J/A+A/702/A213 SN 2021irp polarisation spectra (Reynolds+, 2025)
The bright long-lived Type II SN 2021irp powered by aspherical circumstellar
material interaction. II.
Estimating the CSM mass and geometry with polarimetry and light curve modeling.
Reynolds T.M., Nagao T., Maeda K., Elias-Rosa N., Fraser M., Gutierrez C.,
Kangas T., Kuncarayakti H., Mattila S., Pessi P.J.
<Astron. Astrophys. 702, A213 (2025)>
=2025A&A...702A.213R 2025A&A...702A.213R (SIMBAD/NED BibCode)
ADC_Keywords: Supernovae ; Polarization ; Spectroscopy ; Optical ; Infrared
Keywords: techniques: polarimetric - supernovae: general -
supernovae: individual: SN 2021irp
Abstract:
There is evidence for interaction between supernova (SN) ejecta and
massive circumstellar material (CSM) in various types of SNe. The
mass-ejection mechanisms that produce massive CSM are unclear, and
studying interacting SNe and their CSM can shed light on these
mechanisms and the final stages of stellar evolution. We aim to study
the properties of the CSM in the bright, long-lived, hydrogen-rich
(Type II) SN 2021irp, which is interacting with a massive aspherical
CSM. We present imaging- and spectro-polarimetric observations of SN
2021irp. By modelling its polarisation and bolometric light curve, we
derive the mass and distribution of the CSM. SN 2021irp shows a high
intrinsic polarisation of ∼0.8%. This high continuum polarisation
suggests an aspherical photosphere created by an aspherical CSM
interaction. Based on the bolometric light curve evolution and the
high polarization, SN 2021irp can be explained as a typical Type II SN
interacting with a CSM disk with a corresponding mass-loss rate and
half-opening angle of ∼0.035-0.1M☉/yr and ∼30-50 degrees,
respectively. The total CSM mass derived is >2M☉. We suggest that
this CSM disk was created by some process related to binary
interaction, and that SN 2021irp is the end product of a typical
massive star (i.e. with Zero-Age-Main-Sequence mass of ∼8-18M☉)
that has a separation and/or mass ratio with its companion star that
led to an extreme mass ejection within decades of explosion. Based on
the observational properties of SN 2021irp and similar SNe, we propose
a general picture for the spectroscopic properties of Type II SNe
interacting with a massive disk CSM.
Description:
Photometric and spectroscopic observations of the interact-
ing SN 2021irp are presented and analysed in a companion paper to
this work, Reynolds et al. (2025A&A...702A.212R 2025A&A...702A.212R).
Final reduced spectropolarimetric data for SN 2021irp, both before and
after subtraction of the measured ISP. The spectra are binned into
bins of 50Å. Some of the data are shown in Fig. 1 of the paper.
Objects:
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RA (2000) DE Designation(s)
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05 23 27.45 +17 04 39.8 SN 2021irp = ATLAS 21lhv
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
specpolb.dat 100 120 SN2021irp polarisation spectrum
before ISP correction
specpola.dat 100 120 SN2021irp polarisation spectrum
after ISP correction
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See also:
J/A+A/702/A212 : SN 2021irp photometry (Reynolds+, 2025)
Byte-by-byte Description of file: specpola.dat specpolb.dat
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Bytes Format Units Label Explanations
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1- 11 F11.6 0.1nm lambda Restframe wavelength
13- 26 F14.6 --- Int Intensity
28- 37 F10.6 % Q Stokes parameter Q
39- 47 F9.6 % U Stokes parameter U
49- 56 F8.6 % P Total polarisation
58- 66 F9.6 % e_P Total polarisation error
68- 77 F10.6 deg PA Polarization angle
79- 88 F10.6 deg e_PA Polarization angle error
90-100 F11.6 --- S/N Signal to noise ratio
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Acknowledgements:
Thomas Reynolds (thmire(at)utu.fi) uploaded the data to CDS,
Takashi Nagao processed the data and produced the table.
References:
Reynolds et al., Paper I 2025A&A...702A.212R 2025A&A...702A.212R, Cat. J/A+A/702/A212
(End) Patricia Vannier [CDS] 17-Sep-2025