Fine-Tuned Search for Kilonova Emission in a Short Gamma-Ray Burst: Implications for the Progenitors, GW Sources, and r-Process Nucleosynthesis

0 Assigned ID: 85 ----- Attempting Submission 1 (Tue Apr 02 15:08:57 GMT 2019) ----- HST Phase I Proposal 85 (apt_kilonova.apt) successfully submitted. Receipt: # 85-1 ----- Attempting Submission 2 (Wed Apr 03 16:11:35 GMT 2019) ----- HST Phase I Proposal 85 (apt_kilonova.apt) successfully submitted. Receipt: # 85-2 ----- Attempting Submission 3 (Thu Apr 04 19:20:50 GMT 2019) ----- Trigger for SGRB 200522A. Changed F110W to F125W upon recommendation of Annalisa Calamida. 5/26/2020: Changed Visit 2 from F160W to F125W (corresponded with Alison Vick). 1866571313 ----- Attempting Submission 1 (Mon Jul 08 12:15:14 GMT 2019) ----- ----- Attempting Submission 2 (Tue Aug 27 12:09:15 GMT 2019) ----- ----- Attempting Submission 3 (Fri May 22 16:24:17 GMT 2020) ----- HST Phase II Proposal 15964 successfully submitted. Receipt: # 15964-3 ----- Attempting Submission 4 (Fri May 22 18:37:47 GMT 2020) ----- ----- Attempting Submission 5 (Tue May 26 19:47:00 GMT 2020) ----- Fine-Tuned Search for Kilonova Emission in a Short Gamma-Ray Burst: Implications for the Progenitors, GW Sources, and r-Process Nucleosynthesis The joint gravitational wave and electromagnetic detections of the binary neutron star (BNS) merger GW170817 ushered in a new era of astrophysics. In the UV/optical/NIR the emission (a "kilonova") was powered by radioactive decay of nuclei produced via r-process nucleosynthesis. In the gamma-ray, X-ray, and radio the emission was instead powered by an off-axis jet typical of short gamma-ray bursts (SGRBs); this connection was previously supported by the HST detection of a kilonova in the short GRB130603B. With only a single joint GW-EM detection and a single kilonova detection in an SGRB, the key frontier is to begin to map the distribution of merger outcomes: ejecta mass, velocity, geometry, and nucleosynthetic yields. Here we propose to achieve this goal with HST observations of a kilonova associated with an SGRBs; observations of kilonovae in SGRBs are essential because the orientation is well known (face-on, along the binary's angular momentum axis) and the LIGO/Virgo detection rate is still highly uncertain. Such a study can only be achieved with the sensitivity and resolution of HST, and it matches one of the "special initiatives", namely deep NIR monitoring that is essential for informing future JWST follow-ups ("JWST Preparatory Observations"). We request 10 orbits for 1 SGRB event. The HST observations will be supported by approved programs at Chandra, VLA, ALMA, Gemini, Keck, Magellan, MMT that will provide the targets, cover optical and early NIR follow-up to establish the baseline behavior, and complete the multi-wavelength picture of the event. Given the broad interest in this topic we waive the proprietary period. To determine the expected apparent brightness of the kilonova for the expected range of ejecta masses (0.01-0.1 Msun), and to inform the choice of filters, we convolve the kilonova models of Barnes & Kasen (2013) as a function of redshift with the ACS/F814W, WFC3/F110W, and WFC3/F160W filter response functions. We calculate the resulting apparent brightness in two rest-frame times of 4 days (peak) and 10 days (post-maximum). The actual observer-frame times for the two HST epochs will therefore be 4x(1+z) days and 10x(1+z) days, where the redshift will be known prior to triggering the HST observations from rapid ground-based follow-up. The choice of filters is designed to straddle the break at 1 micron in the rest-frame, in order to capture the unusually red color of a kilonova. We base our HST trigger criteria and time request on the model with 0.01 Msun so that we can probe the wide range of ejecta masses predicted by numerical simulations (rather than just the bright upper bound of 0.1sun); this will allow any non-detections to place meaningful constraints on the r-process yield. Epoch 1 (4x(1+z) days): We find that at z<=0.2 it is advantageous to use the ACS/F814W and WFC3/F110W filters, which give the best combination of sensitivity (5sigma=27.7 and 27.5 AB mag in 2 orbits each, respectively, using the ACS and WFC3 ETCs) and color contrast (F814W-F110W=1.6-2 AB mag). The afterglow color in these filters will be much bluer, F814W-F110W=0.3 AB mag, so a kilonova origin can be robustly demonstrated. At z=0.2-0.4 we will instead use the WFC3/F110W and F160W filters to capture the spectral break (5sigma=26.3 AB mag for F160W in 2 orbits). The resulting color is F110W-F160W=0.6-1.2 AB mag, compared to a bluer color for the afterglow, F110W-F160W=0.3 AB mag. The kilonova emission for 0.1 Msun can be detected to z=0.7, but we truncate our trigger criteria at z=0.4 to be able to detect the emission in the case of 0.01 Msun. Epoch 2 (10x(1 + z) days): In the second epoch we will only observe in a single filter redward of the 1 micron break since we are only concerned with demonstrating a rapid decline that will help to robustly determine the ejecta mass (i.e., the unusually red color will already be established with the first epoch near peak). This will require 2 orbits in F110W (z<=0.2) or F160W (z=0.2-0.4). In this case, if the ejecta mass is 0.01 Msun we will obtain a deep upper limit that will establish the expected rapid fading, while in the case of 0.1 Msun we will have a second detection. Templates (>1 month): We will acquire template images after the kilonova emission has faded away that match the exposure time and filters of the earlier epochs. This will therefore require a total of 4 orbits (2 orbits in each filter). We note, however, that in the case of 0.01 Msun a non-detection in the second epoch could be used as a