutron star or black hole. (Pavlov, et al., 2000)
• In the Crab Nebula, another supernova remnant, Chandra showed a never-before-seen ring around the central pulsar and jets that had only been partially seen by earlier telescopes. (Weisskopf, et al., 2000)
• The first X-ray emission was seen from the super massive black hole, Sagittarius A*, at the center of the Milky Way. (Baganoff, et al., 2001)
• Chandra found much more cool gas than expected spiraling into the center of the Andromeda Galaxy.
• Pressure fronts were observed in detail for the first time in Abell 2142, where clusters of galaxies are merging.
• The earliest images in X-rays of the shock wave of a supernova were taken of SN 1987A.
• Chandra showed for the first time the shadow of a small galaxy as it is being cannibalized by a larger one, in an image of Perseus A.
• A new type of black hole was discovered in galaxy M82, mid-mass objects purported to be the missing link between stellar-sized black holes and super massive black holes. (Griffiths, et al., 2000)
• X-ray emission lines were associated for the first time with a gamma-ray burst, Beethoven Burst GRB 991216. (Piro, et al., 2000)
• High school students, using Chandra data, discovered a neutron star in supernova remnant IC 443
• Observations by Chandra and BeppoSAX suggest that gamma-ray bursts occur in star-forming regions.
• Chandra data suggested that RX J1856.5-3754 and 3C58, previously thought to be pulsars, might be even denser objects: quark stars. These results are still debated.
• Sound waves from violent activity around a super massive black hole were observed in the Perseus Cluster (2003).
• TWA 5B, a brown dwarf, was seen orbiting a binary system of Sun-like stars.
• Nearly all stars on the main sequence are X-ray emitters. (Schmitt & Liefke, 2004)
• The X-ray shadow of Titan was seen when it transitted the Crab Nebula.
• X-ray emissions from materials falling from a protoplanetary disc into a star. (Kastner, et al., 2004)
• Hubble constant measured to be 76.9 km/s/Mpc using Sunyaev-Zel'dovich effect.
• 2006 Chandra found strong evidence that dark matter exists by observing super cluster collision
• 2006 X-ray emitting loops, rings and filaments discovered around a super massive black hole within Messier 87 imply the presence of pressure waves, shock waves and sound waves. The evolution of Messier 87 may have been dramatically affected.
• Observations of the Bullet cluster put limits on the cross-section of the self-interaction of dark matter.
• "The Hand of God" photograph of PSR B1509-58.
• Jupiter's x-rays coming from poles, not auroral ring.
• A large halo of hot gas was found surrounding the Milky Way.

Technical description

Unlike optical telescopes which possess simple aluminized parabolic surfaces (mirrors), X-ray telescopes generally use a Wolter telescope consisting of nested cylindrical paraboloid and hyperboloid surfaces coated with iridium or gold. X-ray photons would be absorbed by normal mirror surfaces, so mirrors with a low grazing angle are necessary to reflect them. Chandra uses four pairs of nested mirrors, together with their support structure, called the High Resolution Mirror Assembly (HRMA); the mirror substrate is 2 cm-thick glass, with the reflecting surface a 33 nm iridium coating, and the diameters are 65 cm, 87 cm, 99 cm and 123 cm. The thick substrate and particularly careful polishing allowed a very precise optical surface, which is responsible for Chandra's unmatched resolution: between 80% and 95% of the incoming X-ray energy is focused into a one-arcsecond circle. However, the thickness of the substrates limit the proportion of the aperture which is filled, leading to the low collecting area compared to XMM-Newton.

Chandra's highly elliptical orbit allows it to observe continuously for up to 55 hours of its 65 hour orbital period. At its furthest orbital point from earth, Chandra is one of the most distant earth-orbiting satellites. This orbit takes it beyond the geostationary satellites and beyond the outer Van Allen belt.

With an angular resolution of 0.5 arcsecond (2.4 µrad), Chandra possesses a resolution over 1000 times better than that of the first orbiting X-ray telescope.

