Strategies to identify strongly lensed type Ia supernovae in Rubin LSST

Prajakta Mane

BS-MS, IISER Mohali, India

Rubin Community Workshop 2024

Anupreeta More, Surhud More

IUCAA, India

23-07-2024

Time delay cosmography:

\frac{D_d D_s}{D_{ds}} = \frac{1}{H_0} f(z_s, z_l, \Omega_m, \Omega_\Lambda )

accurate time delays, surface mass distribution and redshift of lens

Hubble constant with strong lensing time delays

well-constrained Hubble Constant

Why are SNe Ia a better source for TDC?

well-studied light curves -> more accurate time delay measurements
transient source -> improved constraints on the lens galaxy model
standard candle nature -> help overcome degeneracies

How to find lensed SNe Ia?

DIA: run LSST Stack's difference imaging pipeline to identify multiply imaged SNe

CMA: study outliers in the colour-magnitude space for SNe to identify lensed SNe Ia

\Delta t = \frac{D_d D_s}{cD_{ds}}(1+z_l)\Delta\tau \text{+ constant}

Raw exposures from Subaru Hyper-Suprime Cam (HSC) -> Public Data Release 1
UltraDeep Survey's COSMOS region, Tract number 9813 (~1.7 deg wide)
149 visits in grizy from 10 nights in 2014 and 2015: 16,688 CCD images
LSST Science Pipeline w_2022_12

Strong lensing positions, magnifications, and time delays simulated using a code adapted from More & More, 2022

SNe light curves: SALT2 (Guy et al., 2007, 2010) template built in SNCosmo (Barbary et al., 2017) manually incorporating strong lensing observables

SNe light curve simulations

Sky data for DIA

Difference imaging analysis

Template Image

Science Image

Difference Image

Yellow circles of radius 1": injected lensed SNe

Red circles of radius 2": diaSources

\text{unresolved quads}

\text{resolved doubles}

\text{unresolved}\\\text{doubles}

Difference imaging analysis

Total recovery fraction ~70%
Slightly higher for quads
Decreases significantly for the y-band

	Injected	Detected	% recovery
Total	74k	51.5k	70
Doubles	70k	48.3k	70
Quads	4.1k	3.2k	78
g	310	260	83
r	5.4k	4.7k	86
i	14k	11k	80
z	21k	16k	76
y	34k	20k	58

Difference imaging analysis

Preliminary results

Unresolved detections: ~49k

Resolved detections: 1285

Color-magnitude analysis

Quimby et al. 2014

: Unlensed SNIa

: Unlensed core collapse

: Lensed SNIa
: Lensed core collapse

The redder supernovae for given i-band magnitude are more likely to be lensed SNeIa when studied for unresolved photometry on rising phase of light curve.

The black bold curve separates the lensed SNeIa from unlensed both on the rising and the falling edge of light curve for z < 3

Simulated SNe Ia

Contamination from unlensed CC SNe is neglegible.

Contamination from CC SNe

Contamination from unlensed CC SNe is neglegible.

Primary contaminants are lensed SNe Ib and Ic.

Contamination from CC SNe

Summary so far...

In the first run, the DI pipeline recovers ~70% of the injected lensed SNe Ia data. The recovery fraction decreases for fainter injected systems. It is slightly higher for quads and decreases significantly for HSC y-band.
We observe a low resolved fraction, which is seen to be weakly correlated with the angular separation of the system for doubles.
Colour-magnitude-based demarcation effectively selects lensed SNe Ia for simulated and observed (un-)lensed SNe Ia till redshift 3, both on rising and falling edge. Contamination from unlensed CC SNe is low. Primary contaminants are found to be lensed CC SNe Ib and Ic.

Ongoing work