TITLE: GCN CIRCULAR NUMBER: 42145 SUBJECT: GRB 250702B/EP250702a: JWST/NIRCam Observations DATE: 25/10/07 18:49:45 GMT FROM: Huei Sears at Rutgers University <huei.sears@rutgers.edu> H. Sears (Rutgers University), P. K. Blanchard (Harvard), R. Chornock (UC Berkeley), Nayana AJ (UC Berkeley), T. Ahumada (Caltech), K. D. Alexander (Arizona), I. Andreoni, A. Anumarlapudi, J. Carney (UNC), J. Freeburn (UNC), O. Graur (Portsmouth), X. J. Hall (CMU), E. Hammerstein (UC Berkeley), S. W. Jha (Rutgers), M. Kasliwal (Caltech), T. Laskar (Utah), R. Margutti (UC Berkeley), B. O’Connor (CMU), D. Pasham (MIT), I. Sfaradi (UC Berkeley), and Y. Yao (UC Berkeley) report: We obtained imaging of the field of GRB 250702B/EP250702a (GCNs 40883, 40886, 40890, 40906) with JWST/NIRCam under DD program 9447 (PI: H. Sears) starting at 2025-Oct-05 02:05:52 UT (~ 95 days post Fermi Gamma-ray trigger). The images were taken in the F150W, F200W, F277W, F356W, and F444W filters with exposure times of 10,049; 5024; 5024; 5024; and 5024 s, respectively. The host galaxy of the transient has a complex morphology in the short-wavelength filters, F150W and F200W. The prominent separation between two brighter nuclear regions seen in the Hubble Space Telescope (HST) F160W imaging (A. Levan et al. 2025, ApJL, 990, L28; J. Carney et al. 2025, arXiv: 2509.22784) is also visible at these shorter wavelengths. In the long wavelength filters, however, the galaxy has a smooth profile, including near the nucleus. This morphology supports the interpretation that the host is a single system with a prominent dust lane in a disk viewed nearly edge-on. Visual inspection reveals emission near the position of the transient in F150W and F200W that is not apparent in the longer wavelength filters. This excess emission is coincident with the excess flux noted in the HST F160W imaging (A. Levan et al. 2025, ApJL, 990, L28; J. Carney et al. 2025, arXiv: 2509.22784). The associated color and morphology suggests emission from an underlying star-forming region rather than solely from the transient. We use GALFIT to subtract two Sérsic components for the long-wavelength + F200W filters and one component for the F150W filter. To place limits on any transient flux, we additionally include one point source component in all filters fixed at the location of the HAWK-I H+K source as reported in A. Levan et al. 2025, ApJL, 990, L28; R.A. (J2000) = 18h 58m 45.s 57, decl. (J2000) = –07d 52 26.2. While the excess flux noticed in the F150W and F200W imaging is ~0.15’’ offset from the HAWK-I position, we believe this is likely to be due to imprecise absolute astrometry. For completeness, we report photometry for the transient at both locations. At the HAWK-I location, we report preliminary host-galaxy subtracted, 3-sigma upper-limits of m_F444W > 25.5 AB, m_F356W > 25.7 AB, m_F277W > 26.2 AB, m_F200W > 27.8 AB, and m_F150W > 28.6 AB (faint with high uncertainty). If, instead, we force the location of the transient to be at the excess flux noted in F150W and F200W, we report preliminary detections of m_F200W = 27.97 +/- 0.32 AB and m_F150W = 29.01 +/- 0.43 AB and find similar limits in the long-wavelength filters. Of note, these magnitudes are not corrected for Galactic nor host extinction. Further analysis is ongoing. We thank STScI staff members Alison Vick, Ben Sunnquist, and the entire JWST team for the successful implementation of this DD program. View this GCN Circular online at https://gcn.nasa.gov/circulars/42145. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...