1. An Infestation of RRATs Maura McLaughlin West Virginia University 10 May 2013 Latest Results from the Neutron Star Laboratory May 10 2013

2. Introduction - History - What are RRATs? - Current population Properties - spatial distribution - spin-down properties - amplitude distributions, spectra, and on-off timescales - high-energy emission Summary - What do they mean for NS population estimates? - The promise of current and upcoming searches Outline Latest Results from the Neutron Star Laboratory May 10 2013

3. History In 2006, 11 objects discovered through their single, dispersed pulses, with 1 to 7 pulses detected from each RRAT at DMs from 90 to 400 pc cm -3. Termed Repeating Radio Transients (RRATs), then Rotating Radio Transients after periods of 0.9 to 6 seconds measured through single-pulse differencing. Periods not measurable through an FFT or folding. Note that there were 17 original RRATs! McLaughlin et al. 2006, Nature,439, 817 Latest Results from the Neutron Star Laboratory May 10 2013 P = 4.75 s P = 0.77 s P = 2.64 s

4. What are RRATs? Latest Results from the Neutron Star Laboratory May 10 2013 Original paper has 230 citations but we still haven’t converged on what these objects are! ATNF Pulsar Catalog says:

5. What are RRATs? Latest Results from the Neutron Star Laboratory May 10 2013 Not really a definition as it doesn’t provide a means for classification… Original paper has 230 citations but we still haven’t converged on what these objects are! ATNF Pulsar Catalog says:

6. What are RRATs? Latest Results from the Neutron Star Laboratory May 10 2013 Pulsars detected only through their single-pulse emission Pulsars detectable only through their single-pulse emission Pulsars detected with greater SNR through their single-pulse emission Pulsars which have SNR SP > SNR FFT Pulsars which do not emit any consecutive pulses Pulsars where < 1% of pulses are detectable

7. What are RRATs? Latest Results from the Neutron Star Laboratory May 10 2013 Pulsars detected only through their single-pulse emission Pulsars detectable only through their single-pulse emission Pulsars detected with greater SNR through their single-pulse emission Pulsars which have SNR SP > SNR FFT Pulsars which do not emit any consecutive pulses Pulsars where < 1% of pulses are detectable - has been working definition thus far

8. What are RRATs? Latest Results from the Neutron Star Laboratory May 10 2013 Pulsars detected only through their single-pulse emission Pulsars detectable only through their single-pulse emission Pulsars detected with greater SNR through their single-pulse emission Pulsars which have SNR SP > SNR FFT Pulsars which do not emit any consecutive pulses Pulsars where < 1% of pulses are detectable Everything but the first is observation dependent (i.e. could change with observation length, sensitivity, frequency, etc).

9. What are RRATs? Latest Results from the Neutron Star Laboratory May 10 2013 Pulsars detected only through their single-pulse emission! Therefore: “RRATs” are not a group of pulsars with properties clearly separated from the regular pulsar population. While these objects will be more intermittent than normal pulsars in general, there may be some intermittent objects not classified as RRATs or vice versa. ?

10. How related to other objects? Latest Results from the Neutron Star Laboratory May 10 2013 Burke-Spolaor & Bailes, 2010, MNRAS

11. But a diverse group with constantly changing “properties” Latest Results from the Neutron Star Laboratory May 10 2013 With Parkes at 1.4 GHz, 8 pulses in 7 years detected from J1839-01. With GBT at 350 MHz, looks like long-timescale nuller. For high B-field J1119-6127, glitch triggers transition -> reconfiguration of the magnetic field?

12. But a diverse group with constantly changing “properties” Latest Results from the Neutron Star Laboratory May 10 2013 Three pulses detected from J1928+15 with Arecibo with periodicity of 405 ms. Never seen again! Deneva et al., 2009, ApJ, 703, 225

13. And just to muddle things farther… Latest Results from the Neutron Star Laboratory May 10 2013 At least three objects transitioning between RRAT and normal pulsar behavior. For high B-field J1119-6127, glitch triggered transition -> reconfiguration of the magnetic field? Burke-Spolaor & Bailes, 2010, MNRAS, 402, 855 PSR J0941-39 Weltevrede et al. 2011, MNRAS, 411, 1917 PSR J1119-6127

14. Intermittent Pulsars Latest Results from the Neutron Star Laboratory May 10 2013 Intermittent pulsars (6 cases so far) show deep modulation (but detectable via FFT when on) but on much longer timescales than RRATs, and with correlated period derivative changes. Period derivatives during on/off times not measurable for RRATs. Kramer et al. 2006, Science, 312, 549

