  Our recent claims of a Galactic center feature in Fermi-LAT data at
approximately 130 GeV have prompted an avalanche of papers proposing
explanations ranging from dark matter annihilation to exotic pulsar winds.
Because of the importance of such interpretations for physics and astrophysics,
a discovery will require not only additional data, but a thorough investigation
of possible LAT systematics. While we do not have access to the details of each
event reconstruction, we do have information about each event from the public
event lists and spacecraft parameter files. These data allow us to search for
suspicious trends that could indicate a spurious signal. We consider several
hypotheses that might make an instrumental artifact more apparent at the
Galactic center, and find them implausible. We also search for an instrumental
signature in the Earth limb photons, which provide a smooth reference spectrum
for null tests. We find no significant 130 GeV feature in the Earth limb
sample. However, we do find a marginally significant 130 GeV feature in Earth
limb photons with a limited range of detector incidence angles. This raises
concerns about the 130 GeV Galactic center feature, even though we can think of
no plausible model of instrumental behavior that connects the two. A modest
amount of additional limb data would tell us if the limb feature is a
statistical fluke. If the limb feature persists, it would raise doubts about
the Pass 7 processing of E > 100 GeV events. At present we find no instrumental
systematics that could plausibly explain the excess Galactic center emission at
130 GeV.
