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1. Multi-scale feedback and feeding in the closest radio galaxy Centaurus A

Author

MIT Kavli Institute for Astrophysics and Space Research, McKinley, B, Tingay, SJ, Gaspari, M, Kraft, RP, Matherne, C, Offringa, AR, McDonald, M, Calzadilla, MS, Veilleux, S, Shabala, SS, Gwyn, SDJ, Bland-Hawthorn, J, Crnojević, D, Gaensler, BM, Johnston-Hollitt, M, MIT Kavli Institute for Astrophysics and Space Research, McKinley, B, Tingay, SJ, Gaspari, M, Kraft, RP, Matherne, C, Offringa, AR, McDonald, M, Calzadilla, MS, Veilleux, S, Shabala, SS, Gwyn, SDJ, Bland-Hawthorn, J, Crnojević, D, Gaensler, BM, and Johnston-Hollitt, M

Published
2022

2. The GLEAM 200-MHz local radio luminosity function for AGN and star-forming galaxies

Author

Franzen, TMO, Seymour, N, Sadler, EM, Mauch, T, White, SV, Jackson, CA, Chhetri, R, Quici, B, Bell, ME, Callingham, JR, Dwarakanath, KS, For, B, Gaensler, BM, Hancock, PJ, Hindson, L, Hurley-Walker, N, Johnston-Hollitt, M, Kapińska, AD, Lenc, E, McKinley, B, Morgan, J, Offringa, AR, Procopio, P, Staveley-Smith, L, Wayth, RB, Wu, C, Zheng, Q, Franzen, TMO, Seymour, N, Sadler, EM, Mauch, T, White, SV, Jackson, CA, Chhetri, R, Quici, B, Bell, ME, Callingham, JR, Dwarakanath, KS, For, B, Gaensler, BM, Hancock, PJ, Hindson, L, Hurley-Walker, N, Johnston-Hollitt, M, Kapińska, AD, Lenc, E, McKinley, B, Morgan, J, Offringa, AR, Procopio, P, Staveley-Smith, L, Wayth, RB, Wu, C, and Zheng, Q

Abstract

Abstract The GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) is a radio continuum survey at 76–227 MHz of the entire southern sky (Declination $<\!{+}30^{\circ}$ ) with an angular resolution of ${\approx}2$ arcmin. In this paper, we combine GLEAM data with optical spectroscopy from the 6dF Galaxy Survey to construct a sample of 1 590 local (median $z \approx 0.064$ ) radio sources with $S_{200\,\mathrm{MHz}} > 55$ mJy across an area of ${\approx}16\,700\,\mathrm{deg}^{2}$ . From the optical spectra, we identify the dominant physical process responsible for the radio emission from each galaxy: 73% are fuelled by an active galactic nucleus (AGN) and 27% by star formation. We present the local rad

Published
2021

3. The jet/wind outflow in Centaurus A: a local laboratory for AGN feedback

Author

MIT Kavli Institute for Astrophysics and Space Research, McKinley, B, Tingay, SJ, Carretti, E, Ellis, S, Bland-Hawthorn, J, Morganti, R, Line, J, McDonald, M, Veilleux, S, Wahl Olsen, R, Sidonio, M, Ekers, R, Offringa, AR, Procopio, P, Pindor, B, Wayth, RB, Hurley-Walker, N, Bernardi, G, Gaensler, BM, Haverkorn, M, Kesteven, M, Poppi, S, Staveley-Smith, L, MIT Kavli Institute for Astrophysics and Space Research, McKinley, B, Tingay, SJ, Carretti, E, Ellis, S, Bland-Hawthorn, J, Morganti, R, Line, J, McDonald, M, Veilleux, S, Wahl Olsen, R, Sidonio, M, Ekers, R, Offringa, AR, Procopio, P, Pindor, B, Wayth, RB, Hurley-Walker, N, Bernardi, G, Gaensler, BM, Haverkorn, M, Kesteven, M, Poppi, S, and Staveley-Smith, L

Abstract

© 2017 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. We present new radio and optical images of the nearest radio galaxy Centaurus A and its host galaxy NGC 5128.We focus our investigation on the northern transition region, where energy is transported from the ~5 kpc (~5 arcmin) scales of the northern inner lobe (NIL) to the ~30 kpc (~30 arcmin) scales of the northern middle lobe (NML). Our Murchison Widefield Array observations at 154 MHz and our Parkes radio telescope observations at 2.3 GHz show diffuse radio emission connecting the NIL to the NML, in agreement with previous Australia Telescope Compact Array observations at 1.4 GHz. Comparison of these radio data with our wide-field optical emission-line images show the relationship between the NML radio emission and the ionized filaments that extend north from the NIL, and reveal a new ionized filament to the east, possibly associated with a galactic wind. Our deep optical images show clear evidence for a bipolar outflow from the central galaxy extending to intermediate scales, despite the non-detection of a southern radio counterpart to the NML. Thus, our observational overview of Centaurus A reveals a number of features proposed to be associated with active galactic nucleus feedback mechanisms, often cited as likely to have significant effects in galaxy evolution models. As one of the closest galaxies to us, Centaurus A therefore provides a unique laboratory to examine feedback mechanisms in detail.

Published
2021

4. Searching for dark matter signals from local dwarf spheroidal galaxies at low radio frequencies in the GLEAM survey

Author

Cook RHW, Seymour N, Spekkens K, Hurley-Walker N, Hancock PJ, Bell ME, Callingham JR, For BQ, Franzen TMO, Gaensler BM, Hindson L, Johnston-Hollitt M, Kapińska AD, Morgan J, Offringa AR, Procopio P, Staveley-Smith L, Wayth RB, Wu C, and Zheng Q

Subjects
Astrophysics::High Energy Astrophysical Phenomena, 0201 Astronomical and Space Sciences, Astrophysics::Instrumentation and Methods for Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astronomy & Astrophysics, Astrophysics::Galaxy Astrophysics
Abstract

© 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society The search for emission from weakly interacting massive particle (WIMP) dark matter annihilation and decay has become a multipronged area of research not only targeting a diverse selection of astrophysical objects, but also taking advantage of the entire electromagnetic spectrum. The decay of WIMP particles into standard model particles has been suggested as a possible channel for synchrotron emission to be detected at low radio frequencies. Here, we present the stacking analysis of a sample of 33 dwarf spheroidal (dSph) galaxies with low-frequency (72-231 MHz) radio images from the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey. We produce radial surface brightness profiles of images centred upon each dSph galaxy with background radio sources masked. We remove 10 fields from the stacking due to contamination from either poorly subtracted, bright radio sources or strong background gradients across the field. The remaining 23 dSph galaxies are stacked in an attempt to obtain a statistical detection of any WIMP-induced synchrotron emission in these systems. We find that the stacked radial brightness profile does not exhibit a statistically significant detection above the 95 per cent confidence level of ∼1.5 mJy beam−1. This novel technique shows the potential of using low-frequency radio images to constrain fundamental properties of particle dark matter.

