Optical Rebrightening of Extragalactic Transients from the Zwicky Transient Facility

Soraisam, Monika; Matheson, T.; Lee, Chien‐Hsiu; Saha, Abhijit; Narayan, Gautham; Wolf, N.; Scott, A.; Figuereo, Stephanie; Nuñez, Rafael; McKinnon, Kevin; Guhathakurta, Puragra; Brink, Thomas G.; Filippenko, A. V.; Smith, Nathan

doi:10.3847/2041-8213/ac4e99

“…Furthermore, we present optical and near-infrared (NIR) data for two LRNe discovered in 2021: AT 2021afy and AT 2021blu. In the case of the latter, Sloan g-and r-band light curves were also presented by Soraisam et al (2022). In contrast to the monitoring campaigns of other LRNe in our program (Pastorello et al 2021a,b), the follow-up campaigns of these two objects were not significantly affected by the COVID-19 pandemic restrictions to our access to observational facilities.…”

Section: Introductionmentioning

confidence: 68%

“…29 ASAS-SN photometry is publicly released through the Sky Patrol ASAS-SN interface (https://asas-sn.osu.edu). 30 In this case, we used public ZTF forced photometry, which is released through the Lasair (https://lasair.roe.ac.uk/) and ALeRCE (https://alerce.online/) brokers, and already shown by Soraisam et al (2022).…”

Section: Appendix B: Instruments Used In the Spectroscopic Campaignsmentioning

confidence: 99%

Panchromatic evolution of three luminous red novae: Forbidden hugs in pandemic times -- IV

Pastorello¹,

Valerin²,

Fraser³

et al. 2022

Preprint

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We present photometric and spectroscopic data on three extragalactic luminous red novae (LRNe): AT 2018bwo, AT 2021afy, and AT 2021blu. AT 2018bwo was discovered in NGC 45 (at about 6.8 Mpc) a few weeks after the outburst onset. During the monitoring period, the transient reached a peak luminosity of 10 40 erg s −1 . AT 2021afy, hosted by UGC 10043 (∼ 49.2 Mpc), showed a double-peaked light curve, with an early maximum reaching a luminosity of 2.1 × 10 41 erg s −1 . Finally, for AT 2021blu in UGC 5829 (∼ 8.6 Mpc), the pre-outburst phase was wellmonitored by several photometric surveys, and the object showed a slow luminosity rise before the outburst. The light curve of AT 2021blu was sampled with an unprecedented cadence until the object disappeared behind the Sun, and was then recovered at late phases. The light curve of LRN AT 2021blu shows a double peak, with a prominent early maximum reaching a luminosity of 6.5 × 10 40 erg s −1 , half that of AT 2021afy. The spectra of AT 2021afy and AT 2021blu display the expected evolution for LRNe: a blue continuum dominated by prominent Balmer lines in emission during the first peak, and a redder continuum consistent with that of a K-type star with narrow absorption metal lines during the second, broad maximum. The spectra of AT 2018bwo are markedly different, with a very red continuum dominated by broad molecular features in absorption. As these spectra closely resemble those of LRNe after the second peak, probably AT 2018bwo was discovered at the very late evolutionary stages. This would explain its fast evolution and the spectral properties compatible with that of an M-type star. From the analysis of deep frames of the LRN sites years before the outburst, and considerations of the light curves, the quiescent progenitor systems of the three LRNe were likely massive, with primaries ranging from about 13 M ⊙ for AT 2018bwo, to 14 +4 −1 M ⊙ for AT 2021blu, and over 40 M ⊙ for AT 2021afy.

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“…Furthermore, we present optical and near-infrared (NIR) data for two LRNe discovered in 2021: AT 2021afy and AT 2021blu. In the case of the latter, Sloan g-and r-band light curves were also presented by Soraisam et al (2022). In contrast to the monitoring campaigns of other LRNe in our programme (Pastorello et al 2021a;Pastorello 2021b), the follow-up campaigns of these two objects were not significantly affected by the COVID-19 pandemic restrictions as to our access to observational facilities.…”

Section: Introductionmentioning

confidence: 84%

“…While our spectroscopic monitoring campaign of AT 2021blu stopped ∼5 months after maximum brightness, an optical spectrum was obtained by Soraisam et al (2022) ∼8 months after maximum, showing the typical TiO bands observed in LRN spectra at late epochs.…”

