Publications/Technical reports



Publications/Technical Reports

  1. Direction Dependent Corrections in Polarimetric Radio Imaging II: A-Solver Methodology A low-order solver for the A-Term of the A-Projection algorithm, Preshanth Jagannathan, S. Bhatnagar, W. Brisken, A.R. Taylor, 2017, AJ (accepted) [arXiv:1711.00875 [astro-ph]]
  2. The Pointing Self Calibration algorithm for aperture synthesis radio telescopes, S. Bhatnagar and T. J. Cornwell, 2017, AJ, Vol. 154, Number 5 [arXiv:1709.08681 [astro-ph]]
  3. Direction Dependent Corrections in Polarimetric Radio Imaging I : Characterizing the effects of the primary beam on full Stokes imaging , P. Jagannathan, S. Bhatnagar, U. Rau, A. R. Taylor, 2017, AJ (accepted) [arXiv:1706.01501 [astro-ph]]
  4. Deep wideband single pointings and mosaics in radio interferometry - How accurately do we reconstruct intensities and spectral indices of faint sources? , Urvashi Rau, Sanjay Bhatnagar, Frazer N. Owen, 2016, Astronomical Journal, Volume 152, No. 5, October 2016 [arXiv:1605.07640 [astro-ph]]
  5. CASA Imager Parallelization: Measurement and Analysis of Runtime Performance for Continuum Imaging , S. Bhatnagar and The CASA HPC Team, March, 2015
  6. Wide-field wide-band interferometric imaging:The WB A-Projection and hybrid algorithms , S. Bhatnagar, U. Rau and K. Golap, 2013, ApJ (2013,Vol.770, No. 2, 91) [arXiv:1304.4987 [astro-ph]]
  7. Applying full polarization A-Projection to very wide field of view instruments: An imager for LOFAR , C. Tasse, B. van der Tol, J. van Zwieten, Ger van Diepen, S. Bhatnagar, 2012, A&A (in press)
  8. Algorithms Research and Development: Status & Plan, S. Bhatnagar
  9. EVLA Observations of Galactic Supernova Remnants: Wide-field Continuum and Spectral-index Imaging, S. Bhatnagar, U. Rau, D. A. Green, M. P. Rupen, (2011, ApJ, 739, L20 [arXiv:1106.2796v2 [astro-ph]])
  10. Detection of Signals from Cosmic Re-ionization using Radio Interferometric Signal Processing, A. Datta, S. Bhatnagar and C.L. Carilli, (2009, ApJ 703 1851-1862).
  11. Calibration and imaging challenges at low radio frequencies: An overview of the state of the art, S. Bhatnagar, ASP Conference Series, Eds: D.J. Saikia, Dave Green, Y. Gupta and Tiziana Venturi, Vol. 407, 2009
  12. Advances in Calibration and Imaging Techniques in Radio Interferometry, Rau, U.; Bhatnagar, S.; Voronkov, M.A.; Cornwell, T.J., Proc. IEEE, Vol. 97, No. 8, Aug.2009, 1472
  13. Technolog development for computational radio astronomy:2010-2020, Athol Kemball (Univ. of Illinois), James Cordes (Cornell Univ.), Joseph Lazio (NRL), Don Backer (Univ. of California, Berkeley), Geoff Bower (Univ. of California, Berkeley), Sanjay Bhatnagar (NRAO) and Ray Plante (Univ. of Illinois).
  14. Plan for Imaging Algorithm Research and Development, S. Bhatnagar, EVLA Memo #139, July 05, 2009 (Submitted Nov. 04, 2009).
  15. Parallelization of the off-line data processing operations using CASA, S. Bhatnagar, H. Ye and D. Schiebel, EVLA Memo #133, May 18, 2009.
  16. Report on the findings of the CASA Terabyte Initiative: Single-node tests, S. Bhatnagar, EVLA Memo #132, May 18, 2009.
  17. NRAO Lab Notebook: Imaging & Calibration Algorithm Research at the NRAO, A contributed article for the NRAO eNews Letter, Oct. 17, 2008.
  18. The non-coplanar baselines effect in radio interferometry: The W-Projection algorithm, T.J. Cornwell, K. Golap and S. Bhatnagar, IEEE Journal of Selected Topics in Signal Processing, 2008 (in press)
  19. Correcting direction-dependent gains in the deconvolution of radio interferometric images, S.Bhatnagar, T.J.Cornwell, K.Golap, & J. M. Uson, A&A 487, 419-429 (2008) [arXiv:0805.0834v2 [astro-ph]]
  20. Corrections of errors due to antenna power patterns during imaging, S.Bhatnagar, T.J.Cornwell, & K.Golap, EVLA Memo 100, Feb. 23, 2006.[Postscript version] [PDF version]
  21. Imaging and calibration in the presence of image plane errors, S.Bhatnagar, T.J.Cornwell, & K.Golap, Proc. URSI General Assembly Meeting, New Delhi, Oct 23-27, 2005.
  22. Re-factoring of the calibrater related classes, S.Bhatnagar & G.Moellenbrock, AIPS++ Memo, Oct. 2004.

