Scientists Find Scientific Event

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Scientists Find Scientific Event

• A Bright Millisecond Radio Burst of
  Extragalactic Origin D. R. Lorimer, M. Bailes,
  M. A. McLaughlin, D. J. Narkevic F. Crawford,
  Science Express September 27, 2007,
  arXiv0709.4301
• Presenter Paul Edmon
• Journal Club
• 10-04-07

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Scientists Ask Congress To Fund 50 Billion
Science Thing
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Overview

• Observation
• Analysis
• Interpretation
• Science Ends?

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Observation

• Burst found in archival data from a 1.4 GHz
  survey of the Magellanic Clouds
• Data was originally taken between May 2000 and
  November 2001
• Survey Info
• 64m Parkes Radio Telescope in Australia
• 209 Telescope Pointings
• 2.3 hrs per pointing
• 13 beams per pointing on different positions of
  the sky
• Beam Size 5 arcmins
• Sampled every millisecond
• 96 frequency channels over 288 MHz

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Observation

• Burst was detected on August 24, 2001
• Burst was located 3 degrees south of the center
  of the Small Magellanic Cloud (SMC)
• RA(J2000) 01h 18m 06s
• Dec(J2000) -75º 12 19
• Seen in three beams, saturated one of the
  detectors
• Follow up radio observations have not detected
  any new activity

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Observation
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Observation
Credit Stéphane Guisard
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Observation
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Analysis

• Dispersion Measure (DM)
• Typical Dispersion Measures
• Galactic for this line of sight 25 cm-3 pc
• DMs for pulsars in the SMC 70,76,105,125, 205
  cm-3 pc
• Burst DM 375 1 cm-3 pc
• No Ha filaments or HII regions in area of burst
• Higher DM in these regions

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Analysis
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Analysis

• Given the high DM and offset from SMC the burst
  is most likely extragalactic
• Assuming a homogenous Intergalactic Medium (IGM)
  which is fully ionized
• DM 1200 z cm-3 pc for z 2
• Subtracting expected Galactic contribution z
  0.3 which is a distance of 1 Gpc
• Host Galaxy and local environment could
  contribute to DM
• Taking this into account z lt 0.2
• For the sake of making some estimates z.12
  which is a distance of 500 Mpc
• This assumes a host galaxy DM of 200 cm-3 pc

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Analysis

• Pulse width (W) varies with frequency (f) as W a
  f-4.80.4
• This is consistent with interstellar scattering
  with a Kolmogorov power law W a f-4
• Given this pulse width evolution and
  uncertainties in the detectors the pulse width
  upper limit is 5 ms
• Assuming the pulse is 5 ms the burst flux is
  estimated at 30 10 Jy

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Analysis

• Burst Estimates
• Distance 500 Mpc
• Duration 5 ms
• Flux 30 Jy
• Source
• Energy 1040 ergs
• Power 2x1042 ergs/s
• Size from Light-crossing Time 1500 km

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Analysis

• If bursts are isotropically distributed over the
  sky then the inferred rate is 225 similar events
  per day
• Given the above the cosmological rate would be
  about 50 per day per cubic Gpc
• Problems
• Only one event
• Unknown source
• Distance not well known

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Interpretation

• What is it?
• GRB, SN?
• No detected GRB or SN at time or position
• Bizarre nature of the burst does not match any
  current theory
• Terrestrial?
• Telescope was pointed at a high elevation at the
  time
• Difficult to reproduce dispersion and scattering
  profile
• Non-repeating
• Rotating Radio Transient (RRAT)
• Typical pulses only detectable out to 6 kpc
• Giant Pulses
• Brightest Crab giant pulses would be detectable
  out to 100 kpc

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Interpretation

• What is it (continued)?
• Neutron Star Inspiral?
• Estimated Cosmological Rate 3 per day per cubic
  Gpc
• From Hansen Lyutikov (2001)
• Estimated Power extracted from orbit 1046
  ergs/s
• Estimated Duration 10s of seconds
• Should make X-Rays as well
• Black Hole Evaporation?
• From Rees (1977)
• Could be very fast
• Could be seen at large distances

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Science Ends?

• Nope, Science Just Beginning!
• Need to find more of these class of bursts
• Search Pulsar surveys for single energetic bursts
• See if one can see burst at other frequencies
• Need to characterize burst
• Find host galaxy for current burst
• Figure out burst source
• If a large enough population is found
• Use for cosmology
• Use to probe ionized IGM