Precise Pulsar Timing andRadio Follow-Up of Pulsars
Discovered in LAT BlindPeriodicity Searches
Paul S. Ray
on behalf of the LAT Collaborationand theFermi Pulsar Search Consortium (PSC)

Blind Search Pulsars➡ Need precise positions!

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1.5(m) J1958+2846

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21.5(n) J2021+4026

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11.52(h) J1809-2332

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2150800021.5200200.5

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2000.5(d) J1418-6058

12025012(g) J1741-2054

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2(l) J1907+06
Number of Counts-selected” pulsars, but are theyalso radio quiet?
Are there counterparts atother wavelengths?

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Number of Counts• Questions:- What is their timing behavior?
- These are “gamma-ray

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talks on Wednesday)

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25201510500(a) J0007+7303
Number of Counts(see Abdo et al. 2009, Science,325, 840)!

Number of Counts• 16 discovered in first 6 months

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only “gamma-ray only” pulsar

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11.5(o) J2032+4127

2000.51(p) J2238+59

LAT Pulsar Timing• Survey mode observing and large FOV
and area make for excellent long term
timing of pulsars discovered• Developed Maximum Likelihood

method for measuring TOAs from small
numbers of photons (typically ~100
photons per 2-week TOA). Achieves
sub-ms residuals on most pulsars• All 24 blind search pulsars timed, plus

several others where the LAT is better
than any alternative (Geminga,PSR J1124–5916,Vela)

METHOD• Convert photon times to theGeocenter• Assign phases using apreliminary timing model• Construct analytical modelof pulse profile• Divide data set intosegments• Using ML, fit for phase offset
between profile and data ineach segment

LAT Pulsar Timing• Survey mode observing and large FOV
and area make for excellent long term
timing of pulsars discovered• Developed Maximum Likelihood

method for measuring TOAs from small
numbers of photons (typically ~100photons per 2-week TOA). Achieves
sub-ms residuals on most pulsars• All 24 blind search pulsars timed, plus

several others where the LAT is better
than any alternative (Geminga,PSR J1124–5916,Vela)

The Power of Timing• Improved rotational parameters• Study timing noise and glitches (freePSR J1741-2054

from any radio propagation effects)- Glitch detected in CTA1 pulsar on
2009 May 1• Precise positions, which enablemultiwavelength follow up!

- Sub-ms residuals lead to arcsec
position accuracy

PSR J1836+5925
Ray et al. 2009, in preparation

LAT Pulsar Search Consortium (Radio)• All these new pulsars are gamma-ray selected (discovered inblind periodicity searches of LAT data), but are they radio quiet?

• Some (CTA1, 3EG J1835+5918) already have stringent radio limits• For the others, we recruited pulsar observers with expertise at key
observatories (Parkes, Arecibo, GBT, Effelsberg, Nançay)• Radio detection yields-Distance from Dispersion Measure (DM)Information on emission region from radio to gamma-ray offset
Geometry from polarization studies
Population studies of radio quiet vs. radio loud, which constrain models

Fermi PSC• Purpose: To organize deep radio searches of the blind searchpulsars and unidentified LAT sources (see following talk byRansom)• Fermi LAT members:- Ray, Smith, Harding, Thompson, Saz Parkinson, Ziegler,Abdo, Wood, Romani, Kramer (Effelsberg), Johnston(Parkes), Theureau, Cognard (Nançay)• External members on MOU:
- GBT: Camilo, Ransom, Roberts- Arecibo: Freire- Jodrell Bank: Stappers- Parkes: Keith, Weltevrede

PSC Observations• Parkes: 4 of the most southern sources + a dozen UNIDsources• Arecibo: 5 pulsars + 10 UNID sources• GBT: 5 pulsars + 27 UNID sources from the BSL + 50 fainter
UNID sources• Jodrell observes when needed• Effelsberg just started observing with new filterbank• Nançay also contributing

First Two Radio Detections• PSR J1741-2054- Radio pulsar found in archival Parkes-multibeam dataExtremely low DM (4.7 pc cm-3),implies D=400pc
May be lowest luminosity of any young
radio pulsar (L~0.025 mJy kpc2)• PSR J2032+4127- Pulsations discovered at GBT- DM=115 implies D=3.6 kpc, but may beat half that distance (possibly associatedwith Cyg OB2)
Camilo, Ray, et al. 2009, ApJ, 705, 1

New Detection: J1907+06!

• Very faint radio pulsations(~3.5 µJy) detected at Arecibo!

• DM 80 pc cm gives distance of-3

3.1 kpc• Another very low luminositypulsar• See talk by Abdo on Wed.

Abdo et al. 2009, ApJ, submitted

Radio Upper Limits(Pulsars with P>30 ms)• 25 gamma-ray selected pulsars➡ 3 detected, 21 upper limits (all <70 µJy), 1 left to observe

What is “Radio Quiet”?
(Pulsars with P>30 ms and Age<107 yr)• The new radio detections are very low luminosity!

Summary• The LAT has given us an abundance of gamma-ray selectedpulsars• Pulse timing with the LAT yields arcsec accuracy positions
and the spindown behavior of these pulsars• The PSC has made radio observations of all but one- 3 detected in radio, others have deep upper limits- Detections immediately give distance measurement!
• When combined with LAT upper limits on gamma-ray

pulsations from radio pulsars population studies will provide
interesting constraints on models