template in one of the two filters (F110W or F160W depending on the redshift), meaning that the final observation will require only 2 orbits. Since we do not know the ejecta mass in advance we request 4 orbits for the final epoch, but may use only 2 orbits. This will be known following epoch 2. Dr. Edo Berger is an expert in the study of astrophysical transients, including short gamma-ray bursts and gravitational wave events, which are the focus of this Cycle 27 proposal. Dr. Berger has been the PI of 5 previous HST programs (10616, 10641, 10908, 13022, 15329), and is the supervisor of several graduate students and postdoctoral fellows who have been PIs of 10 HST programs over the past decade. The proposed program includes 5 of Dr. Berger's thesis students (Patton, Gomez, Villar, Blanchard, Eftekhari). Raffaella Margutti is the PI of supporting Chandra and NuSTAR programs. Wen-fai Fong and Tarraneh Eftekhari are the PIs of supporting VLA and ALMA programs, as well as Keck and Gemini programs. Philip Cowperthwaite is the PI of a supporting Magellan program (through Carnegie). Griffin Hosseinzadeh is the PI of supporting Magellan and MMT programs (through Harvard). Matt Nicholl provides UK telescope access. Ryan Chornock provides access to MDM. Graduate students Peter Blanchard, Victoria (Ashley) Villar, Sebastian Gomez, Locke Patton, and Tarraneh Eftekhari are students of the PI and will lead various aspects of the HST and supporting observations data analysis and interpretation. They are all experienced with HST data analysis. Chris Fryer, Dan Kasen, and Brian Metzger are experts in theoretical studies of binary neutron star mergers and radiative transfer of r-process material, and they will support the interpretation of the resulting HST data. Our team played a key role in the discovery of the optical counterpart of GW170817 and in the subsequent study of its multi-wavelength emission, including through HST Cycle 25 program 15329. The results of our work were published in 17 papers over the past year, so we are well positioned to rapidly and expertly publish the results of the proposed HST observations. Specifically, the HST Cycle 25 data were used in 4 publications in 2017 and 2018. 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The visit should be executed before 2020 May 27 UT. 1590447273000 245.19739948553934 (Tic-Visit :proposal-id 15964 :visit-id "01" :proposal-version -1 :trans-version "20191203" :date "22-May-2020 14:36:36.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 4 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 2367568 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 15964 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 15964 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2758 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3142 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15964 :visit-id "01" :orbit-number 2 :pcs-time 302 :si-vis-utilization 2758 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3142 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15964 :visit-id "01" :orbit-number 3 :pcs-time 302 :si-vis-utilization 2758 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3142 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15964 :visit-id "01" :orbit-number 4 :pcs-time 302 :si-vis-utilization 2758 :al-overhead-at-end 0 :internal-dur-at-end 690 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3142 :pcs-gap 0 ) true 4 0 Trigger for visit 1 to SGRB200522A. 1590522277036 Timing link suitability includes constraints ([02 After 01 by 7.0 to 9.1 days] [03 After 02 by 30.0 to 50.0 days]) The scheduling data was generated by CASM 28.0. CASM was run in Phase II mode. 1591208107000 245.65726032587952 (Tic-Visit :proposal-id 15964 :visit-id "02" :proposal-version -1 :trans-version "20191203" :date "26-May-2020 14:44:36.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 1183792 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 15964 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 15964 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2758 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3142 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15964 :visit-id "02" :orbit-number 2 :pcs-time 302 :si-vis-utilization 2758 :al-overhead-at-end 0 :internal-dur-at-end 367 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3142 :pcs-gap 0 ) true 2 0 This is the second visit for SGRB 200522A 1591310363712 The scheduling data was generated by CASM 28.2. 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CASM was run in Phase II mode. 1594914390000 247.53615689636 (Tic-Visit :proposal-id 15964 :visit-id "03" :proposal-version -1 :trans-version "20191203" :date "22-May-2020 14:36:30.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 4 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 2367568 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 15964 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 15964 :visit-id "03" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2758 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3142 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15964 :visit-id "03" :orbit-number 2 :pcs-time 302 :si-vis-utilization 2758 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3142 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15964 :visit-id "03" :orbit-number 3 :pcs-time 302 :si-vis-utilization 2758 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3142 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15964 :visit-id "03" :orbit-number 4 :pcs-time 302 :si-vis-utilization 2758 :al-overhead-at-end 0 :internal-dur-at-end 690 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3142 :pcs-gap 0 ) true 4 0 This is the third visit for SGRB 200522A