Hintze Centre for Astrophysical Surveys

Abstract:

We report observations of the optical counterpart of the long gamma-ray burst (LGRB) GRB 221009A. Due to the extreme rarity of being both nearby ($z = 0.151$) and highly energetic ($E_{\gamma,\mathrm{iso}} \geq 10^{54}$ erg), GRB 221009A offers a unique opportunity to probe the connection between massive star core collapse and relativistic jet formation across a very broad range of $\gamma$-ray properties. Adopting a phenomenological power-law model for the afterglow and host galaxy estimates from high-resolution Hubble Space Telescope imaging, we use Bayesian model comparison techniques to determine the likelihood of an associated SN contributing excess flux to the optical light curve. Though not conclusive, we find moderate evidence ($K_{\rm{Bayes}}=10^{1.2}$) for the presence of an additional component arising from an associated supernova, SN 2022xiw, and find that it must be substantially fainter ($<$ 67% as bright at the 99% confidence interval) than SN 1998bw. Given the large and uncertain line-of-sight extinction, we attempt to constrain the supernova parameters ($M_{\mathrm{Ni}}$, $M_{\mathrm{ej}}$, and $E_{\mathrm{KE}}$) under several different assumptions with respect to the host galaxy's extinction. We find properties that are broadly consistent with previous GRB-associated SNe: $M_{\rm{Ni}}=0.05$ - $0.25 \, \rm{M_\odot}$, $M_{\rm{ej}}=3.5$ - $11.1 \, \rm{M_\odot}$, and $E_{\rm{KE}} = (1.6$ - $5.2) \times 10^{52} \, \rm{erg}$. We note that these properties are weakly constrained due to the faintness of the supernova with respect to the afterglow and host emission, but we do find a robust upper limit on the $M_{\rm{Ni}}$ of $M_{\rm{Ni}}<0.36\, \rm{M_\odot}$. Given the tremendous range in isotropic gamma-ray energy release exhibited by GRBs (7 orders of magnitude), the SN emission appears to be decoupled from the central engine in these systems.Comment: 18 pages, accepted to ApJL, 4 tables, 5 figures. Updated abstract in Previe

Abstract:

Most stripped envelope supernova progenitors are formed through binary interaction, losing hydrogen and/or helium from their outer layers. An emerging class of supernovae with the highest degree of envelope-stripping are thought to be the product of stripping by a NS companion. However, relatively few examples are known and the outcomes of such systems can be diverse and are poorly understood at present. Here, we present spectroscopic observations and high cadence multi-band photometry of SN 2023zaw, a low ejecta mass and rapidly evolving supernova. SN 2023zaw was discovered in a nearby spiral galaxy at D = 39.7 Mpc, with significant Milky Way extinction, $E(B-V) = 0.21$, and significant (but uncertain) host extinction. Bayesian evidence comparison reveals that nickel is not the only power source and an additional energy source is required to explain our observations. Our models suggest an ejecta mass of $M_{\rm ej} \sim 0.07\,\rm M_\odot$ and a synthesised nickel mass of $M_{\rm ej} \sim 0.007\,\rm M_\odot$ is required to explain the explosion. However an additional heating from a magnetar or interaction with circumstellar material is required to power the early light curve

Abstract:

We have measured the angular autocorrelation function of near-infrared galaxies in SERVS + DeepDrill, the Spitzer Extragalactic Representative Volume Survey and its follow-up survey of the Deep Drilling Fields, in three large fields totalling over 20 deg² on the sky, observed in two bands centred on 3.6 and 4.5 μm. We performed this analysis on the full sample as well as on sources selected by [3.6]–[4.5] colour in order to probe clustering for different redshift regimes. We estimated the spatial correlation strength as well, using the redshift distribution from S-COSMOS with the same source selection. The strongest clustering was found for our bluest subsample, with 〈z〉 ∼ 0.7, which has the narrowest redshift distribution of all our subsamples. We compare these estimates to previous results from the literature, but also to estimates derived from mock samples, selected in the same way as the observational data, using deep light-cones generated from the SHARK semi-analytical model of galaxy formation. For all simulated (sub)samples, we find a slightly steeper slope than for the corresponding observed ones, but the spatial clustering length is comparable in most cases.

Abstract:

Jets of energetic particles, as seen in FR type-I and FR type-II sources, ejected from the centre of radio-loud AGN affect the sources surrounding the intracluster medium/intergalactic medium. Placing constraints on the age of such sources is important in order to measure the jet powers and determine the effects on feedback. To evaluate the age of these sources using spectral age models, we require high-resolution multiwavelength data. The new sensitive and high-resolution MIGHTEE survey of the XMM-LSS field, along with data from the Low Frequency Array (LOFAR) and the Giant Metrewave Radio Telescope (GMRT) provide data taken at different frequencies with similar resolution, which enables us to determine the spectral age distribution for radio-loud AGN in the survey field. In this study, we present a sample of 28 radio galaxies with their best-fitting spectral age distribution analysed using the Jaffe–Perola (JP) model on a pixel-by-pixel basis. Fits are generally good, and objects in our sample show maximum ages within the range of 2.8 to 115 Myr with a median of 8.71 Myr. High-resolution maps over a range of frequencies are required to observe detailed age distributions for small sources, and high-sensitivity maps will be needed in order to observe fainter extended emission. We do not observe any correlation between the total physical size of the sources and their age, and we speculate that both dynamical models and the approach to spectral age analysis may need some modification to account for our observations.