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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

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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

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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

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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)

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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)

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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

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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

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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

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2012-04-29 Observation of the Crab

• Crab pulsar was observed at L-band from 19:57:00 – 21:40:00

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2012-04-29 Observation of the Crab

• Crab pulsar was observed at L-band from 19:57:00 – 21:40:00

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2012-04-29 Observation of the Crab

13 kJy, 8 s wide

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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

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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 …

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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)

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FIN

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Crab GPsMicrostructure

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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

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Fermi Studies (in progress)• Expect ~100 coincidences over the course of

this study