Gaia DR3 5792808347020475136: onset of a hot circumstellar dust component on a K dwarf in 2018, found in NEOWISE time-domain photometry

Gaia DR3 5792808347020475136 (2MASS J14435201-7611457): onset of a hot circumstellar dust component on a K dwarf in 2018, found in NEOWISE time-domain photometry, working report and data package. A mature K dwarf at 248 pc whose 3.4 and 4.6 µm brightness stepped up by 17 % and 40 % between March and August 2018 and has stayed up since, with no optical change. The extra light is a ~1000 K component carrying about 1.6 % of the star's luminosity at ~0.035 AU. The package contains the report, the NEOWISE single-exposure photometry, an independent PSF-matched re-reduction of 884 raw frames, same-field control stars, the optical light curves (ASAS-SN, SkyMapper, TESS), the catalogue records and the attempts to kill the result. What is new in this version: SPHEREx Quick Release 2 covers the field in two passes (August–September 2025 and February–April 2026, 304 exposures across the six detectors). The star and HD 128641, the bright neighbour 31″ away, were fitted jointly in every exposure with the mission PSF, calibrated against HD 128641 in the same frame, and compared with thirteen control stars reduced identically. The excess is still present eighteen months after the last NEOWISE point, at 85–90 % of its 2018–2024 level (11.91 ± 0.07 ± 0.12 mJy at 3.37 µm and 7.35 ± 0.05 ± 0.07 mJy at 4.62 µm against a photosphere of 10.35 and 5.43 mJy), with a featureless 2.4–5 µm spectrum fitted by a ~1000 K blackbody, the same temperature as before. The two passes agree to 1 %. New files: the SPHEREx per-exposure photometry for all six detectors, the multi-source control-star photometry, the control summary, the WISE-equivalent fluxes, and two figures; the report gains section 5b and an updated summary, §6, §7 and file list.