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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"

21319 results found.

  1. GRB 260411B: GOTO optical counterpart candidate
  2. EP260409a: Gemini/FLAMINGOS2 J-band counterpart
  3. EP-WXT01709259790: Optical Upper limits with kinder observations
  4. EP260409a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  5. EP260321a: Chandra X-ray Non-detection
  6. GRB 260310A/AT2026fgk: Kilonova-Catcher SN peak identification
  7. EP260409a: SVOM/VT optical upper limits
  8. EP260409a: Global MASTER-Net observations report
  9. EP260321a: VLA radio detection
  10. GRB 260402A: SVOM/ECLAIRs refined analysis
  11. GRB 260310A: Continued VLA Multi-frequency Radio Observations
  12. GRB 260310A / AT2026fgk: X-ray rebrightening
  13. EP260402a / GRB 260402A: Mephisto optical upper limits
  14. EP260403a: Mephisto optical upper limits
  15. EP260321a: Upper limits from VLA radio observations
  16. EP260321a: uGMRT observations
  17. EP260405a: SVOM/VT optical upper limits
  18. EP260405a: Global MASTER-Net observations report
  19. EP260405a / EP-WXT 11900672904: COLIBRÍ optical upper limits
  20. Fermi trigger No 797039833: Global MASTER-Net observations report
  21. EP260324A / AT 2026hir: COLIBRÍ further optical observations
  22. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  23. GRB 260330B: SVOM/VT further optical observation
  24. GRB 260330B: SVOM/ECLAIRs refined analysis
  25. EP260403a: LCO optical observations of the counterpart
  26. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  27. EP260403a: LCO optical counterpart detection
  28. EP260403a: COLIBRÍ optical counterpart candidate
  29. GRB 260330B: SVOM/VT optical candidate
  30. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  31. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  32. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  33. EP260324A / AT 2026hir: COLIBRÍ optical observations
  34. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  35. GRB 260402A: WINTER J-band upper limit
  36. GRB260402A: GROWTH-India Telescope optical upper limit
  37. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  38. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  39. GRB 260402A: Kilonova-Catcher optical upper limit
  40. GRB 260402A: MASTER optical observations
  41. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  42. Fermi GRB 260401A: Global MASTER-Net observations report
  43. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  44. EP260321a :Xinglong optical observations
  45. EP260329b: GOTO detection of optical counterpart
  46. GRB 260330B: SVOM/VT optical upper limits
  47. GRB 260321A: SVOM/ECLAIRs refined analysis
  48. EP260329b: J-band upper limits with WINTER
  49. EP260329a: J-band upper limit with WINTER
  50. GRB 260310A: VLA Multi-frequency Radio Observations
  51. Fermi GBM Sub-Threshold Detection of GRB 260330B
  52. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  53. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  54. EP260329a: EP-FXT follow up observation
  55. EP260329b: Global MASTER-Net observations report
  56. Fermi trigger No 796485221: Global MASTER-Net observations report
  57. EP260329b: Optical follow-up with Kinder observations
  58. EP 260329b: COLIBRÍ optical observations
  59. EP260329a: Optical upper limit with Kinder observations
  60. EP260329b: LCO optical observations of the counterpart
  61. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  62. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  63. EP260327a: SVOM/VT optical upper limits
  64. SMA Detection of GRB 260310A / AT 2026fgk
  65. GRB 260307B: ATCA Radio Upper Limits
  66. EP260327a: WINTER J-band upper limit
  67. EP260327a: COLIBRÍ optical upper limits
  68. EP260327a: Gemini-North optical upper limits
  69. EP260324a: GROWTH-India Telescope optical observation
  70. EP260327a: Global MASTER-Net observations report
  71. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  72. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  73. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  74. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  75. EP260321a: JinShan near-infrared observations
  76. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  77. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  78. EP260321a: Gemini-South confirmation of a supernova
  79. EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
  80. GRB 260310A: LBT optical observations
  81. EP260321A: Mondy optical observations
  82. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  83. Fermi GRB 260323A: Global MASTER-Net observations report
  84. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  85. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  86. EP260321a / AT2026gzf: VLT/X-shooter detection of supernova-like spectral features at z = 0.0344
  87. EP260321a: COLIBRÍ further optical observations and brightening
  88. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  89. EP260214b: ATCA 6 GHz detection
  90. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  91. EP260321a: ZTF and Rubin detections of the candidate optical counterpart to EP260321a
  92. EP260321a: GOTO detection of blue variable source
  93. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  94. EP260321a: further Kinder optical observations
  95. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  96. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  97. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  98. EP260321a: SVOM/VT optical upper limit
  99. GRB 260310A: continued optical observation at Mondy
  100. Fermi GBM Sub-Threshold Detection of GRB 260321A

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