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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. EP260602a: Liverpool Telescope optical upper limits
  2. EP260602b: Liverpool Telescope and LCO observations
  3. GRB 260603B: Fermi GBM Final Localization
  4. EP260602a: GTC and Liverpool Telescope optical observations
  5. Konus-Wind detection of GRB 260601B/EP260601a
  6. GRB 260603A: EP-FXT follow-up observation
  7. EP260601a/GRB 260601B: EP-FXT follow-up observation
  8. GRB 260601B / EP260601a: Mondy optical upper limit
  9. EP260602b: EP-FXT follow-up observation
  10. GRB 260601B/EP260601a: Glowbug gamma-ray detection
  11. GRB 260603A: Kilonova-Catcher optical upper limit
  12. GRB 260603A: SVOM/VT optical observations
  13. EP260602a: NOT NIR J-band observations
  14. GRB 260603A: SVOM/COLIBRÍ (FM-GFT) photometric redshift z = 3.57
  15. EP260602d: Einstein Probe detection of a fast X-ray transient
  16. Fermi trigger No 802141998: Global MASTER-Net observations report
  17. EP260602a: SVOM/VT optical magnitudes correction
  18. GRB 260601A: SVOM/GRM observation of a short burst
  19. EP260602c: Einstein Probe detection of a fast X-ray transient
  20. GRB 260603A: SVOM/COLIBRÍ (GFT-FM) optical counterpart candidate
  21. EP260602a: COLIBRÍ optical observations
  22. GRB260601B/EP260601a: NOT near-infrared observations
  23. SVOM GRB260603.23: Global MASTER-Net observations report
  24. GRB 260603A: SVOM detection of a burst
  25. EP260602b: Einstein Probe detection of a fast X-ray transient
  26. GRB 260601B/EP260601a: Insight-HXMT detection
  27. Fermi GRB 260602B: Global MASTER-Net observations report
  28. Fermi GRB 260602B: Global MASTER-Net observations report
  29. EP260530a: Xinglong optical spectroscopy of EP260530a / AT 2026nwl
  30. EP260602a: SVOM/VT optical candidate
  31. EP-WXT trigger 01709266414 (EP260602b): JinShan optical counterpart detection
  32. GRB 260602B: Fermi GBM Final Localization
  33. GRB 260601A: GECAM-B observation of a short burst
  34. GRB 260601B/EP260601a: J-band upper limit with WINTER
  35. EP260530a/AT 2026nwl: COLIBRÍ optical follow up
  36. EP260530a/AT 2026nwl: KAIT optical observations
  37. GRB 260602A: Fermi GBM Final Real-time Localization
  38. GRB 260601B: CALET Gamma-Ray Burst Monitor detection
  39. EP260602a: Optical upper limits with Kinder observations
  40. GRB 260601B / EP260601a: NuSTAR detection of prompt emission
  41. EP260602a: Einstein Probe detection of a fast X-ray transient
  42. GRB 260601B/EP260601a: SVOM/VT optical observations
  43. GRB 260601B/EP260601a: GECAM-B analysis suggests a possible long duration Type I burst
  44. GRB 260601B: GECAM-B detection of a burst probably associated with EP260601a
  45. EP260601a: Einstein Probe detection of an X-ray transient
  46. EP-WXT trigger 01709266307 (EP260601a): COLIBRÍ optical observations
  47. EP-WXT trigger 01709266307 (EP260601a): JinShan optical counterpart detection
  48. GRB 260601A: Glowbug gamma-ray detection of a short burst
  49. GRB 260531B: Glowbug gamma-ray detection
  50. GRB 260516D: VLA radio detection
  51. GRB 260601A: Fermi GBM Observation
  52. EP260530a/AT 2026nwl: COLIBRÍ optical observations
  53. GRB 260530C: SVOM/ECLAIRs detection of a burst through on-ground search
  54. GRB 260527A/EP260527a: Glowbug gamma-ray detection
  55. Fermi GRB 260601A: Global MASTER-Net observations report
  56. GRB 260601A: Fermi GBM Final Real-time Localization
  57. GRB 260531B: GECAM-B observation
  58. GRB 260518B: SVOM/ECLAIRs detection of a soft burst possibly associated with EP 260518a and AT 2026ndp
  59. The EP-WXT trigger 01709266272 is likely a flaring star
  60. GRB 260531C: Fermi GBM Final Localization Correction
  61. Fermi Gamma-ray Burst Monitor trigger 801900520/260531256 is not a GRB
  62. AT2026nik: EP-FXT X-ray counterpart
  63. Fermi trigger No 801900520: Global MASTER-Net observations report
  64. GRB 260531B: Fermi GBM Final Real-time Localization
  65. GRB 260531A: MAXI/GSC detection
  66. AT 2026nuz: COLIBRÍ optical observations
  67. IPN triangulation of GRB 260527A / EP260527a
  68. EP260527a/GRB 260527A: further FTW optical and NIR observations
  69. GRB 260530B: SVOM/GRM detection of a possible bright short GRB
  70. GRB 260530A: Fermi GBM Final Real-time Localization
  71. GRB 260527A / EP260527a: VLA radio detection
  72. EP260527a/GRB 260527A: optical upper limit with Kinder observations
  73. GRB 260429B / EP260429a: COLIBRÍ optical counterpart candidate
  74. GRB 260529A: GOTO tentative optical afterglow candidate
  75. GRB 260527A/EP260527a: VLT/X-shooter tentative redshift
  76. GRB 260527A/EP260527a: Insight-HXMT detection
  77. Fermi GRB 260529A: Global MASTER-Net observations report
  78. GRB 260529A: Fermi GBM Final Real-time Localization
  79. EP260526a: SVOM/VT optical upper limits
  80. GRB 260527A/EP260527a: Gemini GMOS-S Optical Observations
  81. EP260527a / GRB 260527A: VLT detection of the optical and nIR counterpart
  82. EP260527a / GRB 260527A: NOT optical observations
  83. GRB 260527A/EP260527a: FTW optical and NIR observations
  84. EP260527a/GRB 260527A: Infrared J upper limit with MDM/MIRAGE
  85. GRB 260527A: CALET Gamma-Ray Burst Monitor detection
  86. EP260527a/GRB 260527A: EP-FXT follow-up observation
  87. GRB 260527A: GECAM-B detection of a short burst probably associated with EP260527a
  88. GRB 260526A: GECAM-B observation
  89. Konus-Wind detection of GRB 260527A (short/hard) ~4 min before EP260527a
  90. EP260526a: EP-FXT follow-up observation
  91. EP260527a: SVOM/VT optical observation
  92. EP260527a: COLIBRÍ optical detection
  93. EP260527a: Einstein Probe detection of a fast X-ray transient
  94. The EP-WXT trigger 01709266172 is likely a flaring star
  95. The EP-WXT trigger 01709266147 is likely a flaring star
  96. Fermi trigger No 801580882: Global MASTER-Net observations report
  97. GRB 260524A: SVOM/ECLAIRs detection of a burst through on-ground search
  98. EP260526a: LCO optical upper limits
  99. EP260526a: Einstein Probe detection of a fast X-ray transient
  100. GRB 260525A: AstroSat CZTI detection

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