mssl astrophysics group
start
Terribly hot stars.
Liz Puchnarewicz
Mullard Space Science Laboratory, UCL
www.mssl.ucl.ac.uk/www_astro
-ray sources, missions and stars
mssl astrophysics group
introduction
-rays
models
breakthrough
new missions
Terribly hot stars.-ray sources, missions and stars
a brief history of -ray astronomy and a look at the -ray universe
models – collisions, hypernovae and others
finding -rays: mapping and measuring - SWIFT and MSSL’s UVOT
where do we see -rays? what does a g-ray burst look like?
bored
Beppo-SAX, with backup from Hubble, makes a real breakthrough
mssl astrophysics group
introduction
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cosmic -ray sources had been expected for several years.
Cosmic rays + ISM supernovae
high-E electrons + mag field
-ray
CR
-ray
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Introduction first crucial results
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OSO-3
COS-B
SAS-2
• First significant detection of -rays from our galaxy.• 621 cosmic -rays
SAS-2 (NASA) and COS-B (ESA)
• first mapped the -ray sky
• detected the first point sources
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Introduction first conclusions
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1973
GRBs confirmed by SAS-2 and COS-B
BUT distance and origin were unknown
SO energy in burst unknown
SO concluded that sources were in our Galaxy, possibly reconnection of neutron star magnetic field lines with the ISM magnetic field (ie analogous to solar flares).
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-rays
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• a -ray burst occurs about three times a day
• in seconds-to-minutes, it emits more energy than any other known phenomenon (apart from the Big Bang)
• they are distributed evenly over the sky
• they are very hard to study because they disappear before you can ‘catch’ them.
• they are very, very hot
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-rays
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1. Extragalactic in origin
2. VERY energetic (up to 10 ergs) (only
surpassed by the Big Bang)
3. VERY quick (30msec to 1.6 hours) – so must be
emitted from a region only a few 10s of
kilometres across
So what are -rays?
53
mssl astrophysics group
models neutron star mergers
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System emits radiation as neutron stars spiral inwards.
Merger occurs once every 10,000 to a million years in a galaxy.
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models
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A popular model for the origin of -ray bursts is in the merger of two neutron stars.
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models black hole forms
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two stars
collide
Forms a black hole plus a disc
Relativistic jets emerge along disc axis
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models where they might come from
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spatial distribution of counterparts
hypernovae
coalescing neutron stars
den
sity
of c
ou
nte
rpa
rts
distance from centre of host
coalescing neutron stars
hypernovae
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new missions
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Once a burst has been detected, the telescope will slew to position within seconds
X-ray positions to 2.5arcseconds
UVOT positions to 0.3arcseconds
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campaigns
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* identify host galaxies uniquely by obtaining arcsec positions * measure redshift distribution to determine energetics, cosmological evolution, and GRB luminosity function * locate GRBs relative to host galaxies * constrain burst environment using X-ray absorption and optical reddening
* use optical/X-ray afterglow as high redshift beacons * measure Ly-alpha forest * use X-ray absorption to probe intergalactic/cluster medium * extend star formation rate observations to high redshift
Aims of the SWIFT mission