Pursuing Gamma Ray Bursts and Fast Optical Transients with Thinking Telescopes

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Pursuing Gamma Ray Bursts and Fast Optical
Transients with Thinking Telescopes
Tom Vestrand, LANL
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Definition

• The human brain, through a process we loosely
  call thinking, integrates data collection,
  pattern recognition, object classification, and
  memory to obtain a higher understanding of what
  action needs to be taken and promptly takes
  action to respond to a threat or an opportunity.

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Why do Sky Monitoring Telescopes need to think?

• Threat--- interference, telescope malfunction,
  etc.
• Opportunity--- discovery of transients, new stuff
  not predicted. When you start looking at large
  fields (high etendue ?A) you can find ephemeral
  things?time domain astronomy, Space Situational
  Awareness

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We have reached the tipping point

• Time Domain Surveys (e.g. LSST) will generate 100
  Petabytes of data (2 Terabyte per hour) that
  must be mined in real time by the end of the
  decade.
• More than 10 Billion objects will be monitored
  for important variations in real time.
• Humans lack attention span, response time, and
  memory required to monitor the data, recognize
  the important variations, and respond.

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How do we find important changes in persistent
sources and respond in real time?
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Need Integration of Three Components
Advanced Database Tech. Context Knowledge Record
of Sky variability (Virtual Observatory), Massiv
e Distributed Disk Arrays
Machine Learning GENIE, Unsupervised
and Supervised Classifiers, Anomaly
Detection, SVMs, etc.

• Robotic Hardware
• Wide-Field Sky Monitoring Arrays,
• Rapid Response Telescopes,
• Talons Distributed Network Technology

Thinking Telescopes An Engine for Discovery in
the Time Domain
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Three Types of Machine Learning

• Automated Feature Extraction Real time
  identification of artifacts and transients in
  direct and difference images.
• Classifiers Automated classification of
  celestial objects based on temporal and spectral
  properties.
• Anomaly Detection Real time recognition of
  important deviations from normal behavior for
  persistent sources.

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Supervised Machine Learning

• Easier to show a machine what to find
• Machine Learning derives classification
  algorithms directly from examples of data
• ...than to tell a machine how to find it
• Requires domain expertise
• Involves software development
• Demands careful attention to statistical
  characterization
• Entails substantial amount of trial and error

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Classification of Image Objects
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What is an Anomaly?

• Dictionary Gives two Definitions
• 1) Deviation or departure from the normal or
  common order, form, or rule
• 2) One that is peculiar, irregular, abnormal, or
  difficult to classify.

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Anomaly Detection

• Unsupervised machine learning
• Finds things that dont fit in.
• Anomalies do not permit positive definition---If
  I knew what they were, we wouldnt call them
  anomalies.

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http//skydot.lanl.gov
Memory and Context
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Public SkyDOT website
skydot.lanl.gov
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RAPTOR response telescope.

• Deployed RAPTOR-S in October/November 2004 for
  studying the optical emission from gamma ray
  bursts during the critical first few minutes
  after a GRB----slew speed gt100 deg/second,
  acceleration gt100 deg/sec2, can go anywhere in
  the sky and begin imaging in 6 seconds.

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RAPTOR Discovery of Prompt Optical Emission from
GRBs
A new taxonomy for optical emission from GRBs
(Vestrand et al., Nature, 435,178, 2005).
1) Prompt Optical Emission varying
simultaneously with prompt gamma-rays. 2) Early
Afterglow Emission that may start during prompt
gamma-rays, but persists after gamma-rays
fade. 3) Late Afterglow Emission that can last
for hours to days.
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In the Standard Theoretical Framework it makes
physical sense to attribute the components to

• Prompt optical emission is generated by internal
  shocks in ejecta---driven by engine.
• Early afterglow is generated by external shocks
  from interaction with surroundings.
• Measuring the rise timescale of the early
  afterglow is a measure of the amount of stuff
  in the explosion environment.

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RAPTOR discovery of the relationship between
prompt and early optical afterglow emission.
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Afterglow is a Reverberation of the energy input
measured by the prompt emission.
Simple conjecture
Vestrand et al. Nature, 442, 172175 (2006)
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Why is this important?

• The best tool for probing the structure of the
  circum-burst environment and evolution of
  jet/environment interaction.
• Since a significant number of GRBs are expected
  at very high redshifts (zgt4), afterglow response
  can probe the nurseries of the first generations
  of stars.
• The observed response to late-time impulsive
  energy releases can reveal how earlier flaring
  episodes altered the environment.

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Why we need simultaneous 4-color photometry.

