the transient radio sky to be revealed by the ska
DESCRIPTION
Jim Cordes Cornell University AAS Meeting Washington, DC 8 January 2002. The Transient Radio Sky to be Revealed by the SKA. TRANSIENT SOURCES. Sky Surveys: The X-and- -ray sky has been monitored highly successfully with wide FOV detectors (e.g. RXTE/ASM, CGRO/BATSE). - PowerPoint PPT PresentationTRANSCRIPT
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The Transient Radio Sky to be Revealed by the SKA
Jim Cordes Cornell University
AAS MeetingWashington, DC8 January 2002
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TRANSIENT SOURCES TRANSIENT SOURCES
Sky Surveys:Sky Surveys:The X-and-The X-and--ray sky has been monitored highly -ray sky has been monitored highly successfully with wide FOV detectors successfully with wide FOV detectors (e.g. RXTE/ASM, CGRO/BATSE).
Neutrino/gravitational wave detectors are ‘all sky.’Neutrino/gravitational wave detectors are ‘all sky.’
The transient radio sky (e.g. t < 1 month) is largely The transient radio sky (e.g. t < 1 month) is largely unexplored.unexplored.
New objects/phenomena are likely to be discovered New objects/phenomena are likely to be discovered as well as predictable classes of objects.as well as predictable classes of objects.
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TRANSIENT SOURCES (2)TRANSIENT SOURCES (2)
TARGET OBJECTS: TARGET OBJECTS:
• Atmospheric/lunar pulses from neutrinos & cosmic rays
• Accretion disk transients (NS, blackholes)• Neutron star Magnetospheres• Supernovae• Gamma-ray burst sources• Brown dwarf flares (astro-ph/0102301)• Planetary magnetospheres & atmospheres• Maser spikes• ETI
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Phase Space for Transients: SpkD2 vs. W
W
W
Pulse
Process
Spk
log
Sp
kD
2
log W
W = light travel time
brightness temperature:
SpkD2
Tb = ------------- 2k (W)2
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Phase Space for Transients: SpkD2 vs. W
W
W
Pulse
Process
Spk
log
Sp
kD
2
log W
Lines of constant brightness temperature
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Phase Space for Transients: SpkD2 vs. W
W
W
Pulse
Process
Spk
log
Sp
kD
2
log W
Solar system
+
local galactic sources
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Phase Space for Transients: SpkD2 vs. W
W
W
Pulse
Process
Spk
log
Sp
kD
2
log W
OH masers
+
Pulsars (including giant pulses)
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Phase Space for Transients: SpkD2 vs. W
W
W
Pulse
Process
Spk
log
Sp
kD
2
log W
Cosmological sources:
AGNs (including IDV sources)
+
GRB afterglows
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Phase Space for Transients: SpkD2 vs. W
W
W
Pulse
Process
Spk
log
Sp
kD
2
log W
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Phase Space for Transients: SpkD2 vs. W
W
W
Pulse
Process
Spk
log
Sp
kD
2
log W
Interstellar scintillations = apparent fast variations of IDVs & GRBs
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The SKA will thoroughly explore this phase space
W
W
Pulse
Process
Spk
log
Sp
kD
2
log W
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TRANSIENT SOURCES (3)TRANSIENT SOURCES (3)TARGET PROCESSES:TARGET PROCESSES:
• Intrinsic:incoherent:
( inverse Compton brightness limit)coherent: (virtually no limit)continuum: low frequencies favored
spectral line: masers
• Extrinsic:scintillationmaser-maser amplificationgravitational lensingabsorption events
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TRANSIENT SOURCES (4)TRANSIENT SOURCES (4)Sure detectionsSure detections::
• Analogs to giant pulses from the Crab pulsar out to ~5 – 10 Mpc
• Flares from brown dwarfs out to at least 100 pc.
• GRB afterglows to 1 µJy in 10 hours at 10 .
PossibilitiesPossibilities::
• -ray quiet bursts and afterglows?-ray quiet bursts and afterglows?
• Intermittent ETI signals?Intermittent ETI signals?
• Planetary flares?Planetary flares?
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Crab Pulsar
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Giant Pulses from Nearby GalaxiesGiant Pulses from Nearby Galaxies
SCIENTIFIC RETURNSCIENTIFIC RETURN
• Many objects Many objects map out IGM as well as ISM of map out IGM as well as ISM of
galaxiesgalaxies
• IGM: electron density and magnetic fieldIGM: electron density and magnetic field
• NS birth rates in other galaxiesNS birth rates in other galaxies
• Constraints on IMFConstraints on IMF
• Census of young pulsars, clues about magnetars?Census of young pulsars, clues about magnetars?
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M33
Beam 2
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J1907+0918
226 ms
DM = 358
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Working Around Radio Frequency Interference
• Single-dish/single-pixel transient detection:– Very difficult to separate terrestrial & astrophysical
transients (significant overlap in signal parameter space)
• Multiple beam systems (Parkes, Arecibo, the GBT):– Simultaneous on/offs partial discrimination
• Multiple site systems (a la LIGO, PHOENIX)– Very powerful filtering of RFI that is site specific or
delayed or Doppler shifted between sites
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Methods with the SKAMethods with the SKA
I. Target individual SNRs in galaxies to5-10 Mpc
II. Blind Surveys: trade FOV against gain by multiplexing SKA into
subarrays.
III. Exploit coincidence tests to ferret out RFI, use multiple beams.
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Primary beam & station Primary beam & station synthesized beamssynthesized beams
Station subarrays for Station subarrays for larger FOV (mosiacing)larger FOV (mosiacing)
One station of many in SKAOne station of many in SKA
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Summary • Transient science is unexplored territory for radio astronomy:
New looks at known sources, entirely new classes of sources: LOFAR will survey transients at f < 240
MHz; SKA for 240 MHz < f < 22 GHz (or more)• Implications for SKA design: Rapid
imaging/mosaicing of sky (days) Large instantaneous FOV desired for short time scales (e.g. hemispheric). US Plan: Subarrays to allow coincidence tests and maximal sky coverage. Versatile imaging/beamforming/signal processing modes.
• Similar implications from pulsar science