Published
2020

5. Searching for dark matter signals from local dwarf spheroidal galaxies at low radio frequencies in the GLEAM survey

Author

Cook, RHW, Seymour, N, Spekkens, K, Hurley-Walker, N, Hancock, PJ, Bell, ME, Callingham, JR, For, B-Q, Franzen, TMO, Gaensler, BM, Hindson, L, Johnston-Hollitt, M, Kapinska, AD, Morgan, J, Offringa, AR, Procopio, P, Staveley-Smith, L, Wayth, RB, Wu, C, Zheng, Q, Cook, RHW, Seymour, N, Spekkens, K, Hurley-Walker, N, Hancock, PJ, Bell, ME, Callingham, JR, For, B-Q, Franzen, TMO, Gaensler, BM, Hindson, L, Johnston-Hollitt, M, Kapinska, AD, Morgan, J, Offringa, AR, Procopio, P, Staveley-Smith, L, Wayth, RB, Wu, C, and Zheng, Q

Abstract

The search for emission from weakly interacting massive particle (WIMP) dark matter annihilation and decay has become a multipronged area of research not only targeting a diverse selection of astrophysical objects, but also taking advantage of the entire electromagnetic spectrum. The decay of WIMP particles into standard model particles has been suggested as a possible channel for synchrotron emission to be detected at low radio frequencies. Here, we present the stacking analysis of a sample of 33 dwarf spheroidal (dSph) galaxies with low-frequency (72–231 MHz) radio images from the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey. We produce radial surface brightness profiles of images centred upon each dSph galaxy with background radio sources masked. We remove 10 fields from the stacking due to contamination from either poorly subtracted, bright radio sources or strong background gradients across the field. The remaining 23 dSph galaxies are stacked in an attempt to obtain a statistical detection of any WIMP-induced synchrotron emission in these systems. We find that the stacked radial brightness profile does not exhibit a statistically significant detection above the 95 per cent confidence level of ∼1.5 mJy beam−1. This novel technique shows the potential of using low-frequency radio images to constrain fundamental properties of particle dark matter.

Published
2020

6. Murchison Widefield Array and XMM-Newton observations of the Galactic supernova remnant G5.9+3.1

Author

Onic D, Filipovic MD, Bojicic I, Hurley-Walker N, Arbutina B, Pannuti TG, Maitra C, Urosevic D, Haberl F, Maxted N, Wong GF, Rowell G, Bell ME, Callingham JR, Dwarakanath KS, For B-Q, Hancock PJ, Hindson L, Johnston-Hollitt M, Kapinska AD, Lenc E, McKinley B, Morgan J, Offringa AR, Porter LE, Procopio P, Staveley-Smith L, Wayth RB, Wu C, Zheng Q, Onic D, Filipovic MD, Bojicic I, Hurley-Walker N, Arbutina B, Pannuti TG, Maitra C, Urosevic D, Haberl F, Maxted N, Wong GF, Rowell G, Bell ME, Callingham JR, Dwarakanath KS, For B-Q, Hancock PJ, Hindson L, Johnston-Hollitt M, Kapinska AD, Lenc E, McKinley B, Morgan J, Offringa AR, Porter LE, Procopio P, Staveley-Smith L, Wayth RB, Wu C, and Zheng Q

Abstract

Aims. In this paper we discuss the radio continuum and X-ray properties of the so-far poorly studied Galactic supernova remnant (SNR) G5.9 + 3.1. Methods. We present the radio spectral energy distribution (SED) of the Galactic SNR G5.9 + 3.1 obtained with the Murchison Widefield Array (MWA). Combining these new observations with the surveys at other radio continuum frequencies, we discuss the integrated radio continuum spectrum of this particular remnant. We have also analyzed an archival XMM-Newton observation, which represents the first detection of X-ray emission from this remnant. Results. The SNR SED is very well explained by a simple power-law relation. The synchrotron radio spectral index of G5.9 + 3.1 is estimated to be 0.42 ± 0.03 and the integrated flux density at 1 GHz to be around 2.7 Jy. Furthermore, we propose that the identified point radio source, located centrally inside the SNR shell, is most probably a compact remnant of the supernova explosion. The shell-like X-ray morphology of G5.9 + 3.1 as revealed by XMM-Newton broadly matches the spatial distribution of the radio emission, where the radio-bright eastern and western rims are also readily detected in the X-ray while the radio-weak northern and southern rims are weak or absent in the X-ray. Extracted MOS1+MOS2+PN spectra from the whole SNR as well as the north, east, and west rims of the SNR are fit successfully with an optically thin thermal plasma model in collisional ionization equilibrium with a column density NH ~ 0.80 × 1022 cm−2 and fitted temperatures spanning the range kT ~ 0.14–0.23 keV for all of the regions. The derived electron number densi

Published
2019

7. The Murchison Widefield Array Transients Survey (MWATS). A search for low-frequency variability in a bright Southern hemisphere sample

Author

Bell, ME, Murphy, T, Hancock, PJ, Callingham, JR, Johnston, S, Kaplan, DL, Hunstead, RW, Sadler, EM, Croft, S, White, SV, Hurley-Walker, N, Chhetri, R, Morgan, JS, Edwards, PG, Rowlinson, A, Offringa, AR, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Deshpande, AA, Gaensler, BM, Greenhill, LJ, Hazelton, BJ, Johnston-Hollitt, M, Lonsdale, CJ, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Ord, SM, Prabu, T, Shankar, NU, Srivani, KS, Subrahmanyan, R, Tingay, SJ, Wayth, RB, Webster, RL, Williams, A, Williams, CL, Bell, ME, Murphy, T, Hancock, PJ, Callingham, JR, Johnston, S, Kaplan, DL, Hunstead, RW, Sadler, EM, Croft, S, White, SV, Hurley-Walker, N, Chhetri, R, Morgan, JS, Edwards, PG, Rowlinson, A, Offringa, AR, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Deshpande, AA, Gaensler, BM, Greenhill, LJ, Hazelton, BJ, Johnston-Hollitt, M, Lonsdale, CJ, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Ord, SM, Prabu, T, Shankar, NU, Srivani, KS, Subrahmanyan, R, Tingay, SJ, Wayth, RB, Webster, RL, Williams, A, and Williams, CL

Published
2019

8. Galactic synchrotron distribution derived from 152 HII region absorption features in the full GLEAM survey

Author

Su, H, Macquart, JP, Hurley-Walker, N, McClure-Griffiths, NM, Jackson, CA, Tingay, SJ, Tian, WW, Gaensler, BM, McKinley, B, Kapínska, AD, Hindson, L, Hancock, P, Wayth, RB, Staveley-Smith, L, Morgan, J, Johnston-Hollitt, M, Lenc, E, Bell, ME, Callingham, JR, Dwarkanath, KS, For, BQ, Offringa, AR, Procopio, P, Wu, C, Zheng, Q, Su, H, Macquart, JP, Hurley-Walker, N, McClure-Griffiths, NM, Jackson, CA, Tingay, SJ, Tian, WW, Gaensler, BM, McKinley, B, Kapínska, AD, Hindson, L, Hancock, P, Wayth, RB, Staveley-Smith, L, Morgan, J, Johnston-Hollitt, M, Lenc, E, Bell, ME, Callingham, JR, Dwarkanath, KS, For, BQ, Offringa, AR, Procopio, P, Wu, C, and Zheng, Q

Abstract

© 2018 The Author(s) Published by Oxford University Press on behalf of The Royal Astronomical Society. We derive the synchrotron distribution in the Milky Way disc from H II region absorption observations over -40° < l < 40° at six frequencies of 76.2, 83.8, 91.5, 99.2, 106.9, and 114.6 MHz with the GaLactic and Extragalactic All-sky Murchison widefield array survey (GLEAM). We develop a new method of emissivity calculation by taking advantage of the Haslam et al. (1981) map and known spectral indices, which enable us to simultaneously derive the emissivity and the optical depth of H II regions at each frequency. We show our derived synchrotron emissivities based on 152 absorption features of H II regions using both the method previously adopted in the literature and our improved method. We derive the synchrotron emissivity from H II regions to the Galactic edge along the line of sight and, for the first time, derive the emissivity from H II regions to the Sun. These results provide direct information on the distribution of the Galactic magnetic field and cosmic ray electrons for future modelling.

