arXiv subjects

Alexa Gordon

Publications and source records attributed to Alexa Gordon.

3 recordsLinked to original sources

arXiv2026

The Environments of Luminous Fast Blue Optical Transients: Evidence for a Compact Object and Wolf-Rayet Star Merger Origin

We present a comprehensive analysis of the host galaxies of 11 luminous fast blue optical transients (LFBOTs). We model new and archival host photometry and spectroscopy with Prospector. We determine that all LFBOT hosts are actively star-forming with recent bursts of star formation and have a median stellar mass of $\log(M_*/M_\odot)=9.61^{+0.74}_{-1.61}$, present-day star formation rate SFR=$0.99^{+14.85}_{-0.95}$~$M_\odot$~yr$^{-1}$, and gas-phase oxygen abundance metallicity 12+log(O/H)=$8.59^{+0.18}_{-0.22}$. To contextualize these results, we compare them to the host properties of Hydrogen-poor superluminous supernovae (SLSNe-I), several core-collapse supernova subtypes (CCSN; SNe Ibc, II, and Ibn) and long gamma-ray bursts (LGRBs). We find that LFBOT hosts are more star-forming than CCSN hosts, but less star-forming than SLSN-I hosts. We further show that LFBOT hosts are more metal-poor than SN Ibc and II hosts, but more metal-rich than SLSN-I and LGRB hosts. Finally, we find that, similar to SLSNe-I and unlike CCSNe and LGRBs, a large fraction of LFBOTs occur in their hosts' faintest pixel or outside their host galaxy's light. Our results indicate that LFBOTs have a massive stellar origin that do not trace active star-forming regions within their hosts and have a weaker metallicity-dependence than other extreme transients. For these reasons, we favor a compact-object and Wolf-Rayet star merger progenitor scenario over other previously proposed models, such as tidal disruption events and failed or successful CCSN. Future discoveries of LFBOTs with the Rubin observatory will help to increase their sample size and place firmer constraints on their environments and progenitors.

astro-ph.HE↗

arXiv2024

GRB$\,$220831A: a hostless, intermediate Gamma-ray burst with an unusual optical afterglow

GRB$\,$220831A is a gamma-ray burst (GRB) with a duration and spectral peak energy that places it at the interface between the distribution of long-soft and short-hard GRBs. In this paper, we present the multi-wavelength follow-up campaign to GRB$\,$220831A and its optical, near-infrared, X-ray and radio counterparts. Our deep optical and near-infrared observations do not reveal an underlying host galaxy, and establish that GRB$\,$220831A is observationally hostless to depth, $m_i\gtrsim26.6$ AB mag. Based on the Amati relation and the non-detection of an accompanying supernova, we find that this GRB is most likely to have originated from a collapsar at $z>2$, but it could also possibly be a compact object merger at $z<0.4$ with a large separation distance from its host galaxy. Regardless of its origin, we show that its optical and near-infrared counterpart departs from the evolution expected from a forward shock dominated synchrotron afterglow, exhibiting a steep post-break temporal powerlaw index of $-3.83^{+0.62}_{-0.79}$, too steep to be the jet-break. By analysing a range of models, we find that the observed steep departure from forward shock closure relations is likely due to an internal process producing either a flare or a plateau.

astro-ph.HE↗

arXiv2023

The Environments of Fast Radio Bursts Viewed Using Adaptive Optics

We present GeMS/GSAOI observations of five fast radio burst (FRB) host galaxies with sub-arcsecond localizations. We examine and quantify their spatial distributions and locations with respect to their host galaxy light distributions, finding a median host-normalized offset of 2.09 r_e and in fainter regions of the host. When combined with the FRB sample from Mannings et al. (2021), we find that FRBs are statistically distinct from Ca-rich transients in terms of light and from SGRBs and LGRBs in terms of host-normalized offset. We further find that most FRBs are in regions of elevated local stellar mass surface densities in comparison to the mean global values of their hosts. This, in combination with the combined FRB sample trace the distribution of stellar mass, points towards a possible similarity of the environments of CC-SNe and FRBs. We also find that 4/5 FRB hosts exhibit distinct spiral arm features, and the bursts originating from such hosts tend to appear on or close to the spiral structure of their hosts, with a median distance of 0.53 kpc. With many well-localized FRB detections looming on the horizon, we will be able to better characterize the properties of FRB environments relative to their host galaxies and other transient classes.

astro-ph.GA↗