  23. Imaging with Aperture Synthesis Radio Telescopes in the presence of direction dependent effects, S. Bhatnagar, T.J. Cornwell and K. Golap, Proceeding of the Signal Recovery and Synthesis topical meeting of the Optical Society of America, Charlotte, NC, 5-8June 2005.
  24. RFI excision in synthesis imaging without a reference signal, T. J. Cornwell, R. A. Perley, K. Golap and S. Bhatnagar, Dec. 2004, EVLA Memo 87

  25. Solving for the antenna based pointing errors, S. Bhatnagar, T.J. Cornwell and K. Golap, Oct. 18, 2004, EVLA Memo 84

  26. W Projection: A New Algorithm for Non-Coplanar BaselinesT. J. Cornwell, K. Golap, S. Bhatnagar, Dec. 2003, EVLA Memo 67

  27. Radio and near-infrared observations of the steep spectrum Galactic plane radio source WKB 0314+57.8, D.A.Green, M.Lacy, S.Bhatnagar, E.L.Gates, and P.J.Warner, MNRAS, 1159, Vol. 354, N0. 4, 2004.

  28. Scale sensitive deconvolution of astronomical images: I-Adaptive Scale Pixel (Asp) model, S.Bhatnagar & T.J.Corwnell, A&A, 426, 747-754, 2004 (astro-ph/0407225).

  29. The late time radio emission from SN 1993J at meter wavelengths, Chandra, P., Ray, A., & Bhatnagar, S., scheduled for ApJ 10 September 2004, v612 issue.

  30. Synchrotron aging and the radio spectrum of SN 1993J, Chandra, P., Ray, A., & Bhatnagar, S., ApJ. 604 (2004) L97-L100.

  31. Scale sensitive deconvolution, Bhatnagar S., Cornwell T.J., Astronomical Data Analysis Software and Systems Meeting, Strasbourg, France, 2003.

  32. Scale sensitive deconvolution of astronomical images, Bhatnagar S., Cornwell, T.J., SPIE Annual Conference, San Diego, 2003.

  33. Procedure to extend the uv-limits of potential GMRT phase calibraters, Gupta Neeraj and Bhatnagar S., NCRA Tech. Report #RO0203, 2003.[HTML]

    A report on the pilot project done to produce image plane models of moderately resolved phase calibraters. The report also discusses an automated pipe-line for use in a larger such project.

  34. Evolution of imager performance, Bhatnagar S., AIPS++ Internal memo, 2003.

    A progress report on the improvements in the run-time performance of AIPS++ imager tool.

  35. Evolution of imager performance: Gridding optimization, Bhatnagar S., AIPS++ Internal memo, 2003.

    A report on the investigations for the improvements of full Stokes imaging in AIPS++.

  36. Benchmarking in AIPS++, Bhatnagar S., AIPS++ Note No. 258, 2003.

    A note on the general procedure used for benchmarking in AIPS++. In particular it was used for the identification of performance and algorithmic improvements for calibration and imaging tools in AIPS++.

  37. Solving for polarization leakage in radio interferometers using unpolarized source, Bhatnagar S., Urvashi R. V:, Nityananda R., ADASS, XII ASP Conf. Series, Vol 295, p-469, 2003.

  38. Supernova 2002hh in NGC 6946, Chandra, P., Ray, A.K., and Bhatnagar, S., IAU Circular 8041, 2(2003).

  39. The nature of the prompt X-ray and radio emission from SN2002ap, F. K. Sutaria, P. Chandra, S. Bhatnagar,A. Ray,A&A, Vol. 397, p 1011-1018, 2003.

  40. 327-MHz Giant Metrewave Radio Telescope observations of one candidate and three Galactic supernova remnants, Bhatnagar.S, 2002, MNRAS, 332.

  41. Radio Studies of Young Core Collapse Supernovae, Poonam Chandra (Tata Inst., Mumbai, India), Alak Ray (Tata Inst.), Sanjay Bhatnagar (NRAO, Socorro, NM, USA), Bull. Astron. Soc. India, 30, 755-758 (2002).

