Hintze Centre for Astrophysical Surveys

Abstract:

We present an expanded template library for the supernova identification (SNID) software, along with updated source files that make it easy to merge our templates—and other major SNID libraries—into the base code. This expansion, dubbed “Super-SNID,” increases the number of spectra for under-represented supernova classes (e.g., SNe Ia-02cx, Ibn) and adds new classes (e.g., SLSNe, TDEs, LFBOTs). Super-SNID includes 841 spectral templates for 161 objects, primarily from the Public ESO Spectroscopic Survey of Transient Objects Data Releases 1–4. The library is available on GitHub with simple installation instructions.

Abstract:

We present the discovery and early observations of the nearby Type II supernova (SN) 2024ggi in NGC 3621 at 6.64 ± 0.3 Mpc. The SN was caught 5.8−2.9+1.9 hr after its explosion by the ATLAS survey. Early-phase, high-cadence, and multiband photometric follow-up was performed by the Kilonova Finder (Kinder) project, collecting over 1000 photometric data points within 1 week. The combined o- and r-band light curves show a rapid rise of 3.3 mag in 13.7 hr, much faster than SN 2023ixf (another nearby and well-observed SN II). Between 13.8 and 18.8 hr after explosion, SN 2024ggi became bluer, with u − g color dropping from 0.53 to 0.15 mag. The rapid blueward evolution indicates a wind shock breakout (SBO) scenario. No hour-long brightening expected for the SBO from a bare stellar surface was detected during our observations. The classification spectrum, taken 17 hr after the SN explosion, shows flash features of high-ionization species such as Balmer lines, He i, C iii, and N iii. Detailed light-curve modeling provides critical insights into the circumstellar material (CSM). Our favored model has an explosion energy of 2 × 1051 erg, a mass-loss rate of 10−3 M⊙ yr−1 (with an assumed 10 km s−1 wind), and a confined CSM radius of 6 × 1014 cm. The corresponding CSM mass is 0.4 M⊙. Comparisons with SN 2023ixf highlight that SN 2024ggi has a less dense confined CSM, resulting in a faster rise and fainter UV flux. Citizen astronomer collaboration and extensive data are essential for SBO searches and detailed SN characterizations.

Abstract:

Recent results from Type Ia supernovae, baryon acoustic oscillations (BAOs), and the cosmic microwave background (CMB) indicate (1) potentially discrepant measurements of the matter density Ωm and Hubble constant H0 in the ΛCDM model when analyzed individually and (2) hint of dynamical dark energy in a w0waCDM model when data are combined in a joint analysis. We examine whether underlying dynamical dark energy cosmologies favored by data would result in biases in Ωm and H0 for each probe when analyzed individually under ΛCDM. We generate mock data sets in w0waCDM cosmologies, fit the individual probes under the ΛCDM model, and find that expected biases in Ωm are ∼0.03. Notably, the Ωm differences between probes are consistent with values observed in real data sets. We also observe that mock DESI-BAO data sets generated in the w0wa CDM cosmologies will lead to a biased measurement of H0 higher by ∼1.2 km s−1 Mpc−1 when fitted under ΛCDM, appearing to mildly improve the Hubble tension, but as the true underlying H0 is lower, the tension is in fact worsened. We find that the Ωm discrepancies, the high BAO H0 relative to the CMB, and the joint dynamical dark energy signal are all related effects that could be explained simultaneously with either new physics or new systematics. While it is possible to unite many of the discrepancies seen in recent analyses along a single axis, our results underscore the importance of understanding systematic differences in data sets, as they have unique impacts in different cosmological parameter spaces.

Abstract:

A programme to search for radio emission from dwarf-novae-type cataclysmic variables was conducted with the South African MeerKAT radio telescope. The dwarf novae RU Pegasi, V426 Ophiuchi, and IP Pegasi were detected during outburst at L band (1284 MHz central frequency). Previously, only one cataclysmic variable was radio-detected at a frequency this low. We now bring the number to four. With these three newly found radio-emitters, the population of dwarf novae confirmed to be radio-emitting at any frequency reaches 10 systems. We found that the radio luminosity is correlated with the optical luminosity. For V426 Ophiuchi and RU Pegasi we found a radio decline contemporary with the outburst’s optical decline. The peak radio luminosity of dwarf novae in outburst is very similar to that of novalike Cataclysmic Variables and no correlation with orbital period is seen.