Published
2018

9. Erratum: Galactic synchrotron emissivity measurements between 250° < l < 355° from the GLEAM survey with the MWA [MNRAS, 472, (2017), (828-834)] doi:10.1093/mnras/stx2129

Author

Su, H, Hurley-Walker, N, Jackson, CA, McClure-Griffiths, NM, Tingay, SJ, Hindson, L, Hancock, P, Wayth, RB, Gaensler, BM, Staveley-Smith, L, Morgan, J, Johnston-Hollitt, M, Lenc, E, Bell, ME, Callingham, JR, Dwarkanath, KS, For, BQ, Kapińska, AD, McKinley, B, Offringa, AR, Procopio, P, Wu, C, and Zheng, Q

Subjects
Astronomy & Astrophysics
Abstract

© 2017 The Authors. This is an erratum to the paper 'Galactic synchrotron emissivity measurements between 250° < l < 355° from the GLEAM survey with the MWA', published in MNRAS, 465, 3163 (2017).

Published
2017

10. A search for long-time-scale, low-frequency radio transients

Author

Murphy, T, Kaplan, DL, Croft, S, Lynch, C, Callingham, JR, Bannister, K, Bell, ME, Hurley-Walker, N, Hancock, P, Line, J, Rowlinson, A, Lenc, E, Intema, HT, Jagannathan, P, Ekers, RD, Tingay, S, Yuan, F, Wolf, C, Onken, CA, Dwarakanath, KS, For, B-Q, Gaensler, BM, Hindson, L, Johnston-Hollitt, M, Kapinska, AD, McKinley, B, Morgan, J, Offringa, AR, Procopio, P, Staveley-Smith, L, Wayth, R, Wu, C, Zheng, Q, Murphy, T, Kaplan, DL, Croft, S, Lynch, C, Callingham, JR, Bannister, K, Bell, ME, Hurley-Walker, N, Hancock, P, Line, J, Rowlinson, A, Lenc, E, Intema, HT, Jagannathan, P, Ekers, RD, Tingay, S, Yuan, F, Wolf, C, Onken, CA, Dwarakanath, KS, For, B-Q, Gaensler, BM, Hindson, L, Johnston-Hollitt, M, Kapinska, AD, McKinley, B, Morgan, J, Offringa, AR, Procopio, P, Staveley-Smith, L, Wayth, R, Wu, C, and Zheng, Q

Published
2017

11. Low-Frequency Spectral Energy Distributions of Radio Pulsars Detected with the Murchison Widefield Array

Author

Murphy, T, Kaplan, DL, Bell, ME, Callingham, JR, Croft, S, Johnston, S, Dobie, D, Zic, A, Hughes, J, Lynch, C, Hancock, P, Hurley-Walker, N, Lenc, E, Dwarakanath, KS, For, BQ, Gaensler, BM, Hindson, L, Johnston-Hollitt, M, Kapińska, AD, McKinley, B, Morgan, J, Offringa, AR, Procopio, P, Staveley-Smith, L, Wayth, R, Wu, C, Zheng, Q, Murphy, T, Kaplan, DL, Bell, ME, Callingham, JR, Croft, S, Johnston, S, Dobie, D, Zic, A, Hughes, J, Lynch, C, Hancock, P, Hurley-Walker, N, Lenc, E, Dwarakanath, KS, For, BQ, Gaensler, BM, Hindson, L, Johnston-Hollitt, M, Kapińska, AD, McKinley, B, Morgan, J, Offringa, AR, Procopio, P, Staveley-Smith, L, Wayth, R, Wu, C, and Zheng, Q

Abstract

© Astronomical Society of Australia 2017. We present low-frequency spectral energy distributions of 60 known radio pulsars observed with the Murchison Widefield Array telescope. We searched the GaLactic and Extragalactic All-sky Murchison Widefield Array survey images for 200-MHz continuum radio emission at the position of all pulsars in the Australia Telescope National Facility (ATNF) pulsar catalogue. For the 60 confirmed detections, we have measured flux densities in 20 × 8 MHz bands between 72 and 231 MHz. We compare our results to existing measurements and show that the Murchison Widefield Array flux densities are in good agreement.

Published
2017

12. Calibration and Stokes Imaging with Full Embedded Element Primary Beam Model for the Murchison Widefield Array

Author

Sokolowski, M, Colegate, T, Sutinjo, AT, Ung, D, Wayth, R, Hurley-Walker, N, Lenc, E, Pindor, B, Morgan, J, Kaplan, DL, Bell, ME, Callingham, JR, Dwarakanath, KS, For, B-Q, Gaensler, BM, Hancock, PJ, Hindson, L, Johnston-Hollitt, M, Kapinska, AD, McKinley, B, Offringa, AR, Procopio, P, Staveley-Smith, L, Wu, C, Zheng, Q, Sokolowski, M, Colegate, T, Sutinjo, AT, Ung, D, Wayth, R, Hurley-Walker, N, Lenc, E, Pindor, B, Morgan, J, Kaplan, DL, Bell, ME, Callingham, JR, Dwarakanath, KS, For, B-Q, Gaensler, BM, Hancock, PJ, Hindson, L, Johnston-Hollitt, M, Kapinska, AD, McKinley, B, Offringa, AR, Procopio, P, Staveley-Smith, L, Wu, C, and Zheng, Q

Published
2017

13. Extragalactic Peaked-spectrum Radio Sources at Low Frequencies

Author

Callingham, JR, Ekers, RD, Gaensler, BM, Line, JLB, Hurley-Walker, N, Sadler, EM, Tingay, SJ, Hancock, PJ, Bell, ME, Dwarakanath, KS, For, BQ, Franzen, TMO, Hindson, L, Johnston-Hollitt, M, Kapińska, AD, Lenc, E, McKinley, B, Morgan, J, Offringa, AR, Procopio, P, Staveley-Smith, L, Wayth, RB, Wu, C, Zheng, Q, Callingham, JR, Ekers, RD, Gaensler, BM, Line, JLB, Hurley-Walker, N, Sadler, EM, Tingay, SJ, Hancock, PJ, Bell, ME, Dwarakanath, KS, For, BQ, Franzen, TMO, Hindson, L, Johnston-Hollitt, M, Kapińska, AD, Lenc, E, McKinley, B, Morgan, J, Offringa, AR, Procopio, P, Staveley-Smith, L, Wayth, RB, Wu, C, and Zheng, Q

Abstract

© 2017. The American Astronomical Society. All rights reserved. We present a sample of 1483 sources that display spectral peaks between 72 MHz and 1.4 GHz, selected from the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey. The GLEAM survey is the widest fractional bandwidth all-sky survey to date, ideal for identifying peaked-spectrum sources at low radio frequencies. Our peaked-spectrum sources are the low-frequency analogs of gigahertz-peaked spectrum (GPS) and compact-steep spectrum (CSS) sources, which have been hypothesized to be the precursors to massive radio galaxies. Our sample more than doubles the number of known peaked-spectrum candidates, and 95% of our sample have a newly characterized spectral peak. We highlight that some GPS sources peaking above 5 GHz have had multiple epochs of nuclear activity, and we demonstrate the possibility of identifying high-redshift (z > 2) galaxies via steep optically thin spectral indices and low observed peak frequencies. The distribution of the optically thick spectral indices of our sample is consistent with past GPS/CSS samples but with a large dispersion, suggesting that the spectral peak is a product of an inhomogeneous environment that is individualistic. We find no dependence of observed peak frequency with redshift, consistent with the peaked-spectrum sample comprising both local CSS sources and high-redshift GPS sources. The 5 GHz luminosity distribution lacks the brightest GPS and CSS sources of previous samples, implying that a convolution of source evolution and redshift influences the type of peaked-spectrum sources identified below 1 GHz. Finally, we discuss sources with optically thick spectral indices that exceed the synchrotron self-absorption limit.

