Showing papers by "Casey J. Law published in 2022"
TL;DR: In this paper , the authors assess the implications of the large dispersion measure and scattering observed from FRB 20190520B for the host galaxy's plasma properties, and show that scattering of localized FRBs is largely dominated by plasma within host galaxies and the Milky Way.
Abstract: The repeating fast radio burst FRB 20190520B is localized to a galaxy at z = 0.241, much closer than expected given its dispersion measure DM = 1205 ± 4 pc cm−3. Here we assess implications of the large DM and scattering observed from FRB 20190520B for the host galaxy’s plasma properties. A sample of 75 bursts detected with the Five-hundred-meter Aperture Spherical radio Telescope shows scattering on two scales: a mean temporal delay τ(1.41 GHz) = 10.9 ± 1.5 ms, which is attributed to the host galaxy, and a mean scintillation bandwidth Δν d(1.41 GHz) = 0.21 ± 0.01 MHz, which is attributed to the Milky Way. Balmer line measurements for the host imply an Hα emission measure (galaxy frame) EMs = 620 pc cm−6 × (T/104 K)0.9, implying DMHα of order the value inferred from the FRB DM budget, DMh=1121−138+89 pc cm−3 for plasma temperatures greater than the typical value 104 K. Combining τ and DMh yields a nominal constraint on the scattering amplification from the host galaxy F˜G=1.5−0.3+0.8(pc2km)−1/3 , where F˜ describes turbulent density fluctuations and G represents the geometric leverage to scattering that depends on the location of the scattering material. For a two-screen scattering geometry where τ arises from the host galaxy and Δν d from the Milky Way, the implied distance between the FRB source and dominant scattering material is ≲100 pc. The host galaxy scattering and DM contributions support a novel technique for estimating FRB redshifts using the τ–DM relation, and are consistent with previous findings that scattering of localized FRBs is largely dominated by plasma within host galaxies and the Milky Way.
11 citations
TL;DR: In this article , the authors proposed a radio burst source (RSRS) model for the first time and demonstrated that RSRS can be used to detect radio burst sources (RBSs).
Abstract: Radio Burst Source Reshma Anna-Thomas,1,2∗Liam Connor, Sarah Burke-Spolaor, Paz Beniamini, Kshitij Aggarwal, Casey J. Law, Ryan S. Lynch, Di Li, Yi Feng, Stella Koch Ocker, Marilyn Cruces, Shami Chatterjee, Wenfei Yu, Chenhui Niu, Mengyao Xue 1West Virginia University, Department of Physics and Astronomy, P. O. Box 6315, Morgantown, WV, USA 2 Center for Gravitational Waves and Cosmology, West Virginia University, Chestnut Ridge Research Building, Morgantown, WV, USA 3Cahill Center for Astronomy and Astrophysics, MC 249-17 California Institute of Technology, Pasadena, CA 91125, USA 4Owens Valley Radio Observatory, California Institute of Technology, 100 Leighton Lane, Big Pine, CA, 93513, USA 5Department of Natural Sciences, Open University of Israel, 1 University Road, 43107 Ra’anana, Israel 6Astrophysics Research Center of the Open University (ARCO), The Open University of Israel, P.O Box 808, Ra’anana 43537, Israel 7Green Bank Observatory, Green Bank, WV, 24401, USA 8National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, China 9NAOC-UKZN Computational Astrophysics Centre, U. of KwaZulu-Natal, Durban 4000, South Africa 10Zhejiang Lab, Hangzhou, Zhejiang 311121, China 11University of Chinese Academy of Sciences, Beijing 100049, China 12Department of Astronomy and Cornell Center for Astrophysics and Planetary Science, Cornell University, Ithaca, New York, 14853, USA 13Max-Planck Institute for Radio Astronomy, Auf dem Hügel 69, D-53121 Bonn, Germany 14Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, China 15Canadian Institute for Advanced Research, CIFAR Azrieli Global Scholar, MaRS Centre West Tower, 661 University Ave. Suite 505, Toronto ON M5G 1M1, Canada ∗To whom correspondence should be addressed; E-mail: rat0022@mix.wvu.edu.
