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Swift as a Rapid Wide Field Follow-up Instrument
John Nousek & Jamie KenneaPenn State University
Phil EvansUniversity of Leicester
International Workshop on Astronomical X-ray OpticsPrague, Czech Republic
8 December 2015
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¨ GRBs· >1000 GRBs with arcsec positions· Primary GRB mission into the future
¨ Non-GRBs· >1400 TOOs per year· AGN, SNe, novae, CVs, LMXBs, stars, comets, ...· First sensitive hard X-ray all sky survey
¨ GI program· > 4 oversubscription, $1.2M, 5Ms time per year
Swift – The World's GRB FactoryBAT
XRT
UVOT
Swift as an E-M counterpart finder
¨ Swift’s unique capabilities: · Performing rapid Target of Opportunity (TOO) observations
¾TDRSS and Groundstation uploads with low latency.· Rapid slewing allows for high efficiency/low overhead observing
¾Swift average slew rate ~0.6 deg/second. · Ability to see a large area of the sky over a short period (96 min
orbit) vs ground based observatories waiting for night-time, and latitude limited viewing areas.
How do we cover large regions?
¨ In-built tiling can cover hexagonal regions· 4, 7 point tiling utilized frequently by Swift· 19, 37 point tiling recently approved for use and tested (not yet
available to community)¾ 37-point tiling still only covers 1 degree radius error circle!
· Can cover larger regions by uploading multiple TOOs over multiple passes (e.g. IPN error regions).
¾ Inefficient and slow, plus large strain on SOT/FOT!
37-POINT TILING
1 orbit 37 point tiling test
Galaxy targeted search for GW
¨ EM GW search using galaxy targeting, i.e. implementing Phil Evans’ plan:
· First 48 hours, observe every targeted galaxy, selected by convolving GW error region with Galaxy Catalog initially, in descending order of probability, for 60s per field.
· Followed by covering as many galaxies as we can for 500s exposure each in following 4 days to search for afterglows of off-axis sGRBs.
¾ Expect to cover 300 Galaxies, observed in order of probability.
¨ Not previously possible with Swift, but two methods developed to do this:
· Upload lists of RA/Dec to cover non-circular error boxes. BAT FSW in development…
· “PPST Jamming” concept, requires alteration in ground operations, but not FSW.
¾PPST = Pre-Planned Science Timeline
Performing a PPST Jam
¨ Using Phil’s Galaxy Targeting software to generate a list of targets to observe.
¨ Merge this with existing PPST gaps in observations are filled with normal Swift targets
¨ Perform extensive validation of PPST product
¨ Upload to spacecraft for immediate execution at next ground station pass (adds latency - TDRSS can’t be used for this)
¨ Minimum exposure time is 60s per field (hard limit)
¨ Observations of a maximum of 450 targets in 24 hour period (set by onboard buffer size)
¨ So maximum amount of time spent doing this: ~25ks per day, about ~40-50% of available time (overheads are higher due to more slews).
SWIFT SLEW FREQUENCY
• Note previous maximum number of slews in one day is 174! With 450 Swift goes from being 6 observatories to 16 (thanks Rick Edelson!).
Pros and cons
¨ Pros
· Only way to cover large number of sources / sky area
· Can be done without FSW change - FSW change only allows us to get on target quicker.
· Testing appears to show that it’s not going to break Swift. More testing planned.
¨ Cons
· Will knock out a lot of targets when we’re concentrating on GW follow-up!
· BAT triggering severely impacted by short dwell time on tiles.
New Observing mode - new projects
¨ Ability to perform observations of many, short exposures opens up a new mode of operation for Swift!
¨ Large area surveys:
· Can survey whole of the SMC in ~24ks, down to a sensitivity of ~5% LEDD. SMC is packed full of HMXBs, Be/X-ray binaries and we tend to only see them go into outburst when INTEGRAL scans SMC.
· Regular Galactic Bulge survey? M31? LMC?
¨ GRB localization:
· Better coverage of IPN error boxes
· Localization of select GBM GRBs?
¨ Others?
STATUS
¨ 19 and 37 point tiling has been tested and approved for use.
· Importantly shows that many short (45-60s) exposures can be performed by Swift without harming spacecraft.
¨ Software to generate PPSTs from LIGO error regions has been written and tested.
¨ On-board testing to being very soon
· ALIGO is online, so we may get a trigger any day to follow!
· Expect mode to be fully commissioned before end of the year.
¨ Proposal submitted to Swift GI program to support this effort.