In this series of posts, we sit down with a few of the plenary speakers of the 240th AAS meeting to learn more about them and their research. You can see a full schedule of their talks here, and read our other interviews here!
“Magnetars are the perpetrators of (nearly) everything” reads the title of an Astrobite from a few years ago, and Dr. Scholz, one of the subjects of today’s Astrobites feature, would generally tend to agree.
Today’s post will jointly focus on the work and career of Dr. Victoria Kaspi, a professor of physics at McGill University, and her former student and collaborator, Dr. Paul Scholz, a post-doctoral fellow at the Dunlap Institute for Astronomy and Astrophysics at the University of Toronto. As principal investigator of the Canadian Hydrogen Intensity Mapping Experiment (CHIME) Fast Radio Burst Project, Dr. Kaspi is one of many astronomers working towards disentangling the mystery of fast radio bursts (FRBs) – extremely quick and energetic bursts of emission that we observe in the radio band – and figuring out how to leverage these phenomena to answer fundamental questions about the Universe. The CHIME instrument is a unique stationary radio telescope that constructs very wide density maps of hydrogen nearly instantaneously, making it ideal for both science on large scales – for example, measuring the expansion history of the Universe – and on rapid scales – for example, studying rare transient or periodically-emitting objects like FRBs and pulsars.
The strength of Dr. Kaspi’s scientific collaborations is evident as she will be receiving two prizes at AAS this year, focused on two different areas of her expertise. On behalf of the entire CHIME/FRB collaboration, she and Dr. Scholz are accepting the Berkeley Prize for the discovery of a very luminous radio burst from a magnetar (a dense stellar remnant with an unusually strong magnetic field) within our Galaxy and the large catalog of FRBs compiled by the CHIME/FRB collaboration. Until their observation, FRBs had been a purely extragalactic phenomenon and their provenance was an open question, so their discovery showed us that the words of that Astrobite from a few years ago might ring true – magnetars are capable of producing radio bursts such that we can see them from extragalactic distances, and therefore some FRBs could be magnetars. Recalling the moment when they first made that observation, Dr. Scholz recounts their excitement: “that was one of those moments where it felt like nature threw something at you and it’s telling you something – it’s [the kind of observation] that has implications as soon as you see it”. Indeed, that observation was groundbreaking in the field of FRBs and has opened the door to the possibility of more such discoveries within our own Galaxy.
Dr. Kaspi has also received the Shaw Prize, which she was co-awarded with her colleague Dr. Chryssa Kouveliotou, for their independent work on magnetars. Dr. Kaspi led research on observationally anomalous X-ray pulsars that lacked a clear understanding of the origin of the X-rays – her observational work showed that these too were perpetrated by magnetars. Continuing to monitor the sources, they showed the origin of these signals are magnetars, capable of violent bursts of X-rays, (like the other high energy phenomena called Soft Gamma Repeaters studied by Dr. Chryssa Kouveliotou) and provided insight into the range of possible magnetar phenomenology and what causes these systems.
In college at McGill University, Dr. Kaspi intended to pursue a career in particle physics, especially after a summer at CERN in Switzerland. Next, her graduate program at Princeton required students to do some sort of project distinct from their planned thesis work. At the time, she thought astronomy was cool but had no real experience in it. So, she found herself a first year physics graduate student having to learn what “R.A.” and “Dec.” meant (axes for the standard astronomical coordinate system). In fact, Dr. Kaspi recalls much of the astronomy she knows today she learned by teaching it! Her first astronomy project was an observational pulsars program – and she loved it. She remembers being impressed by using a big telescope and collecting the data, and realized she enjoyed that much more than her previous projects in particle physics.
Now a professor at McGill University, Dr. Kaspi has expanded this work in pulsars and then magnetars to working towards answering the question: what are FRBs? The recent work of the CHIME/FRB collaboration has demonstrated that some could be magnetars, but we don’t know what they all are. Dr. Kaspi explained that it’s useful to break it down into smaller questions. For example, do all FRBs have single peaks in their signal, implying they are cataclysmic events? Are there various classes to produce FRBs, and are FRBs a homogeneous, more uniform population or a heterogeneous, mixed population?