8 citations
15 Mar 2022
TL;DR: In this article , the authors reported direct evidence for a B-field reversal based on the observed sign change and extreme variation of FRB 20190520B's rotation measure, which changed from a value of $sim-10000$ rad m$^{-2}$ to a value between June 2021 and January 2022.
Abstract: The environment of actively repeating fast radio bursts (FRBs) has been shown to be complex and varying. The recently localized FRB 20190520B is extremely active, has the largest confirmed host dispersion measure, and is only the second FRB source associated with a compact, persistent radio source (PRS). The main tracer of the magneto-ionic environments is the rotation measure (RM), a path-integral of the line-of-sight component of magnetic field strength (B) and electron density, which does not allow a direct probe of the B-field configuration. Here we report direct evidence for a B-field reversal based on the observed sign change and extreme variation of FRB 20190520B's RM, which changed from $\sim10000$ rad m$^{-2}$ to $\sim-16000$ rad m$^{-2}$ between June 2021 and January 2022. Such extreme RM reversal has never been observed before in any FRB nor in any astronomical object. The implied short-term change of the B-field configuration in or around the FRB could be due to the vicinity of massive black holes, or a magnetized companion star in binary systems, or a young supernova remnant along the line of sight.
5 citations
TL;DR: In this paper , the authors report the detection and interferometric localization of the repeating fast radio burst (FRB) source FRB 20220912A during commissioning observations with the Deep Synoptic Array (DSA-110).
Abstract: We report the detection and interferometric localization of the repeating fast radio burst (FRB) source FRB 20220912A during commissioning observations with the Deep Synoptic Array (DSA-110). Two bursts were detected from FRB 20220912A, one each on 2022 October 18 and 2022 October 25. The best-fit position is (R.A. J2000, decl. J2000) = (23:09:04.9, +48:42:25.4), with a 90% confidence error ellipse with radii ±2″ and ±1″ in R.A. and decl., respectively. The two bursts are polarized, and we find a Faraday rotation measure that is consistent with the low value of +0.6 rad m−2 reported by CHIME/FRB. The DSA-110 localization overlaps with the galaxy PSO J347.2702+48.7066 at a redshift z = 0.0771, which we identify as the likely host. PSO J347.2702+48.7066 has a stellar mass of approximately 1010 M ⊙, modest internal dust extinction, and a star formation rate likely in excess of 0.1 M ⊙ yr−1. The host-galaxy contribution to the dispersion measure is likely ≲50 pc cm−3. The FRB 20220912A source is therefore likely viewed along a tenuous plasma column through the host galaxy.
5 citations
TL;DR: In this paper , the authors reported the detection of scattering times from the repeating FRB 20190520B that vary by up to a factor of two or more on minutes to days-long timescales.
Abstract:
Fast radio bursts (FRBs) are millisecond-timescale radio transients, the origins of which are predominantly extragalactic and likely involve highly magnetized compact objects. FRBs undergo multipath propagation, or scattering, from electron density fluctuations on sub-parsec scales in ionized gas along the line-of-sight. Scattering observations have located plasma structures within FRB host galaxies, probed Galactic and extragalactic turbulence, and constrained FRB redshifts. Scattering also inhibits FRB detection and biases the observed FRB population. We report the detection of scattering times from the repeating FRB 20190520B that vary by up to a factor of two or more on minutes to days-long timescales. In one notable case, the scattering time varied from 7.9 ± 0.4 ms to less than 3.1 ms ($95{{\ \rm per\ cent}}$ confidence) over 2.9 minutes at 1.45 GHz. The scattering times appear to be uncorrelated between bursts or with dispersion and rotation measure variations. Scattering variations are attributable to dynamic, inhomogeneous plasma in the circumsource medium, and analogous variations have been observed from the Crab pulsar. Under such circumstances, the frequency dependence of scattering can deviate from the typical power-law used to measure scattering. Similar variations may therefore be detectable from other FRBs, even those with inconspicuous scattering, providing a unique probe of small-scale processes within FRB environments.
