Imperial College London

DrEmmaChapman

Faculty of Natural SciencesDepartment of Physics

Royal Society Dorothy Hodgkin Fellow
 
 
 
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Contact

 

+44 (0)20 7594 5968e.chapman Website

 
 
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Location

 

1008Blackett LaboratorySouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

22 results found

Hothi I, Chapman E, Pritchard JR, Mertens FG, Koopmans LVE, Ciardi B, Gehlot BK, Ghara R, Ghosh A, Giri SK, Iliev IT, Jelic V, Zaroubi Set al., 2021, Comparing foreground removal techniques for recovery of the LOFAR-EoR 21 cm power spectrum, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 500, Pages: 2264-2277, ISSN: 0035-8711

Journal article

Mertens FG, Mevius M, Koopmans LVE, Offringa AR, Mellema G, Zaroubi S, Brentjens MA, Gan H, Gehlot BK, Pandey VN, Sardarabadi AM, Vedantham HK, Yatawatta S, Asad KMB, Ciardi B, Chapman E, Gazagnes S, Ghara R, Ghosh A, Giri SK, Iliev IT, Jelic V, Kooistra R, Mondal R, Schaye J, Silva MBet al., 2020, Improved upper limits on the 21 cm signal power spectrum of neutral hydrogen at z approximate to 9.1 from LOFAR, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 493, Pages: 1662-1685, ISSN: 0035-8711

Journal article

Ghara R, Giri SK, Mellema G, Ciardi B, Zaroubi S, Iliev IT, Koopmans LVE, Chapman E, Gazagnes S, Gehlot BK, Ghosh A, Jelic V, Mertens FG, Mondal R, Schaye J, Silva MB, Asad KMB, Kooistra R, Mevius M, Offringa AR, Pandey VN, Yatawatta Set al., 2020, Constraining the intergalactic medium at z approximate to 9.1 using LOFAR Epoch of Reionization observations, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 493, Pages: 4728-4747, ISSN: 0035-8711

Journal article

Patil AH, Yatawatta S, Koopmans LVE, de Bruyn AG, Brentjens MA, Zaroubi S, Asad KMB, Hatef M, Jelić V, Mevius M, Offringa AR, Pandey VN, Vedantham H, Abdalla FB, Brouw WN, Chapman E, Ciardi B, Gehlot BK, Ghosh A, Harker G, Iliev IT, Kakiichi K, Majumdar S, Mellema G, Silva MB, Schaye J, Vrbanec D, Wijnholds SJet al., 2017, Upper limits on the 21 cm epoch of reionization power spectrum from one night with LOFAR, Astrophysical Journal, Vol: 838, ISSN: 1538-4357

We present the first limits on the Epoch of Reionization 21 cm H i power spectra, in the redshift range z = 7.9–10.6, using the Low-Frequency Array (LOFAR) High-Band Antenna (HBA). In total, 13.0 hr of data were used from observations centered on the North Celestial Pole. After subtraction of the sky model and the noise bias, we detect a non-zero ${{\rm{\Delta }}}_{{\rm{I}}}^{2}={(56\pm 13\mathrm{mK})}^{2}$ (1-σ) excess variance and a best 2-σ upper limit of ${{\rm{\Delta }}}_{21}^{2}\lt {(79.6\mathrm{mK})}^{2}$ at k = 0.053 h cMpc−1 in the range z = 9.6–10.6. The excess variance decreases when optimizing the smoothness of the direction- and frequency-dependent gain calibration, and with increasing the completeness of the sky model. It is likely caused by (i) residual side-lobe noise on calibration baselines, (ii) leverage due to nonlinear effects, (iii) noise and ionosphere-induced gain errors, or a combination thereof. Further analyses of the excess variance will be discussed in forthcoming publications.

Journal article

Mevius M, van der Tol S, Pandey VN, Vedantham HK, Brentjens MA, de Bruyn AG, Abdalla FB, Asad KMB, Bregman JD, Brouw WN, Bus S, Chapman E, Ciardi B, Fernandez ER, Ghosh A, Harker G, Iliev IT, Jelic V, Kazemi S, Koopmans LVE, Noordam JE, Offringa AR, Patil AH, van Weeren RJ, Wijnholds S, Yatawatta S, Zaroubi Set al., 2016, Probing ionospheric structures using the LOFAR radio telescope, RADIO SCIENCE, Vol: 51, Pages: 927-941, ISSN: 0048-6604

Journal article

Chapman E, Zaroubi S, Abdalla FB, Dulwich F, Jelic V, Mort Bet al., 2016, The effect of foreground mitigation strategy on EoR window recovery, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 458, Pages: 2928-2939, ISSN: 0035-8711

