J/A+A/694/A146 Candidate lensed SNe Ia in the ZTF archive (Townsend+, 2025)
Candidate strongly lensed Type Ia supernovae in the Zwicky Transient Facility
archive.
Townsend A., Nordin J., Sagues Carracedo A., Kowalski M., Arendse N.,
Dhawan S., Goobar A., Johansson J., Moertsell E., Schulze S., Andreoni I.,
Fernandez E., Kim A.G., Nugent P.E., Prada F., Rigault M., Sarin N.,
Sharma D., Bellm E.C., Coughlin M.W., Dekany R., Groom S.L., Lacroix L.,
Laher R., Riddle R., Aguilar J., Ahlen S., Bailey S., Brooks D.,
Claybaugh T., de la Macorra A., Dey A., Dey B., Doel P., Fanning K.,
Forero-Romero J.E., Gaztanaga E., Gontcho A Gontcho S., Honscheid K.,
Howlett C., Kisner T., Kremin A., Lambert A., Landriau M., Le Guillou L.,
Levi M.E., Manera M., Meisner A., Miquel R., Moustakas J., Mueller E.,
Myers A.D., Nie J., Palanque-Delabrouille N., Poppett C., Rezaie M.,
Rossi G., Sanchez E., Schlegel D., Schubnell M., Seo H., Sprayberry D.,
Tarle G., Zou H.
<Astron. Astrophys. 694, A146 (2025)>
=2025A&A...694A.146T 2025A&A...694A.146T (SIMBAD/NED BibCode)
ADC_Keywords: Supernovae ; Gravitational lensing
Keywords: gravitational lensing: strong - methods: observational -
techniques: photometric - supernovae: general
Abstract:
Gravitationally lensed type Ia supernovae (glSNe Ia) are unique
astronomical tools that can be used to study cosmological parameters,
distributions of dark matter, the astrophysics of the supernovae, and
the intervening lensing galaxies themselves. A small number of highly
magnified glSNe Ia have been discovered by ground-based telescopes
such as the Zwicky Transient Facility (ZTF), but simulations predict
that a fainter, undetected population may also exist. We present a
systematic search for glSNe Ia in the ZTF archive of alerts
distributed from June 1 2019 to September 1 2022. Using the AMPEL
platform, we developed a pipeline that distinguishes candidate glSNe
Ia from other variable sources. Initial cuts were applied to the ZTF
alert photometry (with constraints on the peak absolute magnitude and
the distance to a catalogue-matched galaxy, as examples) before forced
photometry was obtained for the remaining candidates. Additional cuts
were applied to refine the candidates based on their light curve
colours, lens galaxy colours, and the resulting parameters from fits
to the SALT2 SN Ia template. The candidates were also cross-matched
with the DESI spectroscopic catalogue. Seven transients were
identified that passed all the cuts and had an associated galaxy DESI
redshift, which we present as glSN Ia candidates. Although
superluminous supernovae (SLSNe) cannot be fully rejected as
contaminants, two events, ZTF19abpjicm and ZTF22aahmovu, are
significantly different from typical SLSNe and their light curves can
be modelled as two-image glSN Ia systems. From this two-image
modelling, we estimate time delays of 22±3 and 34±1 days for the
two events, respectively, which suggests that we have uncovered a
population of glSNe Ia with longer time delays. The pipeline is
efficient and sensitive enough to parse full alert streams. It is
currently being applied to the live ZTF alert stream to identify and
follow-up future candidates while active. This pipeline could be the
foundation for glSNe Ia searches in future surveys, such as the Rubin
Observatory Legacy Survey of Space and Time.
