3I/ATLAS Photometric–Chromatic Anomaly (2025)

3I/ATLAS (C/2025 N1) Photometric–Chromatic Anomaly: Optical Acceleration and Multi-Observatory Validation Version 2.4 — Extended Photometry and Post-Perihelion Deceleration This dataset provides a fully updated, timestamped record of the 2025 photometric–chromatic evolution of the interstellar object 3I/ATLAS (C/2025 N1), extending MPC photometry through 2025-11-13 (4,413 observations). Using an optical activity proxy derived from the time derivative of the inverse magnitude, this work identifies: A revised pre-perihelion optical activity peak on 2025-10-02, A coincident reddening phase in the g−o colour index (+0.7 mag, July–Sept), A post-perihelion deceleration and fading phase (early November), No post-perihelion tail or fragmentation signatures in independent Nordic Optical Telescope (NOT) imaging. What’s new in v2.4: === Data ===• MPC photometry updated through 13 Nov 2025• Clean parsing of all 4,413 records• Fixed duplicate-handling and run-log consistency === Analysis ===• Updated pre-perihelion peak timing• Improved post-perihelion acceleration reversal analysis• Updated plots: acceleration v2, post-perihelion evolution === Documentation ===• Revised paper with new figures and NOT morphological constraints• Corrected pipeline scripts (update_I3_data.sh, append_run_log_v3.sh) === Verification ===• Full OpenTimestamps Bitcoin proofs• GPG signatures• Complete proof bundle with manifests and hashes This release supersedes v2.3 and provides the most temporally complete account of the optical evolution of 3I/ATLAS during its 2025 passage. Key Contents: Extended MPC photometry: 4,413 observations (2025-05-08 to 2025-11-13) Optical acceleration proxy: Temporal derivative analysis revealing pre-perihelion peak (2025-10-02) and post-perihelion fading Color evolution analysis: Strong reddening in g-o index (Δ ≈ +0.7 mag) during activity rise Multi-observatory validation: NOT images showing compact morphology without cometary features Complete research paper: "Photometric and Non-Gravitational Anomalies in 3I/ATLAS" with full methodology Reproducible pipeline: Python scripts, verification proofs, and cryptographic timestamps