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Transcript
Reflections on the early years in X-ray astronomy Ken Pounds University of Leicester 4 October 1957 - Sputnik 1 launches the Space Era 83 kg Al sphere into 230-950 km orbit at 65 deg inclination 20 and 40MHz transmitters powered by battery bleep bleep lasted for only 21 days - but shook the world rocket case visible for several months and orbit decay used to study atmospheric density A strong international response : • with formation of NASA (1958) • and a new Space Research Group at Leicester (1960) 1960 Royal Society/DSIR grant to study ‘Solar and Stellar X-radiation’ but ‘stellar’ source detection seemed an ambitious aim at that time with predicted fluxes a billion times fainter than the Sun The Skylark research rocket • first test flight at Woomera in February 1957 • payload of 150 kg to 300 km • Sun, Moon and star-pointing versions from 1964 • PC on Sun in September 1961 (Sco X-1 also in view !) • Stellar X-ray instrument selected for OAO-C (Copernicus) in 1961 Priority in1960s remained in Solar X-ray studies ESRO-2 (May 1968) Ariel 1 (April 1962) OSO-4 (October 1967) OSO-5 (January 1969) Solar Corona in 1964 • pin-hole camera on sunpointing Skylark • active regions • limb brightening • (coronal holes) examining X-ray images of the solar corona the haircuts confirm it’s the 1960’s! Sco X-1 discovery raised a new challenge, with Skylark from Woomera offering access to the southern sky • SL 118 (10 April 1967) 295 cm2 PC. FOV 30x30 deg. First use of rtd/psd background reduction • Cen X-2 brighter and softer than Sco X-1. Tau X-1 also detected. (Cen X-3 not seen) • SL 723 (July 1968) and 724 (April 1969) with largest PCS to date, 2 x 1380 cm2 • spectra of brightest sources Skylarks 723/724 in 1968/69 GX 3+1 (September/October 1971) Sun-pointing vehicle, with Sco X-1 detector to fix roll angle Launch timing for occultation to occur when rocket at apogee A sub-arc-sec position but no optical counterpart found ! due to heavy dust obscuration in GC region it was time to move into orbit! A final look back at the heroic days of the sounding rockets X-ray astronomy moves into orbit : • to extend exposures from minutes to months and years • hence improve detection sensitivity • and monitor transient or variable nature of many sources NASA responded with the launch by the AS&E group of a small spinning satellite, UHURU, in 1970, detecting several hundred sources, including X-ray binaries and galaxy clusters Ariel 5 followed into a similar low equatorial orbit 4 years later Ariel 5 Scout B-1 launch 15 October 1974 500 km circular, equatorial orbit 129 kg S/C into equatorial LEO 10 rpm spin with axis control by gas jets, later by magnetorquer operated for 5.5 years to re-entry in March 1980 A. Rotation modulation collimator (UCL/MSSL) B. Sky survey Instrument (Leicester) C. Proportional counter spectrometer (UCL/MSSL) D. Bragg Polarimeter (Leicester) F. Hard X-ray scintillation counter (Imperial) G. All sky monitor (Goddard) into Sky Survey Instrument 6 quick-look orbits data in near real-time - adding to the excitement – and to the effective science exploitation bulk data within 24 hours • SSI data (sector, time, energy) stored in 1024 (16 bit) words over each orbit (15 tweets in 2012 currency) • data reduction by PDP-8 computer on to strip chart, labelled with known X-ray sources and candidate objects • revised commands sent if required • data to main frame computer together with S/C housekeeping etc Analysis automated – but quick-look data monitored by duty scientist team (Cooke, Elvis, Griffiths, Lawrence, McHardy, Seward, Turner, Watson, Villa) Sky Survey Instrument PC of 145 cm2 (LE) and 290 cm2 (HE) 0.75 x 10.5 0 FOV, inclined at 65 0 to spin plane 74 orbits data with the spin axis to the Galactic pole strong sources in Galactic bulge Several new detections from long exposure many variable from day to day (Tra X-1) A0620-00 (nova Mon) • new X-ray source seen in SSI over weekend 2/3 August • European Astronomy Society meeting 3 days later – in Leicester • brightest ever cosmic X-ray source after 2 weeks • attracting alarming headlines • but priority target for radio and optical telescopes worldwide Short exposure with UK Schmidt telescope at Siding Springs Palomar Sky Survey red plate V616Mon K5V star (mv 22>11) A0620-00 Ariel 5 monitoring continued for 6 months as X-ray flux fell back exponentially • optical counterpart identified by 7 mag increase, spectroscopy showed a 7.8 hr binary system with unseen companion • high orbital velocity shows companion too massive for neutron star • now confirmed as a 11 (+/- 2) solar mass black hole • predicted to flare again in 2033 What were the UHGLS’s ? Relativistic Astrophysics meeting Boston December 1976 • 21 identified as clusters of galaxies, doubling the number previously identified, mainly in 3U • 10 new Seyfert galaxy id’s, establishing a new class of powerful X-ray emitter Ann New York Acad Sci 1977 Seyfert galaxies a new class of extragalactic X-ray source Sky survey began to find coincidences between Ariel 5 sources and AGN the first was NGC3783 – a bright, very blue galaxy with an unusual optical spectrum further examples reported at Royal Society Ariel 5 review in 1978 Cooke et al, MNRAS1978 1980 launch of Einstein Observatory established X-ray Astronomy as a major branch of observational astrophysics - but NASA follow-up faced 20 year delay Fortunately: • 1983 Europe (ESA) entered the field with EXOSAT • 1987 Japan followed with GINGA • 1990 Germany with ROntgenSAT • 1996 Italy/Netherlands with Beppo-SAX Exosat and Ginga helped establish SMBH in AGN Exosat (1983-86) ESA’s first X-ray mission ME detector array from Leicester/MSSL first X-ray satellite in deep space orbit `long looks’ showed rapid X-ray variability from Seyfert galaxies X-ray variability of order 1 hour showed X-ray source in several bright Seyferts to be very compact Light travel time argument showed r < 12 au Ginga (1987-91) •4000 cm2 LAC developed by a joint Leicester-Japan team powerful instrument for timing and broadband spectra Discovery of ‘reflection’ in AGN using stacked spectra from 10 Seyfert observations and many Fe K appeared broad ! ROSAT (1990-97) WFC carried out the first sky survey at extreme UV wavelengths during 1990/91 Fast forward: X-ray Astronomy in 2012 in excellent shape with 3 major and complementary X-ray Observatories in orbit Chandra XMM -Newton Suzaku BUT: just one massive coronal mass ejection from disaster Photos from Leicester 50th in 2010