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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"

22059 results found.

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

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