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Defending Dunc

Defending Dunc

Evan Keane
LOFAR Transients Key Project Meeting, Meudon, December 2011

transientskp

June 23, 2012
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  1. Defending Dunc
    Evan Keane
    Max Planck Institut für Radioastronomie,
    Bonn, Germany
    LOFAR TKP Meeting
    15 December, 2011,
    Meudon, France.

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  2. Sparkers
    The Lorimer Burst
    Perytons
    A New Sparker
    What to do?

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  3. Single Events?
    As well as PSRs (reliable/erratic in radio) searches
    for single bursts can reveal non-repeating sources.
    Until we see a repeated burst we cannot rule out
    ‘single events’, i.e. supernovae,
    BH annihilation, NS mergers, GRBs
    Detected an isolated burst of radio emission, lasting
    5 milliseconds, at a very high dispersion measure
    SMC
    LB
    A PSR survey of the SMC region was
    searched for transients by Lorimer+

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  4. The Lorimer Burst
    We recall:
    tdelay = 4.150 ms (DM/fGHz
    2)
    DM = ∫ne dl
    Distances usually inferred
    from a model for ne by
    Cordes & Lazio (NE2001)
    LB had DM = 375 cm-3pc
    -> extra-galactic!

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  5. The Lorimer Burst
    Only 25 cm-3pc due to Galaxy
    -> the rest due to IGM and putative host galaxy
    DM-z relation exists -> DM = 1200z -> z = 0.2
    Note that LB was detected in 3 of 13 beams of the
    receiver, saturating one of them
    -> as expected from a bright astrophysical source
    -> obeys the theoretical DM law tdelay∝f-2
    -> obeys a scattering law of the form W∝f-4.8(4)
    -> no coincident high-energy or GW signal
    All the evidence suggests it has extra-galactic origin

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  6. Perytons
    Further searches of archival surveys undertaken ...
    16 sources, known as “perytons” found
    -> detected in all 13 of 13 beams
    -> not very strong in any of them
    Their frequency-delay structure is roughly similar to
    the f-2 dependence of an astrophysical signal
    but not exactly the same as weird “kinks” seen
    strange kink
    in all beams
    So what? the inferred DM very close to LB DM !

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  7. Perytons
    So the DM of the LB has some suspicion over it
    however the LB did not show any kinks & is not in all
    beams -> coincidence?
    Perytons all occured during daylight in June/July
    (mid-winter in Australia) in years 1998-2003
    -> man-made or weather-related?
    The LB occured during the night of 24/8/2001
    Peryton pulse widths 30-50 ms, LB was 5 ms
    Both broadband in legally protected part of spectrum
    Perytons no scattering + ‘lumpy’ freq. modulation

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  8. Perytons
    More results on perytons ...
    Paper by Kocz et al now in press
    (was not put on astro-ph, so you may have missed it)
    Found more in same surveys ...
    New ‘DM’ values are: 278, 279, 386, 393, 402 (LB 375)
    NB Didn’t search >500, whereas <200 “considered RFI”
    Perytons appear at 0.8 seconds past each second UTC
    They are also spaced by 22 seconds ...
    “... suggest that the RFI may not be from a natural
    source ...”

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  9. Pulsar Data
    PSR search data cube: time-freq-amplitude.
    For PMPS tsamp=250μs, Δf=3MHz, amplitudes 1-bit.
    13 of these for each pointing
    x 13
    Find PSRs

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  10. An Unexplained Radio Signal
    Searched the PMPS for DMs <=2000 cm-3pc, pulse
    widths of 0.25 - 128 ms (at lowest DMs)
    19 new discoveries - mostly PSRs with sporadic
    emission, but some single events also ...
    -> one in particular is as yet unexplained
    DM = 745 cm-3pc -> apparently extragalactic
    τobs = 6.8 ms
    gl = 25.4o, gb = -4.0o
    DMextra = 222 cm-3pc -> z = 0.1

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  11. Time delay has freq. dependence of f-α
    where α=2.02(1)
    1250
    1300
    1350
    1400
    1450
    1500
    1550
    1.6 1.8 2 2.2 2.4
    Frequency (MHz)
    Time (seconds)
    No obvious scattering (e.g. an exponential tail)
    visible w. S/N
    Only in 1 of 13 beams
    Not seen to repeat in 16 hours of follow-up!
    What more can one do?
    An Unexplained Radio Signal

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  12. Thank You
    (questions, comments?)

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