The low frequency radio follow-up of gravitational wave merger events with LOFAR Kelly Gourdji PhD student, University of Amsterdam. On behalf of the LOFAR GW follow-up team.
Outline EM follow-ups of GW events LOFAR: What, why and how Our GW follow-up strategy Results for GW170817 Byproduct: extremely deep transient searches Kelly Gourdji 2
Compact mergers involving at least one neutron star: possible evolutionary scenarios and accompanying emission Coherent Incoherent Chu et al. 2016 Kelly Gourdji 3
Multimessenger observations of GW170817 Abbott et al. 2017 Kelly Gourdji 4
� observed for GW170817 � � � � � � � � � � � Coherent Incoherent Chu et al. 2016 (adapted) Kelly Gourdji 5
Some of the proposed emission mechanisms have been confirmed, while there have been additional surprises… Kelly Gourdji 6
Some of the proposed emission mechanisms have been confirmed, while there have been additional surprises… • 1.7 s time delay between GW and GRB • delay in observation of X-rays • dimmest, yet closest sGRB ever observed • Radio emission at unexpected late timescale Kelly Gourdji 7
Some of the proposed emission mechanisms have been confirmed, while there have been additional surprises… • 1.7 s time delay between GW and GRB • delay in observation of X-rays • dimmest, yet closest sGRB ever observed • Radio emission at unexpected late timescale • cocoon vs off-axis jet? High velocity tail of the kilonova merger ejecta? More events & EM follow-ups needed! Kelly Gourdji 8
Low-frequency radio follow-up with the LO w F requency AR ray (LOFAR) We collect data from 110-190 MHz Kelly Gourdji 9
Why LOFAR? Large instantaneous field of view ~60 deg 2 LOFAR follow-up of GW 150914 Contours: cWB probability map Kelly Gourdji 10
Why LOFAR? Low frequency Dispersion delay scales inversely with frequency. Lower frequencies arrive later. Gives us a chance to catch coherent emission related to mergers! Lorimer et al. 2007 Kelly Gourdji 11
LOFAR rapid response On source within <5 mins of trigger! Searching for coherent emission from e.g. FRB related to merger. Check out www.asterics2020.eu (ASTERICS) for more info. Kelly Gourdji 12
Late time follow-up Example for GW170817 Searching for incoherent emission LOFAR observations from e.g. reverse shock and/or afterglow. K. Hotokezaka Kelly Gourdji 13
Why LOFAR? Sensitivity 2017-12-25 to 2018-01-2 Best limit at these frequencies (2 mJy/beam) MWA: 17 mJy/beam Deeper image to come following more calibration/cleaning GW170817 The deepest image ever made at very southerly ~2 mJy/beam declinations with LOFAR. upper limit Max elevation of observation: ~13.7 deg T. Shimwell Kelly Gourdji 14
Late time follow-up 1 week, 1 month, 3 months, 6 months, 1 year timescales Our preliminary images are reaching 0.8 mJy/beam noise. Kelly Gourdji 15
Byproduct: deep transient searches 40-840 MHz Our data Kelly Gourdji 16
Looking ahead • We have 10 triggers for the next 2 years + ~300 hours of follow-up time • we rely on NS system probability • Larger GW detector network • Smaller localization thus deeper images • Lower latencies for GW alerts and LOFAR triggering Kelly Gourdji 17
Thank you 18
Additional slides Kelly Gourdji 19
Turnover in light curve supports structured jet model Alexander et al 2018 Kelly Gourdji 20
Recent light curves disagree somewhat. Somewhere between these two models? Mooley et al 2018 Kelly Gourdji 21
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