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

  • Study if extendedness can be used as a marker for a lensed system.
  • Next DI run: Incorporate LSST cadence.
  • Run it on DC2 data.

Thank You!

Holds well for the observed unlensed and lensed SNeIa.

Also eliminates the unlensed SLSNe sample.

Extra slide

Color-magnitude criteria employed on observed lensed SNe Ia and unlensed SNe Ia and SLSNe

vertical dashed line: median seeing

Variation of the recovery fraction with injected magnitudes and angular separation between images

Extra slide

Recovery fraction shows a 'cut-off magnitude' after which the fraction drops drastically. It also decreases significantly in the HSC-y band.

Resolved fraction is directly proportional to the angular separation of the system.

Template Image

Science Image

Difference Image

Yellow circles of radius 1": injected lensed SNe

Red circles of radius 2": diaSources

Extra slide

Difference image WITH the lens galaxy (not the best for visual representation!!)

Extra slide

Distribution of observables of the simulated lensed SNe Ia

Extra slide

Example of a simulated lensed SNe Ia light curve

Comaparison of unlensed CC SNe CMDs from low and high redshift

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