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Data are from Q1-Q16.  x-axes: “Observed Tc” (Mid-Transit Time): EXOFAST’s best-fits from Kepler light flux vs. time data.  y-axes: “(O – C)”: difference between Observed Tc and the Calculated Tc from the graphically obtained linear ephemeris.  The plots are pictured in the order of orbital periods (smallest first).

Discussion:
This is a classic case of two mutually perturbing planets.  Note how the two TTV curves are almost perfectly anti-correlated and how closely the two P_ttv values match: 440.49 and 444.19 days.  The ratio of orbital periods is 1.172, i.e.: close to a 7:6 ratio (1.167).

1st: KOI-277.02, Kepler-36b, P = 13.85 days [Plot error bars (smaller than symbol) = ± 8.44 min.]
TTV_minimum:   251.67 ± 13.40 days, Amp_ttv_minimum:  -155.05 ± 16.89 min.
TTV_maximum:  471.91 ± 14.58 days, Amp_ttv_maximum:  152.75 ± 16.89 min.
TTV_minimum:   692.15 ± 16.29 days, Amp_ttv_minimum:  -155.05 ± 16.89 min.
TTV_maximum:  912.39 ± 18.40 days, Amp_ttv_maximum:  152.75 ± 16.89 min.
TTV_minimum:   1132.64 ± 20.78 days, Amp_ttv_minimum:  -155.05 ± 16.89 min.
TTV_maximum:  1352.88 ± 23.35 days, Amp_ttv_maximum:  152.75 ± 16.89 min.
P_ttv: 440.49 ± 6.34 days.
Amp_ttv: 307.80 ± 23.89 minutes.
Lomb-Scargle periodogram, candidate P_ttv:  437.21 days; Power: 25.56; P-value: 6.875 x 10^-9.
Linear ephemeris [this work]: Tc = 13.84941122(Tc#) + 74.69896674.
Estimated P_ttv = 1/|(nmmri_a/P_a - nmmri_b/P_b)| = 505.81 days

2nd: KOI-277.01, Kepler-36c, P = 16.23 days [Plot error bars (smaller than symbol) = ± 2.50 min.]
TTV_maximum:  256.56 ± 4.67 days, Amp_ttv_maximum:  129.66 ± 4.66 min.
TTV_minimum:   478.65 ± 5.12 days, Amp_ttv_minimum:  -107.94 ± 4.66 min.
TTV_maximum:  700.75 ± 5.76 days, Amp_ttv_maximum:  129.66 ± 4.66 min.
TTV_minimum:   922.85 ± 6.53 days, Amp_ttv_minimum:  -107.94 ± 4.66 min.
TTV_maximum:  1144.94 ± 7.41 days, Amp_ttv_maximum:  129.66 ± 4.66 min.
TTV_minimum:   1367.04 ± 8.35 days, Amp_ttv_minimum:  -107.94 ± 4.66 min.
P_ttv: 444.19 ± 2.29 days.
Amp_ttv: 237.60 ± 6.59 minutes.
Lomb-Scargle periodogram, candidate P_ttv:  445.63 days; Power: 36.02; P-value: 1.776 x 10^-13.
Linear ephemeris [this work]: Tc = 16.23171916(Tc#) + 104.67792419

References:
• For Q1-Q6 TTV data of 277.01 (thru ~ 563 (BJD-2454900) days), see: Ford2012arXiv-1201.1892.
• P_ttv equation: P_ttv = 1/|(nmmri_a/P_a - nmmri_b/P_b)|…(see Fabrycky, et al., 2012, arXiv-1201.5415)
• Seminal work on this 2-planet system was published by Carter & Agol (ref. 1b; Q0-Q9) and Ofir & Dreizler (ref. 1c; Q0-Q6).
• Planet Hunters notation : http://talk.planethunters.org/discussions/DPH101oxe8.

20 July 2013; updated 15 Aug 2013.
KOI-277 (Kepler-36, KIC-11401755) 2-Planet System