Description:
This is Table A.2 which shows the measured parameters of the 125
candidates that passed the selection criteria in Sects. 4.2 and 4.3,
before the final visual inspection phase. This includes the ZTF ID,
right ascension (RA), declination (dec.), photometric redshift (phot.
z), DESI redshift, angular separation from the catalogue counterpart
(ang. sep.) for both the photometric and DESI redshifts, peak absolute
B-band magnitude from SALT2 (for both the photometric and DESI
redshifts), SALT2 x_1 and associated error, SALT2 c and associated
error, whether it passed selection method 1 with DESI cross-matching
(detailed in Sect. 4.2) and/or selection method 2 with additional cuts
(detailed in Sect. 4.3), and the reason it was rejected from the final
candidate sample (if any).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea2.dat 105 125 Parameters for the 125 candidates that passed
the S1 and S2 criteria
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See also:
J/A+A/642/A148 : SuGOHI VI. List up to 2020 (Sonnenfeld+, 2020)
Byte-by-byte Description of file: tablea2.dat
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Bytes Format Units Label Explanations
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1- 12 A12 --- ZTF Identication name for the ZTF object
(ZTFNNaaaaaaa)
13 A1 --- n_ZTF [*] Note on ZTF (1)
15- 23 F9.5 deg RAdeg Right ascension (J2000)
25- 33 F9.5 deg DEdeg Declinayion (J2000)
35- 38 F4.2 --- zph Photometric redshift as determined by AMPEL
(and may be averaged from more than one
catalogue)
40- 45 F6.2 mag BMAG Peak absolute B-band magnitude as determined
by SALT2 using the photometric redshift
47- 50 F4.2 arcsec PA Angular separation between the object and the
catalogue-matched galaxy with a photometric
redshift
52- 55 F4.2 --- zDESI ?=- Spectroscopic redshift as from
DESI catalogue
57- 62 F6.2 mag BMAGDESI ?=- Peak absolute B-band magnitude as
determined by SALT2 using the DESI redshift
64- 67 F4.2 arcsec PADESI ?=- Angular separation between the object and
the catalogue-matched galaxy from DESI
70- 74 F5.2 --- SALT2x1 ?=- x1 'stretch' parameter from
a SALT2 fit (2)
76- 79 F4.2 --- e_SALT2x1 ?=- Error on x1 'stretch' parameter from
a SALT2 fit (2)
81- 85 F5.2 --- SALT2c ?=- c 'colour' parameter from a SALT2 fit (2)
87- 90 F4.2 --- e_SALT2c ?=- Error on c 'colour' parameter from
a SALT2 fit (2)
92- 96 F5.2 --- chi2r ?=- reduced chi-square from a SALT2 fit (2)
98-101 A4 --- Meth Selection method (3)
103-105 A3 --- Reason Reason for rejection (4)
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Note (1): Objects that passed the visual inspection and are in the final sample.
Note (2): using the DESI z, if available, otherwise with the photometric
redshift.
Note (3): whether the object passed selection method 1 with DESI cross-matching
(detailed in Sect. 4.2) and/or selection method 2 with additional cuts
(detailed in Sect. 4.3).
Note (4): The reasons for rejection are given as follows:
a = Likely AGN/QSO
b = DESI z<0.15
c = Stellar variability
d = Likely a TDE (e.g. due to a dust echo, or light curve decline
matching an exponential decay)
e = Long duration/rise time, so likely SLSN
f = Bumps in light curve suggest circumstellar interaction
g = Lens galaxy would be too faint (from LS colours)
h = Changes in DESI processing meant that the redshift is now too small
i = Issues with ZTF data processing
j = Candidate lens system from SuGOHI VI catalogue Sonnenfeld et al.,
2020A&A...642A.148S 2020A&A...642A.148S, Cat. J/A+A/642/A148, likely lensed QSO
k = More likely associated with closer nearby galaxy
(with LS photo. z=0.090±0.006)
l = Confirmed TDE Yao2022
m = DESI z available that means MB>-20mag
n = Confirmed SN Ia-91T
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Acknowledgements:
Alice Townsend, alice.townsend(at)physik.hu-berlin.de
References:
Sonnenfeld et al., 2020A&A...642A.148S 2020A&A...642A.148S, Cat. J/A+A/642/A148
Yao et al. 2022, Transient Name Server Classification Report, 2022-925, 1
(End) Patricia Vannier [CDS] 02-Jan-2025