Journal article

Majumdar S, Jensen H, Mellema G, Chapman E, Abdalla FB, Lee K-Y, Iliev IT, Dixon KL, Datta KK, Ciardi B, Fernandez ER, Jelić V, Koopmans LVE, Zaroubi Set al., 2016, Effects of the sources of reionization on 21-cm redshift-space distortions, \mnras, Vol: 456, Pages: 2080-2094

Journal article

Jelic V, de Bruyn AG, Pandey VN, Mevius M, Haverkorn M, Brentjens MA, Koopmans LVE, Zaroubi S, Abdalla FB, Asad KMB, Bus S, Chapman E, Ciardi B, Fernandez ER, Ghosh A, Harker G, Iliev IT, Jensen H, Kazemi S, Mellema G, Offringa AR, Patil AH, Vedantham HK, Yatawatta Set al., 2015, Linear polarization structures in LOFAR observations of the interstellar medium in the 3C 196 field, ASTRONOMY & ASTROPHYSICS, Vol: 583, ISSN: 1432-0746

Journal article

Ciardi B, Inoue S, Abdalla FB, Asad K, Bernardi G, Bolton JS, Brentjens M, de Bruyn AG, Chapman E, Daiboo S, Fernandez ER, Ghosh A, Graziani L, Harker GJA, Iliev IT, Jelic V, Jensen H, Kazemi S, Koopmans LVE, Martinez O, Maselli A, Mellema G, Offringa AR, Pandey VN, Schaye J, Thomas R, Vedantham H, Yatawatta S, Zaroubi Set al., 2015, Simulating the 21 cm forest detectable with LOFAR and SKA in the spectra of high-z GRBs, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 453, Pages: 101-105, ISSN: 0035-8711

Journal article

Ghosh A, Koopmans LVE, Chapman E, Jelic Vet al., 2015, A Bayesian analysis of redshifted 21-cm H I signal and foregrounds: simulations for LOFAR, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 452, Pages: 1587-1600, ISSN: 0035-8711

Journal article

Asad KMB, Koopmans LVE, Jelic V, Pandey VN, Ghosh A, Abdalla FB, Bernardi G, Brentjens MA, de Bruyn AG, Bus S, Ciardi B, Chapman E, Daiboo S, Fernandez ER, Harker G, Iliev IT, Jensen H, Martinez-Rubi O, Mellema G, Mevius M, Offringa AR, Patil AH, Schaye J, Thomas RM, van der Tol S, Vedantham HK, Yatawatta S, Zaroubi Set al., 2015, Polarization leakage in epoch of reionization windows - I. Low Frequency Array observations of the 3C196 field, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 451, Pages: 3709-3727, ISSN: 0035-8711

Journal article

Vedantham HK, Koopmans LVE, de Bruyn AG, Wijnholds SJ, Brentjens M, Abdalla FB, Asad KMB, Bernardi G, Bus S, Chapman E, Ciardi B, Daiboo S, Fernandez ER, Ghosh A, Harker G, Jelic V, Jensen H, Kazemi S, Lambropoulos P, Martinez-Rubi O, Mellema G, Mevius M, Offringa AR, Pandey VN, Patil AH, Thomas RM, Veligatla V, Yatawatta S, Zaroubi S, Anderson J, Asgekar A, Bell ME, Bentum MJ, Best P, Bonafede A, Breitling F, Broderick J, Bruggen M, Butcher HR, Corstanje A, de Gasperin F, de Geus E, Deller A, Duscha S, Eisloeffel J, Engels D, Falcke H, Fallows RA, Fender R, Ferrari C, Frieswijk W, Garrett MA, Griessmeier J, Gunst AW, Hassall TE, Heald G, Hoeft M, Hoerandel J, Iacobelli M, Juette E, Kondratiev VI, Kuniyoshi M, Kuper G, Mann G, Markoff S, McFadden R, McKay-Bukowski D, McKean JP, Mulcahy DD, Munk H, Nelles A, Norden MJ, Orru E, Pandey-Pommier M, Pizzo R, Polatidis AG, Reich W, Renting A, Roettgering H, Schwarz D, Shulevski A, Smirnov O, Stappers BW, Steinmetz M, Swinbank J, Tagger M, Tang Y, Tasse C, ter Veen S, Thoudam S, Toribio C, Vocks C, Wise MW, Wucknitz O, Zarka Pet al., 2015, Lunar occultation of the diffuse radio sky: LOFAR measurements between 35 and 80 MHz, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 450, Pages: 2291-2305, ISSN: 0035-8711

Journal article

Koopmans LVE, Pritchard J, Mellema G, Abdalla F, Aguirre J, Ahn K, Barkana R, van Bemmel I, Bernardi G, Bonaldi A, otherset al., 2015, The cosmic dawn and epoch of reionization with the square kilometre array

