A repository of writing by Lachlan Marnoch - short stories, fantasy, science fiction, science fact, and adjacent opinions.
Coming into the research year of my Masters, I was full of uncertainty. If I was either naturally talented or highly motivated - preferably both, as it seems the scientists that surround me are - I knew that I could do it, could become a true scientist. For the previous six months or so I hadn't felt either.
Read MoreI love programming. There is little more satisfying than watching your hard-written program cascade into reality. It's the closest I've ever come to feeling like a god. However, this rarely - perhaps never - happens on the first try. I present the following as an example of the numerous frustrations that can encumber scientific research.
Read MoreMy name is Lachlan Marnoch, and I have just begun a PhD - the degree of a Doctor of Philosophy, an antiquated title from back when philosophy was anything that involved deep thinking about any topic. The specific flavour of thinking which I’ll be doing is on astrophysics. What that means is that I will use physics to try and make sense of information from the night sky. As with my Masters, I’ll be studying fast radio bursts - very brief, very mysterious bursts of radio waves originating from other galaxies. They’re pretty fascinating, and I’ll get to explaining more about them soon.
Read MoreThe culmination of a year’s work, available for your reading pleasure.
Read MoreWay back in first year, for an elective about soft mathematics (that wasn't the official description), I wrote an essay about the advantages and disadvantages of adopting further decimal units. I tidied it up a little, and here it is!
Read MoreHuman beings, the anatomically modern kind, have lived on Earth for the last quarter of a million years. Although that is a tiny amount of time compared to the vast spans I’ve described so far, I feel we’ve achieved rather a lot.
Read MoreMammals lived, for 135 million years, in the shadows of much larger reptiles. Dinosaurs dominated the land, giant marine reptiles owned the seas, and pterosaurs patrolled the skies. Mammals did not rest on their laurels, however, developing the traits that define them today.
Read MoreThe Earth formed in the same manner as its brethren: by accretion from the disk of dust left behind by the sun’s birth. Heated by the many collisions that grew it, the planet was molten at first.
Read MoreAround five billion years ago, an average-sized white star swelled from the dust of a barred spiral galaxy. From the disc of remains that surrounded it, smaller bodies pulled together and fell into line around it, until it was orbited by a swarm of planets, from gas giants to tiny, rocky worlds.
Read MoreWe usually think of time travel as purely fictional. Mostly, it is. Travel into the past is still considered impossible by most physicists, although there are exceptions (more on that later). However, travelling into the future is, with some help from Albert Einstein, perfectly plausible, as long as you have access to either a powerful gravitational field or a craft that can travel near the speed of light.
Read MoreWe present the discovery of an as yet nonrepeating fast radio burst (FRB), FRB 20210117A, with the Australian Square Kilometre Array Pathfinder (ASKAP), as a part of the Commensal Real-time ASKAP Fast Transients Survey. The subarcsecond localization of the burst led to the identification of its host galaxy at z = 0.214(1). This redshift is much lower than what would be expected for a source dispersion measure (DM) of 729 pc cm$^{−3}$, given typical contributions from the intergalactic medium and the host galaxy. Optical observations reveal the host to be a dwarf galaxy with little ongoing star formation—very different to the dwarf host galaxies of the known repeating FRBs 20121102A and 20190520B. We find an excess DM contribution from the host and attribute it to the FRB's local environment. We do not find any radio emission from the FRB site or host galaxy. The low magnetized environment and the lack of a persistent radio source indicate that the FRB source is older than those found in other dwarf host galaxies, establishing the diversity of FRB sources in dwarf galaxy environments. We find our observations to be fully consistent with the "hypernebula" model, where the FRB is powered by an accretion jet from a hyperaccreting black hole. Finally, our high time resolution analysis reveals burst characteristics similar to those seen in repeating FRBs. We encourage follow-up observations of FRB 20210117A to establish any repeating nature.
