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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"
  1. GRB 260603A: NOT optical observations
  2. GRB 260603A: Simeiz Zeiss-1000 optical upper limit
  3. GRB 260604B: Fermi GBM Final Real-time Localization
  4. GRB 260601A: CALET Gamma-Ray Burst Monitor detection
  5. EP260602a: EP-FXT follow-up observation
  6. EP260603a: Global MASTER-Net observations report
  7. EP260603a: Einstein Probe detection of a fast X-ray transient
  8. EP260602d: Optical Upper limits with kinder observations
  9. GRB 260604A: Fermi GBM Final Real-time Localization
  10. EP260602b: Liverpool Telescope observations
  11. EP260602a: Liverpool Telescope optical upper limits
  12. EP260602b: Liverpool Telescope and LCO observations
  13. GRB 260603B: Fermi GBM Final Localization
  14. EP260602a: GTC and Liverpool Telescope optical observations
  15. Konus-Wind detection of GRB 260601B/EP260601a
  16. GRB 260603A: EP-FXT follow-up observation
  17. EP260601a/GRB 260601B: EP-FXT follow-up observation
  18. GRB 260601B / EP260601a: Mondy optical upper limit
  19. EP260602b: EP-FXT follow-up observation
  20. GRB 260601B/EP260601a: Glowbug gamma-ray detection
  21. GRB 260603A: Kilonova-Catcher optical upper limit
  22. GRB 260603A: SVOM/VT optical observations
  23. EP260602a: NOT NIR J-band observations
  24. GRB 260603A: SVOM/COLIBRÍ (FM-GFT) photometric redshift z = 3.57
  25. EP260602d: Einstein Probe detection of a fast X-ray transient
  26. Fermi trigger No 802141998: Global MASTER-Net observations report
  27. EP260602a: SVOM/VT optical magnitudes correction
  28. GRB 260601A: SVOM/GRM observation of a short burst
  29. EP260602c: Einstein Probe detection of a fast X-ray transient
  30. GRB 260603A: SVOM/COLIBRÍ (GFT-FM) optical counterpart candidate
  31. EP260602a: COLIBRÍ optical observations
  32. GRB260601B/EP260601a: NOT near-infrared observations
  33. SVOM GRB260603.23: Global MASTER-Net observations report
  34. GRB 260603A: SVOM detection of a burst
  35. EP260602b: Einstein Probe detection of a fast X-ray transient
  36. GRB 260601B/EP260601a: Insight-HXMT detection
  37. Fermi GRB 260602B: Global MASTER-Net observations report
  38. Fermi GRB 260602B: Global MASTER-Net observations report
  39. EP260530a: Xinglong optical spectroscopy of EP260530a / AT 2026nwl
  40. EP260602a: SVOM/VT optical candidate
  41. EP-WXT trigger 01709266414 (EP260602b): JinShan optical counterpart detection
  42. GRB 260602B: Fermi GBM Final Localization
  43. GRB 260601A: GECAM-B observation of a short burst
  44. GRB 260601B/EP260601a: J-band upper limit with WINTER
  45. EP260530a/AT 2026nwl: COLIBRÍ optical follow up
  46. EP260530a/AT 2026nwl: KAIT optical observations
  47. GRB 260602A: Fermi GBM Final Real-time Localization
  48. GRB 260601B: CALET Gamma-Ray Burst Monitor detection
  49. EP260602a: Optical upper limits with Kinder observations
  50. GRB 260601B / EP260601a: NuSTAR detection of prompt emission
  51. EP260602a: Einstein Probe detection of a fast X-ray transient
  52. GRB 260601B/EP260601a: SVOM/VT optical observations
  53. GRB 260601B/EP260601a: GECAM-B analysis suggests a possible long duration Type I burst
  54. GRB 260601B: GECAM-B detection of a burst probably associated with EP260601a
  55. EP260601a: Einstein Probe detection of an X-ray transient
  56. EP-WXT trigger 01709266307 (EP260601a): COLIBRÍ optical observations
  57. EP-WXT trigger 01709266307 (EP260601a): JinShan optical counterpart detection
  58. GRB 260601A: Glowbug gamma-ray detection of a short burst
  59. GRB 260531B: Glowbug gamma-ray detection
  60. GRB 260516D: VLA radio detection
  61. GRB 260601A: Fermi GBM Observation
  62. EP260530a/AT 2026nwl: COLIBRÍ optical observations
  63. GRB 260530C: SVOM/ECLAIRs detection of a burst through on-ground search
  64. GRB 260527A/EP260527a: Glowbug gamma-ray detection
  65. Fermi GRB 260601A: Global MASTER-Net observations report
  66. GRB 260601A: Fermi GBM Final Real-time Localization
  67. GRB 260531B: GECAM-B observation
  68. GRB 260518B: SVOM/ECLAIRs detection of a soft burst possibly associated with EP 260518a and AT 2026ndp
  69. The EP-WXT trigger 01709266272 is likely a flaring star
  70. GRB 260531C: Fermi GBM Final Localization Correction
  71. Fermi Gamma-ray Burst Monitor trigger 801900520/260531256 is not a GRB
  72. AT2026nik: EP-FXT X-ray counterpart
  73. Fermi trigger No 801900520: Global MASTER-Net observations report
  74. GRB 260531B: Fermi GBM Final Real-time Localization
  75. GRB 260531A: MAXI/GSC detection
  76. AT 2026nuz: COLIBRÍ optical observations
  77. IPN triangulation of GRB 260527A / EP260527a
  78. EP260527a/GRB 260527A: further FTW optical and NIR observations
  79. GRB 260530B: SVOM/GRM detection of a possible bright short GRB
  80. GRB 260530A: Fermi GBM Final Real-time Localization
  81. GRB 260527A / EP260527a: VLA radio detection
  82. EP260527a/GRB 260527A: optical upper limit with Kinder observations
  83. GRB 260429B / EP260429a: COLIBRÍ optical counterpart candidate
  84. GRB 260529A: GOTO tentative optical afterglow candidate
  85. GRB 260527A/EP260527a: VLT/X-shooter tentative redshift
  86. GRB 260527A/EP260527a: Insight-HXMT detection
  87. Fermi GRB 260529A: Global MASTER-Net observations report
  88. GRB 260529A: Fermi GBM Final Real-time Localization
  89. EP260526a: SVOM/VT optical upper limits
  90. GRB 260527A/EP260527a: Gemini GMOS-S Optical Observations
  91. EP260527a / GRB 260527A: VLT detection of the optical and nIR counterpart
  92. EP260527a / GRB 260527A: NOT optical observations
  93. GRB 260527A/EP260527a: FTW optical and NIR observations
  94. EP260527a/GRB 260527A: Infrared J upper limit with MDM/MIRAGE
  95. GRB 260527A: CALET Gamma-Ray Burst Monitor detection
  96. EP260527a/GRB 260527A: EP-FXT follow-up observation
  97. GRB 260527A: GECAM-B detection of a short burst probably associated with EP260527a
  98. GRB 260526A: GECAM-B observation
  99. Konus-Wind detection of GRB 260527A (short/hard) ~4 min before EP260527a
  100. EP260526a: EP-FXT follow-up observation

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