18194( 2) - 01-Oct-2025 18:12:11 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 18194 Version: 2 Check-in Time: 01-Oct-2025 18:12:11 STScI Edit Number: 0 Title Community Discovery Program: panchromatic CXO/VLA/HST observations of a NS merger ------------------------------------------------------------------------------------ Type Cycle GO 33 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Wen-fai Fong Northwestern University Y CoI: Dr. Raffaella Margutti University of California - Berkeley Y CoI: Prof. Daryl Haggard McGill University Y CoI: Dr. Sergio Campana INAF - Osservatorio Astronomico di Brera Y CoI: Prof. Edo Berger Harvard University N CoI: Dr. Peter Blanchard Harvard University N CoI: Dr. Andrea Bulgarelli INAF - Osservatorio di Astrofisica e N Scienza dello Spazio CoI: Mr. Daniel Brethauer University of California - Berkeley N CoI: Prof. Ryan Chornock University of California - Berkeley N CoI: Kristen Dage Curtin University N CoI: Collin Christy University of Arizona N CoI: Dr. Paolo D'Avanzo N CoI: Dr. Fabio De Colle University of California - Santa Cruz N CoI: Maria Drout University of Toronto N CoI: Tarraneh Eftekhari Northwestern University N CoI: Nicole Ford McGill University N CoI: Noah Franz University of Arizona N CoI: Dr. Andrew S. Fruchter Space Telescope Science Institute N CoI: Dr. Giancarlo Ghirlanda INAF - Osservatorio Astronomico di Brera N CoI: Prof. Ore Gottlieb Massachusetts Institute of Technology N CoI: Dr. D Giannios Purdue University N CoI: Dr. Sebastian Gomez University of Texas at Austin N CoI: Dr. Benjamin Paul Gompertz University of Birmingham N CoI: Dr. Cristiano Guidorzi Universita degli studi di Ferrara N CoI: Aprajita Hajela Northwestern University N CoI: Dr. Erica Hammerstein University of California - Berkeley N CoI: Prof. Griffin Hosseinzadeh University of California - San Diego N CoI: Dr. Daniel Kasen University of California - Berkeley N CoI: Dr. Charles Kilpatrick Northwestern University N CoI: Dr. Adithan Kathirgamaraju Purdue University N CoI: Dr. Gavin Lamb Liverpool John Moores University N CoI: Dr. Tanmoy Laskar University of Utah N CoI: Natalie LeBaron University of California - Berkeley N CoI: Prof. Andrew James Levan Radboud University Nijmegen N CoI: Dr. Andrea Melandri INAF - Osservatorio Astronomico di Brera N CoI: Ben Margalit University of Minnesota - Twin Cities N CoI: Dr. Andrew MacFadyen New York University N CoI: Prof. Brian Metzger Columbia University in the City of New N York CoI: Nayana AJ University of California - Berkeley N CoI: Dr. Matt Nicholl Queen's University Belfast N CoI: Sam Oates Lancaster University N 18194( 2) - 01-Oct-2025 18:12:11 - [ 2] CoI: Dr. Antonella Palmese Carnegie Mellon University N CoI: Dr. Richard M. Plotkin University of Nevada - Reno N CoI: Prof. David Radice The Pennsylvania State University N CoI: Jillian Rastinejad University of Maryland N CoI: Dr. Alicia Rouco Escorial ESA, European Space Astronomy Centre N CoI: John Ruan Bishop's University N CoI: Prof. Samar Safi-Harb University of Manitoba N CoI: Prof. David J. Sand University of Arizona N CoI: Dr. Om Sharan Salafia INAF - Osservatorio Astronomico di Brera N CoI: Dr. Huei Sears Rutgers the State University of New Jersey N CoI: Mr. Itai Sfaradi University of California - Berkeley N CoI: Dr. Daniel Siegel Perimeter Institute for Theoretical N Physics CoI: Dr. Lorenzo Sironi Columbia University in the City of New N York CoI: Dr. Gregory R. Sivakoff University of Alberta N CoI: Dr. Michael Cullen Stroh Northwestern University N CoI: Prof. Nial Rahil Tanvir University of Leicester N CoI: Nicholas Vieira McGill University N CoI: Eli Wiston University of California - Berkeley N CoI: Dr. Melania Nynka Massachusetts Institute of Technology N CoI: Dr. Rodolfo Barniol Duran California State University - Sacramento N CoI: Dr. Maria Grazia Bernardini INAF - Osservatorio Astronomico di Brera N CoI: Prof. Sebastiano Bernuzzi Friedrich Schiller Universitat Jena N CoI: Dr. Phil Evans University of Leicester N ------------------------------------------------------------------------------------ Abstract Chandra was the first facility to detect X-ray light from a neutron star (NS) merger. This ToO program continues Chandra's legacy in the revolutionary field of gravitational wave astronomy. Our goals are three-fold: (i) to characterize the diversity of emission from NS-NS mergers; (ii) to enable breakthroughs, such as the discovery of emission from a mass-gap or neutron star-black hole (NS-BH) merger; and (iii) to model panchromatic jet emission to constrain system parameters, particularly inclination and jet structure. This program will maximize the scientific output of LVK O4 and the first year of operations of new novel surveys, including Rubin/LSST and the La Silla Schmidt Southern Survey. We will support these Chandra observations via coordinated follow-up with the VLA and HST. ------------------------------------------------------------------------------------ Observations Description ------------------------ This is a joint TOO program with Chandra as the main facility (and the VLA as an additional secondary facility) focused on gravitational wave (GW) events. There are two targets in this proposal: a GW trigger that occurs prior to Cycle 27, and a GW trigger that occurs during Cycle 27. All observations are imaging with WFC3/UVIS F606W and are non-disruptive TOO. Below we outline the nominal plan although it is subject to change based on the specific event details. For the pre-cycle 27 target, we will trigger 2 epochs of 6 orbits each to roughly align in time with our Chandra observations (target 3-sigma limit of m 18194( 2) - 01-Oct-2025 18:12:11 - [ 3] = 28.5 AB). If a source is detected in the second epoch, we may trigger one final epoch to serve as a host galaxy template. For the cycle 27 target, we will trigger one 3-orbit epoch to occur approximately 20-30 days after the GW trigger, to achieve a 3-sigma limit of m = 28 AB. We will trigger 2 epochs of 6 orbits each to roughly align in time with our Chandra observations, beyond 100 days after the GW trigger (target 3-sigma limit of m = 28.5 AB). If a source is detected in the second epoch, we may trigger one final epoch to serve as a host galaxy template. The total time allocated to this program is 33 orbits. ------------------------------------------------------------------------------------ 18194( 2) - 01-Oct-2025 18:12:11 - [ 4] TARGET LIST Generic Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Selection Criteria | Flux data No | Name | Description | | ------------------------------------------------------------------------------------------------------------------------------------ 2 GW-CYC27 OTHER: GW EVENT V = 28 Comments: GW trigger for which we have also triggered or plan to trigger Chandra observations ------------------------------------------------------------------------------------------------------------------------------------ 1 GW-PRECYC27 STAR, GAMMA RAY OTHER: GW EVENT V = 28 BURSTER, NEUTRON STAR Comments: GW trigger for which we have also triggered or plan to trigger Chandra observations ------------------------------------------------------------------------------------------------------------------------------------ 18194( 2) - 01-Oct-2025 18:12:11 - [ 5] Visit: 01 (GW-preCyc27) Visit Requirements: TOO RESPONSE TIME 30.0D On Hold Comments: Additional Comments: pre-cycle 27 target, 100-150 day epoch Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 GW-PRECYC27 WFC3/UVI ACCUM UVIS F606W 6 2400 S S (14400 S) Comments: TOO observation ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ GW-PRECYC27 1 WFC3/UVI ACCUM UVIS F606W none none 1 none 1 N/A S GW-PRECYC27 1 WFC3/UVI ACCUM UVIS F606W none none 2 none 2 N/A S GW-PRECYC27 1 WFC3/UVI ACCUM UVIS F606W none none 3 none 3 N/A S GW-PRECYC27 1 WFC3/UVI ACCUM UVIS F606W none none 4 none 4 N/A S GW-PRECYC27 1 WFC3/UVI ACCUM UVIS F606W none none 5 none 5 N/A S GW-PRECYC27 1 WFC3/UVI ACCUM UVIS F606W none none 6 none 6 N/A S 18194( 2) - 01-Oct-2025 18:12:11 - [ 6] Visit: 02 (GW-preCyc27) Visit Requirements: TOO RESPONSE TIME 30.0D On Hold Comments: Additional Comments: pre-cycle 27 target, 200-300 day epoch Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 GW-PRECYC27 WFC3/UVI ACCUM UVIS F606W 6 2400 S S (14400 S) Comments: TOO observation ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ GW-PRECYC27 1 WFC3/UVI ACCUM UVIS F606W none none 1 none 1 N/A S GW-PRECYC27 1 WFC3/UVI ACCUM UVIS F606W none none 2 none 2 N/A S GW-PRECYC27 1 WFC3/UVI ACCUM UVIS F606W none none 3 none 3 N/A S GW-PRECYC27 1 WFC3/UVI ACCUM UVIS F606W none none 4 none 4 N/A S GW-PRECYC27 1 WFC3/UVI ACCUM UVIS F606W none none 5 none 5 N/A S GW-PRECYC27 1 WFC3/UVI ACCUM UVIS F606W none none 6 none 6 N/A S 18194( 2) - 01-Oct-2025 18:12:11 - [ 7] Visit: 03 (GW-Cyc27) Visit Requirements: TOO RESPONSE TIME 21.0D On Hold Comments: Additional Comments: cycle 27 target, 20-30 day epoch Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 GW-CYC27 WFC3/UVI ACCUM UVIS F606W 3 2400 S S (7200 S) Comments: TOO observation ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ GW-CYC27 1 WFC3/UVI ACCUM UVIS F606W none none 1 none 1 N/A S GW-CYC27 1 WFC3/UVI ACCUM UVIS F606W none none 2 none 2 N/A S GW-CYC27 1 WFC3/UVI ACCUM UVIS F606W none none 3 none 3 N/A S 18194( 2) - 01-Oct-2025 18:12:11 - [ 8] Visit: 04 (GW-Cyc27) Visit Requirements: TOO RESPONSE TIME 30.0D On Hold Comments: Additional Comments: cycle 27 target, 100-150 day epoch Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 GW-CYC27 WFC3/UVI ACCUM UVIS F606W 6 2400 S S (14400 S) Comments: TOO observation ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ GW-CYC27 1 WFC3/UVI ACCUM UVIS F606W none none 1 none 1 N/A S GW-CYC27 1 WFC3/UVI ACCUM UVIS F606W none none 2 none 2 N/A S GW-CYC27 1 WFC3/UVI ACCUM UVIS F606W none none 3 none 3 N/A S GW-CYC27 1 WFC3/UVI ACCUM UVIS F606W none none 4 none 4 N/A S GW-CYC27 1 WFC3/UVI ACCUM UVIS F606W none none 5 none 5 N/A S GW-CYC27 1 WFC3/UVI ACCUM UVIS F606W none none 6 none 6 N/A S 18194( 2) - 01-Oct-2025 18:12:11 - [ 9] Visit: 05 (GW-Cyc27) Visit Requirements: TOO RESPONSE TIME 30.0D On Hold Comments: Additional Comments: cycle 27 target, 200-300 day epoch Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 GW-CYC27 WFC3/UVI ACCUM UVIS F606W 6 2400 S S (14400 S) Comments: TOO observation ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ GW-CYC27 1 WFC3/UVI ACCUM UVIS F606W none none 1 none 1 N/A S GW-CYC27 1 WFC3/UVI ACCUM UVIS F606W none none 2 none 2 N/A S GW-CYC27 1 WFC3/UVI ACCUM UVIS F606W none none 3 none 3 N/A S GW-CYC27 1 WFC3/UVI ACCUM UVIS F606W none none 4 none 4 N/A S GW-CYC27 1 WFC3/UVI ACCUM UVIS F606W none none 5 none 5 N/A S GW-CYC27 1 WFC3/UVI ACCUM UVIS F606W none none 6 none 6 N/A S 18194( 2) - 01-Oct-2025 18:12:11 - [ 10] Visit: 06 (template) Visit Requirements: TOO RESPONSE TIME 30.0D On Hold Comments: Additional Comments: template for either target Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 GW-CYC27 WFC3/UVI ACCUM UVIS F606W 6 2400 S S (14400 S) Comments: TOO observation ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ GW-CYC27 1 WFC3/UVI ACCUM UVIS F606W none none 1 none 1 N/A S GW-CYC27 1 WFC3/UVI ACCUM UVIS F606W none none 2 none 2 N/A S GW-CYC27 1 WFC3/UVI ACCUM UVIS F606W none none 3 none 3 N/A S GW-CYC27 1 WFC3/UVI ACCUM UVIS F606W none none 4 none 4 N/A S GW-CYC27 1 WFC3/UVI ACCUM UVIS F606W none none 5 none 5 N/A S GW-CYC27 1 WFC3/UVI ACCUM UVIS F606W none none 6 none 6 N/A S 18194( 2) - 01-Oct-2025 18:12:11 - [ 11] Summary Form for Proposal 18194 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements TOO RESPONSE TIME 21.0D, TOO RESPONSE TIME 30.0D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F606W ------------------------------------------------------------------------------------------------------------------------------------ Target Names GW-CYC27, GW-PRECYC27 ------------------------------------------------------------------------------------------------------------------------------------