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- HIGHER ORDER ROTATIONAL PARAMETERS Masa's vision, as we understood it in March, is that no matter how complex a multi-year timing solution might be, it can always be broken down into piecewise phase-connected bits, for which f0, f1, and f2 suffice. The classic illustration of this is the monthly Crab ephemeris provided by Jodrell. What's wrong with this is that it is not necessarily what the radio and/or Xray timing people would most naturally provide to us. Some examples...
- The Jodrell Crab ephemeris is done by hand by Mark Roberts, a senior staff scientist who has been doing this for years. He takes a couple of hours each month to find a solution that is phase-connected to the previous months. This level of effort is unlikely to be made for a large number of young, noisy pulsars.
- What they more naturally do is use lots and lots of higher order coefficients to "whiten" the timing noise. Here are some fun examples --
- "Long-term Phase-coherent X-ray Timing of PSR B0540-69", Maggie Livingstone, Vicki Kaspi, Fotis Gavril in ApJ 633:1095-1100, (2005). Using ELEVEN (!) frequency derivatives they obtain timing residuals of +/- 15 ms from 1996 to 2003 for this 50 ms pulsar. They state (figure 4) that they needed so many to have residuals less than one-half period. It is a great gamma candidate and they (or John Marshall maybe, I don't remember) Frank Marshall will be providing us RXTE measurements after GLAST launch. How will we shoe-horn their 11 parameters into the D4 and gtpphase? We probably won't. We'll probably extract gamma times from the LAT data and do the analysis with TEMPO. Adding many higher order terms to the Taylor series expansion in gtpphase strikes Bordeaux as a small pain-to-gain issue.
- "The Magnetar XTE J1810-197: Variations in Torque, Radio Flux Density, and Pulse Profile Morphology", F. Camilo, I. Cognard, S. Ransom, et al in ApJ 663:497-504 (2007). Figure 1 is worth taking a look at --daily radio pulse profiles changing weirdly. Absolute phase coherence is critical for this study (as it is for the LAT). The caption says "eleven frequency derivatives". Speculation is rampant about whether or not GLAST will detect magnetars in gamma rays. To give it our best shot, we'll use the best long term ephemeris that the radio folks can build.
- "A Statistical Study of Pulsar Timing Irregularites Using Observations from Jodrell Bank Observatory", Hobbs, Lyne, and Kramer in MNRAS draft attached. They show how very weird pulsar spin down is, and how f0, f1, f2 just ain't enough over years and years. Check out their pages of residuals, they're neat.
- GLITCHES Recently we've been having a lot of fun in Bordeaux searching EGRET data for pulsations, for one really hot pulsar discovered recently at Parkes, and two very warm pulsars discovered about ten years ago at Nancay, that they never got around to publishing. For the latter, after ten years of timing, they have an accurate proper motion and a series of glitches.
- If gtbary doesn't handle proper motion, then that means that the multi-year timing solution provided by the timing people can't be used to stack gamma rays over a long period. We need to specifically ask them to provide piecewise, phase-coherent solutions. As a matter of fact... we did already ask them to do this, when Johnston was in Bordeaux and when we were in Manchester, and they said "yes". They took it as one more, reasonable task to do for us. In the case of Nancay, it's in any case Lucas who builds the timing solutions on the Nancay computers from the Nancay raw data, and so he builds them with the D4 & Science Tools limitations in mind. Oh but I was supposed to be talking about glitches not proper motion.
- Glitches are intrinsically interesting. Speculation abounds (wrongly, in our mind) that there could be "puffs" of gamma rays when one occurs.
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