Published
2017

14. Spectral Energy Distribution and Radio Halo of NGC 253 at Low Radio Frequencies

Author

Kapińska, AD, Staveley-Smith, L, Crocker, R, Meurer, GR, Bhandari, S, Hurley-Walker, N, Offringa, AR, Hanish, DJ, Seymour, N, Ekers, RD, Bell, ME, Callingham, JR, Dwarakanath, KS, For, BQ, Gaensler, BM, Hancock, PJ, Hindson, L, Johnston-Hollitt, M, Lenc, E, McKinley, B, Morgan, J, Procopio, P, Wayth, RB, Wu, C, Zheng, Q, Barry, N, Beardsley, AP, Bowman, JD, Briggs, F, Carroll, P, Dillon, JS, Ewall-Wice, A, Feng, L, Greenhill, LJ, Hazelton, BJ, Hewitt, JN, Jacobs, DJ, Kim, HS, Kittiwisit, P, Line, J, Loeb, A, Mitchell, DA, Morales, MF, Neben, AR, Paul, S, Pindor, B, Pober, JC, Riding, J, Sethi, SK, Shankar, NU, Subrahmanyan, R, Sullivan, IS, Tegmark, M, Thyagarajan, N, Tingay, SJ, Trott, CM, Webster, RL, Wyithe, SB, Cappallo, RJ, Deshpande, AA, Kaplan, DL, Lonsdale, CJ, McWhirter, SR, Morgan, E, Oberoi, D, Ord, SM, Prabu, T, Srivani, KS, Williams, A, Williams, CL, Kapińska, AD, Staveley-Smith, L, Crocker, R, Meurer, GR, Bhandari, S, Hurley-Walker, N, Offringa, AR, Hanish, DJ, Seymour, N, Ekers, RD, Bell, ME, Callingham, JR, Dwarakanath, KS, For, BQ, Gaensler, BM, Hancock, PJ, Hindson, L, Johnston-Hollitt, M, Lenc, E, McKinley, B, Morgan, J, Procopio, P, Wayth, RB, Wu, C, Zheng, Q, Barry, N, Beardsley, AP, Bowman, JD, Briggs, F, Carroll, P, Dillon, JS, Ewall-Wice, A, Feng, L, Greenhill, LJ, Hazelton, BJ, Hewitt, JN, Jacobs, DJ, Kim, HS, Kittiwisit, P, Line, J, Loeb, A, Mitchell, DA, Morales, MF, Neben, AR, Paul, S, Pindor, B, Pober, JC, Riding, J, Sethi, SK, Shankar, NU, Subrahmanyan, R, Sullivan, IS, Tegmark, M, Thyagarajan, N, Tingay, SJ, Trott, CM, Webster, RL, Wyithe, SB, Cappallo, RJ, Deshpande, AA, Kaplan, DL, Lonsdale, CJ, McWhirter, SR, Morgan, E, Oberoi, D, Ord, SM, Prabu, T, Srivani, KS, Williams, A, and Williams, CL

Abstract

© 2017. The American Astronomical Society. All rights reserved. We present new radio continuum observations of NGC 253 from the Murchison Widefield Array at frequencies between 76 and 227 MHz. We model the broadband radio spectral energy distribution for the total flux density of NGC 253 between 76 MHz and 11 GHz. The spectrum is best described as a sum of a central starburst and extended emission. The central component, corresponding to the inner 500 pc of the starburst region of the galaxy, is best modeled as an internally free-free absorbed synchrotron plasma, with a turnover frequency around 230 MHz. The extended emission component of the spectrum of NGC 253 is best described as a synchrotron emission flattening at low radio frequencies. We find that 34% of the extended emission (outside the central starburst region) at 1 GHz becomes partially absorbed at low radio frequencies. Most of this flattening occurs in the western region of the southeast halo, and may be indicative of synchrotron self-absorption of shock-reaccelerated electrons or an intrinsic low-energy cutoff of the electron distribution. Furthermore, we detect the large-scale synchrotron radio halo of NGC 253 in our radio images. At 154-231 MHz the halo displays the well known X-shaped/horn-like structure, and extends out to ∼8 kpc in the z-direction (from the major axis).

Published
2017

15. Ionospheric Modelling using GPS to Calibrate the MWA. I: Comparison of First Order Ionospheric Effects between GPS Models and MWA Observations

Author

Arora, BS, Morgan, J, Ord, SM, Tingay, SJ, Hurley-Walker, N, Bell, M, Bernardi, G, Bhat, NDR, Briggs, F, Callingham, JR, Deshpande, AA, Dwarakanath, KS, Ewall-Wice, A, Feng, L, For, B-Q, Hancock, P, Hazelton, BJ, Hindson, L, Jacobs, D, Johnston-Hollitt, M, Kapinska, AD, Kudryavtseva, N, Lenc, E, McKinley, B, Mitchell, D, Oberoi, D, Offringa, AR, Pindor, B, Procopio, P, Riding, J, Staveley-Smith, L, Wayth, RB, Wu, C, Zheng, Q, Bowman, JD, Cappallo, RJ, Corey, BE, Emrich, D, Goeke, R, Greenhill, LJ, Kaplan, DL, Kasper, JC, Kratzenberg, E, Lonsdale, CJ, Lynch, MJ, McWhirter, SR, Morales, MF, Morgan, E, Prabu, T, Rogers, AEE, Roshi, A, Shankar, NU, Srivani, KS, Subrahmanyan, R, Waterson, M, Webster, RL, Whitney, AR, Williams, A, Williams, CL, Arora, BS, Morgan, J, Ord, SM, Tingay, SJ, Hurley-Walker, N, Bell, M, Bernardi, G, Bhat, NDR, Briggs, F, Callingham, JR, Deshpande, AA, Dwarakanath, KS, Ewall-Wice, A, Feng, L, For, B-Q, Hancock, P, Hazelton, BJ, Hindson, L, Jacobs, D, Johnston-Hollitt, M, Kapinska, AD, Kudryavtseva, N, Lenc, E, McKinley, B, Mitchell, D, Oberoi, D, Offringa, AR, Pindor, B, Procopio, P, Riding, J, Staveley-Smith, L, Wayth, RB, Wu, C, Zheng, Q, Bowman, JD, Cappallo, RJ, Corey, BE, Emrich, D, Goeke, R, Greenhill, LJ, Kaplan, DL, Kasper, JC, Kratzenberg, E, Lonsdale, CJ, Lynch, MJ, McWhirter, SR, Morales, MF, Morgan, E, Prabu, T, Rogers, AEE, Roshi, A, Shankar, NU, Srivani, KS, Subrahmanyan, R, Waterson, M, Webster, RL, Whitney, AR, Williams, A, and Williams, CL

Abstract

We compare first-order (refractive) ionospheric effects seen by the MWA with the ionosphere as inferred from GPS data. The first-order ionosphere manifests itself as a bulk position shift of the observed sources across an MWA field of view. These effects can be computed from global ionosphere maps provided by GPS analysis centres, namely the CODE. However, for precision radio astronomy applications, data from local GPS networks needs to be incorporated into ionospheric modelling. For GPS observations, the ionospheric parameters are biased by GPS receiver instrument delays, among other effects, also known as receiver DCBs. The receiver DCBs need to be estimated for any non-CODE GPS station used for ionosphere modelling. In this work, single GPS station-based ionospheric modelling is performed at a time resolution of 10 min. Also the receiver DCBs are estimated for selected Geoscience Australia GPS receivers, located at Murchison Radio Observatory, Yarragadee, Mount Magnet and Wiluna. The ionospheric gradients estimated from GPS are compared with that inferred from MWA. The ionospheric gradients at all the GPS stations show a correlation with the gradients observed with the MWA. The ionosphere estimates obtained using GPS measurements show promise in terms of providing calibration information for the MWA.

