arXiv subjects

S. Zha

Publications and source records attributed to S. Zha.

5 recordsLinked to original sources

arXiv2026

The transitional Type Ibn/IIn SN 2022pda, with pre-explosion outbursts and a double-peaked light curve

We report the results of a photometric and spectroscopic follow-up campaign of the unusual interacting supernova (SN) 2022pda. Precursor variability lasting $\sim 100$ days is observed before the explosion. The SN light curve has a double peak shape. It reached a first maximum of $M_{\rm{r}} = -19.6 \pm 0.2$\,mag, followed by an initial two-month decline and a second, broad peak lasting about six months. The early spectra show a blue continuum with dominant H and He emission lines. A high-resolution pre-maximum spectrum shows that the profile of the \Hei~$\lambda$5876 line consists of a moderately narrow ($\sim 1900$ \kms) P~Cygni absorption superposed on a broader ($\sim 3300$ \kms) component. In the blue region, several spectral features are identified, including C {\sc iii}/N {\sc iii}/O {\sc ii} blends. Two broad bumps at 4600--5200 \AA, 6400--6800~\AA\ regions reveal a complex profile, which are likely due to blends of H, He, and other emission lines. Late-time spectra are still dominated by prominent and broad H and He lines in emission. Shock-driven model fits to the bolometric light curve suggest that the SN is powered by interaction with a massive CSM with enhanced mass loss rates $\sim 5$ \msun yr$^{-1}$, expelled during two events occurred $\sim 1$ and $\sim 0.2$ years before the explosion. The overall SN evolution indicates that SN\,2022pda is a transitional event between a H-rich SN IIn (SN\,2009ip-like) and a He-rich SN Ibn. Our findings suggest that the progenitor was likely a Luminous Blue Variable transitioning towards a Wolf--Rayet stage.

astro-ph.HE↗

arXiv2025

SN 2016iog: A fast declining Type II-L supernova with an ultra-faint tail, persistently interacting with circumstellar material

We present optical photometric and spectroscopic observations of the rapidly declining Type IIL supernova (SN) 2016iog. SN 2016iog reached its peak $\sim$ 14 days after explosion, with an absolute magnitude in the $V$ band of $-18.64 \pm 0.15$ mag, followed by a steep decline of $8.85 \pm 0.15$~mag~(100\,d)$^{-1}$ post-peak. Such a high decline rate makes SN~2016iog one of the fastest declining Type~IIL SNe observed to date. The rapid rise in the light curve, combined with the nearly featureless continuum observed in the spectrum at +9.3 days, suggests the presence of interaction. In the recombination phase, we observed broad H$\alpha$ lines that persist at all epochs. In addition, the prominent double-peaked H$\alpha$ feature observed in the late-time spectrum (+190.8 days) is likely attributable either to significant dust formation within a cool dense shell or to asymmetric circumstellar material. These features suggest the presence of sustained interaction around SN~2016iog. We propose that the observed characteristics of SN~2016iog can be qualitatively explained by assuming a low-mass H-rich envelope surrounding a red supergiant progenitor star with low-density circumstellar material.

astro-ph.SR↗

arXiv2025

Massive stars exploding in a He-rich circumstellar medium XII. SN 2024acyl: A fast, linearly declining Type Ibn supernova with early flash-ionisation features

We present a photometric and spectroscopic analysis of the Type Ibn supernova (SN) 2024acyl. It rises to an absolute magnitude peak of about -17.58 mag in 10.6 days, and displays a rapid linear post-peak light-curve decline in all bands, similar to most SNe Ibn. The optical pseudobolometric light curve peaks at $(3.5\pm0.8) \times 10^{42}$ erg s$^{-1}$, with a total radiated energy of $(5.0\pm0.4) \times 10^{48}$ erg. The spectra are dominated by a blue continuum at early stages, with narrow P Cygni He I lines and flash-ionisation emission lines of C III, N III, and He II. The P Cygni He I features gradually evolve and become emission-dominated in late-time spectra. Our multi-band light-curve modelling yields estimates of the ejecta mass of $M_{\rm ej} = 0.49^{+0.11}_{-0.09}$ M$_\odot$ with a kinetic energy of $E_{\rm k} = 0.06^{+0.01}_{-0.01} \times 10^{51}$ erg, and a $^{56}$Ni mass of $M_{\rm Ni} = 0.018$ M$_\odot$. The inferred CSM properties are characterised by a mass of $M_{\rm CSM} = 0.51^{+0.05}_{-0.04}$ M$_\odot$, an inner radius of $R_0 = 17.8^{+3.6}_{-3.0}$ AU, and a density of $\rho_{\rm CSM} =(8.3_{-1.2}^{+2.7})\times10^{-12}$ g cm$^{-3}$. The multi-epoch spectra are well reproduced by the CMFGEN/he4p0 model, corresponding to a He-ZAMS mass of 4 M$_\odot$ (H-ZAMS mass 18.11 M$_\odot$, pre-SN mass 3.16 M$_\odot$). These findings are consistent with a scenario of an SN powered by ejecta-CSM interaction, originating from a low-mass helium star that evolved within an interacting binary system where the CSM with some residual hydrogen may originate from the mass-transfer process. In addition, a channel of core-collapse explosion of a late-type Wolf-Rayet star with H, or an Ofpe/WN9 star with fallback accretion, cannot be entirely ruled out.

