Lise Meitner Research Group
Early in my career I developed new hardware and algorithms needed to discover what were, at the time, called "fast transients". Now we call extragalactic fast transients "fast radio bursts", and I have spent the last 10 years searching for new FRBs and characterizing their properties.
In 2019 my Lise Meitner research group began, and since then I have expanded my research focus to include understanding for which cosmological and astrophysical applications FRBs will be useful. In addition, my group continues follow-up observations of repeating FRBs, primarily with Effelsberg and the GMRT, in order to understand their physical origins.
Group members
- Charles Walker, post doc
- Joscha Jahns-Schindler, PhD student
- Surya Bethapudi, PhD student
- Marlon Bause, PhD student
- Sachin Thuli, masters student
Former and partner members
- Marilyn Cruces
- Henning Hilmarsson
- Leon Houben
- Sonia Munjal
See below and here for some of our publications.
Fast radio bursts as astrophysical and cosmological probes
Shortly after their discovery, many uses of FRBs for astrophysics and cosmology were proposed, often using optimistic assumptions. My group brings the experience of FRB observers to confront some of these assumptions:
How limiting is optical follow-up for fast radio burst applications?
Publication: Jahns et al. 2023, MNRAS, 523, 5006
Joscha simulates a sample of FRBs detected by three, major FRB surveys and assigns each FRB to a host galaxy from the galform simulation. He investigates the amount of dedicated optical follow-up required to amass a large sample of localized FRBs by estimating the fraction of the detected FRBs that could have photometric redshifts in ongoing and future large-scale optical surveys, such as SDSS and LSST. He found that the low-redshift population can be localized from the catalogs, but significant follow-up will be required for the population at higher redshifts. This bias of low redshift localizations limits our ability to realize some cosmological tests, and Joscha suggests follow-up strategies to mitigate this issue.
How much does the cosmic web contribute to fast radio burst DMs?
Publication: Walker et al. 2023, A&A, submitted
Over the evolution of the Universe, the intergalactic medium has collapsed into the so-called "cosmic web", which can be divided into voids, filaments and halos. Our primary scientific question was to understand how much each of these structures contributes to the observed DMs of FRBs. Charlie conducted a synthetic FRB survey by generating lines of sight through the Illustris TNG-300 simulation. He found that filaments dominate the measured DM from the IGM, which suggests that FRBs are probing the warm-hot intergalactic medium, thought to be the largest reservoir of "missing baryons".
Understanding repeating fast radio bursts
For recent work on FRB 121102, please see this page.
Below is a sample of recent work the group has been doing on understanding other repeating FRBs.
Extending chromatic periodicity of FRB 20180916B to higher frequencies
Publication: Bethapudi et al. 2022, MNRAS accepted
By modeling the chromatic, active window of FRB 20180916B, we predicated when bursts should be detectable at 4-8 GHz. Surya successfully detected six bursts from this repeater at around 5 GHz using the 100-m Effelsberg telescope. The bursts are mostly unresolved in time, suggesting that bursts at high frequency are systematically narrower than at low frequencies. The bursts are also highly linearly polarized and show scintillation in their spectra consistent with the Milky Way foreground.
Complex polarization from FRB 20201124A
Publication: Hilmarsson et al. 2021, MNRAS, 508, 5354
Henning detected 20 bursts from FRB 20201124A, an active repeater, with the Effelsberg telescope at 1.4 GHz. He found that the bursts showed rapid changes in both the linear and circular polarization fractions, as well as rotation measure. These were the first bursts from a repeater to show circular polarization. Note, these bursts were also used by Main et al. 2022 to constrain the position of the Milky Way scattering screen, which dominates this repeater's scattering properties.
Early in my career I developed new hardware and algorithms needed to discover what were, at the time, called "fast transients". Now we call extragalactic fast transients "fast radio bursts", and I have spent the last 10 years searching for new FRBs and characterizing their properties.
In 2019 my Lise Meitner research group began, and since then I have expanded my research focus to include understanding for which cosmological and astrophysical applications FRBs will be useful. In addition, my group continues follow-up observations of repeating FRBs, primarily with Effelsberg and the GMRT, in order to understand their physical origins.
Group members
- Charles Walker, post doc
- Joscha Jahns-Schindler, PhD student
- Surya Bethapudi, PhD student
- Marlon Bause, PhD student
- Sachin Thuli, masters student
Former and partner members
- Marilyn Cruces
- Henning Hilmarsson
- Leon Houben
- Sonia Munjal
See below and here for some of our publications.
Fast radio bursts as astrophysical and cosmological probes
Shortly after their discovery, many uses of FRBs for astrophysics and cosmology were proposed, often using optimistic assumptions. My group brings the experience of FRB observers to confront some of these assumptions:
How limiting is optical follow-up for fast radio burst applications?
Publication: Jahns et al. 2023, MNRAS, 523, 5006
Joscha simulates a sample of FRBs detected by three, major FRB surveys and assigns each FRB to a host galaxy from the galform simulation. He investigates the amount of dedicated optical follow-up required to amass a large sample of localized FRBs by estimating the fraction of the detected FRBs that could have photometric redshifts in ongoing and future large-scale optical surveys, such as SDSS and LSST. He found that the low-redshift population can be localized from the catalogs, but significant follow-up will be required for the population at higher redshifts. This bias of low redshift localizations limits our ability to realize some cosmological tests, and Joscha suggests follow-up strategies to mitigate this issue.
How much does the cosmic web contribute to fast radio burst DMs?
Publication: Walker et al. 2023, A&A, submitted
Over the evolution of the Universe, the intergalactic medium has collapsed into the so-called "cosmic web", which can be divided into voids, filaments and halos. Our primary scientific question was to understand how much each of these structures contributes to the observed DMs of FRBs. Charlie conducted a synthetic FRB survey by generating lines of sight through the Illustris TNG-300 simulation. He found that filaments dominate the measured DM from the IGM, which suggests that FRBs are probing the warm-hot intergalactic medium, thought to be the largest reservoir of "missing baryons".
Understanding repeating fast radio bursts
For recent work on FRB 121102, please see this page.
Below is a sample of recent work the group has been doing on understanding other repeating FRBs.
Extending chromatic periodicity of FRB 20180916B to higher frequencies
Publication: Bethapudi et al. 2022, MNRAS accepted
By modeling the chromatic, active window of FRB 20180916B, we predicated when bursts should be detectable at 4-8 GHz. Surya successfully detected six bursts from this repeater at around 5 GHz using the 100-m Effelsberg telescope. The bursts are mostly unresolved in time, suggesting that bursts at high frequency are systematically narrower than at low frequencies. The bursts are also highly linearly polarized and show scintillation in their spectra consistent with the Milky Way foreground.
Complex polarization from FRB 20201124A
Publication: Hilmarsson et al. 2021, MNRAS, 508, 5354
Henning detected 20 bursts from FRB 20201124A, an active repeater, with the Effelsberg telescope at 1.4 GHz. He found that the bursts showed rapid changes in both the linear and circular polarization fractions, as well as rotation measure. These were the first bursts from a repeater to show circular polarization. Note, these bursts were also used by Main et al. 2022 to constrain the position of the Milky Way scattering screen, which dominates this repeater's scattering properties.