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PPTA observing strategies
Ryan M. Shannon/21 Jan 2015

· Current state of play
­ Schedule lists pulsars in order of increasing right ascension ­ Access to S/N diagnosDcs ­ Observers typically observe either in increasing RA or in "closest-
non-
observed" order) ­ While some are cognizant of S/N of observaDons many are not.


Why care?
· Strategy is essenDal to any observing program. · What is the PPTA observing strategy? · What mo5vates this strategy? · Observe 20 pulsars every ~two weeks in three bands to achieve 100 ns Dming precision. Detect GWB in 5 years
­ (Based on Jenet et al. 2005)

· How can we do beVer?


Parkes basics #1
· Sources locaDon: Right Ascension (RA) and declinaDon (DEC) · Local Sidereal Time (LST): Tells you what is visible when RA=LST sources are highest on sky
­ Sources with RA < LST are in the west (se]ng) ­ Sources with RA > LST are in the east (rising)
· Generally we observe GalacDc plane from rise to set

· Parkes (AlDtude-
Azimuth telescope)

­ AlDtude limits -
> 30 degrees from horizon ~ 1 degree from zenith (tells you when source is above horizon) ­ Azimuth limits -
> wraps (more about this on next side)


Parkes basics #2
· Telescope sensiDvity is defined by its gain (or system equivalent flux density), system temperature, received bandwidth, observing Dme
­ Parkes: 0.9 K/Jy ­ Green Bank/MeerKAT 2 K/Jy ­ Arecibo/FAST: 12 K/Jy (AO 20 K/Jy for 430 MHz line feed)

· Why Parkes/PPTA does well
­ ­ ­ ­ ­

LocaDon/laDtude (0437/1909), relaDvely clean 20cm-
band CalibraDon (PolarizaDon/instrument stability) InstrumentaDon (UWL/10cm system/mulDple backends) Cadence (lots of observing Dme sensiDvity ~ sqrt(t)) Clever people (y'all)


Parkes basics #3: Receivers
· Parkes receivers are mounted at prime focus (in the focus cabin) with a translator stage that physically moves between the receivers · To switch receivers currently requires the observer to park the telescope (drive toward zenith)
­ Drive Dme long ­ RestarDng tcs, running LO scripts ­ Even for experts, this process takes 15 minutes

· Strategy: minimize receiver changes by observing for ~ 24 hours with one receiver set-
up


·

Parkes is a large telescope
­ ­

Strategy 1: Slew Dme


Slew rate 15 degrees per minute in azimuth "North and South" at transit require long slews to go from "northern sources" (dec > -
30 degrees) to "southern sources" (dec < -
30 degrees)

Long Dme to slew here

·

Wraps:
­ ­ ­ ­

Will define slew Dmes Telescope can rotate 540 degrees. Wrap limits located in West (as sources are se]ng) If in Northern wrap, can have long slew to Southern source and vice versa
· · · J1600-
3053 and J1603-
7202 J1024-
0719 and J1045-
4509 J1744-
1134, J1713+0747

Wrap limit South wrap

·

Consequence: it is omen advantageous to not observe sources in increasing RA (as previously displayed on dashboard)
­

4 long slews over an observing session -
> one fewer pulsar observed

·

Strategy: Observe sources close to minimize slew 7me
­ Note dashboard doesn't correctly calculate slew 7me.


Wind
· ObservaDons cannot occur during high wind · During marginal wind condiDons, the telescope is more safe when the dish is pointed into the wind and close to zenith · If the winds are ~ 30-
40 km/h less likely to be wind-
stowed · Q: If LST is 14:45 and moderate winds are coming from north east, what would be a good pulsar to observe?


