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7/26/12 W. Majid 1
Crab Giant Pulses
W. Majid*, S. Ellingson (PI), C. Garcia-Miro, T. Kuiper, J. Lazio, S. Lowe, C. Naudet, D. Thompson,
K. Wagstaff*Jet Propulsion Laboratory, California Institute of Technology
7/26/12 W. Majid 2
Some Facts about Giant Pulses• Intense narrow pulses with a pulse energy many
times that of mean pulse energy: Speak >~ 100 x <S>• Characterized by a power-law distribution of pulse
energies• Extremely rare phenomenon
– To date only ~10 pulsars have been known to exhibit this behavior out of ~2000 known pulsars
• Bursts fall into narrow phase window in pulse profile• The Crab exhibits ns bursts - limited by hardware
(Hankins et al. 2007)– Suggests region of emission is size of a basketball– Smallest entity ever detected outside Solar system– Extreme brightness temperature - brightest in galaxy
• Coincident with high frequency emission
7/26/12 W. Majid 3
Why GPs?• Only way to detect extragalactic pulsars• Important for understanding the magnetospheres of
pulsars• Emission mechanism is not well understood• How high energy emission might be linked with
radio emission• Conflicting claims on few detections• Are GPs restricted to small group of pulsars or
many waiting to be discovered• Galactic pulsar population may be larger than we
thought• Wide range of single pulse properties apparent• Algorithms relevant to transient detection
phenomenon
7/26/12 W. Majid 4
Low Frequency Studies• Why at Low Frequencies
– Examine how the properties of pulse emission evolves• Pulse energy frequency dependence
– Scattering and dispersive effects more prominent
• Previous Studies– Early studies at 200 MHz suggested a turnover of
the spectrum (Manchester & Taylor 1977)– 23, 111, and 600 MHz studies by Popov et al. 2006
suggests very steep falloff at low frequencies– MWA detected a handful of GPs at 200 MHz, none
at 100 MHz (Bhat et al. 2007)– LOFAR LBA studies 32-80 MHz (Stappers et al.
2011)
7/26/12 W. Majid 5
Low Frequency Studies• Why at Low Frequencies
– Examine how the properties of pulse emission evolves• Pulse energy frequency dependence
– Scattering and dispersive effects more prominent
• Previous Studies– Early studies at 200 MHz suggested a turnover of
the spectrum (Manchester & Taylor 1977)– 23, 111, and 600 MHz studies by Popov et al. 2006
suggests very steep falloff at low frequencies– MWA detected a handful of GPs at 200 MHz, none
at 100 MHz (Bhat et al. 2007)– LOFAR LBA studies 32-80 MHz (Stappers et al.
2011)
7/26/12 W. Majid 6
Low Frequency Studies
• LWA Advantages– 30% greater sensitivity
(256 stands, coherently combined)
– Up to ~80 MHz BW (with 3 beams)
– Location better for Crab– Multi-beaming capability– Low RFI environment– Excellent prospects for
pulsar and transient science
7/26/12 W. Majid 7
Single Dispersed Pulses with the LWA (P. Ray)
• Crab Giant Pulse Campaign– 160 hours over 10 months– Can coordinate with higher frequencies at GAVRT, GBT– Can coordinate with Fermi for radio/gamma
correlation studies
• Single Dispersed Pulse Survey– 160 hours over 11 months– Survey will establish limits on LIGO sources, discover
or study RRATs
• GCN-triggered observations of GRBs– 80 hours over 10 months– Dispersive delay gives time for interrupting observing
and repointing– New MCS event-triggered observing capability
applicable to other projects
7/26/12 W. Majid 8
Crab Pulsar Observations
Date HH:MM (UTC) Duration (hr)
2012-02-19 00:53 4
2012-02-20 00:49 4
2012-02-23 00:36 4
2012-02-26 00:24 4
2012-03-03 01:01 2
2012-03-04 02:00 1
2012-03-11 00:29 2
2012-03-17 23:02 4
2012-04-09 21:31 4
2012-04-29 19:00 4
S. Ellingson
7/26/12 W. Majid 9
2012-04-29 Observation of the Crab
• Crab pulsar was observed at L-band from 19:57:00 – 21:40:00
7/26/12 W. Majid 10
2012-04-29 Observation of the Crab
• Crab pulsar was observed at L-band from 19:57:00 – 21:40:00
7/26/12 W. Majid 11
2012-04-29 Observation of the Crab
13 kJy, 8 s wide
7/26/12 W. Majid 12
2012-04-29 Observation of the Crab
• LWA Observation:• 4 Beams: 2 pointed at the Crab; 2 pointed off the Crab 0.7 hr
in RA• Beams 1&3: 60, 76 MHz (dual pol)• Beams 2&4: 28, 44 MHz• BW = 19.6 MHz• 4x1TB drives (mattingly,koubek,kalbfus, and roosa - MLB?)
Frequency (MHz) Dispersive Delay (s)
76 17
60 35
44 90
28 390
7/26/12 W. Majid 13
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7/26/12 W. Majid 16
2012-04-29 Observation of the Crab
• Using LSL tools: looking at spectra, waterfall plots, time series
• Extracting voltage data to apply coherent dedispersion on 50s of data starting at the time of the L-band GP
• Stay tuned …
7/26/12 W. Majid 17
Implications for Single Dispersed Pulse Detections
• Pulsars Sources (Known)– Giant Pulses– Rotating Radio Transients
(RRATs)– Anomalously Intensive
Pulses (AIPs)
• Suspected Sources– Prompt Emission from
GRBs– Compact Object Mergers
(LIGO/VIRGO events)– Evaporating Primordial
Black Holes– Cosmic Strings
• Unknowns– Magnetars?– Much unexplored search
space
Pe
riod
de
rivat
ive
(s
s-1)
(Keane et al. 2011) Period (s)
7/26/12 W. Majid 18
FIN
7/26/12 W. Majid 19
Crab GPsMicrostructure
7/26/12 W. Majid 20
Fermi Studies• Source of GP emission currently
unknown– Changes in coherence of radio emission– Changes in pair creation rate in the
pulsar magnetosphere– Changes in beaming direction
• Correlation studies with high energy emission is one way to pin-point the origin of GP emission– Look for increase in high-energy flux
during GP emission– Look for frequency dependence of GP
emission and coincidence with high energy emission
7/26/12 W. Majid 21
Fermi Studies (in progress)• Expect ~100 coincidences over the course of
this study