Search for: All records

Context.There is a growing number of peculiar events that cannot be assigned to any of the main classes. SN 1987A and a handful of similar objects, thought to be explosive outcomes of blue supergiant stars, is one of them: while their spectra closely resemble those of H-rich (IIP) SNe, their light curve (LC) evolution is very different. Aims.Here we present the detailed photometric and spectroscopic analysis of SN 2021aatd, a peculiar Type II explosion. While its early-time evolution resembles that of the slowly evolving double-peaked SN 2020faa (although at a lower luminosity scale), after ∼40 days its LC shape becomes similar to that of SN 1987A-like explosions. Methods.In addition to comparing LCs, color curves, and spectra of SN 2021aatd to those of SNe 2020faa, 1987A, and other objects, we compared the observed spectra with our ownSYN++models and with the outputs of published radiative transfer models. We also carried out a detailed modeling of the pseudo-bolometric LCs of SNe 2021aatd and 1987A with a self-developed semi-analytical code, assuming a two-component ejecta (core + shell), and involving the rotational energy of a newborn magnetar in addition to radioactive decay. Results.We find that the photometric and the spectroscopic evolution of SN 2021aatd can be well described with the explosion of a ∼15M_⊙blue supergiant star. Nevertheless, SN 2021aatd shows higher temperatures and weaker Na ID and Ba II6142 Å lines than SN 1987A, which is instead reminiscent of IIP-like atmospheres. With the applied two-component ejecta model (accounting for decay and magnetar energy), we can successfully describe the bolometric LC of SN 2021aatd, including the first ∼40-day phase showing an excess compared to 87A-like SNe, but being strikingly similar to that of the long-lived SN 2020faa. Nevertheless, finding a unified model that also explains the LCs of more luminous events (e.g., SN 2020faa) is still a matter of debate. 

Abstract Multi-pulsed GRB 190530A, detected by the GBM and LAT onboard Fermi, is the sixth most fluent GBM burst detected so far. This paper presents the timing, spectral, and polarimetric analysis of the prompt emission observed using AstroSat and Fermi to provide insight into the prompt emission radiation mechanisms. The time-integrated spectrum shows conclusive proof of two breaks due to peak energy and a second lower energy break. Time-integrated (55.43 ± 21.30 %) as well as time-resolved polarization measurements, made by the Cadmium Zinc Telluride Imager (CZTI) onboard AstroSat, show a hint of high degree of polarization. The presence of a hint of high degree of polarization and the values of low energy spectral index (αpt) do not run over the synchrotron limit for the first two pulses, supporting the synchrotron origin in an ordered magnetic field. However, during the third pulse, αpt exceeds the synchrotron line of death in few bins, and a thermal signature along with the synchrotron component in the time-resolved spectra is observed. Furthermore, we also report the earliest optical observations constraining afterglow polarization using the MASTER (P < 1.3 %) and the redshift measurement (z= 0.9386) obtained with the 10.4m GTC telescopes. The broadband afterglow can be described with a forward shock model for an ISM-like medium with a wide jet opening angle. We determine a circumburst density of n0 ∼ 7.41, kinetic energy EK ∼ 7.24 × 1054 erg, and radiated γ-ray energy Eγ, iso ∼ 6.05 × 1054 erg, respectively. 

Abstract SN 2017jgh is a type IIb supernova discovered by Pan-STARRS during the C16/C17 campaigns of the Kepler/K2 mission. Here we present the Kepler/K2 and ground based observations of SN 2017jgh, which captured the shock cooling of the progenitor shock breakout with an unprecedented cadence. This event presents a unique opportunity to investigate the progenitors of stripped envelope supernovae. By fitting analytical models to the SN 2017jgh lightcurve, we find that the progenitor of SN 2017jgh was likely a yellow supergiant with an envelope radius of ∼50 − 290 R⊙, and an envelope mass of ∼0 − 1.7 M⊙. SN 2017jgh likely had a shock velocity of ∼7500 − 10300 km s−1. Additionally, we use the lightcurve of SN 2017jgh to investigate how early observations of the rise contribute to constraints on progenitor models. Fitting just the ground based observations, we find an envelope radius of ∼50 − 330 R⊙, an envelope mass of ∼0.3 − 1.7 M⊙ and a shock velocity of ∼9, 000 − 15, 000 km s−1. Without the rise, the explosion time can not be well constrained which leads to a systematic offset in the velocity parameter and larger uncertainties in the mass and radius. Therefore, it is likely that progenitor property estimates through these models may have larger systematic uncertainties than previously calculated.