Strategy 2: RFI
· · Monitor RFI using web monitors (CASPSR and PSRMON) and SPD (real-
Dme) Satellite: (20cm)
­ ­ ­ Use FROG to monitor locaDon of Beidou satellites Strategy: Change sources Strategy: Wait it out (DR2 pipeline will edit it out)

·

Dish CafÈ: (Azimuth and Diurnal dependence on RFI)
­ ­ Observe at night Observe with telescope towards East (dish blocks visitors centre)

·

Midweek RFI
­ ­

DevastaDng 20cm RFI Coordinate with ATNF Sciops to figure out when it is occurring (RMS has been asking Phil Edwards before recent sessions) ­ IdenDfy on Parkes RFI weather monitor ­ Switch to 10cm/50cm band


ScinDllaDon
· All of our pulsars experience refracDvely and diffracDvely scinDllate · Some can easily see factor of 20 variaDon in flux density with long exponenDal tails · If pulsar is bright, stays bright for some Dme (hours) · If pulsar is faint, remains faint for a similar length · Results in large variaDons in TOA uncertainty · Non-
detecDons (5-
sigma) detecDons are worthless · ScinDllaDon can change the gain of Parkes to Green Bank (or even larger) · We want to observe as much as possible on those exponenDal tails!


ScinDllaDon #2
· TOA error ~ (Pulse EffecDve Width)/(S/N raDo) · SensiDvity to GWs ~ (1/TOA error)^2
­ (True for clock signal as well/planet ephemeris)

· We want high S/N observa7ons of pulsars with narrow profiles (narrow features)


Strategy #3 ScinDllaDon
· Where does the current observaDon stand · Monitor flux using the CASPSR flux monitor · S/N state of play is plots provided on dashboard · Black-
belt -
-
Get TOAs and compare S/N of observaDon with historical observaDons



Pulsar prioriDsaDon
· · · · Grey area Handful of pulsars central to our array (Priority 1) Northern pulsars are well observed (Priority 3)
­ How does data quality compare to NANOGrav/EPTA?

Some pulsars show evidence for strong Dming noise (Priority 4)
­ J1024-
0719, J0613-
0200, J1643-
1224, J1824-
2452A, J1939+2134 ­ Probably aren't of much use to any of the goals

· ·

Legacy Dming baseline for SKA era/Moderately useful southern pulsars (Priority 2) M. Keith/X. Siemens ­ detecDon significance accelerates with addiDon of more pulsars
­ Assume that pulsars are relaDvely equal ­ Work of acDve research that we should be looking at (Kobi?) in the realiDes of PPTA/IPTA observaDons.


Current scheme
· 1: Highest priority (dominate limit, searches for correlated signals) · 2: Important southern pulsars · 3: Northern pulsars/legacy southern pulsars · 4: Poor pulsars of liVle use to Dming array · This is a logarithmic scale
­ RMS wouldn't observe priority 4 pulsar if there was a priority 1 pulsar visible


Histogram

Time series for PSR J2145-
0750 Histogram for PSR J1017-
7156


ScinDllaDon observing strategy
· If a high priority (1/2) pulsar is in a high scinDllaDon state (top quarDle), it should be re-
observed · If any pulsar is a low state amer 5 minutes it observing should be abandoned and a nearby (unobserved/non-
weak pulsar should be observed)
­ Nearby in slew Dme

· Regardless of state of second pulsar observe it for full hour
­ Mindful of wasDng Dme slewing between sources


Concluding thoughts
· Our high grade and generous Dme allocaDon allow us to be clever with how we observe. "Observing every pulsar for the sake of checking them all off" every session is a waste of this allocaDon · ObservaDons of pulsars when they are bright are important. If a pulsar is bright (as seen on a web monitor/SPD) it should be re-
observed.
­ Benefits both our primary scienDfic objecDves, secondary scienDfic objecDves

· If a pulsar is faint it, should be ditched

­ We don't understand the staDsDcs fully yet (Renee started working on this), but as a general rule of thumb, I wouldn't re-
observe it in the same band unDl it rises again.

· All of us should be thinking "why are we doing this". A lot of these thoughts were formed amer trips to Parkes, talking to Mike Keith, MaVhew Bailes