Conference paper

Patil AH, Zaroubi S, Chapman E, Jelic V, Harker G, Abdalla FB, Asad KMB, Bernardi G, Brentjens MA, de Bruyn AG, Bus S, Ciardi B, Daiboo S, Fernandez ER, Ghosh A, Jensen H, Kazemi S, Koopmans LVE, Labropoulos P, Mevius M, Martinez O, Mellema G, Offringa AR, Pandey VN, Schaye J, Thomas RM, Vedantham HK, Veligatla V, Wijnholds SJ, Yatawatta Set al., 2014, Constraining the epoch of reionization with the variance statistic: simulations of the LOFAR case, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 443, Pages: 1113-1124, ISSN: 0035-8711

Journal article

Jelic V, de Bruyn AG, Mevius M, Abdalla FB, Asad KMB, Bernardi G, Brentjens MA, Bus S, Chapman E, Ciardi B, Daiboo S, Fernandez ER, Ghosh A, Harker G, Jensen H, Kazemi S, Koopmans LVE, Labropoulos P, Martinez-Rubi O, Mellema G, Offringa AR, Pandey VN, Patil AH, Thomas RM, Vedantham HK, Veligatla V, Yatawatta S, Zaroubi S, Alexov A, Anderson J, Avruch IM, Beck R, Bell ME, Bentum MJ, Best P, Bonafede A, Bregman J, Breitling F, Broderick J, Brouw WN, Brueggen M, Butcher HR, Conway JE, de Gasperin F, de Geus E, Deller A, Dettmar R-J, Duscha S, Eisloeffel J, Engels D, Faleke H, Fallows RA, Fender R, Ferrari C, Frieswijk W, Garrett MA, Griessmeier J, Gunst AW, Hamaker JP, Hassall TE, Haverkorn M, Heald G, Hessels JWT, Hoeft M, Hoerandel J, Horneffer A, van der Horst A, Iacobelli M, Juette E, Karastergiou A, Kondratiev VI, Kramer M, Kuniyoshi M, Kuper G, van Leeuwen J, Maat P, Mann G, McKay-Bakowski D, MeKean JP, Mank H, Nelles A, Morden MJ, Paas H, Pandey-Pornmier M, Pietka G, Pizzo R, Polatidis AG, Reich W, Roettgering H, Rowlinson A, Scaife AMM, Schwarz D, Serylak M, Smirnov O, Steinmetz M, Stewart A, Tagger M, Tang Y, Tasse C, ter Veen S, Thoudam S, Toribio C, Vermeulen R, Voeks C, van Weeren RJ, Wijers RAMJ, Wijnholds SJ, Wucknitz O, Zarka Pet al., 2014, Initial LOFAR observations of epoch of reionization windows II. Diffuse polarized emission in the ELAIS-N1 field, ASTRONOMY & ASTROPHYSICS, Vol: 568, ISSN: 0004-6361

Journal article

Wolz L, Abdalla FB, Blake C, Shaw JR, Chapman E, Rawlings Set al., 2014, The effect of foreground subtraction on cosmological measurements from intensity mapping, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 441, Pages: 3271-3283, ISSN: 0035-8711

Journal article

Jensen H, Datta KK, Mellema G, Chapman E, Abdalla FB, Iliev IT, Mao Y, Santos MG, Shapiro PR, Zaroubi S, Bernardi G, Brentjens MA, de Bruyn AG, Ciardi B, Harker GJA, Jelic V, Kazemi S, Koopmans LVE, Labropoulos P, Martinez O, Offringa AR, Pandey VN, Schaye J, Thomas RM, Veligatla V, Vedantham H, Yatawatta Set al., 2013, Probing reionization with LOFAR using 21-cm redshift space distortions, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 435, Pages: 460-474, ISSN: 0035-8711

Journal article

Chapman E, Abdalla FB, Bobin J, Starck J-L, Harker G, Jelic V, Labropoulos P, Zaroubi S, Brentjens MA, de Bruyn AG, Koopmans VEet al., 2013, The scale of the problem: recovering images of reionization with Generalized Morphological Component Analysis, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 429, Pages: 165-176, ISSN: 0035-8711

