1. Pulsar Timing with the GBT Scott Ransom National Radio Astronomy Observatory

2. Why NRAO's GBT for pulsars? 100-m fully steerable telescope in West Virginia The GBT provides: Sensitivity 2-5x more sensitive than Jodrell Bank or Parkes (Arecibo is ~3-4x better) Sky Coverage ~85% of total sky 65-75% for Parkes and JB 33% for Arecibo National Radio-Quiet Zone Does not provide: Extremely large amounts of dedicated pulsar time (currently ~20%)

3. Pulsar Timing with the GBT Young Old High Magnetic Field Low Magnetic Field Approx 10 projects: ~50 millisecond pulsars (MSPs) in clusters ~12 high-precision MSPs 5-6 interesting binaries (e.g. J0737-3039) 1-2 young pulsars (e.g. G21.5-0.9) 1 radio-loud magnetar 10-15 “normal” PSRs

4. Pulsars in Globular Clusters Clusters of ancient stars (9-12 billion years old) that orbit our galaxy Contain 10 5 -10 6 stars, many of which have binary companions Very high densities (100- 10,000 stars/ly 3 ) result in stellar encounters and collisions! They are effectively millisecond pulsar factories (and exotic ones at that!) Number known has more than tripled since 2000

6. Globular Cluster MSP Timing Almost all of the new pulsars are MSPs (~50-716 Hz) Approx half are isolated (this is a selection effect) Many exotic systems:  10 highly eccentric (e>0.2) binaries  2+ with main sequence companions? (Ter5ad and Ter5P – the 1 st and 5 th fastest MSPs known)  7 eclipsing systems Timing precisions typically 20-50 μs (~1% pulse period) Terzan 5 (32 timing solns)

7. Fastest Millisecond Pulsars: Are many of the fastest-spinning pulsars hidden? 5 of the 10 fastest-spinning pulsars show eclipses. 5 of the 10 fastest-spinning pulsars are found in Terzan 5 47 Tucanae0.1476J0023-7203J Terzan 5None483J1748-2446V Terzan 5None488J1748-2446Y Gal. PlaneNone533J0034-0534 Gal. PlaneIsolated542J1843-1113 Terzan 50.4578J1748-2446P Terzan 50.05596J1748-2446O Gal. Plane0.1622B1957+20 Gal. PlaneIsolated642B1937+21 Terzan 50.4716J1748-2446ad Location Eclipse Fraction Spin Freq. (Hz) Pulsar Name Are the frequencies limited by gravitational radiation?

10. Pulsar Timing with the GBT Young Old High Magnetic Field Low Magnetic Field Approx 10 projects: ~50 millisecond pulsars (MSPs) in clusters ~12 high-precision MSPs 5-6 interesting binaries (e.g. J0737-3039) 1-2 young pulsars (e.g. G21.5-0.9) 1 radio-loud magnetar 10-15 “normal” PSRs

11. High-Precision Timing: A Pulsar Timing Array for GW Detection Currently a large group including people from: Berkeley, UBC, NRL, Bryn Mawr, NRAO, etc... Need 12-20 MSPs spread across the full sky Requires timing precisions of ~100ns-1μs 10 -4 -10 -3 in phase Competing projects at Parkes and in Europe Will likely become a true international effort within the next couple years Long-term project (5-10 yrs)

12. Current GBT PTA Status

13. Pulsar Timing with the GBT Young Old High Magnetic Field Low Magnetic Field Approx 10 projects: ~50 millisecond pulsars (MSPs) in clusters ~12 high-precision MSPs 5-6 interesting binaries (e.g. J0737-3039) 1-2 young pulsars (e.g. G21.5-0.9) 1 radio-loud magnetar 10-15 “normal” PSRs

14. The Double-Pulsar Binary: J0737-3039 This system has two visible pulsars and is currently being studied primarily with the GBT. At least 5 tests of General Relativity have already been made, to a precision of better than 0.05%! From: Kramer et al., 2005, astro-ph/0503386

15. Pulsar Timing with the GBT Young Old High Magnetic Field Low Magnetic Field Approx 10 projects: ~50 millisecond pulsars (MSPs) in clusters ~12 high-precision MSPs 5-6 interesting binaries (e.g. J0737-3039) 1-2 young pulsars (e.g. G21.5-0.9) 1 radio-loud magnetar 10-15 “normal” PSRs

16. Young Pulsar in G21.5-0.9 PSR J1833-1034 61.8ms, likely <1000 yo Very weak: ~70 μJy (Camilo et al 2005) 2 nd highest Edot in galaxy (3x10 37 ergs/s) Very stable timing for a such a young PSR More likely due to GLAST

17. Outlook for the future... Prospects for new discoveries with the GBT are good  Many more clusters to observe and search  Upcoming all-sky surveys (many more MSPs) We really want more “Holy Grails”:  MSP-MSP binary  PSR-BH binary  sub-MSP Longer term, an “Arecibo in the South” would find and time hundreds of new cluster MSPs... (FAST?) Even longer term, the Square Kilometer Array will find thousands of new pulsars