The outburst of an embedded low-mass YSO in L1641

Context. Strong outbursts in very young and embedded protostars are rare and not yet fully understood. They are believed to originate from an increase in the mass accretion rate ((M) over dot(acc)) onto the source. Aims. We report the discovery of a strong outburst in a low-mass embedded young stellar object (YSO), namely 2MASS-J05424848-0816347 or [CTF93]216-2, as well as its photometric and spectroscopic follow-up. Methods. Using near-to mid-IR photometry and NIR low-resolution spectroscopy, we monitor the outburst, deriving its magnitude, duration, as well as the enhanced accretion luminosity and mass accretion rate. Results. [CTF93] 216-2 increased in brightness by similar to 4.6, 4.0, 3.8, and 1.9 mag in the J, H, K-s bands and at 24 mu m, respectively, corresponding to an L-bol increase of similar to 20 L-circle dot. Its early spectrum, probably taken soon after the outburst, displays a steep almost featureless continuum, with strong CO band heads and H2O broad-band absorption features, and Br. line in emission. A later spectrum reveals more absorption features, allowing us to estimate T-eff similar to 3200 K, M-* similar to 0.25 M-circle dot, and (M) over dot(acc) similar to 1.2 x 10(-6) M(circle dot)yr(-1). This makes it one of the lowest mass YSOs with a strong outburst so far discovered.