J/MNRAS/544/321 uGMRT Observations for HERA Calibration (Elahi+, 2025)
Deep uGMRT observations for enhanced calibration of 21cm arrays.
I. First image and source catalogue.
Elahi K.M.A., Choudhuri S., Roy N., Rashid M., Bull P., Vir Lal D.
<Mon. Not. R. Astron. Soc. 544, 321-342 (2025)>
=2025MNRAS.544..321E 2025MNRAS.544..321E (SIMBAD/NED BibCode)
ADC_Keywords: Surveys ; Radio continuum ; Galaxy catalogs ; Radio sources
Keywords: instrumentation: interferometers -
methods: data analysis, dark ages, reionization, first stars -
radio continuum: general
Abstract:
Radio-interferometric arrays require very precise calibration to
detect the Epoch of Reionization 21-cm signal. A remarkably complete
and accurate sky model is therefore needed in the patches of the sky
used to perform the calibration. Instruments such as HERA, which use a
redundant calibration strategy, also require a reference sky model to
fix degenerate gain solutions.
We have carried out a deep (20 hours) observation using the upgraded
GMRT to make a high-fidelity sky model of one of the HERA calibration
fields, GLEAM 02H (J0200-3053). In this paper, we present the results
from a 16.7MHz bandwidth dataset centred at 147.4MHz. Multiple GMRT
pointings are combined to make a 6.9degx6.9deg mosaic, yielding a
median rms of 3.9+3.7-1.4mJy/beam, which reduces to approximately
2mJy/beam in source-free regions. In the overlapping patch, this rms
is deeper than the GLEAM catalogue, which is used for HERA
calibration.
Using the mosaic, we have made a catalogue of 640 sources (26%
extended) with flux densities in the range 0.02-19.08Jy. The catalogue
has sub-arcsecond positional accuracy, and the estimated fluxes are
consistent with existing catalogues. The differential source counts
are deeper than GLEAM and consistent with LoTSS. A preliminary
simulation comparing the sky models from GLEAM and our catalogue shows
10-25% differences in the visibility amplitude, with a relatively
small change of approximately 2 degrees in phases. Future work is
planned for larger survey areas and wider bandwidths to reduce the rms
and measure in-band source spectral indices, which are expected to
enhance the fidelity of the HERA calibration model.
Description:
A catalogue of 640 sources in a 6.9degx6.9deg patch of sky around
the HERA calibration source PKS 0157-31 at LST 02H.
The analysis pipeline can be found here:
https://github.com/aecosmo/RADIOcat
Objects:
---------------------------------------------------------
RA (2000) DE Designation(s)
---------------------------------------------------------
02 00 12.17 -30 53 26.6 PKS 0157-31 = MRC 0157-311
---------------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
gmrt2hss.dat 730 640 uGMRT 147 MHz catalogue around PKS 0157-31
list.dat 109 1 Information on fits image
fits/* . 1 fits image
--------------------------------------------------------------------------------
Byte-by-byte Description of file: gmrt2hss.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- Source Source identification number
(Source_id)
5- 7 I3 --- Isl Island identification number (Isl_id)
9- 23 F15.11 deg RAdeg Right Ascension (J2000) (RA)
25- 36 E12.6 deg e_RAdeg Uncertainty in RA (E_RA)
38- 52 F15.11 deg DEdeg Declination (J2000) (DEC)
54- 65 E12.6 deg e_DEdeg Uncertainty in DEC (E_DEC)
67- 84 F18.15 Jy FluxTot Integrated flux density at 147MHz
(Total_flux)
86-102 F17.15 Jy e_FluxTot Error in integrated flux density
at 147MHz (ETotalflux)