15. Giant pulsing pulsars Latest Results from the Neutron Star Laboratory May 10 2013 The Crab is a RRAT given proposed definition. Giant-pulsing pulsars show pulses > 100 times mean pulse flux. Amplitude distribution is typically power-law instead of lognormal. GPs typically detected from pulsars with high Edot or magnetic field at the light cylinder. Cordes et al. 2004, ApJ, 612, 375

16. Emission physics - Almost-dead pulsars, brought back to life temporarily (Zhang and Gil 2006). - Radio emission direction reversal (Zhang and Gil 2006). - “Rocking the Lighthouse” - asteroid belts can “trigger, detune, or extinguish” radio emission (Cordes & Shannon 2008 and Li 2006). - Transition objects between pulsars and X-ray Isolated Neutron Stars (XINSs) or magnetars (Popov et al. 2006, MNRAS, 369, 23). - Part of normal pulsar intermittency spectrum (Zhang & Gil 2006, Weltevrede et al. 2006, Lyne et al. 2010). - ALL OF THE ABOVE? NASA/JPL Caltech Latest Results from the Neutron Star Laboratory May 10 2013

17. Population Latest Results from the Neutron Star Laboratory May 10 2013 Nearly 100 of these objects known today – 85 listed in http://astro.phys.wvu.edu/rratalog.http://astro.phys.wvu.edu/rratalog Many from recent surveys: -18+ from 350-MHz GBT surveys (Chen Karako) -10+ from PALFA (Julia Deneva, Laura Spitler) -26 from HTRU (Sarah Burke-Spolaor) - 29 from PMSURV (Evan Keane) -Many others….long lag time to publish due to difficulty following up.

18. Spatial Distribution Latest Results from the Neutron Star Laboratory May 10 2013 Galactic latitudes and longitudes roughly consistent with other non-recycled pulsars. DM distributions differ (P = 2x10 -7 ), presumably due to selection effects. Non-recycled pulsarsRRATs

19. Spin-Down Properties Latest Results from the Neutron Star Laboratory May 10 2013 Only 68/85 have measured periods. Periods are longer than for other non- recycled pulsars (P = 9x10 -11 ). Non-recycled pulsarsRRATs

20. Spin-Down Properties Latest Results from the Neutron Star Laboratory May 10 2013 Only 68/85 have measured periods. Periods are longer than for other pulsars (P = 9x10 -11 ). However, significant selection effects at play… Ratio of “giant” to “regular” pulses vs McLaughlin & Cordes, 2003, ApJ, 596, 982 Ratio of “regular” to “giant” intensities

21. Spin-Down Properties Latest Results from the Neutron Star Laboratory May 10 2013 Only 23/85 have timing solutions. Some RRATs lie in sparsely populated regions.  ★ Magnetars X-ray isolated NSs Intermittent pulsars ★ RRATs

22. Spin-Down Properties Latest Results from the Neutron Star Laboratory May 10 2013 Period derivatives (P = 0.0008) and surface dipole inferred magnetic fields (P = 0.002) are larger. Non-recycled pulsars RRATs

23. Spin-Down Properties Latest Results from the Neutron Star Laboratory May 10 2013 Period derivatives (P = 0.0008) and surface dipole inferred magnetic fields (P = 0.002) are larger. This trend persists even when using pulsars with periods > 1 s. Non-recycled pulsars RRATs

24. Spin-Down Properties Latest Results from the Neutron Star Laboratory May 10 2013 Nulling pulsars show larger ages but no clear relationship with magnetic field. Pulsars which emit giant pulses show relationship with magnetic field at the light cylinder but no relationship with magnetic field. Intermittent pulsars have no obvious common spin-down property. Wang et al. 2007, MNRAS, 377, 1383

25. A (Somewhat Incomplete) Overview of Other Properties of this (Somewhat Arbitrarily Defined) Population Latest Results from the Neutron Star Laboratory May 10 2013

26. Glitches Latest Results from the Neutron Star Laboratory May 10 2013 Glitches measured from J1819-1458. Largest glitch resulted in a permanent decrease in period derivative accompanied by an increase in the burst rate at the time of the glitch. Evidence of evolution from a magnetar? Similar to emission changes which accompany magnetar glitches (Dib et al. 2009). Similar behavior seen from high-B pulsar J1846-0258 (Gavriil et al. 2008) and J1119-6127 (Weltevrede et al. 2011). Lyne et al. 2009, MNRAS, 400, 1439

