  We present the detection at 89 $\mu$m (observed frame) of the {\it
Herschel}-selected gravitationally lensed starburst galaxy HATLASJ1429-0028
(also known as G15v2.19) in 15 minutes with the High-resolution Airborne
Wideband Camera-plus (HAWC+) onboard the Stratospheric Observatory for Infrared
Astronomy (SOFIA). The spectacular lensing system consists of an edge-on
foreground disk galaxy at $z$ = 0.22 and a nearly complete Einstein ring of an
intrinsic ultra-luminous infrared galaxy at $z$ = 1.03. Is this high IR
luminosity powered by pure star formation (SF) or also an active galactic
nucleus (AGN)? Previous nebular line diagnostics indicate that it is
star-formation dominated. We perform a 27-band multi-wavelength spectral energy
distribution modeling (SED) including the new SOFIA/HAWC+ data to constrain the
fractional AGN contribution to the total IR luminosity. The AGN fraction in the
IR turns out to be negligible. In addition, J1429-0028 serves as a testbed for
comparing SED results from different models/templates and SED codes (MAGPHYS,
SED3FIT, and CIGALE). We stress that star formation history is the dominant
source of uncertainty in the derived stellar mass (as high as a factor of
$\sim$ 10) even in the case of extensive photometric coverage. Furthermore, the
detection of a source at $z$ $\sim$ 1 with SOFIA/HAWC+ demonstrates the
potential of utilizing this facility for distant galaxy studies including the
decomposition of SF/AGN components, which cannot be accomplished with other
current facilities.
