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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. EP260530a/AT 2026nwl: COLIBRÍ optical observations
  2. GRB 260530C: SVOM/ECLAIRs detection of a burst through on-ground search
  3. GRB 260527A/EP260527a: Glowbug gamma-ray detection
  4. Fermi GRB 260601A: Global MASTER-Net observations report
  5. GRB 260601A: Fermi GBM Final Real-time Localization
  6. GRB 260531B: GECAM-B observation
  7. GRB 260518B: SVOM/ECLAIRs detection of a soft burst possibly associated with EP 260518a and AT 2026ndp
  8. The EP-WXT trigger 01709266272 is likely a flaring star
  9. GRB 260531C: Fermi GBM Final Localization Correction
  10. Fermi Gamma-ray Burst Monitor trigger 801900520/260531256 is not a GRB
  11. AT2026nik: EP-FXT X-ray counterpart
  12. Fermi trigger No 801900520: Global MASTER-Net observations report
  13. GRB 260531B: Fermi GBM Final Real-time Localization
  14. GRB 260531A: MAXI/GSC detection
  15. AT 2026nuz: COLIBRÍ optical observations
  16. IPN triangulation of GRB 260527A / EP260527a
  17. EP260527a/GRB 260527A: further FTW optical and NIR observations
  18. GRB 260530B: SVOM/GRM detection of a possible bright short GRB
  19. GRB 260530A: Fermi GBM Final Real-time Localization
  20. GRB 260527A / EP260527a: VLA radio detection
  21. EP260527a/GRB 260527A: optical upper limit with Kinder observations
  22. GRB 260429B / EP260429a: COLIBRÍ optical counterpart candidate
  23. GRB 260529A: GOTO tentative optical afterglow candidate
  24. GRB 260527A/EP260527a: VLT/X-shooter tentative redshift
  25. GRB 260527A/EP260527a: Insight-HXMT detection
  26. Fermi GRB 260529A: Global MASTER-Net observations report
  27. GRB 260529A: Fermi GBM Final Real-time Localization
  28. EP260526a: SVOM/VT optical upper limits
  29. GRB 260527A/EP260527a: Gemini GMOS-S Optical Observations
  30. EP260527a / GRB 260527A: VLT detection of the optical and nIR counterpart
  31. EP260527a / GRB 260527A: NOT optical observations
  32. GRB 260527A/EP260527a: FTW optical and NIR observations
  33. EP260527a/GRB 260527A: Infrared J upper limit with MDM/MIRAGE
  34. GRB 260527A: CALET Gamma-Ray Burst Monitor detection
  35. EP260527a/GRB 260527A: EP-FXT follow-up observation
  36. GRB 260527A: GECAM-B detection of a short burst probably associated with EP260527a
  37. GRB 260526A: GECAM-B observation
  38. Konus-Wind detection of GRB 260527A (short/hard) ~4 min before EP260527a
  39. EP260526a: EP-FXT follow-up observation
  40. EP260527a: SVOM/VT optical observation
  41. EP260527a: COLIBRÍ optical detection
  42. EP260527a: Einstein Probe detection of a fast X-ray transient
  43. The EP-WXT trigger 01709266172 is likely a flaring star
  44. The EP-WXT trigger 01709266147 is likely a flaring star
  45. Fermi trigger No 801580882: Global MASTER-Net observations report
  46. GRB 260524A: SVOM/ECLAIRs detection of a burst through on-ground search
  47. EP260526a: LCO optical upper limits
  48. EP260526a: Einstein Probe detection of a fast X-ray transient
  49. GRB 260525A: AstroSat CZTI detection
  50. EP260526.405: COLIBRÍ optical upper limits
  51. The EP-WXT trigger 01709266106 is not a real source
  52. Fermi GRB 260526A: Global MASTER-Net observations report
  53. GRB 260526A: Fermi GBM Final Real-time Localization
  54. EP01709266106 (EP260526a?): Liverpool Telescope upper limits
  55. EP-WXT 01709266106: NOT optical upper limits
  56. Fermi GRB 260525A: Global MASTER-Net observations report
  57. GRB 260525A: Fermi GBM Final Real-time Localization
  58. GRB 260523B: AstroSat CZTI detection
  59. GRB 260523B: GECAM-B observation
  60. Fermi GRB 260523A: Global MASTER-Net observations report
  61. GRB 260523B: Fermi GBM Final Real-time Localization
  62. GRB 260523A: Fermi GBM Final Real-time Localization
  63. GRB 260522A: Fermi GBM Observation
  64. GRB 260522B: NuSTAR detection of prompt emission
  65. EP260518a (AT2026ndp): LCO observations and Gemini-South Redshift z = 2.28
  66. GRB 260522B: Fermi GBM Final Real-time Localization
  67. GRB 260522A: GOTO optical upper limit
  68. Fermi trigger No 801135305: Global MASTER-Net observations report
  69. Fermi GRB 260522A: Global MASTER-Net observations report
  70. EP260518a: Einstein Probe detection of an sub-threshold X-ray transient with counterpart AT 2026ndp
  71. GRB 260522A: Fermi-LAT detection
  72. GRB 260519C: SVOM/GRM observation
  73. GRB 260522A: Fermi GBM Final Real-time Localization
  74. GRB 260511A: iTelescope T-75 optical detection
  75. GRB 260520B: SVOM/GRM observation
  76. GRB 260411B: TERI Gamma-ray detection
  77. GRB 260407A: TERI Gamma-ray detection
  78. GRB 260307A: TERI Gamma-ray detection
  79. GRB 260225D: TERI Gamma-ray detection
  80. GRB 251118A: TERI Gamma-ray detection
  81. GRB 251113A: TERI Gamma-ray detection
  82. GRB 260428A: TERI Gamma-ray detection
  83. Konus-Wind detection of GRB 260519C
  84. GRB 260520B: Fermi GBM Final Localization
  85. GRB 260509A: SVOM/ECLAIRs refined analysis
  86. GRB 260520A: Fermi GBM Final Localization
  87. GRB 260519D: Fermi GBM Final Localization Correction
  88. GRB 260519C: NuSTAR detection of prompt emission
  89. Konus-Wind detection of GRB 260518A
  90. GRB 260519B: Fermi GBM Final Localization
  91. GRB 260519A: Fermi GBM Final Localization
  92. GRB 260518A: AstroSat CZTI detection of a long burst
  93. GRB 260516D: SVOM/ECLAIRs refined analysis
  94. GRB 260515A: SVOM/ECLAIRs refined analysis
  95. GRB 260421B: radio detection with the VLA
  96. GRID detection of GRB 260511A
  97. GRB 260509A: CrAO ZTSh optical upper limit (Duplicate Submission)
  98. GRB 260509A: CrAO ZTSh optical upper limit
  99. GRB 260516D: EP-FXT follow-up observation
  100. GRB 260516D: GOTO optical counterpart detection

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