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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"

22060 results found.

  1. EP260409a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  2. EP260321a: Chandra X-ray Non-detection
  3. GRB 260310A/AT2026fgk: Kilonova-Catcher SN peak identification
  4. EP260409a: SVOM/VT optical upper limits
  5. EP260409a: Global MASTER-Net observations report
  6. EP260321a: VLA radio detection
  7. GRB 260402A: SVOM/ECLAIRs refined analysis
  8. GRB 260310A: Continued VLA Multi-frequency Radio Observations
  9. GRB 260310A / AT2026fgk: X-ray rebrightening
  10. EP260402a / GRB 260402A: Mephisto optical upper limits
  11. EP260403a: Mephisto optical upper limits
  12. EP260321a: Upper limits from VLA radio observations
  13. EP260321a: uGMRT observations
  14. EP260405a: SVOM/VT optical upper limits
  15. EP260405a: Global MASTER-Net observations report
  16. EP260405a / EP-WXT 11900672904: COLIBRÍ optical upper limits
  17. Fermi trigger No 797039833: Global MASTER-Net observations report
  18. EP260324A / AT 2026hir: COLIBRÍ further optical observations
  19. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  20. GRB 260330B: SVOM/VT further optical observation
  21. GRB 260330B: SVOM/ECLAIRs refined analysis
  22. EP260403a: LCO optical observations of the counterpart
  23. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  24. EP260403a: LCO optical counterpart detection
  25. EP260403a: COLIBRÍ optical counterpart candidate
  26. GRB 260330B: SVOM/VT optical candidate
  27. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  28. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  29. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  30. EP260324A / AT 2026hir: COLIBRÍ optical observations
  31. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  32. GRB 260402A: WINTER J-band upper limit
  33. GRB260402A: GROWTH-India Telescope optical upper limit
  34. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  35. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  36. GRB 260402A: Kilonova-Catcher optical upper limit
  37. GRB 260402A: MASTER optical observations
  38. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  39. Fermi GRB 260401A: Global MASTER-Net observations report
  40. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  41. EP260321a :Xinglong optical observations
  42. EP260329b: GOTO detection of optical counterpart
  43. GRB 260330B: SVOM/VT optical upper limits
  44. Konus-Wind detection of GRB 260320A
  45. GRB 260321A: SVOM/ECLAIRs refined analysis
  46. EP260329b: J-band upper limits with WINTER
  47. EP260329a: J-band upper limit with WINTER
  48. GRB 260310A: VLA Multi-frequency Radio Observations
  49. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  50. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  51. EP260329a: EP-FXT follow up observation
  52. EP260329b: Global MASTER-Net observations report
  53. Fermi trigger No 796485221: Global MASTER-Net observations report
  54. EP260329b: Optical follow-up with Kinder observations
  55. EP 260329b: COLIBRÍ optical observations
  56. EP260329a: Optical upper limit with Kinder observations
  57. EP260329b: LCO optical observations of the counterpart
  58. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  59. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  60. EP260327a: SVOM/VT optical upper limits
  61. SMA Detection of GRB 260310A / AT 2026fgk
  62. GRB 260307B: ATCA Radio Upper Limits
  63. EP260327a: WINTER J-band upper limit
  64. EP260327a: COLIBRÍ optical upper limits
  65. EP260327a: Gemini-North optical upper limits
  66. EP260324a: GROWTH-India Telescope optical observation
  67. EP260327a: Global MASTER-Net observations report
  68. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  69. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  70. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  71. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  72. EP260321a: JinShan near-infrared observations
  73. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  74. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  75. EP260321a: Gemini-South confirmation of a supernova
  76. EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
  77. GRB 260310A: LBT optical observations
  78. EP260321A: Mondy optical observations
  79. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  80. Fermi GRB 260323A: Global MASTER-Net observations report
  81. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  82. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  83. EP260321a / AT2026gzf: VLT/X-shooter detection of supernova-like spectral features at z = 0.0344
  84. EP260321a: COLIBRÍ further optical observations and brightening
  85. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  86. EP260214b: ATCA 6 GHz detection
  87. EP260321a: ZTF and Rubin detections of the candidate optical counterpart to EP260321a
  88. EP260321a: GOTO detection of blue variable source
  89. EP260321a: further Kinder optical observations
  90. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  91. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  92. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  93. EP260321a: SVOM/VT optical upper limit
  94. GRB 260310A: continued optical observation at Mondy
  95. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  96. EP260321a: Global MASTER-Net observations report
  97. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS new optical observations
  98. GRB 260310A / AT 2026fgk: KAIT optical observations
  99. GRB 260310A / AT 2026fgk: FTW optical and NIR observations show no rebrightening
  100. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy

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