1. Rotating Radio Transients
Maura McLaughlin
West Virginia University
12 September 2007

2. The transient radio sky is relatively UNEXPLORED!
In contrast to the situation at high energies…
The transient radio sky is relatively UNEXPLORED!
Radio telescopes have short time scale sensitivity
but very narrow fields of view.
Most transient radio sources are follow-ups of
high energy detections.
But studying radio transients can teach us about
-> compact sources and explosive/dynamic events
-> fundamental physics/astrophysics
-> intervening media

3. Outline Parkes observations and phenomenology
GBT, Arecibo and XMM follow-up observations
What are they?
Population estimates
New Arecibo RRATs
Arecibo’s role in RRAT studies

4. RRATs Discovery As part of PMPS reprocessing
Largest scale search for ms-s radio
transients ever
Parkes Telescope
Over 750 pulsars discovered in PMPS
About 20 sources discovered just in SP
- a few `bursty’ pulsars, a few objects
missed in original search and 11
mysterious sources not detectable in
periodicity searches
More recent reprocessing shows that there are at least twice as many as this….
Parkes Multibeam
1400-MHz receiver
McLaughlin et al. 2007, Nature, 439, 817

5. RRATs Discovery J1819–1458 DM = 194 pc cm-3 J1443–60
No periodicities detected in FFT/FFA!

6. RRATs Discovery Can measure periodicities
from single pulse arrival times
J1819–1458
DM = 194 pc cm-3
Periodicity of 4.26 s.
J1443–60
DM = pc cm-3
Periodicity of 4.76 s.
No periodicities detected in FFT/FFA!

7. RRATs Discovery - periods
Name P
(s)
J0848-43
5.98 J
2.64 J
4.76 J
1.32 J
4.26 J
0.77 J
0.93 J
4.47 J
6.79 J ? J
0.92
Periods show they must be neutron stars -> Rotating Radio Transients

8. RRATs Discovery - timing
For RRATs with highest
bursting rates, can time
just like normal pulsars
(but from single pulses!)
Timing residuals for J

9. RRATs Discovery - timingJ
Timing properties generally consistent with those of normal pulsars.
RRATs
SGRs
AXPs
XDINSs

10. RRATs Discovery - locations
Slight concentration
towards Galactic
plane (but small
number stats!)
Consistent with pulsar
distribution

11. RRATs Discovery - bursts
Name
w50
S1400
Np/Tobs
Ndet/Nobs Np
(ms)
(mJy)
(hr-1)
(%) J 30
100
4.2 32 58 J 10
1100
4.5 93
144 J 20
280
0.8 68 42 J 16
160
0.6 55 25 J 3
3800
18.0
363 J 2
600
1.0 62 18 J 15
0.4 7 8 J
250 50 13 J
450
0.7 57 11 J 5
0.3 45 J
650
4.7 60
McLaughlin et al. 2007, Nature, 439, 817

12. GBT Follow-up ObservationsJ J
normal pulsars
GBT observation of J at 350 MHz

13. GBT Follow-up ObservationsJ J J J
NOT normal pulsars
Never detected again in
Parkes or GBT observations!
Original detection of J

14. AO Follow-up ObservationsJ J
NOT normal pulsars
Observation with AO at 327 MHz of J
No period measurable with Parkes, with only 11 pulses in total over 2 years of observations. But 6.9 s period from Arecibo observations at 327 MHz.

15. AO Follow-up ObservationsJ J
Arecibo observations of J at 327 MHz
NOT normal pulsars
Several minutes in “on” state

16. XMM Follow-up Observations
Recent XMM Epic PN data - 43 ks on RRAT J
Radio and X-ray pulses are aligned (within uncertainties).
Spectrum fit well by absorbed blackbody plus + Gaussian.
kT ~ 140 eV, nH ~ 8x1021 cm-2.
McLaughlin et al. 2007, ApJ, in press

17. RRAT properties - Summary
New sources class or one end of spectrum of normal pulsar emission? Properties vary widely from object to object!
The more we observe them the more muddled things become
- two RRATs look like normal pulsars with higher
sensitivity obs (but some not detected at all!)
- some RRATs occasionally detected in FFT/FFA searches (but rare)
No obvious relationship between strange emission and P/Pdot (for RRATs with measured quantities)
P/Pdots (and positions) exceedingly slow going for other RRATs…..
X-ray observations for one RRAT show it is similar to both XDINSs and normal pulsars…and need positions to get obs for other sources!

18. What are they? Radio populations: Pulsars with giant pulses
Intermittent pulsars
Nulling pulsars
Pulsars like B
B (Kramer et al. 2006)
Weltevrede et al. 2006

19. What are they? Explanations:
Almost-dead pulsars, brought back to life temporarily
(Zhang and Gil 2005)
Pulsars with temporary reversal of radio emission direction
(Dyks et al. 2005)
Pulsars with asteroid belts
(Cordes & Shannon 2006 and Li 2006)

20. How do we define a RRAT/normal/intermittent/
What a mess!!!
How do we define a RRAT/normal/intermittent/
nulling/giant pulsar????
Where do we go from here???

21. Population Estimates Expect 20,000 RRATs detectable by SKA!
Expect over twice as many
RRATs as normal pulsars.
With intermittent pulsars
-> three times as many??
Highly dependent on assumed
minimum luminosity…
Expect 20,000 RRATs detectable by SKA!
Lorimer et al. in preparation

22. New PALFA objects J0628+09 - PALFA discovery with P = 1.24 s
There are RRATs in
the tropics too!
J PALFA
discovery with P = 1.24 s
and DM = 88 pc cm-3

23. New PALFA objects J1928+15 - PALFA RRAT candidate
There are RRATs in
the tropics too!
J PALFA
RRAT candidate
Three bursts separated
by 405 ms at
DM = 240 pc cm-3
An extreme nuller?

24. New PALFA objects
There are RRATs in
the tropics too!
PALFA survey is crucial for understanding the nature of the RRATs and the total population of neutron stars.
And for discovering new classes of objects!
ala Cordes & McLaughlin (2003)

25. An extragalactic transient!
- Not man-made
- Cold plasma dispersion law and W~f-4.4
- Not Galactic
- DM = 375 cm-3 pc -
Extragalactic!
- DM ~ 1200 x z implies
z < 0.3 !!!
- Conservative estimate D = 500 Mpc.
Lorimer et al. 2007, Science, in press

26. An extragalactic transient!
- Energy budget 500 Mpc)
- Radio energy output ~ 1040 erg
Brightness temperature ~1039 K
- Possible sources
GRB? NS-NS coalescence? Sne?
- PALFA surveys -> cosmology!
Parkes could detect out to z ~ 0.25 (1 Gpc)
AO could detect out to z ~ 0.5 (2 Gpc)
extra motivation for high-b surveys!
8 times the number of sources!!!!
Lorimer et al. 2007, Science, in press

27. AO’s role in transient studies
Essential for measuring periods and timing parameters of RRATs discovered with other telescopes -> only way to understand relationship to other NSs and facilitate high-frequency and high-E obs
PALFA (and future) surveys will discover many more such objects -> crucial for understanding the population and making accurate estimates of total NS population
Such objects discovered with Arecibo will only be able to be followed up with Arecibo!
PALFA surveys should revolutionize our view of the transient radio sky in general.
Future? Low-frequency multibeam system!! .

28. Stay tuned!
Even 40 years after their discovery, there is still much to be learned about radio pulsars!