The Dynamic Radio Sky and Future Instruments

1
The Dynamic Radio Sky and Future Instruments

• Jim Cordes
• Cornell University
• AAS Meeting
• Nashville
• 28 May 2003

2
Dynamic Radio Sky

• We know enough about the DRS to know that there
  is a great deal yet to be discovered
• c.f. the high energy universe, optical, etc.
• What is in the DRS?
• What are the prospects for new discoveries?
• Astrophysical parameters
• Extrinsic effects
• RFI
• Instruments surveys that will reveal the DRS

3
TRANSIENT SOURCES
Sky Surveys The X-and-?-ray skies have been
monitored highly successfully with wide FOV
detectors (e.g. RXTE/ASM, CGRO/BATSE). Neutrino/
gravitational wave detectors are all
sky. Optical transient surveys (ROTSE, RAPTOR,
LSST) are/will revolutionalize our knowledge of
the optical transient sky and will drive the
trend toward data mining of petabyte
databases. The transient radio sky (e.g. t lt 1
month) is largely unexplored.
New objects/phenomena are likely to be discovered
as well as extreme cases in predictable classes
of objects.
4
Ingredients for transient detection

• A?T needs to be large
• A collecting area
• ? solid angle covered (instantaneous FOV)
• T time per sky position
• Issue to dwell (stare), or tile the sky, or be
  triggered?

5
Successes in transient astronomy
Vela
ROTSE
RAPTOR
RXTE/ASM
6
(No Transcript)
7
Why is the Dynamic Radio Sky Largely Uncharted?

• Large collecting areas, A, needed for
  sensitivity
• Typically A? is small enough that telescope
  throughput is small
• Telescope time is expensive so dwell times are
  short
• Sources cover a wide range of time scale and sky
  density
• ? insufficient sky and temporal coverage

8
Giant pulse from the Crab pulsar S 160 x Crab
Nebula 200 kJy Detectable to 1.5 Mpc with
Arecibo
Arecibo
2-ns giant pulses from the Crab (Hankins et al.
2003)
Giant Pulses seen from B0540-69 in LMC (Johnston
Romani 2003)
9
Giant pulses are the fastest known transients

• Giant pulses from Crab detectable to 1.5 Mpc
  with Arecibo _at_ 1/hour
• 2-ns wide nano-Giant pulses identified from
  Crab (Hankins et al. 2003)
• GPs seen from Crab clone in LMC (B0540-69) by
  Johnston Romani (2003) w/ similar intrinsic
  amplitude
• GPs from two millisecond pulsars
• Radio GPs in pulse components also seen in X-rays
• GP-emitting objects have same B fields at their
  light cylinders

10
Nano-giant pulses (Hankins et al. 2003)
Arecibo 5 GHz 0.5 GHz bw coherent dedispersion
11
STARE 611 MHz 3-station radio transient
detector (Katz, Hewitt, Corey, Moore 2003)
Solar Radio Bursts
12
GRB 980519 variability (Frail et al. 2000)
Interstellar scintillations
13
TRANSIENT SOURCES

• 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

14
TRANSIENT SOURCES

• TARGET PROCESSES
• Intrinsic incoherent (?
  inverse Compton brightness limit) coherent
  (virtually no limit) continuum low
  frequencies favored spectral line masers
• Extrinsic scintillation maser-mase
  r amplification gravitational
  lensing absorption events

15
Phase Space for Transients SpkD2 vs. ?W
W light travel time brightness
temperature SpkD2 Tb
------------- 2k (?W)2
Pulse
Spk
W
log SpkD2
W
Process
log ?W
16
Phase Space for Transients SpkD2 vs. ?W
Pulse
Lines of constant brightness temperature
Spk
W
log SpkD2
W
Process
log ?W
17
Phase Space for Transients SpkD2 vs. ?W
Pulse
Solar system local galactic sources
Spk
W
log SpkD2
W
Process
log ?W
18
Phase Space for Transients SpkD2 vs. ?W
Pulse
OH masers Pulsars (including giant pulses)
Spk
W
log SpkD2
W
Process
log ?W
19
Phase Space for Transients SpkD2 vs. ?W
Pulse
Cosmological sources AGNs (including IDV
sources) GRB afterglows
Spk
W
log SpkD2
W
Process
log ?W
20
Phase Space for Transients SpkD2 vs. ?W
Pulse
Spk
W
log SpkD2
W
Process
log ?W
21
Phase Space for Transients SpkD2 vs. ?W
Pulse
Interstellar scintillations apparent fast
variations of IDVs GRBs
Spk
W
log SpkD2
W
Process
log ?W
22
New instruments can cover this phase space
Pulse
Spk
W
log SpkD2
W
Process
log ?W
23
Exploring the Transient Radio SkyStriving for
large A?T

