The GMRT Search for Reionization

Pen, Ue-Li; Chang, Tzu-Ching; Peterson, Jeff B.; Roy, Jayanta; Gupta, Yashwant; Bandura, Kevin; Minchin, Robert; Momjian, Emmanuel

doi:10.1063/1.2973618

Cited by 7 publications

(8 citation statements)

References 1 publication

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“…for any function g. Combining equation (3) with equation (6) implies that the correlation between two measurements, traditionally referred to as a visibility, has the expectation value…”

Section: A Interferometry Without the Flat Sky Approximationmentioning

confidence: 99%

“…This number can be compared with the number of modes measured to date with various other techniques such as galaxy surveys, the CMB, etc. In figure 7, we show the number of modes measured by past surveys and some planned probes including 21 cm experiments 6 . The figure illustrates a trend akin to Moore's law: exponential progress as a function of year.…”

Section: The Sensitivity Frontiermentioning

confidence: 99%

“…For the emerging field of 21 cm tomography, which holds the potential to one day overtake the microwave background as our most sensitive cosmological probe [18][19][20][21][22][23][24], the challenge is completely different: it involves mapping a faint and diffuse cosmic signal that covers all of the sky and needs to be separated from foreground contamination that is many orders of magnitude brighter, requiring extreme sensitivity and beam control. This 21cm science application and the major efforts devoted to it by experiments such as MWA [1], LOFAR [2], PAPER [4], 21CMA [3], GMRT [5,6] and SKA [7] makes our paper timely.…”

Section: Introductionmentioning

confidence: 99%

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Fast Fourier transform telescope

2009

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We propose an all-digital telescope for 21 cm tomography, which combines key advantages of both single dishes and interferometers. The electric field is digitized by antennas on a rectangular grid, after which a series of Fast Fourier Transforms recovers simultaneous multifrequency images of up to half the sky. Thanks to Moore's law, the bandwidth up to which this is feasible has now reached about 1 GHz, and will likely continue doubling every couple of years. The main advantages over a single dish telescope are cost and orders of magnitude larger field-of-view, translating into dramatically better sensitivity for large-area surveys. The key advantages over traditional interferometers are cost (the correlator computational cost for an N -element array scales as N log 2 N rather than N 2 ) and a compact synthesized beam. We argue that 21 cm tomography could be an ideal first application of a very large Fast Fourier Transform Telescope, which would provide both massive sensitivity improvements per dollar and mitigate the off-beam point source foreground problem with its clean beam. Another potentially interesting application is cosmic microwave background polarization.

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“…for any function g. Combining equation (3) with equation (6) implies that the correlation between two measurements, traditionally referred to as a visibility, has the expectation value…”

Section: A Interferometry Without the Flat Sky Approximationmentioning

confidence: 99%

Section: The Sensitivity Frontiermentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Fast Fourier transform telescope

2009

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“…Some of the limitations are: (i) high-speed sampling techniques have higher measurement noise and hence are less capable of identifying weak but constantly present RFI, (ii) the requirement of clean reference areas to identify RFI (iii) the necessity of specialised hardware. A different class of techniques have used eigen decompositions of the correlation matrices to isolate and excise RFI in interferometry (Lesham et al 2000;Kocz 2004;Boonstra & van der Tol 2005;Pen et al 2008). The reader is refered to the proceedings of the RFI2004 workshop in Radio Science 2005, vol 40, and URSI 2008, Chicago, for a compendium of RFI-related literature).…”

Section: Introductionmentioning

confidence: 99%

A New Approach to Mitigation of Radio Frequency Interference in Interferometric Data

Athreya

2009

ApJ

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Radio frequency interference (RFI) is the principal factor limiting the sensitivities of radio telescopes, particularly at frequencies below 1 GHz. I present a conceptually new approach to mitigation of RFI in interferometric data. This has been used to develop a software tool (RfiX) to remove RFI from observations using the Giant Metrewave Radio Telescope, India. However, the concept can be used to excise RFI in any interferometer. Briefly, the fringe-stopped correlator output of an interferometer baseline oscillates with the fringe-stop period in the presence of RFI. RfiX works by identifying such a pattern and subtracting it from the data. It is perhaps the only purely software technique which can salvage the true visibility value from RFI-corrupted data. It neither requires high-speed hardware nor real-time processing and works best on normal correlator output integrated for 1-10s. It complements other mitigation schemes with its different approach and the regime it addresses. Its ability to work with data integrated over many seconds gives it an advantage while excising weak, persistent RFI unlike most other techniques which use high-speed sampling to localise RFI in time-frequency plane. RfiX is also different in that it does not require RFI-free data to identify corrupted sections. Some results from the application of RfiX is presented including an image at 240 MHz with a Peak/noise ratio of 43000, the highest till date at wavelengths > 1m.

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“…Several experiments aimed at detecting and characterizing this radiation are currently in progress or under construction (MWA, 1 PAPER, 2 LOFAR, 3 GMRT (Pen et al 2008)). The EOR signal is also one of the main science targets of next-generation radio facilities such as the SKA.…”

Section: Introductionmentioning

confidence: 99%

Subtraction of Bright Point Sources from Synthesis Images of the Epoch of Reionization

Pindor

Wyithe

Mitchell

et al. 2011

Publ. – Astron. Soc. Aust

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Bright point sources associated with extragalactic active galactic nuclei and radio galaxies are an important foreground for low-frequency radio experiments aimed at detecting the redshifted 21-cm emission from neutral hydrogen during the epoch of reionization. The frequency dependence of the synthesized beam implies that the sidelobes of these sources will move across the field of view as a function of observing frequency, hence frustrating line-of-sight foreground subtraction techniques. We describe a method for subtracting these point sources from dirty maps produced by an instrument such as the MWA. This technique combines matched filters with an iterative centroiding scheme to locate and characterize point sources in the presence of a diffuse background. Simulations show that this technique can improve the dynamic range of epoch-of-reionization maps by 2-3 orders of magnitude.

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The GMRT Search for Reionization

Cited by 7 publications

References 1 publication

Fast Fourier transform telescope

Fast Fourier transform telescope

A New Approach to Mitigation of Radio Frequency Interference in Interferometric Data

Subtraction of Bright Point Sources from Synthesis Images of the Epoch of Reionization

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