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JWST/MIRI has sharpened our infrared eyes toward the star formation process.This paper presents the first mid-infrared detection of gaseous SO$_2$ emissionin an embedded low-mass protostellar system. MIRI-MRS observations of thelow-mass protostellar binary NGC 1333 IRAS2A are presented from the JWSTObservations of Young protoStars (JOYS+) program, revealing emission from theSO$_2~\nu_3$ asymmetric stretching mode at 7.35 micron. The results arecompared to those derived from high-angular resolution SO$_2$ data obtainedwith ALMA. The SO$_2$ emission from the $\nu_3$ band is predominantly locatedon $\sim50-100$ au scales around the main component of the binary, IRAS2A1. Arotational temperature of $92\pm8$ K is derived from the $\nu_3$ lines. This isin good agreement with the rotational temperature derived from pure rotationallines in the vibrational ground state (i.e., $\nu=0$) with ALMA ($104\pm5$ K).However, the emission of the $\nu_3$ lines is not in LTE given that the totalnumber of molecules predicted by a LTE model is found to be a factor$2\times10^4$ higher than what is derived for the $\nu=0$ state. Thisdifference can be explained by a vibrational temperature that is $\sim100$ Khigher than the derived rotational temperature of the $\nu=0$ state. Thebrightness temperature derived from the continuum around the $\nu_3$ band ofSO$_2$ is $\sim180$ K, which confirms that the $\nu_3=1$ level is notcollisionally populated but rather infrared pumped by scattered radiation. Thisis also consistent with the non-detection of the $\nu_2$ bending mode at 18-20micron. Given the rotational temperature, the extent of the emission ($\sim100$au in radius), and the narrow line widths in the ALMA data (3.5 km/s), theSO$_2$ in IRAS2A likely originates from ice sublimation in the central hot corearound the protostar rather than from an accretion shock at the disk-envelopeboundary.

JOYS+: mid-infrared detection of gas-phase SO$_2$ emission in a low-mass protostar. The case of NGC 1333 IRAS2A: hot core or accretion shock?