Defending Dunc

Transcript

1. Defending Dunc Evan Keane Max Planck Institut für Radioastronomie, Bonn,

   Germany LOFAR TKP Meeting 15 December, 2011, Meudon, France.

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

   do?

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+

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!

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

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 !

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

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 ...”

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

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

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

12. Thank You (questions, comments?)