Published
2015

16. FOREGROUNDS IN WIDE-FIELD REDSHIFTED 21 cm POWER SPECTRA

Author

Thyagarajan, N, Jacobs, DC, Bowman, JD, Barry, N, Beardsley, AP, Bernardi, G, Briggs, F, Cappallo, RJ, Carroll, P, Corey, BE, de Oliveira-Costa, A, Dillon, JS, Emrich, D, Ewall-Wice, A, Feng, L, Goeke, R, Greenhill, LJ, Hazelton, BJ, Hewitt, JN, Hurley-Walker, N, Johnston-Hollitt, M, Kaplan, DL, Kasper, JC, Kim, H-S, Kittiwisit, P, Kratzenberg, E, Lenc, E, Line, J, Loeb, A, Lonsdale, CJ, Lynch, MJ, McKinley, B, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Neben, AR, Oberoi, D, Offringa, AR, Ord, SM, Paul, S, Pindor, B, Pober, JC, Prabu, T, Procopio, P, Riding, J, Rogers, AEE, Roshi, A, Shankar, NU, Sethi, SK, Srivani, KS, Subrahmanyan, R, Sullivan, IS, Tegmark, M, Tingay, SJ, Trott, CM, Waterson, M, Wayth, RB, Webster, RL, Whitney, AR, Williams, A, Williams, CL, Wu, C, Wyithe, JSB, Thyagarajan, N, Jacobs, DC, Bowman, JD, Barry, N, Beardsley, AP, Bernardi, G, Briggs, F, Cappallo, RJ, Carroll, P, Corey, BE, de Oliveira-Costa, A, Dillon, JS, Emrich, D, Ewall-Wice, A, Feng, L, Goeke, R, Greenhill, LJ, Hazelton, BJ, Hewitt, JN, Hurley-Walker, N, Johnston-Hollitt, M, Kaplan, DL, Kasper, JC, Kim, H-S, Kittiwisit, P, Kratzenberg, E, Lenc, E, Line, J, Loeb, A, Lonsdale, CJ, Lynch, MJ, McKinley, B, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Neben, AR, Oberoi, D, Offringa, AR, Ord, SM, Paul, S, Pindor, B, Pober, JC, Prabu, T, Procopio, P, Riding, J, Rogers, AEE, Roshi, A, Shankar, NU, Sethi, SK, Srivani, KS, Subrahmanyan, R, Sullivan, IS, Tegmark, M, Tingay, SJ, Trott, CM, Waterson, M, Wayth, RB, Webster, RL, Whitney, AR, Williams, A, Williams, CL, Wu, C, and Wyithe, JSB

Abstract

Detection of 21~cm emission of HI from the epoch of reionization, at redshifts z>6, is limited primarily by foreground emission. We investigate the signatures of wide-field measurements and an all-sky foreground model using the delay spectrum technique that maps the measurements to foreground object locations through signal delays between antenna pairs. We demonstrate interferometric measurements are inherently sensitive to all scales, including the largest angular scales, owing to the nature of wide-field measurements. These wide-field effects are generic to all observations but antenna shapes impact their amplitudes substantially. A dish-shaped antenna yields the most desirable features from a foreground contamination viewpoint, relative to a dipole or a phased array. Comparing data from recent Murchison Widefield Array observations, we demonstrate that the foreground signatures that have the largest impact on the HI signal arise from power received far away from the primary field of view. We identify diffuse emission near the horizon as a significant contributing factor, even on wide antenna spacings that usually represent structures on small scales. For signals entering through the primary field of view, compact emission dominates the foreground contamination. These two mechanisms imprint a characteristic "pitchfork" signature on the "foreground wedge" in Fourier delay space. Based on these results, we propose that selective down-weighting of data based on antenna spacing and time can mitigate foreground contamination substantially by a factor ~100 with negligible loss of sensitivity.

Published
2015

17. Limits on low-frequency radio emission from southern exoplanets with the Murchison Widefield Array

Author

Murphy, T, Bell, ME, Kaplan, DL, Gaensler, BM, Offringa, AR, Lenc, E, Hurley-Walker, N, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Corey, BE, Deshpande, AA, Emrich, D, Goeke, R, Greenhill, LJ, Hazelton, BJ, Hewitt, JN, Johnston-Hollitt, M, Kasper, JC, Kratzenberg, E, Lonsdale, CJ, Lynch, MJ, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Ord, SM, Prabu, T, Rogers, AEE, Roshi, DA, Shankar, NU, Srivani, KS, Subrahmanyan, R, Tingay, SJ, Waterson, M, Wayth, RB, Webster, RL, Whitney, AR, Williams, A, Williams, CL, Murphy, T, Bell, ME, Kaplan, DL, Gaensler, BM, Offringa, AR, Lenc, E, Hurley-Walker, N, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Corey, BE, Deshpande, AA, Emrich, D, Goeke, R, Greenhill, LJ, Hazelton, BJ, Hewitt, JN, Johnston-Hollitt, M, Kasper, JC, Kratzenberg, E, Lonsdale, CJ, Lynch, MJ, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Ord, SM, Prabu, T, Rogers, AEE, Roshi, DA, Shankar, NU, Srivani, KS, Subrahmanyan, R, Tingay, SJ, Waterson, M, Wayth, RB, Webster, RL, Whitney, AR, Williams, A, and Williams, CL

Abstract

We present the results of a survey for low frequency radio emission from 17 known exoplanetary systems with the Murchison Widefield Array. This sample includes 13 systems that have not previously been targeted with radio observations. We detected no radio emission at 154 MHz, and put 3 sigma upper limits in the range 15.2-112.5 mJy on this emission. We also searched for circularly polarised emission and made no detections, obtaining 3 sigma upper limits in the range 3.4-49.9 mJy. These are comparable with the best low frequency radio limits in the existing literature and translate to luminosity limits of between 1.2 x 10^14 W and 1.4 x 10^17 W if the emission is assumed to be 100% circularly polarised. These are the first results from a larger program to systematically search for exoplanetary emission with the MWA.

Published
2015

18. Power spectrum analysis of ionospheric fluctuations with the Murchison Widefield Array

Author

Loi, ST, Trott, CM, Murphy, T, Cairns, IH, Bell, M, Hurley-Walker, N, Morgan, J, Lenc, E, Offringa, AR, Feng, L, Hancock, PJ, Kaplan, DL, Kudryavtseva, N, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Corey, BE, Deshpande, AA, Emrich, D, Gaensler, BM, Goeke, R, Greenhill, LJ, Hazelton, BJ, Johnston-Hollitt, M, Kasper, JC, Kratzenberg, E, Lonsdale, CJ, Lynch, MJ, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Ord, SM, Prabu, T, Rogers, AEE, Roshi, A, Shankar, NU, Srivani, KS, Subrahmanyan, R, Tingay, SJ, Waterson, M, Wayth, RB, Webster, RL, Whitney, AR, Williams, A, Williams, CL, Loi, ST, Trott, CM, Murphy, T, Cairns, IH, Bell, M, Hurley-Walker, N, Morgan, J, Lenc, E, Offringa, AR, Feng, L, Hancock, PJ, Kaplan, DL, Kudryavtseva, N, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Corey, BE, Deshpande, AA, Emrich, D, Gaensler, BM, Goeke, R, Greenhill, LJ, Hazelton, BJ, Johnston-Hollitt, M, Kasper, JC, Kratzenberg, E, Lonsdale, CJ, Lynch, MJ, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Ord, SM, Prabu, T, Rogers, AEE, Roshi, A, Shankar, NU, Srivani, KS, Subrahmanyan, R, Tingay, SJ, Waterson, M, Wayth, RB, Webster, RL, Whitney, AR, Williams, A, and Williams, CL

Abstract

Low‐frequency, wide field‐of‐view (FOV) radio telescopes such as the Murchison Widefield Array (MWA) enable the ionosphere to be sampled at high spatial completeness. We present the results of the first power spectrum analysis of ionospheric fluctuations in MWA data, where we examined the position offsets of radio sources appearing in two data sets. The refractive shifts in the positions of celestial sources are proportional to spatial gradients in the electron column density transverse to the line of sight. These can be used to probe plasma structures and waves in the ionosphere. The regional (10–100 km) scales probed by the MWA, determined by the size of its FOV and the spatial density of radio sources (typically thousands in a single FOV), complement the global (100–1000 km) scales of GPS studies and local (0.01–1 km) scales of radar scattering measurements. Our data exhibit a range of complex structures and waves. Some fluctuations have the characteristics of traveling ionospheric disturbances, while others take the form of narrow, slowly drifting bands aligned along the Earth's magnetic field.

