FRB 121102 Bursts Show Complex Time–Frequency Structure

Hessels, J. W. T. and Spitler, L. G. and Seymour, A. D. and Cordes, J. M. and Michilli, D. and Lynch, R. S. and Gourdji, K. and Archibald, A. M. and Bassa, C. G. and Bower, G. C. and Chatterjee, S. and Connor, L. and Crawford, F. and Deneva, J. S. and Gajjar, V. and Kaspi, V. M. and Keimpema, A. and Law, C. J. and Marcote, B. and McLaughlin, M. A. and Paragi, Z. and Petroff, E. and Ransom, S. M. and Scholz, P. and Stappers, B. W. and Tendulkar, S. P. (2019) FRB 121102 Bursts Show Complex Time–Frequency Structure. The Astrophysical Journal, 876 (2). L23. ISSN 2041-8213

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Abstract

FRB 121102 is the only known repeating fast radio burst source. Here we analyze a wide-frequency-range (1–8 GHz) sample of high signal-to-noise, coherently dedispersed bursts detected using the Arecibo and Green Bank telescopes. These bursts reveal complex time–frequency structures that include subbursts with finite bandwidths. The frequency-dependent burst structure complicates the determination of a dispersion measure (DM); we argue that it is appropriate to use a DM metric that maximizes frequency-averaged pulse structure, as opposed to peak signal-to-noise, and find DM = 560.57 ± 0.07 pc cm−3 at MJD 57,644. After correcting for dispersive delay, we find that the subbursts have characteristic frequencies that typically drift lower at later times in the total burst envelope. In the 1.1–1.7 GHz band, the ∼0.5–1 ms subbursts have typical bandwidths ranging from 100 to 400 MHz, and a characteristic drift rate of ∼200 MHz ms−1 toward lower frequencies. At higher radio frequencies, the subburst bandwidths and drift rate are larger, on average. While these features could be intrinsic to the burst emission mechanism, they could also be imparted by propagation effects in the medium local to the source. Comparison of the burst DMs with previous values in the literature suggests an increase of ΔDM ∼ 1–3 pc cm−3 in 4 yr; though, this could be a stochastic variation as opposed to a secular trend. This implies changes in the local medium or an additional source of frequency-dependent delay. Overall, the results are consistent with previously proposed scenarios in which FRB 121102 is embedded in a dense nebula.

Item Type: Article
Subjects: STM Open Library > Physics and Astronomy
Depositing User: Unnamed user with email support@stmopenlibrary.com
Date Deposited: 03 Jun 2023 06:26
Last Modified: 04 Mar 2024 05:28
URI: http://ebooks.netkumar1.in/id/eprint/1561

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