New Results on Rotating Radio Transients

Maura McLaughlin
LOFAR and the Transient Radio Sky, Amsterdam, December 2008

Transcript

1. Recent Results on ! Peek-A-Boo Pulsars! In collaboration with Andrew Lyne, Nanda! Rea, Jim Cordes, Duncan Lorimer, Michael! Kramer, Aris Karastergiou, Aidan Hotan, Dick Manchester, Andrea Possenti,! Marta Burgay, Ingrid Stairs, Nichi D’Amico, ! Fernando Camilo, Bryan Gaensler, Shami Chatterjee and Gianluca Israel ! " ! and PhD students! Evan Keane, Josh Miller and Julia Deneva ! Russell Kightley Media!
2.   A very transient history and introduction!   Rotating Radio Transients!   Properties (timing, spectra, multi-wavelength, etc.)!   What are they?!   Summary!   Lessons for LOFAR! Outline!
3. Several classes of short- duration radio transients are known (but none but a few pulsars discovered in blind radio transient searches!)! Pulsars are by far the ! brightest of these sources.! Cordes & McLaughlin (2003)! Radio Transient Phase Space (5 years ago)!
4. Cordes & McLaughlin (2003)! Huge gaps in known radio transient phase space!! Radio Transient Phase Space (5 years ago)!
5. Cordes & McLaughlin (2003)! -  Galactic Center Radio " ! Transient (GCRT) ! Hyman et al. (2005,2006,2007)! - Radio pulses from ! magnetars! Camilo et al. (2006,2007)! - Radio pulses from brown ! dwarf TVLM 513-46546! Hallinan et al. (2007) ! -  Rotating Radio ! Transients (RRATs) ! McLaughlin et al. (2006)! -  Millisecond extragalactic! radio burst (MERB)! Lorimer et al. (2007)! Radio Transient Phase Space (today)!
6. 1)  Take data with radio telescope(s) with as wide a bandwidth (50-500 MHz) as possible. 2) Signals go to filterbank or correlator to give you good time (< 1 ms) and frequency (< 1 MHz) resolution. 3) Dedisperse the data over a number of trial DMs. 4) Search each dedispersed times series for events above some threshold. 5) Repeat for different smoothings and iterate, removing bright sources. Transient radio searches!
7. Rotating Radio Transients!   11 original sources discovered in a ! reanalysis of data from the Parkes ! Multibeam Pulsar Survey.!   Characterized by repeated, dispersed ! radio bursts of millisecond widths.!   Not detectable in standard (FFT) pulsar searches.!   Periods (0.7-7 s) measured for some sources (through individual bursts) indicate they are rotating neutron stars.! J1444–6026! DM = 374.2 pc cm-3! P = 4.75 s!
8. Unlike normal pulsars, RRATs are only detectable through single-pulse searches and can only be studied through individual pulses….Why are they different?! Let’s look at their! 1) Numbers! 2) Burst rates and amplitude statistics! 3) Spin-down properties! 4) Spectra! 5) Polarization! 6) Multi-wavelength properties!
9. 1) Numbers! We know now of roughly 40 objects detected through their single pulses. Nearly 30 of these objects are true RRATs (i.e. only detectable through single pulses):! - 18 in Parkes multibeam survey (Keane et al. & " " McLaughlin et al.)! - 1 in Parkes high-latitude survey (McLaughlin et al.)! - 3 in GBT surveys (Hessels et al. & drifters)! - 4 in PALFA survey (Deneva et al.)! - ? with WSRT (Stappers et al.)! These numbers are all changing rapidly! The more carefully we look, the more RRATs we seem to find!! Parkes RRATs have been followed up for roughly 4 years with monthly monitoring observations. 800 hours of time.!
10. 2) Burst rate and amplitude statistics! Average burst rates vary from (3 minutes)-1 to (5 hours)-1.! J1819-1458! P = 4.26! J1444-6026! P = 4.75!
11. 2) Burst rate and amplitude statistics! Some sources are extreme nullers, with short ‘on’ periods.! J1839-01! P = 932 ms! 7 pulses detected in initial ! obs and none thereafter!! J1928+15! P = 405 ms! 3 pulses detected in initial ! obs and none thereafter!!
12. 2) Burst rate and amplitude statistics! J1928+15! P = 405 ms! 3 pulses detected in initial ! obs and none thereafter!! These three pulses are consecutive!!
13. 2) Burst rate and amplitude statistics! J1444-6036" " " " J1317-5759! P = 4.75" " " " P = 2.64! But the bursts of other sources are consistent with a random distribution, and there is no evidence for quasi-periodicities (on the timescales to which we are sensitive!)!
14. 2) Burst rate and amplitude statistics! For the sources with the most pulses, a log-normal + power-law distribution seems to fit the data well (though there are unexplained outliers!)!
15. 2) Burst rate and amplitude statistics! For some it is difficult to quantify…!
16. 2) Burst rate and amplitude statistics! In general, single pulses are quite narrow, with varying phenomenology.!
