A micronova burst in the intermediate polar IGR J17014-4306

We report the detection of a short optical burst in TESS data of IGR J17014-4306, the eclipsing intermediate polar with the longest known orbital period. The burst lasts 1.56 d and shows multiple peaks, reaching (9.3 ± 0.2) × 1033 erg s−1, and releases a total energy of (3.25 ± 0.01) × 1038 erg. The burst parameters are consistent with those of a micronova eruption, currently understood as a thermonuclear runaway in the magnetically-confined accretion column. From its energy, we infer a burned column mass of ∼1.6 × 10−11 M⊙ which, under several assumptions, suggests a recurrence time of ∼20 d. Our search for similar events in long-term Gaia, ASAS-SN, and AAVSO light curves reveals 16 possible fast brightenings over ∼11 yr, suggesting that micronova events may be frequent in IGR J17014-4306. Timing analysis of the TESS data shows that the white-dwarf spin signal remains stable before and after the burst, but is not clearly detectable during the eruption. Its extreme orbital period and eclipsing nature make IGR J17014-4306 an ideal test-bed for further studies of magnetically confined thermonuclear burning on white dwarfs.