27. Glitches Latest Results from the Neutron Star Laboratory May 10 2013 Glitches measured from J1819-1458. Largest glitch resulted in a permanent decrease in period derivative accompanied by an increase in the burst rate at the time of the glitch. Evidence of evolution from a magnetar? Similar to emission changes which accompany magnetar glitches (Dib et al. 2009). Similar behavior seen from high-B pulsar J1846-0258 (Gavriil et al. 2008) and J1119-6127 (Weltevrede et al. 2011). No glitches from other RRATs… Lyne et al. 2009, MNRAS, 400, 1439

28. Quasi-Periodicities Nearly all of the RRATs show significant quasi-periodicities in burst arrival times. These range from minutes to days and are not detected in random sequences. J1839-01 shows 0.9 hr periodicity. Palliyaguru et al. 2011, MNRAS, 417, 1871Cui et al. in preparation Latest Results from the Neutron Star Laboratory May 10 2013

29. Quasi-Periodicities Nearly all of the RRATs show significant quasi-periodicities in burst arrival times. These range from minutes to days and are not detected in random sequences. J1839-01 shows 0.9 hr periodicity. We see similar phenomena for pulsars, however! (Marchiny et al. in prep). Palliyaguru et al. 2011, MNRAS, 417, 1871 Latest Results from the Neutron Star Laboratory May 10 2013

30. Spectra Spectra appear “normal”, though puzzling non-detections of J1819-1458 at 350 MHz. Miller et al. 2013, in preparationLatest Results from the Neutron Star Laboratory May 10 2013

31. Amplitude Distributions Appear to be fit well by lognormal distributions (like pulsars!) with power-law tails (like giant-pulsing pulsars!). Miller et al. 2013, in preparationLatest Results from the Neutron Star Laboratory May 10 2013

32. High-Energy Properties Only one RRAT, J1819-1458, has been detected at high energies. Thermal spectrum shows evidence for one, possibly two, absorption lines. If cyclotron, B = 2x10 14 G. McLaughlin et al. 2007, ApJ, 670, 1307 Miller et al. 2013, submitted Latest Results from the Neutron Star Laboratory May 10 2013

33. High-Energy Properties Correlation of X-ray photons with radio pulses reveals 2.7 sigma correlation. Process producing radio pulses is heating the polar cap? Miller et al. 2013, submitted Latest Results from the Neutron Star Laboratory May 10 2013

34. High-Energy Properties Chandra observations reveal bright nebula with power-law spectrum surrounding J1819-1458. Implied X-ray efficiency is 15%, much higher than typical for PWN. Rea et al. 2009, ApJ, 703, 41Camero-Arroz, 2012, MNRAS, 439, 3493 Latest Results from the Neutron Star Laboratory May 10 2013

35. NS populations If RRATs are separate population, SN rate estimates are challenged. Latest Results from the Neutron Star Laboratory May 10 2013 Keane & Kramer, 2008, MNRAS, 391, 2009

36. The Future Continuing pulsar surveys and upcoming surveys with LOFAR, ASKAP, MeerKAT, MWA should result in > 1000 RRATs. Detection of RRATs with interferometric searches will dramatically facilitate follow-up and measurement of period derivatives. Law et al. 2012, ApJ, 760, 124 Latest Results from the Neutron Star Laboratory May 10 2013

37. Summary There are a growing number of pulsars being detected through their single-pulse emission. Definition of a RRAT is ongoing (and is it necessary?) There is no single reason for the RRAT’s sporadicity. They have disparate properties and lie at varying degrees within the spectrum of pulsar intermittency. More surveys and follow-up at radio and high energies are necessary to determine whether there might be some link between RRATs and other classes of objects. Understanding their emission mechanism is challenging and a small part of the (much larger!) problem of understanding the pulsar emission mechanism in general. Many of their properties are consistent with other pulsars’ emission. We expect upcoming surveys to identify a large number of these objects. Regardless of the reasons for intermittency, full population analyses are necessary for NS birthrate estimates (for every object we find, many other remain undiscovered!) Latest Results from the Neutron Star Laboratory May 10 2013

38. Why have we seen none of these in PALFA or GBT 350-MHz surveys? In Lorimer et al. (2007) we declared they would not be detectable due to scattering, BUT given measured burst properties, may not be an issue. Extragalactic Bursts Southampton3 May 2013

39. Extragalactic Bursts Southampton3 May 2013 Assuming we are sensitive to 10 ms of scattering, we expect one burst in entire 350-MHz GBT drift-scan survey and none in AO drift-scans.