Please find attached our submission of a DDT for the recently discovered repeating gamma-ray burst GRB 250702BDE. As ever this has a tight timing window, observations that can recover the transient light are only possible until 17 July, and would be most valuable. However, since a core diagnostic is to distinguish between a host galaxy or confused Galactic point sources, these would still be valuable even if executed in the next visibility window. 1324212967 Assigned ID: 6904 ----- Attempting Submission 1 (Mon Jul 07 12:33:27 GMT 2025) ----- Dear Bill, This is a resubmission with i) the orient constraint removed and ii) the dither pattern spacings multiplied by 5 to insure against persistence etc. Best Wishes, Andrew 2029880241 ----- Attempting Submission 1 (Wed Jul 09 19:18:16 GMT 2025) ----- ----- Attempting Submission 2 (Wed Jul 09 20:48:44 GMT 2025) ----- 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. 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. This team has substantial expertise in studying transient events across the electromagnetic spectrum and in particular also with HST. In particular, the PI is the PI of 50 HST proposals over the past 20 years, many of which relate to study of gamma-ray bursts and related phenomena, including detailed studies of the host galaxies, and of the transients themselves. The CoIs also have extensive experience with HST, JWST and with ground based observations. For this particular event, the CoIs contain members of the Stargate collaboration that have obtained extensive ground-based observations that are presented in the proposal, as well as of the Swift and Einstein Probe teams. The combined expertise means that we have both the resources and necessary expertise to analyse the data and bring it to a timely publication. Stellar Physics and Stellar Types 0 false SUPPORTED EXT-STAR GAMMA RAY BURSTER SUPERNOVA J2000 J2000 WFC3/IR Imaging No No F160W POS-TARG DITHER 2.860 LINE 1.825 false false 74.653 4 18.528 WFC3-IR-DITHER-BOX-MIN 1 false 1752094049725 The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 17988 :visit-id "01" :proposal-version -1 :trans-version "20250321" :date "09-Jul-2025 22:47:29.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 1061936 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17988 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17988 :visit-id "01" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2454 :al-overhead-at-end 0 :internal-dur-at-end 424 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2913 :pcs-gap 0 ) true 1 0