Early light curve of PTF10iam (red circles are detections and the triangle is an upper limit) and the parabolic fit to the pre-peak data used to infer the rise time (solid red line). We compare the rise of PTF10iam to those of the normal Type Ia SN 2011fe (dashed purple line; data from Vinkó et al. 2012; distance modulus from Lee & Jang 2012), the 91bg-like SN 1999by (dotted–dashed blue line; data from Garnavich et al. 2004; distance modulus from NED), the Ia–CSM PTF11kx (dotted dark green line; Firth et al. 2015)—all shifted in brightness to match the peak of PTF10iam—and the Ia–CSM SN 2005gj (dotted light green line; Aldering et al. 2006). PTF10iam has a faster rise compared to SN 2011fe and SN 2005gj. The rises of PTF10iam, SN1˙999by, and PTF11kx are similar, but their peak magnitudes are very different. If this difference were due to interaction power it should have imprinted strong CSM signatures in the spectrum.