• Pilot observations
• Arecibo single pixel and multibeam (ALFA)
• STARE and similar multisite arrays
• GBT single pixel and multibeam arrays
• ATA 2.5 deg FOV, 8 array beams
• EVLA (wideband, high sensitivity spatial
  resolution)
• LOFAR low frequencies (lt 240 MHz)
• SKA broad frequency range (0.15 to 25 GHz)

24
Giant pulses from M33 Arecibo observations
(Maura Mclaughlin Cordes, submitted to ApJ,
astro-ph
25
Galactic Center Transients
VLA 0.33 GHz Hyman et al. 2002
26
Exploring the Transient Radio SkyCovering the
Sky

• Staring vs. mosaicing (tiling)?
• Radio sky needs both
• Fast transients too fast to raster scan the sky
  (lt hours to months) (e.g. GPs)
• Slower transients
• raster scan (e.g. for objects showing radio only)
• trigger from other wide-field instruments (GRB
  afterglows)

27
TRANSIENT SOURCES

• Sure 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 ?.
• Possibilities
• ?-ray quiet bursts and afterglows?
• Intermittent ETI signals?
• Planetary flares?

28
Re-ignition of pulsar action in mergers?
Isolated pulsar
Hansen Lyutikov 2000
29
RFI Editing in the f-t plane
RFI dynamic spectra (from AO monitoring program)
Dynamic spectrum of pulsar scintillation
30
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

31
LOFAR Low Frequency Array
Stations of dipoles 30 to 240 MHz Large
A?T Optimal for coherent continuum transients
32
China KARST Canadian aerostat US Large
N Australian Luneburg Lenses Dutch fixed
planar array
SKA Square Kilometer Array Current
Concepts
(cf. Allen Telescope Array, Extended VLA)
(cf. LOFAR Low Freqency Array)
33
Current Baseline Specifications
34
Methods with LOFAR SKA

• I. Target individual objects
• II. Blind Surveys trade FOV against gain
  by multiplexing SKA into subarrays.
• III. Allow rapid response to triggers
• IV. Exploit coincidence tests to ferret out
  RFI, use multiple beams.

35
Station subarrays for larger FOV
Primary beam station synthesized beams
One station of many in SKA
36
Blind Surveys with SKA

• Number of pixels needed to cover
  FOV Npix(bmax/D)2 104-109
• Number of operations Nops petaops/s
• Post processing per beam e.g. standard pulsar
  periodicity analysis

37
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 lt 240 MHz
• SKA for 0.15 GHz lt f lt 25 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 for pulsar science

38
Radio Pulsars

• 1400 known (doubled by Parkes MB)
• 100 millisecond pulsars
• 2 to 3 with planets
• 5 NS-NS binaries (Porb gt 8 hr)
• MSPs have exceedingly stable spins, suitable for
  seeking gravitational wave perturbations

39
Why more pulsars?

• Extreme Pulsars
• P lt 1 ms P gt 8 sec
• Porb lt hours B gt 1013 G (link to magnetars?)
• V gt 1000 km s-1

• NS-NS NS-BH binaries
• Population Stellar Evolution Issues
• The high-energy connection (e.g. GLAST)
• Physics payoff (GR, Gwaves, EOS, LIGO, GRBs)
• Serendipity (strange stars, transient sources)
• New instruments (AO, GBT, LOFAR, SKA) will
  dramatically increase the volume searched
  (galactic extragalactic)

40
Parkes MB Feeds
41
Parkes MB Feeds
42
ALFA Science Goals Massive Surveys

• Drift scan surveys (14 sec across 3.5
  arcmin)
• Deep Galactic plane survey (GPS) (5-10min, b
  lt 5 deg, 30 lt l lt 80 anticenter)
• Medium latitude surveys ( 5 lt b lt 25 deg)
• Targeted globular clusters, high EM/DM HII
  regions, SNRs, Galactic chimneys, M33, X/? -ray
  selected objects (long dwell times, up to 2.5
  hr)

43
Surveys with Parkes, Arecibo GBT. Simulated
actual Yield 1000 pulsars.
44
ALFA Surveys at Arecibo

• ALFA surveys can be viewed as part of a
  long-term, grander effort (Full Galactic
  Census) (LOFAR, SKA, ??)
• RFI mitigation required and provides general
  purpose tools
• Data data products long term resources ?
  data management policy resources 1 petabyte
  of survey raw data 1 petabyte of data
  products
• Exploit telescope time fully (transients,
  piggybacking)

45
SKA pulsar survey 600 s per beam 104 psrs
46
(No Transcript)