Precise Pulsar Timing and Radio Follow-Up of Pulsars Discovered in LAT Blind Periodicity Searches Paul S. Ray on behalf of the LAT Collaboration and the Fermi Pulsar Search Consortium (PSC)
Blind Search Pulsars • Before Fermi, Geminga was the only “gamma-ray only” pulsar Number of Counts Number of Counts Number of Counts Number of Counts 70 35 140 160 60 30 120 140 • 50 25 120 100 16 discovered in first 6 months 100 20 40 80 80 30 15 60 60 10 20 40 (see Abdo et al. 2009, Science, 40 20 5 10 20 0 0 0 0 0 0.5 1 1.5 2 0 0.5 1 1.5 2 0 0.5 1 1.5 2 0 0.5 1 1.5 2 325 , 840)! (a) J0007+7303 (b) J0357+32 (c) J0633+0632 (d) J1418-6058 250 Number of Counts Number of Counts Number of Counts Number of Counts 70 200 70 • 180 60 60 200 8 new discoveries since then! 160 50 140 50 150 120 40 40 100 30 (see Saz Parkinson and Dormody 30 100 80 60 20 20 40 50 10 10 20 talks on Wednesday) 0 0 0 0 0 0.5 1 1.5 2 0 0.5 1 1.5 2 0 0.5 1 1.5 2 0 0.5 1 1.5 2 (e) J1459-60 (f) J1732-31 (g) J1741-2054 (h) J1809-2332 • Number of Counts Number of Counts Number of Counts Number of Counts Questions: 160 90 300 120 140 80 250 100 70 120 - 60 200 80 100 What is their timing behavior? 50 80 150 60 40 60 30 100 40 40 - 20 50 20 20 10 These are “gamma-ray 0 0 0 0 0 0.5 1 1.5 2 0 0.5 1 1.5 2 0 0.5 1 1.5 2 0 0.5 1 1.5 2 (i) J1813-1246 (j) J1826-1256 (k) J1836+5925 (l) J1907+06 selected” pulsars, but are they 200 200 Number of Counts Number of Counts Number of Counts Number of Counts 90 180 180 60 80 also radio quiet? 160 160 70 50 140 140 60 120 120 40 50 - 100 100 30 40 80 80 Are there counterparts at 30 60 60 20 20 40 40 10 10 20 20 0 0 0 0 other wavelengths? 0 0.5 1 1.5 2 0 0.5 1 1.5 2 0 0.5 1 1.5 2 0 0.5 1 1.5 2 (m) J1958+2846 (n) J2021+4026 (o) J2032+4127 (p) J2238+59 ➡ Need precise positions!
LAT Pulsar Timing • Survey mode observing and large FOV METHOD and area make for excellent long term • Convert photon times to the timing of pulsars discovered Geocenter • Developed Maximum Likelihood • Assign phases using a method for measuring TOAs from small preliminary timing model numbers of photons (typically ~100 • Construct analytical model photons per 2-week TOA). Achieves of pulse profile sub-ms residuals on most pulsars • Divide data set into segments • All 24 blind search pulsars timed, plus • Using ML, fit for phase offset several others where the LAT is better between profile and data in than any alternative (Geminga, each segment PSR J1124–5916, Vela)
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)
The Power of Timing PSR J1741-2054 • Improved rotational parameters • Study timing noise and glitches (free from any radio propagation effects) - Glitch detected in CTA1 pulsar on 2009 May 1 • Precise positions , which enable multiwavelength 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 in blind 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 search pulsars and unidentified LAT sources (see following talk by Ransom) • 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 UNID sources • 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 data - Extremely low DM (4.7 pc cm -3 ), implies D=400pc - May be lowest luminosity of any young radio pulsar (L~0.025 mJy kpc 2 ) • PSR J2032+4127 - Pulsations discovered at GBT - DM=115 implies D=3.6 kpc, but may be at half that distance (possibly associated with 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 -3 gives distance of 3.1 kpc • Another very low luminosity pulsar • 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<10 7 yr) • The new radio detections are very low luminosity!
Summary • The LAT has given us an abundance of gamma-ray selected pulsars • 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
Recommend
More recommend
