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GCN Circulars

GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.

Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
Advanced Search

To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.

Advanced Search Examples (click to copy):

subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"

15714 results found.

  1. EP260402a/GRB 260402A: Xinglong optical upper limit
  2. EP260321a: Upper limits from VLA radio observations
  3. EP260321a: uGMRT observations
  4. EP260405a: GMOS-N optical upper limits
  5. EP260405a: SVOM/VT optical upper limits
  6. EP260405a / EP-WXT 11900672904: COLIBRÍ optical upper limits
  7. EP260324A / AT 2026hir: COLIBRÍ further optical observations
  8. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  9. GRB 260330B: SVOM/VT further optical observation
  10. EP260403a: LCO optical observations of the counterpart
  11. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  12. EP260403a: LCO optical counterpart detection
  13. EP260403a: COLIBRÍ optical counterpart candidate
  14. GRB 260330B: SVOM/VT optical candidate
  15. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  16. EP260324A / AT 2026hir: COLIBRÍ optical observations
  17. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  18. GRB 260402A: WINTER J-band upper limit
  19. GRB260402A: GROWTH-India Telescope optical upper limit
  20. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  21. GRB 260401A: SVOM/GRM observation
  22. GRB 260402A: Kilonova-Catcher optical upper limit
  23. GRB 260402A: MASTER optical observations
  24. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  25. EP260329b: Mondy and Assy-Turgen optical upper limits
  26. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  27. EP260321a :Xinglong optical observations
  28. EP260327a: Xinglong optical upper limit
  29. EP260329b: GOTO detection of optical counterpart
  30. GRB 260330B: SVOM/VT optical upper limits
  31. GRB 260321A: SVOM/ECLAIRs refined analysis
  32. EP260329b: J-band upper limits with WINTER
  33. EP260329a: J-band upper limit with WINTER
  34. GRB 260330B: LCO optical upper limits
  35. GRB 260330B: SVOM detection of a burst
  36. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  37. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  38. EP260329a: COLIBRÍ optical upper limit
  39. EP260329a: EP-FXT follow up observation
  40. EP260329a: NOT optical counterpart candidate
  41. EP260329b: Optical follow-up with Kinder observations
  42. EP 260329b: COLIBRÍ optical observations
  43. EP260329a: Optical upper limit with Kinder observations
  44. EP260329b: LCO optical observations of the counterpart
  45. EP260329b: Einstein Probe detection of an X-ray transient
  46. EP-WXT trigger 01709259209: TRT optical counterpart detection
  47. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  48. GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
  49. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  50. EP260327a: SVOM/VT optical upper limits
  51. EP260327a: WINTER J-band upper limit
  52. EP260327a: COLIBRÍ optical upper limits
  53. EP260327a: Gemini-North optical upper limits
  54. EP260324a: GROWTH-India Telescope optical observation
  55. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  56. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  57. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  58. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  59. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  60. EP260321a: JinShan near-infrared observations
  61. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  62. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  63. EP260321a: Gemini-South confirmation of a supernova
  64. EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
  65. GRB 260310A: LBT optical observations
  66. EP260321A: Mondy optical observations
  67. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  68. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  69. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  70. EP260321a: COLIBRÍ further optical observations and brightening
  71. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  72. EP260214b: ATCA 6 GHz detection
  73. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  74. EP260321a: ZTF and Rubin detections of the candidate optical counterpart to EP260321a
  75. EP260321a: GOTO detection of blue variable source
  76. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  77. EP260321a: further Kinder optical observations
  78. GRB 260321A: SVOM/VT optical upper limits
  79. EP260321a: Las Cumbres upper limit
  80. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  81. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  82. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  83. EP260321a: SVOM/VT optical upper limit
  84. GRB 260310A: continued optical observation at Mondy
  85. GRB 260321A: SVOM detection of a burst
  86. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  87. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS new optical observations
  88. GRB 260310A / AT 2026fgk: KAIT optical observations
  89. GRB 260310A / AT 2026fgk: FTW optical and NIR observations show no rebrightening
  90. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
  91. GRB 260318A: SVOM/GRM observation
  92. GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT
  93. GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
  94. GRB 260310A / AT 2026fgk: radio detection with the VLA
  95. GRB 260310A / AT2026fgk: SVOM/VT optical observations
  96. GRB 260310A / AT2026fgk: LCO optical observations
  97. IceCube-260315A/AT2026fpm: EP-FXT follow-up observation
  98. GRB 260316B: SVOM/GRM observation
  99. EP260316a / GRB 260316A: SVOM/VT optical upper limits
  100. EP260316a: COLIBRÍ faint optical counterpart candidate

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