Swift as a Rapid Wide Field Follow-up Instrument John Nousek & Jamie Kennea Penn State University Phil Evans University of Leicester International Workshop on Astronomical X-ray Optics Prague, Czech Republic 8 December 2015

2  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 Factory BAT XRT UVOT

Swift as an E-M counterpart finder  Swift’s unique capabilities:  Performing rapid Target of Opportunity (TOO) observations  TDRSS and Groundstation uploads with low latency.  Rapid slewing allows for high efficiency/low overhead observing  Swift 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.

Upload time statistics Median delay = ~2 hours Fastest upload = 9 minutes Within 4 hours = ~ 80%

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)  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).  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.  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.  PPST = 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% L EDD. 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.