Beyond understanding these fundamental characteristics of FRBs, Dr. Kaspi and her team are looking towards using FRBs as novel cosmological probes with new techniques. One such avenue is studying reionization, the last major phase change of the Universe, as it transformed from primarily neutral gas to ionized gas. FRBs are tremendous probes of ionized gas, as they can help detect scatter by the inhomogeneity of gas in the early Universe.
Dr. Scholz began his career in science similarly to Dr. Kaspi – he came into his undergraduate program at the University of Victoria studying physics. After a few terms of co-ops (the Canadian equivalents of REUs) where he had the opportunity to dip his toes into the field, he began to seriously consider astronomy research as a viable career. This interest carried him into graduate school at McGill University, where he was supervised by Dr. Kaspi and worked on X-ray observations of magnetars. As he neared the end of his PhD in 2015, he found himself inadvertently drawn into the world of FRBs as he and his group discovered the first repeating FRB while reprocessing some pulsar observations from the Pulsar Arecibo L-band Feed Array (PALFA) instrument. Coincidentally enough, he was already in the process of applying for post-doctoral positions hoping to study the exciting new topic of FRBs, so this was a serendipitous segue into that field.
Since his PhD, he has completed a post-doctoral appointment at the Dominion Radio Astrophysical Observatory (DRAO) where he was part of the team that oversaw the development and construction of the CHIME instrument. Given that CHIME continuously monitors large swaths of the sky for FRBs, the instrument receives several terabytes of data – the equivalent of few laptop hard drives – per second, so it cannot feasibly store all the data for subsequent analysis. Instead, Dr. Scholz described that the real beauty of the telescope’s engineering is in its software pipeline, which helps deal with the “firehoseness of [the data intake rate]”. Nearby to the instrument are a few hundred computers – housed in a pair of radio frequency (RF) shielding shipping containers – that instantaneously parse the data so that it is only saved when an FRB has occurred.
Now a post-doctoral fellow at the Dunlap Institute, Dr. Scholz has continued his work on the software and data analysis pipelines of the CHIME FRB instrument, but has also come full circle as he once again works on magnetars, searching for high energy observational counterparts to the FRB observations made with CHIME.
Besides research, Dr. Kaspi recognized the importance of trying to help pave the way for future generations of scientists. During her studies she remembers “feeling a lot of angst”, and recalled advocating for more women’s bathrooms in the physics building – there was one per floor at the time, compared to numerous men’s restrooms in convenient locations. Still, she advises that while this sort of pioneering is important, one can’t do everything, and it’s much better to focus on doing some things really well. “The years go by very very fast!” she remarked.
Recognizing the value of the co-ops in helping him identify his excitement for astronomy, Dr. Scholz advises students to explore their interests by trying out research as early as they can. Additionally – and perhaps a bit more jokingly – he advises up-and-coming astronomers to always document their code.
Throughout the interview, Dr. Kaspi emphasized the excellence of her students and the entire CHIME/FRB collaboration. “They are the lifeblood and energy of the group. Well, I guess I still have some energy…” she quipped. Among her many students are Ketan Sand, who wrote a paper using CHIME data to analyze a periodic repeating FRB, and Astrobiter Alice Curtin. Dr. Kaspi also highlighted a recent analysis paper by student Alex Josephy, which investigated the sky distribution of FRBs and found no apparent correlation with the galactic plane to determine if the FRB population is contaminated with intermittent radio pulsars nearby.
Find out more about the work of the CHIME/FRB collaboration and the FRBs they are demystifying at the Berkeley Prize plenary (Thursday, June 16, 2022 at 4:40 PM PT – 5:30 PM PT) and about magnetars at the Shaw Prize special session (Monday, June 13, 2022 at 10:00 AM PT – 11:30 AM PT).
Astrobite co-written by Sahil Hegde and Olivia Cooper
Astrobite edited by Graham Doskoch
Featured image credit: American Astronomical Society