ZTF SN Ia DR2: Searching for late-time interaction signatures in Type Ia supernovae from the Zwicky Transient Facility

Open Access

Table 1.

Initial sample size and its reduction in each step of the analysis process.

Criterion	Removed	Objects left
Initial DR2 sample	–	3628
No photometry at 100+ days	109	3519
No robust late-time detections ^(a)	2953	566
Presence of SN Ia tail ^(b)	432	134
Removed on visual inspection ^(c)	101	33
No late-time CSM interaction ^(d)	30	3

Notes.

^(a)

For a ‘robust detection’, at least four positive detections (two or more adjacent bins with ≥5σ) are required out of the 16 possible combinations of bin size (25, 50, 75, 100 d), and the starting position of the bin varied by 25, 50 or 75% of the bin size.

^(b)

We tested for the presence of a radioactive tail of the SN Ia as described in Sect. 3.2 and removed those where this was the most plausible explanation.

^(c)

Each remaining light curve was inspected using SNAP (Sect. 3.3) for possible issues causing late-time detections. See Sect. 4 for a discussion of the reasons events were removed.

^(d)

For each remaining light curve we checked in detail if the late-time detections could be explained without CSM interaction starting at late times.

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