Journal article

Yatawatta S, de Bruyn AG, Brentjens MA, Labropoulos P, Pandey VN, Kazemi S, Zaroubi S, Koopmans LVE, Offringa AR, Jelic V, Rubi OM, Veligatla V, Wijnholds SJ, Brouw WN, Bernardi G, Ciardi B, Daiboo S, Harker G, Mellema G, Schaye J, Thomas R, Vedantham H, Chapman E, Abdalla FB, Alexov A, Anderson J, Avruch IM, Batejat F, Bell ME, Bell MR, Bentum M, Best P, Bonafede A, Bregman J, Breitling F, van de Brink RH, Broderick JW, Brueggen M, Conway J, de Gasperin F, de Geus E, Duscha S, Falcke H, Fallows RA, Ferrari C, Frieswijk W, Garrett MA, Griessmeier JM, Gunst AW, Hassall TE, Hessels JWT, Hoeft M, Iacobelli M, Juette E, Karastergiou A, Kondratiev VI, Kramer M, Kuniyoshi M, Kuper G, van Leeuwen J, Maat P, Mann G, McKean JP, Mevius M, Mol JD, Munk H, Nijboer R, Noordam JE, Norden MJ, Orru E, Paas H, Pandey-Pommier M, Pizzo R, Polatidis AG, Reich W, Rottgering HJA, Sluman J, Smirnov O, Stappers B, Steinmetz M, Tagger M, Tang Y, Tasse C, ter Veen S, Vermeulen R, van Weeren RJ, Wise M, Wucknitz O, Zarka Pet al., 2013, Initial deep LOFAR observations of epoch of reionization windows I. The north celestial pole, ASTRONOMY & ASTROPHYSICS, Vol: 550, ISSN: 1432-0746

Journal article

Chapman E, Abdalla FB, Harker G, Jelic V, Labropoulos P, Zaroubi S, Brentjens MA, de Bruyn AG, Koopmans LVEet al., 2012, Foreground removal using fastica: a showcase of LOFAR-EoR, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 423, Pages: 2518-2532, ISSN: 0035-8711

Journal article

Chapman E, Bonaldi A, Harker G, Jelić V, Abdalla FB, Bernardi G, Bobin J, Dulwich F, Mort B, Santos M, Starck J-Let al., Cosmic Dawn and Epoch of Reionization Foreground Removal with the SKA

The exceptional sensitivity of the SKA will allow observations of the CosmicDawn and Epoch of Reionization (CD/EoR) in unprecedented detail, bothspectrally and spatially. This wealth of information is buried under Galacticand extragalactic foregrounds, which must be removed accurately and preciselyin order to reveal the cosmological signal. This problem has been addressedalready for the previous generation of radio telescopes, but the application toSKA is different in many aspects. In this chapter we summarise the contributions to the field of foregroundremoval in the context of high redshift and high sensitivity 21-cmmeasurements. We use a state-of-the-art simulation of the SKA Phase 1observations complete with cosmological signal, foregrounds andfrequency-dependent instrumental effects to test both parametric andnon-parametric foreground removal methods. We compare the recoveredcosmological signal using several different statistics and explore one of themost exciting possibilities with the SKA --- imaging of the ionized bubbles. We find that with current methods it is possible to remove the foregroundswith great accuracy and to get impressive power spectra and images of thecosmological signal. The frequency-dependent PSF of the instrument complicatesthis recovery, so we resort to splitting the observation bandwidth into smallersegments, each of a common resolution. If the foregrounds are allowed a random variation from the smooth power lawalong the line of sight, methods exploiting the smoothness of foregrounds or aparametrization of their behaviour are challenged much more than non-parametricones. However, we show that correction techniques can be implemented to restorethe performances of parametric approaches, as long as the first-orderapproximation of a power law stands.

Journal article

Chapman E, Zaroubi S, Abdalla F, Dulwich F, Jelić V, Mort Bet al., The Effect of Foreground Mitigation Strategy on EoR Window Recovery, MNRAS, Vol: 458

The removal of the Galactic and extragalactic foregrounds remains a majorchallenge for those wishing to make a detection of the Epoch of Reionization21-cm signal. Multiple methods of modelling these foregrounds with varyinglevels of assumption have been trialled and shown promising recoveries onsimulated data. Recently however there has been increased discussion of usingthe expected shape of the foregrounds in Fourier space to define an EoR windowfree of foreground contamination. By carrying out analysis within this windowonly, one can avoid the foregrounds and any statistical bias they mightintroduce by instead removing these foregrounds. In this paper we discuss theadvantages and disadvantages of both foreground removal and foregroundavoidance. We create a series of simulations with noise levels in line withboth current and future experiments and compare the recovered statisticalcosmological signal from foreground avoidance and a simplified, frequencyindependent foreground removal model. We find that while, for currentgeneration experiments, foreground avoidance enables a better recovery at$k_{perp} > 0.6 \mathrm{Mpc}^{-1}$, foreground removal is able to recoversignificantly more signal at small $k_{los}$ for both current and futureexperiments. We also relax the assumption that the foregrounds are smooth byintroducing a Gaussian random factor along the line-of-sight and then alsospatially. We find that both methods perform well for foreground models withline-of-sight and spatial variations around $0.1\%$ however at levels largerthan this foregrounds removal shows a greater signal recovery.

Journal article

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