astro-ph.SR↗

arXiv2025

Precision mass measurements around ${}^{84}$Mo rule out ZrNb cycle formation in the rapid proton-capture process at type I X-ray bursts

The rapid proton-capture ($rp$-) process is one of the primary, explosive thermonuclear burning processes that drive type I X-ray bursts. A possible termination of the $rp$-process at around ${}^{84}$Mo was previously suggested by the formation of a ZrNb cycle. We report here precision mass measurements at around ${}^{84}$Mo, which have concluded the possibility of the cycle. The experiment was conducted using the multi-reflection time-of-flight spectrograph at RIKEN RI Beam Factory, and the masses of ${}^{79}$Y, ${}^{83}$Nb, ${}^{84}$Mo, ${}^{88}$Ru, and an isomer in ${}^{78}$Y were measured. For ${}^{84}$Mo, and ${}^{88}$Ru, and the isomeric state of ${}^{78}$Y, their masses are experimentally determined for the first time with uncertainties of $\delta m \approx 20~{\rm keV/c^2}$. The mass precision of ${}^{79}$Y and ${}^{83}$Nb is improved to $13~{\rm keV/c^2}$ and $9.6~{\rm keV/c^2}$, respectively. The new $\alpha$-separation energy of ${}^{84}$Mo, 1.434(83) MeV, unambiguously rules out the possibility of forming the ZrNb cycle. The X-ray burst simulation with the new masses shows that our measurements effectively remove the large final abundance uncertainties in the $A=80-90$ mass region. The new mass values improve the prediction power for the composition of the nuclear ashes in X-ray bursts.

nucl-ex↗

arXiv2018

Constraints on the Chemical Enrichment History of the Perseus Cluster of Galaxies from High-Resolution X-ray Spectroscopy

High-resolution spectroscopy of the core of the Perseus Cluster of galaxies, using the $Hitomi$ satellite above 2 keV and the $XMM$-$Newton$ Reflection Grating Spectrometer at lower energies, provides reliable constraints on the abundances of O, Ne, Mg, Si, S, Ar, Ca, Cr, Mn, Fe, and Ni. Accounting for all known systematic uncertainties, the Ar/Fe, Ca/Fe, and Ni/Fe ratios are determined with a remarkable precision of less than 10%, while the constraints on Si/Fe, S/Fe, and Cr/Fe are at the 15% level, and Mn/Fe is measured with a 20% uncertainty. The average biases in determining the chemical composition using archival CCD spectra from $XMM$-$Newton$ and $Suzaku$ range typically from 15-40%. A simple model in which the enrichment pattern in the Perseus Cluster core and the proto-solar nebula are identical gives a surprisingly good description of the high-resolution X-ray spectroscopy results, with $χ^2=10.7$ for 10 d.o.f. However, this pattern is challenging to reproduce with linear combinations of existing supernova nucleosynthesis calculations, particularly given the precise measurements of intermediate $α$-elements enabled by $Hitomi$. We discuss in detail the degeneracies between various supernova progenitor models and explosion mechanisms, and the remaining uncertainties in these theoretical models. We suggest that including neutrino physics in the core-collapse supernova yield calculations may improve the agreement with the observed pattern of $α$-elements in the Perseus Cluster core. Our results provide a complementary benchmark for testing future nucleosynthesis calculations required to understand the origin of chemical elements.

astro-ph.HE↗