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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