  42. Supernova 2001gd in NGC 5003, Chandra, P., Bhatnagar, S., and Ray, A.K, IAU Circular 7982, 2(2002).

  43. Supernova 200lg in NGC 7424, Chandra, P., Ray, A.K., and Bhatnagar, S.,IAU Circular 7994, 2 (2002) .

  44. Solving for closure errors due to polarization leakage in radio interferometry of unpolarized sources, Bhatnagar, S., Nityananda, A&A, v.375, p.344-350 (2001).

  45. Supernovae 1993J and 1979C, Chandra, P.; Bhatnagar, S.; Ray, A. 2001IAUC. 7657 2C.

  46. Confirmation of three candidate Galactic Supernova Remnants from GMRT observations, Bhatnagar S., MNRAS, 317, 453 (2000).

  47. Astronomical calibration of the GMRT antenna positions, Chengalur, J. N. and Bhatnagar, S., NCRA Tech. Report #ROOI78, 2001.

    A repeat of the work reported in NCRA Tech. Report (Baseline and Delay Calibration, Bhatnagar and Rao, 1996; and Ph.D. Thesis, Bhatnagar, S., Chapter 2).

  48. Deep imaging of Supernova Remnants at low frequency, Bhatnagar S., The Universe at Low Radio Frequencies, Proceedings ofIAU Symposium 199, held 30 Nov 4 Dec 1999, Pune, India. Edited by A. Pramesh Rao, G. Swarup, and Gopal-Krishna, 2002., p.307.

  49. Supernova Remnants: GMRT based results, Bhatnagar S., Invited talk at the Annual Meeting of the Astronomical Society of India, Bulletin of the Astronomical Society of India, Vol. 29, p. 277-281.

  50. HE 1127-1304: the largest radio quasar, Bhatnagar, S., Gopal-Krishna, Wistozki, L.; MNRAS, 299, L25-L28, 1998.

  51. Computation Of Antenna Dependent Complex Gains, S. Bhatnagar, NCRA Tech. Report #ROOl72 (1998). [PDF Version]

    Formulation and implementation of a robust algorithm for antenna based complex gain and bandpass calibration.

  52. xtract: A Flexible Data Extraction Program, S. Bhatnagar,NCRA Tech. Report #ROOl71 (1997).

    A programmable application for off-line and on-line extracting and displaying data recorded in the GMRT native data recording format.

  53. The User Interface Libraries, S. Bhatnagar,NCRA Tech. Report #00173 (1997).

    A description of the user interface libraries used in off-line/quasi on-line software.

  54. Tips for programming with GMRT off-line software, S. Bhatnagar,NCRA Tech. Report #ROO189 (1997).

    A astronomical programmers guide for developing off-line data analysis applications.

  55. The FFTMac data structure, S. Bhatnagar,NCRA Tech. Report #ROO188 (1997).

    The description of the data structure/Object which defines the mapping of the hardware (FFT and MAC cards) in the off-line software libraries for the GMRT correlator.

  56. Tools for Handling GMRT Native Data Recording Format, S. Bhatnagar, NCRA Tech. Report #ROOl87 (1997).

    Complete technical description of the suite of libraries to manipulate the GMRT native data recording file format.

  57. Tools for off-line applications, S. Bhatnagar,NCRA Tech. Report (1997).

    A astro-programmer oriented description of the off-line software system.

  58. Baseline and Delay Calibration, S. Bhatnagar andA.P.Rao, NCRA Tech. Report(1996).

    Procedure used for the baseline and fixed delay calibration for the GMRT and the results.

  59. The Sub-array controller, S. Bhatnagar and A.P.Rao, NCRA Tech. Report(1995).

    A description of the state machine implemented in the GMRT On-line system for antenna pointing and tracking.

  60. Software Environment for Parallel Processing: Implementation of the Clean algorithm, S. Bhatnagar, NCRA Tech. Report #090204 (1993).

    Description of the software environment for implementing parallelized data analysis algorithms. The Clean algorithm was implement as an example. The resulting speed up and the performance bottlenecks are also discussed.

  61. Exotic imaging methods: A guide for masochistic AIPS++ Designers, Holdaway, M. A. and Bhatnagar, S., Tech. Report #090220, 1992

  62. The imaging model design, Bhatnagar, S., Holdaway, M. A., Tech. Report #090221 1992.

  63. Timing evaluation of the C-DOT Parallel Processing Machine, S. Bhatnagar, NCRA Tech. Report #090233 (1992).

Sanjay Bhatnagar 2005-06-29