We present the localization and host galaxies of one repeating and two apparently non-repeating Fast Radio Bursts. FRB20180301A was detected and localized with the Karl G. Jansky Very Large Array to a star-forming galaxy at z=0.3304. FRB20191228A, and FRB20200906A were detected and localized by the Australian Square Kilometre Array Pathfinder to host galaxies at z=0.2430 and z=0.3688, respectively. We combine these with 13 other well-localised FRBs in the literature, and analyse the host galaxy properties. We find no significant differences in the host properties of repeating and apparently non-repeating FRBs. FRB hosts are moderately star-forming, with masses slightly offset from the star-forming main-sequence. Star formation and low-ionization nuclear emission-line region (LINER) emission are major sources of ionization in FRB host galaxies, with the former dominant in repeating FRB hosts. FRB hosts do not track stellar mass and star formation as seen in field galaxies (95% confidence). FRBs are rare in massive red galaxies, suggesting that progenitor formation channels are not solely dominated by delayed channels which lag star formation by gigayears. The global properties of FRB hosts are indistinguishable from core-collapse supernovae (CCSNe) and short gamma-ray bursts (SGRBs) hosts (95% confidence), and the spatial offset (from galaxy centers) of FRBs is consistent with that of the Galactic neutron star population. The spatial offsets of FRBs (normalized to the galaxy effective radius) mostly differs from that of globular clusters (GCs) in late- and early-type galaxies with 95% confidence.
Context. Fast radio bursts (FRBs) are extremely energetic pulses of millisecond duration and unknown origin. To understand the phenomenon that emits these pulses, targeted and un-targeted searches have been performed for multiwavelength counterparts, including the optical.
Aims. The objective of this work is to search for optical transients at the positions of eight well-localized (< 1″) FRBs after the arrival of the burst on different timescales (typically at one day, several months, and one year after FRB detection). We then compare this with known optical light curves to constrain progenitor models.
Methods. We used the Las Cumbres Observatory Global Telescope (LCOGT) network to promptly take images with its network of 23 telescopes working around the world. We used a template subtraction technique to analyze all the images collected at differing epochs. We have divided the difference images into two groups: In one group we use the image of the last epoch as a template, and in the other group we use the image of the first epoch as a template. We then searched for optical transients at the localizations of the FRBs in the template subtracted images.
Results. We have found no optical transients and have therefore set limiting magnitudes to the optical counterparts. Typical limits in apparent and absolute magnitudes for our LCOGT data are ∼22 and −19 mag in the r band, respectively. We have compared our limiting magnitudes with light curves of super-luminous supernovae (SLSNe), Type Ia supernovae (SNe Ia), supernovae associated with gamma-ray bursts (GRB-SNe), a kilonova, and tidal disruption events (TDEs).
Conclusions. Assuming that the FRB emission coincides with the time of explosion of these transients, we rule out associations with SLSNe (at the ∼99.9% confidence level) and the brightest subtypes of SNe Ia, GRB-SNe, and TDEs (at a similar confidence level). However, we cannot exclude scenarios where FRBs are directly associated with the faintest of these subtypes or with kilonovae.
Fast radio bursts (FRBs) are millisecond-scale radio pulses, which originate in distant galaxies and are produced by unknown sources. The mystery remains partially because of the typical difficulty in localising FRBs to host galaxies. Accurate localisations delivered by the Commensal Real-time ASKAP Fast Transients (CRAFT) survey now provide an opportunity to study the host galaxies and potential transient counterparts of FRBs at a large range of wavelengths. In this work, we investigate whether the first three FRBs accurately localised by CRAFT have supernova-like transient counterparts. We obtained two sets of imaging epochs with the Very Large Telescope for three host galaxies, one soon after the burst detection and one several months later. After subtracting these images no optical counterparts were identified in the associated FRB host galaxies, so we instead place limits on the brightness of any potential optical transients. A Monte Carlo approach, in which supernova light curves were modelled and their base properties randomised, was used to estimate the probability of a supernova associated with each FRB going undetected. We conclude that Type Ia and IIn supernovae are unlikely to accompany every apparently non-repeating FRB.
Present-day galaxies are surrounded by cool and enriched halo gas extending for hundreds of kiloparsecs. This halo gas is thought to be the dominant reservoir of material available to fuel future star formation, but direct constraints on its mass and physical properties have been difficult to obtain. We report the detection of a fast radio burst (FRB 181112), localized with arcsecond precision, that passes through the halo of a foreground galaxy. Analysis of the burst shows that the halo gas has low net magnetization and turbulence. Our results imply predominantly diffuse gas in massive galactic halos, even those hosting active supermassive black holes, contrary to some previous results.
I’m Lachlan Marnoch, and I’m on my way to a PhD in astrophysics. What this means is that I’ll be spending the next three years researching a very specific scientific niche, and then composing a monstrous piece of writing that describes all of the useful work that I’ve done. Tune in to this tale of discovery and human endeavour, and I'll fill you in on my experiences, the science of what I’m studying, and how many tears I've shed along the way.
Read More