Published
2015

19. Quantifying ionospheric effects on time-domain astrophysics with the Murchison Widefield Array

Author

Loi, ST, Murphy, T, Bell, ME, Kaplan, DL, Lenc, E, Offringa, AR, Hurley-Walker, N, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Corey, BE, Deshpande, AA, Emrich, D, Gaensler, BM, Goeke, R, Greenhill, LJ, Hazelton, BJ, Johnston-Hollitt, M, Kasper, JC, Kratzenberg, E, Lonsdale, CJ, Lynch, MJ, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Ord, SM, Prabu, T, Rogers, AEE, Roshi, A, Shankar, NU, Srivani, KS, Subrahmanyan, R, Tingay, SJ, Waterson, M, Wayth, RB, Webster, RL, Whitney, AR, Williams, A, Williams, CL, Loi, ST, Murphy, T, Bell, ME, Kaplan, DL, Lenc, E, Offringa, AR, Hurley-Walker, N, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Corey, BE, Deshpande, AA, Emrich, D, Gaensler, BM, Goeke, R, Greenhill, LJ, Hazelton, BJ, Johnston-Hollitt, M, Kasper, JC, Kratzenberg, E, Lonsdale, CJ, Lynch, MJ, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Ord, SM, Prabu, T, Rogers, AEE, Roshi, A, Shankar, NU, Srivani, KS, Subrahmanyan, R, Tingay, SJ, Waterson, M, Wayth, RB, Webster, RL, Whitney, AR, Williams, A, and Williams, CL

Published
2015

20. Real-time imaging of density ducts between the plasmasphere and ionosphere

Author

Loi, ST, Murphy, T, Cairns, IH, Menk, FW, Waters, CL, Erickson, PJ, Trott, CM, Hurley-Walker, N, Morgan, J, Lenc, E, Offringa, AR, Bell, ME, Ekers, RD, Gaensler, BM, Lonsdale, CJ, Feng, L, Hancock, PJ, Kaplan, DL, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Deshpande, AA, Greenhill, LJ, Hazelton, BJ, Johnston-Hollitt, M, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Ord, SM, Prabu, T, Shankar, NU, Srivani, KS, Subrahmanyan, R, Tingay, SJ, Wayth, RB, Webster, RL, Williams, A, Williams, CL, Loi, ST, Murphy, T, Cairns, IH, Menk, FW, Waters, CL, Erickson, PJ, Trott, CM, Hurley-Walker, N, Morgan, J, Lenc, E, Offringa, AR, Bell, ME, Ekers, RD, Gaensler, BM, Lonsdale, CJ, Feng, L, Hancock, PJ, Kaplan, DL, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Deshpande, AA, Greenhill, LJ, Hazelton, BJ, Johnston-Hollitt, M, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Ord, SM, Prabu, T, Shankar, NU, Srivani, KS, Subrahmanyan, R, Tingay, SJ, Wayth, RB, Webster, RL, Williams, A, and Williams, CL

Abstract

Ionization of the Earth's atmosphere by sunlight forms a complex, multilayered plasma environment within the Earth's magnetosphere, the innermost layers being the ionosphere and plasmasphere. The plasmasphere is believed to be embedded with cylindrical density structures (ducts) aligned along the Earth's magnetic field, but direct evidence for these remains scarce. Here we report the first direct wide‐angle observation of an extensive array of field‐aligned ducts bridging the upper ionosphere and inner plasmasphere, using a novel ground‐based imaging technique. We establish their heights and motions by feature tracking and parallax analysis. The structures are strikingly organized, appearing as regularly spaced, alternating tubes of overdensities and underdensities strongly aligned with the Earth's magnetic field. These findings represent the first direct visual evidence for the existence of such structures.

Published
2015

21. The Low-Frequency Environment of the Murchison Widefield Array: Radio-Frequency Interference Analysis and Mitigation

Author

Offringa, AR, Wayth, RB, Hurley-Walker, N, Kaplan, DL, Barry, N, Beardsley, AP, Bell, ME, Bernardi, G, Bowman, JD, Briggs, F, Callingham, JR, Cappallo, RJ, Carroll, P, Deshpande, AA, Dillon, JS, Dwarakanath, KS, Ewall-Wice, A, Feng, L, For, B-Q, Gaensler, BM, Greenhill, LJ, Hancock, P, Hazelton, BJ, Hewitt, JN, Hindson, L, Jacobs, DC, Johnston-Hollitt, M, Kapinska, AD, Kim, H-S, Kittiwisit, P, Lenc, E, Line, J, Loeb, A, Lonsdale, CJ, McKinley, B, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Morgan, J, Neben, AR, Oberoi, D, Ord, SM, Paul, S, Pindor, B, Pober, JC, Prabu, T, Procopio, P, Riding, J, Shankar, NU, Sethi, S, Srivani, KS, Staveley-Smith, L, Subrahmanyan, R, Sullivan, IS, Tegmark, M, Thyagarajan, N, Tingay, SJ, Trott, CM, Webster, RL, Williams, A, Williams, CL, Wu, C, Wyithe, JS, Zheng, Q, Offringa, AR, Wayth, RB, Hurley-Walker, N, Kaplan, DL, Barry, N, Beardsley, AP, Bell, ME, Bernardi, G, Bowman, JD, Briggs, F, Callingham, JR, Cappallo, RJ, Carroll, P, Deshpande, AA, Dillon, JS, Dwarakanath, KS, Ewall-Wice, A, Feng, L, For, B-Q, Gaensler, BM, Greenhill, LJ, Hancock, P, Hazelton, BJ, Hewitt, JN, Hindson, L, Jacobs, DC, Johnston-Hollitt, M, Kapinska, AD, Kim, H-S, Kittiwisit, P, Lenc, E, Line, J, Loeb, A, Lonsdale, CJ, McKinley, B, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Morgan, J, Neben, AR, Oberoi, D, Ord, SM, Paul, S, Pindor, B, Pober, JC, Prabu, T, Procopio, P, Riding, J, Shankar, NU, Sethi, S, Srivani, KS, Staveley-Smith, L, Subrahmanyan, R, Sullivan, IS, Tegmark, M, Thyagarajan, N, Tingay, SJ, Trott, CM, Webster, RL, Williams, A, Williams, CL, Wu, C, Wyithe, JS, and Zheng, Q

Abstract

The Murchison Widefield Array is a new low-frequency interferometric radio telescope built in Western Australia at one of the locations of the future Square Kilometre Array. We describe the automated radio-frequency interference detection strategy implemented for the Murchison Widefield Array, which is based on the aoflagger platform, and present 72–231 MHz radio-frequency interference statistics from 10 observing nights. Radio-frequency interference detection removes 1.1% of the data. Radio-frequency interference from digital TV is observed 3% of the time due to occasional ionospheric or atmospheric propagation. After radio-frequency interference detection and excision, almost all data can be calibrated and imaged without further radio-frequency interference mitigation efforts, including observations within the FM and digital TV bands. The results are compared to a previously published Low-Frequency Array radio-frequency interference survey. The remote location of the Murchison Widefield Array results in a substantially cleaner radio-frequency interference environment compared to Low-Frequency Array’s radio environment, but adequate detection of radio-frequency interference is still required before data can be analysed. We include specific recommendations designed to make the Square Kilometre Array more robust to radio-frequency interference, including: the availability of sufficient computing power for radio-frequency interference detection; accounting for radio-frequency interference in the receiver design; a smooth band-pass response; and the capability of radio-frequency interference detection at high time and frequency resolution (second and kHz-scale respectively).

