Hi all! I would like to raise an issue that has been discussed often in the lensed supernova community, but as far as I know we don’t have a solution for yet: What will the difference imaging and the real bogus pipeline do with an unresolved lensed supernova (or other lensed transient)? In this scenario, there are 2 or 4 multiple images of the lensed transient that are so close together that they cannot be resolved into multiple detections, while they also do not appear as a single point source (instead: a combination of 2 or 4 point sources). Since the RB score algorithm is trained at recognising single point sources, I’m wondering what it will do with a blend of multiple point sources. It’s a worrying idea that a significant fraction of lensed transients could be thrown away because of low RB scores.
Hi @nikki_arendse, thanks for the question. While it’s difficult to make general projections without performing appropriate injection tests (which to my knowledge have not yet been done), I would expect that the difference imaging pipeline would detect such an unresolved lensed SN (because it has a difference flux above threshold). As you note the corresponding spuriousness score is unlikely to be extremely high (as the sources won’t be pure point sources). On the other hand it’s not clear that the scores would obviously be so low that they would be rejected as artifacts.
Moreover, our general philosophy is to include as many DIASources as we technically can in the catalogs and alerts, allowing users to adjust their spuriousness thresholds as desired for greater purity (just point-like transients) or greater completeness (to allow users to sort through more alerts for rare events like the one you describe). We aim to reject the gross artifacts but pass through the marginal cases. The impact of this on lensed transients should then be assessed with simulations.
I’ll note that the Alert Production team is working directly with several members of the Strong Lensing Science Collaboration as part of the Difference Image Analysis Commissioning Science Unit to perform tests exactly like these.