17. 3) Spin-down properties! Periods can be measured for most RRATs. All of the RRATs (new and old) in general have long periods.! Three timing solutions ! published in discovery! paper. Three more! since that time. Large timing! errors due to pulse-! to-pulse profile ! changes.! All properties are! consistent with those! or normal pulsars,! though two have! high Bfields.!
18. 3) Spin-down properties! Two (and maybe more) glitches observed for J1819-1458.! Post-glitch recovery is anomalous (magnetarish?) ! Delta f/f = 7 x 10-7! Delta f/f = 7 x 10-8!
19. 3) Spin-down properties! Evidence for more bursts post-glitch!! Similar to magnetar glitch/outbursts.!
20. 3) Spin-down properties! Glitches consistent with those observed for other pulsars.! Kaspi et al. 2006 ! magnetars! pulsars! ★ ★! ★! ★! ★! Hobbs et al. 2002 !
21. 4) Spectra! Spectra consistent with those observed for other pulsars.! In general, indices range from -1 to -3 (difficult to quantify for faintest sources).! We don’t detect 1819 at 350 MHz at all. Evidence for high low-frequency turnover for 1819? (magnetarish?)!
22. 5) Polarization! Polarization consistent with seen from middle-Edot pulsars.! In general, indices range from -1 to -3 (difficult to quantify for faintest sources).!
23. 6) Multi-wavelength properties!   Period derivatives allow accurate positions, which facilitate follow-up obs at other energies.!   Possible IR counterparts to J1819-1458.! VLT Infrared image of J1819-1458 field!
24. 6) Multi-wavelength properties!   J1819-1458 is a bright X-ray source detected with Chandra and XMM. Pulsations and thermal spectrum. Slightly hotter than expected for age.! X-ray and radio burst profile of J1819-1458.!
25. 6) Multi-wavelength properties!   XMM obs of J1819-1458 raise more questions than they answer! Similarities to many classes of neutron stars. !   Currently analyzing joint 100-ks radio/XMM observation of J1819-1458.! X-ray spectra of J1819-1458. Strange absorption features!!!
26. 6) Multi-wavelength properties!   Chandra obs of J1819-1458 shows PWN/bowshock.!
27.   Extreme nullers or almost-dead pulsars, brought back to life temporarily (Zhang and Gil 2006). (Maybe some…)!   “Rocking the Lighthouse” - Pulsars with asteroid belts (Cordes & Shannon 2008 and Li 2006). (How test?)!   Radio counterparts to X-ray Dim Isolated Neutron Stars (XDINSs) or transient radio magnetars….continued X-ray monitoring is crucial. (Maybe some…)!   Nulling pulsars? Giant-pulsing pulsars? Intermittent pulsars? Part of the normal spectrum of pulsar emission?! (For sure some relationships…)! What are they?!! Weltevrede et al. (2006) suggest B0656+14 would appear as a RRAT were it farther away.!
28.   First of all what is a RRAT? Does it even make sense to describe a population of RRATs? !   We expect roughly ~10 RRATs! in PALFA and ~20 in Parkes! high-latitude surveys. ! •  LOFAR surveys should! Detect many(+/-many), and over ! 30,000 could be detected! by the SKA! (Lorimer et al.! in preparation)! Population:! N RRATS ≈2×105(L min /100mJy⋅kpc2)−1 ×(0.5/ f on )×(0.5/ f rfi )×(0.1/ f beam )
29. Summary: Rotating Radio Transients!   The sporadicity (and associated detection difficulty) of known RRATs implies that there must be a large Galactic population of these objects, perhaps four times as many as the population of normal pulsars!!   Spin-down, timing, spectral and multi-wavelength properties consistent with normal radio pulsars (but also show some similarities with other classes of neutron stars….two classes of RRAT – nullers and bursters?).!   Timing solutions difficult but possible with continued monitoring.!   The cause of the unusual radio emission is an open question.!   Searches on new and archival data are continuing to yield more of these objects.!
30. Lessons for LOFAR:! •  We need better RFI mitigation techniques (Eatough et al. submitted) and automated search algorithms (dynamic spectra, on-the-fly processing, automated periodicity searches, machine learning). See Kondratiev et al. 2008, WVU student Smithbauer.! •  We need to search more parameter space (broader pulses! narrower band signals!) You will only find what you look for! ! •  BETTER POSITION LOCALIZATION CRUCIAL!! •  Improved methods for pulse detection/timing in known RRATs. ! •  Need better understanding of selection effects.! •  Lower frequency surveys may reveal a new population of nearby transient sources.! •  Follow-up is very time intensive. How will all the new sources be followed up? Are frequent short or infrequent long obs better? Will all the new sources be followed up? How will multi-wavelength follow-ups be done?!