Published
2015

22. Empirical covariance modeling for 21 cm power spectrum estimation: A method demonstration and new limits from early Murchison Widefield Array 128-tile data

Author

Dillon, JS, Neben, AR, Hewitt, JN, Tegmark, M, Barry, N, Beardsley, AP, Bowman, JD, Briggs, F, Carroll, P, de Oliveira-Costa, A, Ewall-Wice, A, Feng, L, Greenhill, LJ, Hazelton, BJ, Hernquist, L, Hurley-Walker, N, Jacobs, DC, Kim, HS, Kittiwisit, P, Lenc, E, Line, J, Loeb, A, McKinley, B, Mitchell, DA, Morales, MF, Offringa, AR, Paul, S, Pindor, B, Pober, JC, Procopio, P, Riding, J, Sethi, S, Shankar, NU, Subrahmanyan, R, Sullivan, I, Thyagarajan, N, Tingay, SJ, Trott, C, Wayth, RB, Webster, RL, Wyithe, S, Bernardi, G, Cappallo, RJ, Deshpande, AA, Johnston-Hollitt, M, Kaplan, DL, Lonsdale, CJ, McWhirter, SR, Morgan, E, Oberoi, D, Ord, SM, Prabu, T, Srivani, KS, Williams, A, Williams, CL, Dillon, JS, Neben, AR, Hewitt, JN, Tegmark, M, Barry, N, Beardsley, AP, Bowman, JD, Briggs, F, Carroll, P, de Oliveira-Costa, A, Ewall-Wice, A, Feng, L, Greenhill, LJ, Hazelton, BJ, Hernquist, L, Hurley-Walker, N, Jacobs, DC, Kim, HS, Kittiwisit, P, Lenc, E, Line, J, Loeb, A, McKinley, B, Mitchell, DA, Morales, MF, Offringa, AR, Paul, S, Pindor, B, Pober, JC, Procopio, P, Riding, J, Sethi, S, Shankar, NU, Subrahmanyan, R, Sullivan, I, Thyagarajan, N, Tingay, SJ, Trott, C, Wayth, RB, Webster, RL, Wyithe, S, Bernardi, G, Cappallo, RJ, Deshpande, AA, Johnston-Hollitt, M, Kaplan, DL, Lonsdale, CJ, McWhirter, SR, Morgan, E, Oberoi, D, Ord, SM, Prabu, T, Srivani, KS, Williams, A, and Williams, CL

Abstract

The separation of the faint cosmological background signal from bright astrophysical foregrounds remains one of the most daunting challenges of mapping the high-redshift intergalactic medium with the redshifted 21 cm line of neutral hydrogen. Advances in mapping and modeling of diffuse and point source foregrounds have improved subtraction accuracy, but no subtraction scheme is perfect. Precisely quantifying the errors and error correlations due to missubtracted foregrounds allows for both the rigorous analysis of the 21 cm power spectrum and for the maximal isolation of the "EoR window" from foreground contamination. We present a method to infer the covariance of foreground residuals from the data itself in contrast to previous attempts at a priori modeling. We demonstrate our method by setting limits on the power spectrum using a 3 h integration from the 128-tile Murchison Widefield Array. Observing between 167 and 198 MHz, we find at 95% confidence a best limit of Delta^2(k) < 3.7 x 10^4 mK^2 at comoving scale k = 0.18 hMpc^-1 and at z = 6.8, consistent with existing limits.

Published
2015

23. CONFIRMATION OF WIDE-FIELD SIGNATURES IN REDSHIFTED 21 cm POWER SPECTRA

Author

Thyagarajan, N, Jacobs, DC, Bowman, JD, Barry, N, Beardsley, AP, Bernardi, G, Briggs, F, Cappallo, RJ, Carroll, P, Deshpande, AA, de Oliveira-Costa, A, Dillon, JS, Ewall-Wice, A, Feng, L, Greenhill, LJ, Hazelton, BJ, Hernquist, L, Hewitt, JN, Hurley-Walker, N, Johnston-Hollitt, M, Kaplan, DL, Kim, H-S, Kittiwisit, P, Lenc, E, Line, J, Loeb, A, Lonsdale, CJ, McKinley, B, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Neben, AR, Oberoi, D, Offringa, AR, Ord, SM, Paul, S, Pindor, B, Pober, JC, Prabu, T, Procopio, P, Riding, J, Shankar, NU, Sethi, SK, Srivani, KS, Subrahmanyan, R, Sullivan, IS, Tegmark, M, Tingay, SJ, Trott, CM, Wayth, RB, Webster, RL, Williams, A, Williams, CL, Wyithe, JSB, Thyagarajan, N, Jacobs, DC, Bowman, JD, Barry, N, Beardsley, AP, Bernardi, G, Briggs, F, Cappallo, RJ, Carroll, P, Deshpande, AA, de Oliveira-Costa, A, Dillon, JS, Ewall-Wice, A, Feng, L, Greenhill, LJ, Hazelton, BJ, Hernquist, L, Hewitt, JN, Hurley-Walker, N, Johnston-Hollitt, M, Kaplan, DL, Kim, H-S, Kittiwisit, P, Lenc, E, Line, J, Loeb, A, Lonsdale, CJ, McKinley, B, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Neben, AR, Oberoi, D, Offringa, AR, Ord, SM, Paul, S, Pindor, B, Pober, JC, Prabu, T, Procopio, P, Riding, J, Shankar, NU, Sethi, SK, Srivani, KS, Subrahmanyan, R, Sullivan, IS, Tegmark, M, Tingay, SJ, Trott, CM, Wayth, RB, Webster, RL, Williams, A, Williams, CL, and Wyithe, JSB

Abstract

We confirm our recent prediction of the "pitchfork" foreground signature in power spectra of high-redshift 21 cm measurements where the interferometer is sensitive to large-scale structure on all baselines. This is due to the inherent response of a wide-field instrument and is characterized by enhanced power from foreground emission in Fourier modes adjacent to those considered to be the most sensitive to the cosmological H I signal. In our recent paper, many signatures from the simulation that predicted this feature were validated against Murchison Widefield Array (MWA) data, but this key pitchfork signature was close to the noise level. In this paper, we improve the data sensitivity through the coherent averaging of 12 independent snapshots with identical instrument settings and provide the first confirmation of the prediction with a signal-to-noise ratio > 10. This wide-field effect can be mitigated by careful antenna designs that suppress sensitivity near the horizon. Simple models for antenna apertures that have been proposed for future instruments such as the Hydrogen Epoch of Reionization Array and the Square Kilometre Array indicate they should suppress foreground leakage from the pitchfork by ~40 dB relative to the MWA and significantly increase the likelihood of cosmological signal detection in these critical Fourier modes in the three-dimensional power spectrum.