• The prompt optical is not a low-frequency tail of
  the gamma-rays, the variability of the optical
  spectrum is the key to understanding the physics.
• Most GRBs occur in dusty, star forming regions.
  The intense radiation field destroys the grains
  during the first minutes?variable extinction

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Simultaneous Multi-color Measurements during the
first minute

• Color measurements? slope of continuum, that plus
  time evolution yields basic parameters of flow
  the Lorentz factor, the ambient density, the
  fraction of the energy in mass of the particles,
  and the fraction of the energy in the magnetic
  field

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New Generation of RAPTOR response
telescopes(Observations starting 6 seconds
after alert)
RAPTOR-Z Ultra-fast imaging cadence (EMCCD) for
studying prompt emission RAPTOR-T Simultaneous
Multicolor Imaging of prompt and early afterglow
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GRBs as Cosmological Beacons Finding the most
distant objects through multi-color observations

• Most important GRBs are at redshifts larger than
  z5 when the Universe was lt10 of its current
  age.
• Can act as beacons to map diffuse material that
  never condensed into stars (4 of the Universe is
  in baryons1/10 of that is in visible stars and
  dust) This diffuse matter is in filaments that
  can be seen in absorption, if the GRB can be
  recognized when they are bright.
• RAPTOR can find them using a very simple
  technique---look for the cutoff at 912 Angstroms
  due to absorption by neutral hydrogen.
• This cutoff is redshifted to wavelengths longer
  than 5000 Angstroms for Z5 or more (out of Swift
  band-pass). So look for optical counterparts only
  visible in the red.
• Simultaneous multicolor observations during the
  first minute are the best way to quickly identify
  these distant GRBs and enable high-resolution
  spectroscopic observations while they are still
  bright.

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Identification of a Salient Class of Optical
Afterglows from GRBs
All GRB afterglows with measured redshifts
transformed to z2. (From Panaitescu Vestrand,
MNRAS, 387, 497 (2008))
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Discovery of relationship between peak time and
peak flux of early rising afterglows
Crude Standard Candles---but potentially usable
out to z10 . We are currently exploring other
properties that may refine the correlation. From
Panaitescu Vestrand 2008
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Toward continuous sky monitoringThe next
generation untriggered optical searchand why it
matters

• Motivation stronger than ever
• Transients are there (GRB 060206, DLS, radio
  etc.)
• Incredibly productive interplay between Swift and
  ground based robotic instruments
• Pre-Swift OT concepts completely revised
• Guaranteed result down to 16.0 mag
• We are looking one step ahead
• Orphans, on-axis optical GRBs, TGBNs, etc.
• Thinking Telescopes distributed aperture

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Precursors, Short GRBs, Optically-Rich Fast
Transients

• Monitor 1000 sq-degrees simultaneously
• Sensitivity 16th magnitude in 30 second exposure
• Carried on fast slewing mount--- can cover the
  full sky on 5-10 minute circuit.

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RAPTOR Network Detection of a Naked Eye GRB in
March 2008 (Mv-38.6!)
Persistent Monitoring
Follow-up Observations
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Discoveries from GRB 080319b

• Synchrotron Self-Compton is the emission process
  in GRBs
• Synchrotron Self-Absorption cut-off moved through
  optical band
• Large Angle off-axis emission in optical
• Strongest limits on precursor activity
• (from Wozniak, Vestrand, Panaitescu, et al. ,
  2008)

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First Simultaneous Multi-color Optical
Observations---Mixture of two different color
components
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GRB 060206 existence proofbright, high
redshift, explosion with few gamma-rays

• Low fluence, high redshift (z4.05) gamma-ray
  burst.
• Flared to R16.4 mag. at 1 hour without
  producing significant gamma-ray emission.
• Important implications for untriggered searches
  for fast optical transients and studies of GRB
  environments at high redshifts. (Wozniak et al.
  ApJ, 642, L99, 2006)

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Other exciting possibilities

• Off-axis orphan GRBs
• Strange fast transients (100-1000) are showing
  up in other surveys Deep Lens Survey, Quest,
  etc.
• On-axis orphans

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Other Optical Transients Outburst of Comet 17P
Holmes
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Conclusions GRBs

• We are now able to measure the relationship
  between the prompt optical emission and the early
  optical afterglow.
• The early afterglow can be understood as a
  response of the energy input measured by the
  prompt emission.
• Early afterglow structure is a new tool for
  probing the nature of the circumburst environment
  and the evolution of the jet/environment
• The observed response to late time impulsive
  energy releases can reveal how earlier flaring
  episodes have altered the jet/environment
  parameters
• Since a significant number of GRBs are expected
  to occur at high redshifts, afterglow response
  can probe the nurseries of the first generations
  of stars.

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Conclusions

• Fast optical transients are a powerful
  cosmological probes, but Time Domain Astronomy is
  too important to be left to the Astronomers.
• To be effective it requires real-time follow-up
  observations.
• We do not have the attention span, response
  time, or memory required to monitor the huge
  volume of data, recognize important variations,
  and respond.
• Autonomous Robotic Telescopes with smarts and
  the ability to learn will be essential for
  exploring the Time Domain in astronomy.