17988( 3) - 09-Jul-2025 21:02:29 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 17988 Version: 3 Check-in Time: 09-Jul-2025 21:02:29 STScI Edit Number: 1 Title Galactic or extragalactic? Unravelling the extraordinary GRB 250702BDE ------------------------------------------------------------------------------------ Type Cycle GO/DD 32 ------------------------------------------------------------------------------------ Investigators Contact? PI: Prof. Andrew James Levan Radboud University Nijmegen Y CoI: Dr. Antonio Martin-Carrillo University College Dublin N CoI: Prof. Peter G. Jonker Radboud University Nijmegen N CoI: Prof. Lex Kaper Universiteit van Amsterdam N CoI: Dr. Dong Xu University of Copenhagen, Niels Bohr N Institute CoI: Dr. Patricia Schady University of Bath N CoI: Dr. Paul Thomas O'Brien University of Leicester N CoI: Dr. Robert Eyles-Ferris University of Leicester N CoI: Dr. Giovanna Pugliese Universiteit van Amsterdam N CoI: Dr. Benjamin Schneider Massachusetts Institute of Technology N CoI: Prof. Nial Rahil Tanvir University of Leicester N CoI: Dr. Massimiliano De Pasquale Universita degli Studi di Messina N CoI: Dr. Emeric Le Floc'h University of Arizona N CoI: Dr. Silvia Piranomonte INAF - Osservatorio Astronomico di Roma N CoI: Dr. Valerio D'Elia Agenzia Spaziale Italiana (ASI) Science N Data Center (ASDC) CoI: Dr. Susanna Vergani Observatoire de Paris - Section de Meudon N CoI: Dr. Luca Izzo INAF - Osservatorio Astronomico di N Capodimonte CoI: Dr. Dimple Dimple University of Birmingham N CoI: Dr. Tanmoy Laskar University of Utah N ------------------------------------------------------------------------------------ Abstract Gamma-ray bursts are extreme flashes of gamma-ray radiation typically lasting from a fraction of a second to tens of minutes. A critical feature is that they DO NOT repeat, nor, even in the extrema of ultra-long GRBs, do they last for more than a few hours. A very recent GRB has broken these paradigms. It triggered Fermi on no fewer than three occasions over several hours, and subsequent investigations show it was detected at high energies at least a day earlier. An infrared counterpart has been discovered that behaves temporally like a GRB afterglow but has colours unlike any transient seen before, with exceptionally reddening between H and K (a factor of ~30 in flux). Ground-based IR imaging in excellent (~0.4") seeing suggests that the transient is overlapping an extended source. If this is a galaxy, the probability of chance alignment is very small, but the field is also 5 degrees from the Galactic plane, and the extended nature could be due to source confusion in ground-based imaging. Here, we propose HST observations that can both track the late-time behaviour of the source beyond ground-based capabilities and also unambiguously distinguish between a background galaxy and several foreground stars by using exquisite HST resolution to resolve any foreground systems. These observations would ideally be taken within the current observing window, which runs until 17 July, but would still be of great value even if executed in a subsequent window. 17988( 3) - 09-Jul-2025 21:02:29 - [ 2] ------------------------------------------------------------------------------------ Observations Description ------------------------ We propose to obtain a single orbit of F160W observations of GRB 250702BDE. The observations will consist of an initial short exposure (in which bright stars won't be saturated, and the STEP sequence will give excellent dynamic range). This will be of value for astrometry to ground based images if the counterpart is faint. We will then proceed with a 4-point dither pattern, again using the STEP sequences. ------------------------------------------------------------------------------------ 17988( 3) - 09-Jul-2025 21:02:29 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 GRB250702BDE EXT-STAR, GAMMA RAY RA=18H58M45.5700S, J2000 V = 25 +/- 2 BURSTER, SUPERNOVA DEC=-07D52'26.20" Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 17988( 3) - 09-Jul-2025 21:02:29 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-IR-DITHER-BOX-MIN Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 2.860 Line_Spacing 1.825 Coordinate_Frame POS-TARG Pattern_Orient 18.528 Angle_Between_Sides 74.653 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 17988( 3) - 09-Jul-2025 21:02:29 - [ 5] Visit: 01 Visit Requirements: SCHED 100%; TOO RESPONSE TIME 6.0D On Hold Comments: Additional Comments: 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 GRB250702BD WFC3/IR MULTIAC IR F160W SAMP-SEQ=STEP25, NSAMP=12 1 DEF E CUM (199.233 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 GRB250702BD WFC3/IR MULTIAC IR F160W NSAMP=11, SAMP-SEQ=STEP100 1 DEF PATTERN 1 2 E CUM (1996.928 S) ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ GRB250702BDE 1 WFC3/IR MULTIAC IR F160W none none none none 1 N/A CUM GRB250702BDE 2 WFC3/IR MULTIAC IR F160W 1 none none none 1 N/A CUM GRB250702BDE 2 WFC3/IR MULTIAC IR F160W 2 none none none 1 N/A CUM GRB250702BDE 2 WFC3/IR MULTIAC IR F160W 3 none none none 1 N/A CUM GRB250702BDE 2 WFC3/IR MULTIAC IR F160W 4 none none none 1 N/A CUM 17988( 3) - 09-Jul-2025 21:02:29 - [ 6] Summary Form for Proposal 17988 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures IR ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/IR ------------------------------------------------------------------------------------------------------------------------------------ Opmodes MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters NSAMP=11, NSAMP=12, SAMP-SEQ=STEP100, SAMP-SEQ=STEP25 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 1 2, SCHED 100%, TOO RESPONSE TIME 6.0D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F160W ------------------------------------------------------------------------------------------------------------------------------------ Target Names GRB250702BDE ------------------------------------------------------------------------------------------------------------------------------------