Published
2015

24. BROADBAND SPECTRAL MODELING OF THE EXTREME GIGAHERTZ-PEAKED SPECTRUM RADIO SOURCE PKS B0008-421

Author

Callingham, JR, Gaensler, BM, Ekers, RD, Tingay, SJ, Wayth, RB, Morgan, J, Bernardi, G, Bell, ME, Bhat, R, Bowman, JD, Briggs, F, Cappallo, RJ, Deshpande, AA, Ewall-Wice, A, Feng, L, Greenhill, LJ, Hazelton, BJ, Hindson, L, Hurley-Walker, N, Jacobs, DC, Johnston-Hollitt, M, Kaplan, DL, Kudrayvtseva, N, Lenc, E, Lonsdale, CJ, McKinley, B, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Offringa, AR, Ord, SM, Pindor, B, Prabu, T, Procopio, P, Riding, J, Srivani, KS, Subrahmanyan, R, Shankar, NU, Webster, RL, Williams, A, Williams, CL, Callingham, JR, Gaensler, BM, Ekers, RD, Tingay, SJ, Wayth, RB, Morgan, J, Bernardi, G, Bell, ME, Bhat, R, Bowman, JD, Briggs, F, Cappallo, RJ, Deshpande, AA, Ewall-Wice, A, Feng, L, Greenhill, LJ, Hazelton, BJ, Hindson, L, Hurley-Walker, N, Jacobs, DC, Johnston-Hollitt, M, Kaplan, DL, Kudrayvtseva, N, Lenc, E, Lonsdale, CJ, McKinley, B, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Offringa, AR, Ord, SM, Pindor, B, Prabu, T, Procopio, P, Riding, J, Srivani, KS, Subrahmanyan, R, Shankar, NU, Webster, RL, Williams, A, and Williams, CL

Abstract

We present broadband observations and spectral modeling of PKS B0008-421, and identify it as an extreme gigahertz-peaked spectrum (GPS) source. PKS B0008-421 is characterized by the steepest known spectral slope below the turnover, close to the theoretical limit of synchrotron self-absorption, and the smallest known spectral width of any GPS source. Spectral coverage of the source spans from 0.118 to 22 GHz, which includes data from the Murchison Widefield Array and the wide bandpass receivers on the Australia Telescope Compact Array. We have implemented a Bayesian inference model fitting routine to fit the data with various absorption models. We find that without the inclusion of a high-frequency exponential break the absorption models can not accurately fit the data, with significant deviations above and below the peak in the radio spectrum. The addition of a high-frequency break provides acceptable spectral fits for the inhomogeneous free-free absorption and double-component synchrotron self-absorption models, with the inhomogeneous free-free absorption model statistically favored. The requirement of a high-frequency spectral break implies that the source has ceased injecting fresh particles. Additional support for the inhomogeneous free-free absorption model as being responsible for the turnover in the spectrum is given by the consistency between the physical parameters derived from the model fit and the implications of the exponential spectral break, such as the necessity of the source being surrounded by a dense ambient medium to maintain the peak frequency near the gigahertz region. The discovery of PKS B0008-421 suggests that the next generation of low radio frequency surveys could reveal a large population of GPS sources that have ceased activity, and that a portion of the ultra-steep spectrum source population could be composed of these GPS sources in a relic phase.

Published
2015

25. The First Murchison Widefield Array low-frequency radio observations of cluster scale non-thermal emission: the case of Abell 3667

Author

Hindson, L, Johnston-Hollitt, M, Hurley-Walker, N, Buckley, K, Morgan, J, Carretti, E, Dwarakanath, KS, Bell, M, Bernardi, G, Bhat, NDR, Bowman, JD, Briggs, F, Cappallo, RJ, Corey, BE, Deshpande, AA, Emrich, D, Ewall-Wice, A, Feng, L, Gaensler, BM, Goeke, R, Greenhill, LJ, Hazelton, BJ, Jacobs, D, Kaplan, DL, Kasper, JC, Kratzenberg, E, Kudryavtseva, N, Lenc, E, Lonsdale, CJ, Lynch, MJ, McWhirter, SR, McKinley, B, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Ord, SM, Pindor, B, Prabu, T, Procopio, P, Offringa, AR, Riding, J, Rogers, AEE, Roshi, A, Shankar, NU, Srivani, KS, Subrahmanyan, R, Tingay, SJ, Waterson, M, Wayth, RB, Webster, RL, Whitney, AR, Williams, A, Williams, CL, Hindson, L, Johnston-Hollitt, M, Hurley-Walker, N, Buckley, K, Morgan, J, Carretti, E, Dwarakanath, KS, Bell, M, Bernardi, G, Bhat, NDR, Bowman, JD, Briggs, F, Cappallo, RJ, Corey, BE, Deshpande, AA, Emrich, D, Ewall-Wice, A, Feng, L, Gaensler, BM, Goeke, R, Greenhill, LJ, Hazelton, BJ, Jacobs, D, Kaplan, DL, Kasper, JC, Kratzenberg, E, Kudryavtseva, N, Lenc, E, Lonsdale, CJ, Lynch, MJ, McWhirter, SR, McKinley, B, Mitchell, DA, Morales, MF, Morgan, E, Oberoi, D, Ord, SM, Pindor, B, Prabu, T, Procopio, P, Offringa, AR, Riding, J, Rogers, AEE, Roshi, A, Shankar, NU, Srivani, KS, Subrahmanyan, R, Tingay, SJ, Waterson, M, Wayth, RB, Webster, RL, Whitney, AR, Williams, A, and Williams, CL

Abstract

We present the first Murchison Widefield Array observations of the well-known cluster of galaxies Abell 3667 (A3667) between 105 and 241 MHz. A3667 is one of the best known examples of a galaxy cluster hosting a double radio relic and has been reported to contain a faint radio halo and bridge. The origins of radio halos, relics and bridges is still unclear, however galaxy cluster mergers seems to be an important factor. We clearly detect the North-West (NW) and South-East (SE) radio relics in A3667 and find an integrated flux density at 149 MHz of 28.1 +/- 1.7 and 2.4 +/- 0.1 Jy, respectively, with an average spectral index, between 120 and 1400 MHz, of -0.9 +/- 0.1 for both relics. We find evidence of a spatial variation in the spectral index across the NW relic steepening towards the centre of the cluster, which indicates an ageing electron population. These properties are consistent with higher frequency observations. We detect emission that could be associated with a radio halo and bridge. How- ever, due to the presence of poorly sampled large-scale Galactic emission and blended point sources we are unable to verify the exact nature of these features.

Published
2014

26. Observing the Sun with the Murchison Widefield Array

Author

Oberoi, D, Sharma, R, Bhatnagar, S, Lonsdale, CJ, Matthews, LD, Cairns, IH, Tingay, SJ, Benkevitch, L, Donea, A, White, SM, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Corey, BE, Deshpande, A, Emrich, D, Gaensler, BM, Goeke, R, Greenhill, LJ, Hazelton, BJ, Johnston-Hollitt, M, Kaplan, DL, Kasper, JC, Kratzenberg, E, Lynch, MJ, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Offringa, AR, Ord, SM, Prabu, T, Rogers, AEE, Roshi, A, Salah, JE, Shankar, NU, Srivani, KS, Subrahmanyan, R, Waterson, M, Wayth, RB, Webster, RL, Whitney, AR, William, A, Williams, CL, Oberoi, D, Sharma, R, Bhatnagar, S, Lonsdale, CJ, Matthews, LD, Cairns, IH, Tingay, SJ, Benkevitch, L, Donea, A, White, SM, Bernardi, G, Bowman, JD, Briggs, F, Cappallo, RJ, Corey, BE, Deshpande, A, Emrich, D, Gaensler, BM, Goeke, R, Greenhill, LJ, Hazelton, BJ, Johnston-Hollitt, M, Kaplan, DL, Kasper, JC, Kratzenberg, E, Lynch, MJ, McWhirter, SR, Mitchell, DA, Morales, MF, Morgan, E, Offringa, AR, Ord, SM, Prabu, T, Rogers, AEE, Roshi, A, Salah, JE, Shankar, NU, Srivani, KS, Subrahmanyan, R, Waterson, M, Wayth, RB, Webster, RL, Whitney, AR, William, A, and Williams, CL

Published
2014

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