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MWA upper limit on low-frequency emission from FRB 190806

ATel #13121; M. Sokolowski, N. D. R. Bhat, M. Johnston-Hollitt, T. Hodgson, B. McKinley, G. Sleap, A. Williams and J. P. Macquart (ICRAR/Curtin University)
on 23 Sep 2019; 14:33 UT
Credential Certification: Marcin Sokolowski (marcin.sokolowski@curtin.edu.au)

Subjects: Radio, Fast Radio Burst

The Murchison Widefield Array (MWA; Wayth et al 2018, PASA 35; Tingay et al 2013, PASA 30, 21) fortuitously shadowed (co-tracked) the error box for the recently reported UTMOST FRB190806 (Gupta et al. ATEL #12995 ) during an ongoing science program. Data were collected in the form of correlated visibilities at 0.5-second temporal resolution and 10-kHz spectral resolution over the frequency band 138.88 - 169.6 MHz. Data processing involved forming 0.5-second /1.28-MHz snapshot images using standard MWA data reduction tools and de-dispersing these images for a dispersion measure of 388.5 pc cm^-3 as reported by the UTMOST detection. The de-dispersed images were subsequently searched for transient emission within the error box provided by the UTMOST telescope, using software tools described in Sokolowski et al. (2018, ApJ, 867) . Our analysis did not reveal any low-frequency counterpart brighter than 5sigma, corresponding to an upper limit in fluence of approximately 540 Jy ms at a frequency of 154.88 MHz. The implied constraint on the spectral index (between 835 and 154.88 MHz) is alpha >~ -1.5. This limit is consistent with the spectral index constraints obtained from dedicated observations with the MWA shadowing ASKAP field of view ( Sokolowski et al. 2018, ApJ, 867).