J/A+A/712/A173 SN 2024gy photometry and polarimetry (Terwel+, 2026)
An analysis of the Type Ia SN 2024gy and a comparison of different host
extinction estimation techniques.
Terwel J.H., Maguire K., O'Donnell C., Pursiainen M., Casasbuenas A.,
Thiim Gadeberg J., Godson B., Harvey L., Nobre Hauptmann B., Koivisto N.,
Liu C., Shenoy S., Grund Sorensen S., Diaz Teodori M.A., Guldberg Theil A.,
Turkki M., Alburai A., Anderson J., de Boer T., Mueller Bravo T., Burgaz U.,
Chambers K.C., Chen T.-W., Duarte J., Galbany L., Gromadzki M., Inserra C.,
Johansson J., Kim Y.-L., Lowe T., Magnier E., Santos R.P., Sollerman J.,
Wainscoat R., Young D.R., Chen T.X., Graham M.J., Kasliwal M.M.,
Masci F.J., Purdum J.N., Belkhodja I.
<Astron. Astrophys. 712, A173 (2026)>
=2026A&A...712A.173T 2026A&A...712A.173T (SIMBAD/NED BibCode)
ADC_Keywords: Supernovae ; Photometry ; Optical ; Polarization
Keywords: dust extinction - supernovae: individual: SN 2024gy
Abstract:
Type Ia supernovae (SNe Ia) are well-known standardisable candles, and
are one of the main ways to measure the distance to their host
galaxies. However, extinction due to interstellar dust causes objects
to appear fainter and redder. Correcting for this requires estimating
the amount of intervening material and how the extinction changes as a
function of wavelength. We present and analyse optical and
near-infrared data of the well-observed SN 2024gy and use these to
compare different extinction estimation techniques, making use of
photometric, spectroscopic, and polarimetric data. SN 2024gy is a
normal SN Ia with high velocity (HV) components in SiIIλ6355
(phase←10-days) and a particularly strong HV feature in the CaII
near-infrared triplet (up to peak). Modelling SN 2024gy with TARDIS
shows better matches with a double-detonation scenario compared to a
delayed-detonation scenario due to a better match to the CaII HV
component. A measurement of the stable Ni/Fe ratio however favours a
delayed-detonation scenario. Host extinction estimates range from
E(B-V)host=0.12±0.02mag (narrow interstellar absorption
lines) to E(B-V)host=0.24±0.06mag (Lira law) with a mean of
E(B-V)host=0.22±0.04mag, assuming RV=3.1. The spread
between different methods highlights the challenge of accurately
estimating the amount of extinction light suffers before being
observed.
Description:
Photometric and polarimetric data for SN 2024gy. LT, and GOTO data
only cover phases when the SN was active. ATLAS, PS, and ZTF data
include pre-SN observations. All observations have been scaled to a
common 30 mag zero point (AB system) and binned on a nightly basis.
This data is not corrected for extinction. Polarimetry observations
were taken with ALFOSC at the NOT.
Objects:
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RA (2000) DE Designation(s)
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12 15 51.28 +13 06 56.1 SN 2024gy = ZTF24aaaiocv
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
atlas.dat 86 1019 ATLAS photometry (c and o filters)
asassn.dat 86 228 ASAS-SN photometry (g filter)
goto.dat 86 130 GOTO photometry (L filter)
ltlc.dat 86 30 Liverpool Telescope photometry
(ltu ltg ltr lti ltz filters)
pslc.dat 86 26 Pan-STARRS photometry (i w y z filters)
ztflc.dat 86 1034 ZTF photometry (ztfg ztfr ztfi filters)
pol.dat 85 15 Imaging polarimetry
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Byte-by-byte Description of file: a* goto.dat ltlc.dat pslc.dat ztflc.dat
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Bytes Format Units Label Explanations
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1- 14 F14.6 d JD Julian Date
16- 21 A6 --- Filter Used broadband filter
24- 25 I2 mag zp Zero point
27- 41 F15.6 --- Flux Flux in Filter
43- 56 F14.6 --- e_Flux Flux error
58- 66 F9.6 mag mag ?=99 Magnitude in filter (1)
68- 76 F9.6 mag e_mag ?=99 Magnitude error (1)
78- 86 F9.6 mag ulmag 5 sigma upper limit (2)
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Note (1): if flux < 5 * flux_err, the value in this column is 99.
Note (2): if flux ≥ 5 * flux_err, the value in this column is 99.
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Byte-by-byte Description of file: pol.dat
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Bytes Format Units Label Explanations
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2- 6 F5.2 d Phase Phase relative to peak (JD 2460330.2)
8- 17 F10.2 d JD Julian Date
19- 24 A6 --- Filter Used broadband filter
26- 30 F5.2 pix Aper Aperture size in pixels
32- 36 F5.2 % Q Stokes Q polarization
38- 41 F4.2 % e_Q Error on Stokes Q polarization
43- 47 F5.2 % U Stokes U polarization
49- 52 F4.2 % e_U Error on Stokes U polarization
54- 57 F4.2 % P Total polarization
59- 62 F4.2 % e_P Error on total polarization
64- 69 F6.2 deg theta Polarization angle
72- 78 F7.2 deg e_theta Error on polarization angle
80- 85 F6.2 --- SNR Signal to Noise Ratio
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Acknowledgements:
Jacco H. Terwel, terwelj(at)tcd.ie
License: CC-BY-4.0
(End) Jacco Terwel [Trinity College Dublin], Patricia Vannier [CDS] 01-Jun-2026