Pulsar luminosity Pulsar luminosity distribution in 47-Tucdistribution in 47-Tuc

Tim Connors, Vacation studentTim Connors, Vacation student

University of SydneyUniversity of Sydney

Galactic Pulsar Distribution

• Luminosity distribution of galactic pulsars is dN = L-1d logL.

Same everywhere -> reasonable?

• Every lower decade of flux has 10 times more pulsars -> same integrated flux1

• To a point anyway - where is the low luminosity cutoff?

47 Tuc

• Have ~22 known pulsars in 47 Tuc, of which we know 14 positions from timing

• The unlocated pulsars are ~10 times fainter than the located pulsars - however, all are only visible during scintillation

• Up to 200 pulsars below current limit predicted to lie in cluster1

47 Tuc

• Spacial distribution of unresolved pulsars same as those resolved

• These should contribute about the same amount of flux as the identified pulsars

• In all, we expect 4mJy of integrated flux, since the known pulsars integrate to 2mJy

Project Setup• We have quite a few days of observing, at

different configurations• Wide (6km), for a high resolution image• Several (375m, 750m) arrays to be sensitive to

extended componentObservation Date 12/02/99-31/12/99 25/01/99 8/05/00 23/12/00 25/12/00 27/12/00Config many: 1.5A,1.5B,6A,6C,6D 750B 375 750C 750C 750CImage type Large array for high res image

Comments

Many days combined to make a high res image with very high S/N. 28 Jy RMS.

Because of maintenance, 3rd antenna missing most of day, and many faults during observing -> only 4 antennae left. Data unused currently

Loss of several hours because of error and thunderstorm

5 antennae for extended sources. 6th for removal of pulsars

Surrounding field• -0.3 - +1 mJy• The field is

typical of 20cm data

• Got to make sure potential interferers are removed from UV data before imaging

Image from 6km arrays

•1408 MHz•8x10” beam

•28Jy•3, 6, 12, 24•0-4mJy

Combined 375m/750m image (Grand sum)

•1408 MHz•63x68” beam•35Jy•2.5, 5, 10, 20

•Scintillation changes sources between days, so we get the ‘average’

•Subtract point sources from UV data

•Should be left with extended or possibly variable sources

Grand sum, with point sources removed

Don’t discard the 6th antenna!

• 27th Dec, 2000• 50Jy x 3,4,5,8

• Ok, so the pulsars scintillate. How bright are they today?

• Then model the pulsars that we can see

Each point above 3 that corresponded to a located pulsar, plus the two bright constant sources ( = 643Jy, = 226Jy) near the centre were scaled so the brightest source () was the same as in the high resolution mosaic (ie, it was used as a calibrator)

Pulsar and calibrator fluxes

Only 6km Rescaled Only 6km Rescaled Only 6km Rescaled Only 6km Rescaled Only 6km Rescaled 564 643 839 643 761 643 715 643 285 218 270 313C 360 172 132 202 171 178 160D 220 244 278 311 238 285 256E 210 365 328F 150 318 268J 540 175 148 268 241Q 50 287 220

Flux (Jy)

Source/ Pulsar number

Observation Date23/12/00 25/12/00 27/12/0005/08/0025/01/99

Camilo et al flux

27th Dec, pulsars, and removed

• 27th Dec, 2000• 50Jy• 1.7, 3.4, 6.8

• Removed 2 constant sources (, ), and 3 pulsars

• Peak is 380Jy

Grand sum, and removed• 2 sources too

close to remove automatically finally removed from grand sum.

• also served as a calibrator - fix flux given by 6th antenna

• Peak is 510Jy

Grand sum, pulsars, and removed

• Which enabled us to subtract the pulsars visible on any day

• Then imaged the whole thing

• Peak is 230Jy

Now what?• Now we just have to work out what it all means!

• Did we get a significant flux there in the centre? There are a lot of hills around - RMS is still bigger than theoretical

• What proportion of flux at end is due to known, but unlocated pulsars, and what is due to an unknown quantity of unresolved pulsars? (Should be safe from sources that aren’t pulsars, because they don’t scintillate2)

• We don’t even see the 2mJy expected from the known pulsars, let alone 2mJy once we have subtracted the ~0.5 - 1mJy from the unresolved pulsars.

Why don’t we see these - has the Parkes group overestimated the mean fluxes of the 22 pulsars, or is our array not compact enough, or something entirely else?

• Unfinished project, but only 2 weeks left!

Now what?

References[1] F Camilo, D.R. Lorimer, P. Freire, A.G. Lyne, R.N. Manchester, Observations of 20 millisecond pulsars in 47 Tucanae at 20cm, 2000, ApJ, 535, 975

[2] D. McConnell, J.G. Ables, Radio sources near the core of globular cluster 47 Tucanae, 2000, MNRAS, 311, 841

[3] A.G. Lyne, R.N. Manchester, J.H. Taylor, The galactic population of pulsars, 1985, MNRAS, 213, 613

AcknowledgmentsATCA and ATNF for providing the vacation scholarship program and the invaluable observing experienceDave McConnell for being an excellent supervisor