Section: At 2021blumentioning

confidence: 90%

Forbidden hugs in pandemic times

Pastorello

¹

,

Valerin

²

,

Fraser

³

et al. 2023

A&A

4

1

0

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We present photometric and spectroscopic data on three extragalactic luminous red novae (LRNe): AT 2018bwo, AT 2021afy, and AT 2021blu. AT 2018bwo was discovered in NGC 45 (at about 6.8 Mpc) a few weeks after the outburst onset. During the monitoring period, the transient reached a peak luminosity of 1040 erg s−1. AT 2021afy, hosted by UGC 10043 (∼49.2 Mpc), showed a double-peaked light curve, with the two peaks reaching a similar luminosity of 2.1(±0.6)×1041 erg s−1. Finally, for AT 2021blu in UGC 5829 (∼8.6 Mpc), the pre-outburst phase was well-monitored by several photometric surveys, and the object showed a slow luminosity rise before the outburst. The light curve of AT 2021blu was sampled with an unprecedented cadence until the object disappeared behind the Sun, and it was then recovered at late phases. The light curve of LRN AT 2021blu shows a double peak, with a prominent early maximum reaching a luminosity of 6.5 × 1040 erg s−1, which is half of that of AT 2021afy. The spectra of AT 2021afy and AT 2021blu display the expected evolution for LRNe: a blue continuum dominated by prominent Balmer lines in emission during the first peak, and a redder continuum consistent with that of a K-type star with narrow absorption metal lines during the second, broad maximum. The spectra of AT 2018bwo are markedly different, with a very red continuum dominated by broad molecular features in absorption. As these spectra closely resemble those of LRNe after the second peak, AT 2018bwo was probably discovered at the very late evolutionary stages. This would explain its fast evolution and the spectral properties compatible with that of an M-type star. From the analysis of deep frames of the LRN sites years before the outburst, and considerations of the light curves, the quiescent progenitor systems of the three LRNe were likely massive, with primaries ranging from about 13 M⊙ for AT 2018bwo, to 14−1+4 M⊙ for AT 2021blu, and over 40 M⊙ for AT 2021afy.

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“…Observational studies of evolved massive stars are starting to reveal an eventful history of mass loss as these stars approach core collapse. Observational evidence has been accumulating from a variety of independent lines, including: the direct detection of pre-supernova outbursts from across the mass spectrum of exploding stars (e.g., Pastorello et al 2007Pastorello et al , 2013Margutti et al 2014;Ofek et al 2014;Pastorello et al 2018;Strotjohann et al 2021;Jacobson-Galán et al 2022b); bright UV emission in type IIP supernovae (SNe IIP) at early times (e.g., Morozova et al 2018;Bostroem et al 2019;Morozova et al 2020;Dessart & John Hillier 2022); narrow spectral lines originating from a dense circumstellar medium ionized by the explosion's shock (as in type IIn, type Ibn, and type Icn SNe; e.g., Schlegel 1990;Filippenko 1997;Pastorello et al 2008;Perley et al 2022); re-brightening of optical light curves (e.g., Sollerman et al 2020;Jin et al 2021;Soraisam et al 2022); and luminous X-ray and radio emission powered by efficient conversion of shock kinetic energy into radiation as the SN shock is decelerated in the environment by mass lost by the star before stellar demise (e.g., Chevalier & Fransson 2006;Soderberg et al 2006;Dwarkadas et al 2010;Chevalier & Fransson 2017;Stroh et al 2021). Here we present the results from a coordinated campaign on SN 2014C with the Chandra X-ray Observatory (CXO) and the Nuclear Spectroscopic Telescope Array (NuSTAR) during the first 7 yr after core collapse, and update the analysis by Margutti et al (2017).…”

Section: Introductionmentioning

confidence: 99%

Seven Years of Coordinated Chandra–NuSTAR Observations of SN 2014C Unfold the Extreme Mass-loss History of Its Stellar Progenitor

Brethauer

¹

,

Margutti

²

,

Milisavljevic

³

et al. 2022

ApJ

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We present the results from our 7 yr long broadband X-ray observing campaign of SN 2014C with Chandra and NuSTAR. These coordinated observations represent the first look at the evolution of a young extragalactic SN in the 0.3–80 keV energy range in the years after core collapse. We find that the spectroscopic metamorphosis of SN 2014C from an ordinary type Ib SN into an interacting SN with copious hydrogen emission is accompanied by luminous X-rays reaching L x ≈ 5.6 × 1040 erg s−1 (0.3–100 keV) at ∼1000 days post-explosion and declining as L x ∝ t −1 afterwards. The broadband X-ray spectrum is of thermal origin and shows clear evidence for cooling after peak, with T ( t ) ≈ 20 keV ( t / t pk ) − 0.5 . Soft X-rays of sub-keV energy suffer from large photoelectric absorption originating from the local SN environment with NH int ( t ) ≈ 3 × 10 22 ( t / 400 days ) − 1.4 cm − 2 . We interpret these findings as the result of the interaction of the SN shock with a dense (n ≈ 105 − 106 cm−3), H-rich disk-like circumstellar medium (CSM) with inner radius ∼2 × 1016 cm and extending to ∼1017 cm. Based on the declining NHint(t) and X-ray luminosity evolution, we infer a CSM mass of ∼(1.2 f–2.0 f ) M ⊙ , where f is the volume filling factor. We place SN 2014C in the context of 121 core-collapse SNe with evidence for strong shock interaction with a thick circumstellar medium. Finally, we highlight the challenges that the current mass-loss theories (including wave-driven mass loss, binary interaction, and line-driven winds) face when interpreting the wide dynamic ranges of CSM parameters inferred from observations.

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Optical Rebrightening of Extragalactic Transients from the Zwicky Transient Facility

Cited by 6 publications

References 41 publications

Panchromatic evolution of three luminous red novae: Forbidden hugs in pandemic times -- IV

Panchromatic evolution of three luminous red novae: Forbidden hugs in pandemic times -- IV

Forbidden hugs in pandemic times

Seven Years of Coordinated Chandra–NuSTAR Observations of SN 2014C Unfold the Extreme Mass-loss History of Its Stellar Progenitor

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