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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"

22062 results found.

  1. EP260409a: Gemini/FLAMINGOS2 J-band counterpart
  2. EP-WXT01709259790: Optical Upper limits with kinder observations
  3. EP260409a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  4. EP260321a: Chandra X-ray Non-detection
  5. GRB 260310A/AT2026fgk: Kilonova-Catcher SN peak identification
  6. EP260409a: SVOM/VT optical upper limits
  7. EP260409a: Global MASTER-Net observations report
  8. EP260321a: VLA radio detection
  9. GRB 260402A: SVOM/ECLAIRs refined analysis
  10. GRB 260310A: Continued VLA Multi-frequency Radio Observations
  11. GRB 260310A / AT2026fgk: X-ray rebrightening
  12. EP260402a / GRB 260402A: Mephisto optical upper limits
  13. EP260403a: Mephisto optical upper limits
  14. EP260321a: Upper limits from VLA radio observations
  15. EP260321a: uGMRT observations
  16. EP260405a: SVOM/VT optical upper limits
  17. EP260405a: Global MASTER-Net observations report
  18. EP260405a / EP-WXT 11900672904: COLIBRÍ optical upper limits
  19. Fermi trigger No 797039833: Global MASTER-Net observations report
  20. EP260324A / AT 2026hir: COLIBRÍ further optical observations
  21. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  22. GRB 260330B: SVOM/VT further optical observation
  23. GRB 260330B: SVOM/ECLAIRs refined analysis
  24. EP260403a: LCO optical observations of the counterpart
  25. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  26. EP260403a: LCO optical counterpart detection
  27. EP260403a: COLIBRÍ optical counterpart candidate
  28. GRB 260330B: SVOM/VT optical candidate
  29. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  30. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  31. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  32. EP260324A / AT 2026hir: COLIBRÍ optical observations
  33. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  34. GRB 260402A: WINTER J-band upper limit
  35. GRB260402A: GROWTH-India Telescope optical upper limit
  36. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  37. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  38. GRB 260402A: Kilonova-Catcher optical upper limit
  39. GRB 260402A: MASTER optical observations
  40. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  41. Fermi GRB 260401A: Global MASTER-Net observations report
  42. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  43. EP260321a :Xinglong optical observations
  44. EP260329b: GOTO detection of optical counterpart
  45. GRB 260330B: SVOM/VT optical upper limits
  46. Konus-Wind detection of GRB 260320A
  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. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  52. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  53. EP260329a: EP-FXT follow up observation
  54. EP260329b: Global MASTER-Net observations report
  55. Fermi trigger No 796485221: Global MASTER-Net observations report
  56. EP260329b: Optical follow-up with Kinder observations
  57. EP 260329b: COLIBRÍ optical observations
  58. EP260329a: Optical upper limit with Kinder observations
  59. EP260329b: LCO optical observations of the counterpart
  60. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  61. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  62. EP260327a: SVOM/VT optical upper limits
  63. SMA Detection of GRB 260310A / AT 2026fgk
  64. GRB 260307B: ATCA Radio Upper Limits
  65. EP260327a: WINTER J-band upper limit
  66. EP260327a: COLIBRÍ optical upper limits
  67. EP260327a: Gemini-North optical upper limits
  68. EP260324a: GROWTH-India Telescope optical observation
  69. EP260327a: Global MASTER-Net observations report
  70. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  71. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  72. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  73. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  74. EP260321a: JinShan near-infrared observations
  75. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  76. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  77. EP260321a: Gemini-South confirmation of a supernova
  78. EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
  79. GRB 260310A: LBT optical observations
  80. EP260321A: Mondy optical observations
  81. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  82. Fermi GRB 260323A: Global MASTER-Net observations report
  83. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  84. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  85. EP260321a / AT2026gzf: VLT/X-shooter detection of supernova-like spectral features at z = 0.0344
  86. EP260321a: COLIBRÍ further optical observations and brightening
  87. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  88. EP260214b: ATCA 6 GHz detection
  89. EP260321a: ZTF and Rubin detections of the candidate optical counterpart to EP260321a
  90. EP260321a: GOTO detection of blue variable source
  91. EP260321a: further Kinder optical observations
  92. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  93. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  94. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  95. EP260321a: SVOM/VT optical upper limit
  96. GRB 260310A: continued optical observation at Mondy
  97. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  98. EP260321a: Global MASTER-Net observations report
  99. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS new optical observations
  100. GRB 260310A / AT 2026fgk: KAIT optical observations

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