4 citations
TL;DR: Smith et al. as discussed by the authors reported observations of the repeating fast radio bursts (FRB 20190520B) spanning 17 months, which show that the FRB's Faraday rotation is highly variable and twice changes sign.
Abstract: Fast radio bursts (FRBs) are brief, intense flashes of radio waves from unidentified extragalactic sources. Polarized FRBs originate in highly magnetized environments. We report observations of the repeating FRB 20190520B spanning 17 months, which show that the FRB’s Faraday rotation is highly variable and twice changes sign. The FRB also depolarizes below radio frequencies of about 1 to 3 gigahertz. We interpret these properties as being due to changes in the parallel component of the magnetic field integrated along the line of sight, including reversing direction of the field. This could result from propagation through a turbulent magnetized screen of plasma, located 10–5 to 100 parsecs from the FRB source. This is consistent with the bursts passing through the stellar wind of a binary companion of the FRB source. Description Editor’s summary Fast radio bursts (FRBs) are brief flashes of radio waves from distant galaxies that are probably emitted by neutron stars. Some FRBs repeat, which enables follow-up observations to constrain their local environments. Anna-Thomas et al. have observed more than a hundred bursts from a single FRB source, of which 13 were bright enough to measure the polarization (see the Perspective by Paragi). The fluctuating polarization properties indicate that the magnetic field close to the FRB source was highly variable, twice reversing direction. The authors contend that the most likely explanation is that the FRB source orbits in a binary system, with the radio waves passing through the magnetized stellar wind of the companion star. —Keith T. Smith The variable polarization properties of a repeating fast radio burst indicate that the source is in a binary system.
4 citations
TL;DR: In this paper , Zhang et al. presented a survey of the authors' work and concluded that the majority of the participants in the survey were women, and that women are more likely to vote for women than men.
Abstract: C.-H. Niu1 *, K. Aggarwal2,6 *, BD. Li1,11 *, X. Zhang3,11 , S. Chatterjee4 , C.-W. Tsai1 , BW. Yu3, BC. J. Law5,8 , S. Burke-Spolaor2,6,7 , J. M. Cordes4 , Y.-K. Zhang1,11 , S. K. Ocker4 , J.-M. Yao1,12, P. Wang1, Y. Feng1,11 , Y. Niino9,19 , C. Bochenek5, M. Cruces16 , L. Connor5, J.-A. Jiang17 , S. Dai13,18, R. Luo13 , G.-D. Li1,11 , C.-C. Miao1,11, J.-R. Niu1,11, R. Anna-Thomas2,6 , J. Sydnor2,6 , D. Stern10 , W.-Y. Wang1,14 , M. Yuan1,11, Y.-L. Yue1, D.-J. Zhou1,11, Z. Yan3, W.-W. Zhu1, B. Zhang15
4 citations
TL;DR: In this paper , an extreme radio flare, VT J024345.08, was observed from the nucleus of a galaxy with evidence for historic Seyfert activity at redshift z = 0.074.
Abstract: We present observations of an extreme radio flare, VT J024345.70-284040.08, hereafter VT J0243, from the nucleus of a galaxy with evidence for historic Seyfert activity at redshift z = 0.074. Between NRAO Very Large Array (VLA) Sky Survey observations in 1993 to VLA Sky Survey observations in 2018, VT J0243 rose from a ∼ GHz radio luminosity of ν L ν ≲ 1038 erg s−1 to ν L ν ∼ 1040 erg s−1, and still continues to brighten. The radio spectral energy distribution evolution is consistent with a nascent jet that has slowed over ∼3000 days with an average 0.1 <〈β〉< 0.6. The jet is energetic (∼1051–52 erg), and had a radius ∼0.7 pc in 2021 December. X-ray observations suggest a persistent or evolving corona, possibly associated with an accretion disk, and IR and optical observations constrain any high-energy counterpart to be sub-Eddington. VT J0243 may be an example of a young, off-axis radio jet from a slowly evolving tidal disruption event. Other more mysterious triggers for the accretion enhancement and jet launching are possible. In either case, VT J0243 is a unique example of a nascent jet, highlighting the unknown connection between supermassive black holes, the properties of their accretion flows, and jet launching.