Instruments

M31 Core in X-rays

The Science Instrument Module (SIM) holds the two focal plane instruments, the Advanced CCD Imaging Spectrometer (ACIS) and the High Resolution Camera (HRC), moving whichever is called for into position during an observation.

ACIS consists of 10 CCD chips and provides images as well as spectral information of the object observed. It operates in the range of 0.2–10 keV. HRC has two micro-channel plate components and images over the range of 0.1–10 keV. It also has a time resolution of 16 microseconds. Both of these instruments can be used on their own or in conjunction with one of the observatory's two transmission gratings.

The transmission gratings, which swing into the optical path behind the mirrors, provide Chandra with high resolution spectroscopy. The High Energy Transmission Grating Spectrometer (HETGS) works over 0.4–10 keV and has a spectral resolution of 60–1000. The Low Energy Transmission Grating Spectrometer (LETGS) has a range of 0.09–3 keV and a resolution of 40–2000.

See also

• X-ray astronomy
• NASA - Great Observatories program

Further reading

• Pavlov GG, Zavlin VE, Aschenbach B, Trumper J, Sanwal D (2000). "The Compact Central Object in Cassiopeia A: A Neutron Star with Hot Polar Caps or a Black Hole?". Astrophysical Journal 531 (1): L53–L56. arXiv:astro-ph/9912024. Bibcode:2000ApJ...531L..53P. doi:10.1086/312521. PMID 10673413. 
• Weisskopf MC, Hester JJ, Tennant AF, Elsner RF, Schulz NS, Marshall HL, Karovska M, Nichols JS, Swartz DA, Kolodziejczak JJ, O'Dell SL (2000). "Discovery of Spatial and Spectral Structure in the X-Ray Emission from the Crab Nebula". Astrophysical Journal 536 (2): L81–L84. arXiv:astro-ph/0003216. Bibcode:2000ApJ...536L..81W. doi:10.1086/312733. PMID 10859123. 
• Baganoff FK, Bautz MW, Brandt WN, Chartas G, Feigelson ED, Garmire GP, Maeda Y, Morris M, Ricker GR, Townsley LK, Walter F (2001). "Rapid X-ray flaring from the direction of the supermassive black hole at the Galactic Centre". Nature 413 (6851): 45–8. arXiv:astro-ph/0109367. Bibcode:2001Natur.413...45B. doi:10.1038/35092510. PMID 11544519. 
• Griffiths RE, Ptak A, Feigelson ED, Garmire G, Townsley L, Brandt WN, Sambruna R, Bregman JN (2000). "Hot plasma and black hole binaries in starburst galaxy M82". Science 290 (5495): 1325–8. Bibcode:2000Sci...290.1325G. doi:10.1126/science.290.5495.1325. PMID 11082054. 
• Piro L, Garmire G, Garcia M, Stratta G, Costa E, Feroci M, Meszaros P, Vietri M, Bradt H, Frail D, Frontera F, Halpern J, Heise J, Hurley K, Kawai N, Kippen RM, Marshall F, Murakami T, Sokolov VV, Takeshima T, Yoshida A (2000). "Observation of X-ray lines from a gamma-ray burst (GRB991216): evidence of moving ejecta from the progenitor". Science 290 (5493): 955–8. arXiv:astro-ph/0011337. Bibcode:2000Sci...290..955P. doi:10.1126/science.290.5493.955. PMID 11062121. 
• Kastner JH, Richmond M, Grosso N, Weintraub DA, Simon T, Frank A, Hamaguchi K, Ozawa H, Henden A (2004). "An X-ray outburst from the rapidly accreting young star that illuminates McNeil's nebula". Nature 430 (6998): 429–31. arXiv:astro-ph/0408332. Bibcode:2004Natur.430..429K. doi:10.1038/nature02747. PMID 15269761. 

External links

• Audio - Cain/Gay (2010) Astronomy Cast Chandra X-Ray Observatory
• NASA Chandra Mission Site
• Chandra X-ray Observatory Center
• Chandra Mission Profile by NASA's Solar System Exploration
• iTunes University iPod feed URL
• Chandra Deep Field South