104-121 F18.15 Jy/beam FluxP Peak flux density at 147MHz
(Peak_flux)
123-139 F17.15 Jy/beam e_FluxP Error in peak flux density at 147MHz
(EPeakflux)
141-155 F15.11 deg RAMdeg Right Ascension (J2000) of maximum
pixel (RA_max)
157-168 E12.6 deg e_RAMdeg Error in RA_max (ERAmax)
170-184 F15.11 deg DEMdeg Declination (J2000) of maximum pixel
(DEC_max)
186-197 E12.6 deg e_DEMdeg Error in DEC_max (EDECmax)
199-215 F17.15 deg Maj Fitted major axis (deconvolved) (Maj)
217-233 F17.15 deg e_Maj Error in major axis (E_Maj)
235-251 F17.15 deg Min Fitted minor axis (deconvolved) (Min)
253-269 F17.15 deg e_Min Error in minor axis (E_Min)
271-289 F19.15 deg PA Position angle (deconvolved) (PA)
291-308 F18.15 deg e_PA Error in position angle (E_PA)
310-326 F17.15 deg Majimgplane Fitted major axis (image plane)
(Majimgplane)
328-344 F17.15 deg e_Majimgplane Error in major axis (image plane)
(EMajimg_plane)
346-362 F17.15 deg Minimgplane Fitted minor axis (image plane)
(Minimgplane)
364-380 F17.15 deg e_Minimgplane Error in minor axis (image plane)
(EMinimg_plane)
382-400 F19.15 deg PAimgplane Position angle (image plane)
(PAimgplane)
402-419 F18.15 deg e_PAimgplane Error in PA (image plane)
(EPAimg_plane)
421-437 F17.15 deg DCMaj ?=0 Deconvolved major axis (corrected)
(DC_Maj)
439-460 D22.15 deg e_DCMaj ?=0 Error in DC_Maj (EDCMaj)
462-478 F17.15 deg DCMin ?=0 Deconvolved minor axis (corrected)
(DC_Min)
480-482 F3.1 deg e_DCMin ?=0 Error in DC_Min (EDCMin)
484-502 F19.15 deg DCPA ?=0 Deconvolved position angle (DC_PA)
504-506 F3.1 deg e_DCPA ?=0 Error in DC_PA (EDCPA)
508-524 F17.15 deg DCMajimgplane ?=0 Deconvolved major axis
(image plane) (DCMajimg_plane)
526-542 F17.15 deg e_DCMajimgplane ?=0 Error in DCMajimg_plane
(EDCMajimgplane)
544-560 F17.15 deg DCMinimgplane ?=0 Deconvolved minor axis
(image plane) (DCMinimg_plane)
562-578 F17.15 deg e_DCMinimgplane ?=0 Error in DCMinimg_plane
(EDCMinimgplane)
580-598 F19.15 deg DCPAimgplane ?=0 Deconvolved PA (image plane)
(DCPAimg_plane)
600-617 F18.15 deg e_DCPAimgplane ?=0 Error in DCPAimg_plane
(EDCPAimgplane)
619-636 F18.15 Jy FluxIsl Island total flux density at 147MHz
(IslTotalflux)
638-654 F17.15 Jy e_FluxIsl Error in island total flux at 147MHz
(EIslTotal_flux)
656-672 F17.15 Jy/beam Islrms Local rms in the island (Isl_rms)
674-691 F18.15 Jy/beam Islmean Mean flux in the island (Isl_mean)
693-709 F17.15 Jy/beam ResidIslrms Residual rms in the island at 147MHz
(ResidIslrms)
711-728 F18.15 Jy/beam ResidIslmean Residual mean in the island at 147MHz
(ResidIslmean)
730 A1 --- SCode [CMS] S_Code (1)
--------------------------------------------------------------------------------
Note (1): S code as follows:
S = fit with a single Gaussian
M = fit with multiple Gaussians
C = one of multiple sources on the same island)
-------------------------------------------------------------------------------
Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 23 I4 --- Nx Number of pixels along X-axis
25- 28 I4 --- Ny Number of pixels along Y-axis
30- 39 A10 "datime" Obs.date Observation date
41- 47 F7.3 MHz Freq Observed frequency
49- 54 I6 Kibyte size Size of FITS file
56- 72 A17 --- FileName Name of FITS file, in subdirectory fits
74-109 A36 --- Title Title of the FITS file
--------------------------------------------------------------------------------
History:
Khandakar md Asif Elahi, asifelahi999(at)gmail.com
ORCID: 0000-0003-1206-8689
(End) Khandakar Md Asif Elahi [IIT Madras], Patricia Vannier [CDS] 09-Oct-2025