James Webb Space Telescope Feed Post

JWST NIRCam Observations of SN 1987A: Spitzer Comparison and Spectral Decomposition

The top row shows (left) apertures used to replicate the IRAC photometry that had been performed on much lower-resolution data, and (right) the resulting SED. These flux densities are the sum of those for the SN and stars 2, 3, and 4. The horizontal lines indicate the bandwidths for wide bands (filled circles) and narrow bands (open circles). The middle row shows results with a smaller aperture that includes only the SN. Star 3 is specifically excluded from the background region. The bottom row shows the SEDs of stars 2, 3, and 4, with 21,000 K stellar atmosphere models from Coelho (2014) shown for comparison. Star 3 is a classical Be star with excess emission at >3 µm. The green dashed line shows the SED of the B2IIIe star SMC5_074402 from Bonanos et al. (2010) for comparison (multiplied by a factor of 0.8). The display range on the bottom left panel is altered such that the stars are not saturated. Abstract: JWST Near Infrared Camera (NIRCam) observations at 1.5–4.5 µm have provided broadband and narrowband imaging of the evolving remnant of SN 1987A with unparalleled sensitivity and spatial resolution. Comparing with previous marginally spatially resolved Spitzer Infrared Array Camera (IRAC) observations from 2004 to 2019 confirms that the emission arises from the circumstellar equatorial ring (ER), and the current brightness at 3.6 and 4.5 µm was accurately predicted by extrapolation of the declining brightness tracked by IRAC. Despite the regular light curve, the NIRCam observations clearly reveal that much of this emission is from a newly developing outer portion of the ER. Spots in the outer ER tend to lie at position angles in between the well-known ER hotspots. We show that the bulk of the emission in the field can be represented by five standard spectral energy distributions, each with a distinct origin and spatial distribution. This spectral decomposition provides a powerful technique for distinguishing overlapping emission from the circumstellar medium and the supernova ejecta, excited by the forward and reverse shocks, respectively.