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TBD + update on FRATs WG activities
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transientskp
June 23, 2012
Science
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75
TBD + update on FRATs WG activities
Sander ter Veen
LOFAR Transients Key Project Meeting, Meudon, December 2011
transientskp
June 23, 2012
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Transcript
Progress on the TBB front: FRATS and Cosmic Rays Sander ter Veen For the FRATS working group and the Cosmic Ray KSP
Transient Buffer Board (TBB) Store the raw data of each dipole/1le signal in a RAM ring buffer
Taking TBB data Step 1: Step 2: Select dipoles/staEons Select 5 μs – >1.3s of data
Turn the LOFAR telescope ….
into the Virtual LOFAR telescope
High Eme resoluEon (5ns) Large bandwidth (100 MHz) Lightning flash recorded with TBBs
All/large sky coverage Lightning direc1on finding LBA all‐sky image with 1 sta1on
Near‐field imaging Cosmic Rays Pulsed RFI
Parallel system Imaging + Beamformed And TBB Cosmic Rays! Credit: George Heald and LOFAR Pulsar Working Group
Limited Eme • 1.3 s at full resoluEon • More Eme by: – Less bandwidth – 25s @ 5 MHz – Less elements – More memory (upgrade to 5.2 s?)
– 100s @ 5 MHz
Obtaining TBB data • Current framework: Python scripts – Trigger handling program listens for triggers (UDP packages) – If a trigger is received check if dumping is allowed: • Is there an observaEon running? • Does the current project allow dumping?
• Does the current observaEon allow dumping? • Is dumping allowed on all observaEons at this Eme? – Is the current observaEon excluded? • Wanted: key that tells if dumping is allowed – Execute ssh commands at the staEon to tell them to dump data
Official TBB Trigger handling framework • Triggerbox (astronomer program) sends requests (STOP, DUMP, RESTART) • Requests are handled by central system (MAC) • Central system checks if requests can be complied to
• Central system asks the staEons to send TBB data. • Coming soon…
TBB data writer • A new data writer is started on each storage node at every new observaEon • Part of the metadata is added to the previous observaEon by a separate program • ASTRON is working on a new official supported data writer including metadata
• Similar to beam‐formed HDF5 data writer. • New data writer should support subband data
Science cases • Fast Radio Transients (FRATs) • Very High Energy Cosmic Rays (VHECR) • Ultra High Energy Cosmic Rays (NuMoon)
Possible FRATs Sources Millisecond pulses from: Pulsars/ RRATs (exo) planets Flare stars
Other sparkers? Lorimer et al. 2007 Keane et al. 2011
DetecEon • Rare events – Cover large area: • Incoherent beam – Cover long duraEon: • Parallel observaEons • Dispersed events: – MulEple DM trials
• Source idenEficaEon: – Use Transient Buffer Boards
FRATS ObservaEon Diagram Transient Buffer Board Data storage LOFAR dipoles Trigger algorithm Dump request handler
“Transient detected” ObservaEon parameters BlueGene/P UV Data BF Data BF Data TBB Data
FRATS Real‐Eme detecEon. Dedispersion in mulEple frequency bands Coincidence requirement between the bands Image from TBB data Used to idenEfy source
MSSS + FRATS • Piggy‐back on MSSS observaEons • Add incoherent stokes to MSSS observaEon • Send incoherent stokes to separate node • Test observaEons showed no severe data loss on imaging data
• Test run last weekend (9‐11 december) – No imaging dataloss in all but 1 (Cal.) observaEon • Incoherent stokes can be added
Current Trigger algorithm issues • In progress: Allow for non‐conEnuous frequency axis (MSSS) • To Do: Smarter RFI checks – MulE‐beam anE‐coincidence – DM=0 veto with last N samples – Pelican rouEnes? •
To Do: Check if pulse is likely from a known pulsar (k3match)
To Do: TBB data reducEon • TBB data volume is very large ~ 2 TB • Data volume can be reduced in two ways: • “staEon beamforming” – Some dipoles to form a staEon beams – Factor 48 reducEon – But: Lose sensiEvity outside primary beam (RFI in sidelobes)
• Coherent dedispersion – Only keep a fracEon of the Emeseries – Factor 10‐100 – But: Unable to analyse for other DMs
Cosmic Rays Very High Energy Cosmic Rays
Why study Cosmic Rays? • Most energeEc parEcles • Origin: AGN ? • To determine – Chemical composiEon – DirecEon – Energy
• Radio emission – complementary probe – 100% duty cycle
Radia1on mechanisms • Two main coherent emission mechanisms: • Charge excess (Askaryan, NuMoon in air) • GeomagneEc effect
Why CR + LOFAR • Dense instrumentaEon (polarizaEon!) • Probe electromagneEc field at many points • Pin down emission processes • Derive the properEes of air showers through radio emission
• Measure spectrum and composiEon of CR from 1017 ‐1019 eV (transiEon GalacEc to extragalacEc origin)
Cosmic Ray Detec1on • Two methods: – Radio self‐trigger • Any LOFAR staEon (large area) • But also RFI triggers – LORA triggered • No false triggers • Small area (only CRs near Superterp) • Train radio‐only trigger
• Obtain 1‐5 ms of Transient Buffer Board data
Royal Fes1ve Intermezzo (RFI)
Effec1ve RFI excision
There is another way: • LOFAR Radboud air shower Array (LORA) • ScinEllator array on superterp detects electrons and muons. • Coincidence between the scinEllators are cosmic rays
• Trigger TBBs from LORA
ObservaEon Diagram Transient Buffer Board Data storage LOFAR dipoles Dump request handler ObservaEon parameters
BlueGene/P UV Data BF Data TBB Data LORA ParEcle detector “Cosmic Ray Detected”
Cosmic Ray Foot(finger) Print
The Virtual LOFAR telescope: TBB data + pycrtools (LUS)
Analysis pipeline
Calibra1on
Peak IdenEficaEon
Find delays between dipoles
DirecEon esEmaEon
Delay stability
Beamforming
Lateral DistribuEon FuncEon
Theory matches signal?
Where is the shower core?
Where is the shower core? LDF, LORA esEmated core
Where is the shower core? LDF, Core by LOFAR Barycenter
Where is the shower core? LDF, LOFAR ConEnuity requirement
NuMoon • CR and neutrino > 10^21 eV • Large surface: Moon • Nanosecond pulses • Skip 2nd PPF Works •
Invert staEon PPF • Correct for misalignment from clocks • Noise analysis on 5 min data chunks
Conclusion • TBBs are a very usefull addiEon to the system • First tests FRATs + MSSS succesful • LOFAR is a major facility for radio detecEon of cosmic rays • Cosmic Ray observaEons and analysis (almost)
automated – SEll manually set permissions – Manually start trigger system and datawriters on CEP once.