Defending Dunc

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

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?)