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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: SVOM/VT optical observations
  2. EP260602a: NOT NIR J-band observations
  3. GRB 260603A: SVOM/COLIBRÍ (FM-GFT) photometric redshift z = 3.57
  4. EP260602d: Einstein Probe detection of a fast X-ray transient
  5. Fermi trigger No 802141998: Global MASTER-Net observations report
  6. EP260602a: SVOM/VT optical magnitudes correction
  7. GRB 260601A: SVOM/GRM observation of a short burst
  8. EP260602c: Einstein Probe detection of a fast X-ray transient
  9. GRB 260603A: SVOM/COLIBRÍ (GFT-FM) optical counterpart candidate
  10. EP260602a: COLIBRÍ optical observations
  11. GRB260601B/EP260601a: NOT near-infrared observations
  12. SVOM GRB260603.23: Global MASTER-Net observations report
  13. GRB 260603A: SVOM detection of a burst
  14. EP260602b: Einstein Probe detection of a fast X-ray transient
  15. GRB 260601B/EP260601a: Insight-HXMT detection
  16. Fermi GRB 260602B: Global MASTER-Net observations report
  17. Fermi GRB 260602B: Global MASTER-Net observations report
  18. EP260530a: Xinglong optical spectroscopy of EP260530a / AT 2026nwl
  19. EP260602a: SVOM/VT optical candidate
  20. EP-WXT trigger 01709266414 (EP260602b): JinShan optical counterpart detection
  21. GRB 260602B: Fermi GBM Final Localization
  22. GRB 260601A: GECAM-B observation of a short burst
  23. GRB 260601B/EP260601a: J-band upper limit with WINTER
  24. EP260530a/AT 2026nwl: COLIBRÍ optical follow up
  25. EP260530a/AT 2026nwl: KAIT optical observations
  26. GRB 260602A: Fermi GBM Final Real-time Localization
  27. GRB 260601B: CALET Gamma-Ray Burst Monitor detection
  28. EP260602a: Optical upper limits with Kinder observations
  29. GRB 260601B / EP260601a: NuSTAR detection of prompt emission
  30. EP260602a: Einstein Probe detection of a fast X-ray transient
  31. GRB 260601B/EP260601a: SVOM/VT optical observations
  32. GRB 260601B/EP260601a: GECAM-B analysis suggests a possible long duration Type I burst
  33. GRB 260601B: GECAM-B detection of a burst probably associated with EP260601a
  34. EP260601a: Einstein Probe detection of an X-ray transient
  35. EP-WXT trigger 01709266307 (EP260601a): COLIBRÍ optical observations
  36. EP-WXT trigger 01709266307 (EP260601a): JinShan optical counterpart detection
  37. GRB 260601A: Glowbug gamma-ray detection of a short burst
  38. GRB 260531B: Glowbug gamma-ray detection
  39. GRB 260516D: VLA radio detection
  40. GRB 260601A: Fermi GBM Observation
  41. EP260530a/AT 2026nwl: COLIBRÍ optical observations
  42. GRB 260530C: SVOM/ECLAIRs detection of a burst through on-ground search
  43. GRB 260527A/EP260527a: Glowbug gamma-ray detection
  44. Fermi GRB 260601A: Global MASTER-Net observations report
  45. GRB 260601A: Fermi GBM Final Real-time Localization
  46. GRB 260531B: GECAM-B observation
  47. GRB 260518B: SVOM/ECLAIRs detection of a soft burst possibly associated with EP 260518a and AT 2026ndp
  48. The EP-WXT trigger 01709266272 is likely a flaring star
  49. GRB 260531C: Fermi GBM Final Localization Correction
  50. Fermi Gamma-ray Burst Monitor trigger 801900520/260531256 is not a GRB
  51. AT2026nik: EP-FXT X-ray counterpart
  52. Fermi trigger No 801900520: Global MASTER-Net observations report
  53. GRB 260531B: Fermi GBM Final Real-time Localization
  54. GRB 260531A: MAXI/GSC detection
  55. AT 2026nuz: COLIBRÍ optical observations
  56. IPN triangulation of GRB 260527A / EP260527a
  57. EP260527a/GRB 260527A: further FTW optical and NIR observations
  58. GRB 260530B: SVOM/GRM detection of a possible bright short GRB
  59. GRB 260530A: Fermi GBM Final Real-time Localization
  60. GRB 260527A / EP260527a: VLA radio detection
  61. EP260527a/GRB 260527A: optical upper limit with Kinder observations
  62. GRB 260429B / EP260429a: COLIBRÍ optical counterpart candidate
  63. GRB 260529A: GOTO tentative optical afterglow candidate
  64. GRB 260527A/EP260527a: VLT/X-shooter tentative redshift
  65. GRB 260527A/EP260527a: Insight-HXMT detection
  66. Fermi GRB 260529A: Global MASTER-Net observations report
  67. GRB 260529A: Fermi GBM Final Real-time Localization
  68. EP260526a: SVOM/VT optical upper limits
  69. GRB 260527A/EP260527a: Gemini GMOS-S Optical Observations
  70. EP260527a / GRB 260527A: VLT detection of the optical and nIR counterpart
  71. EP260527a / GRB 260527A: NOT optical observations
  72. GRB 260527A/EP260527a: FTW optical and NIR observations
  73. EP260527a/GRB 260527A: Infrared J upper limit with MDM/MIRAGE
  74. GRB 260527A: CALET Gamma-Ray Burst Monitor detection
  75. EP260527a/GRB 260527A: EP-FXT follow-up observation
  76. GRB 260527A: GECAM-B detection of a short burst probably associated with EP260527a
  77. GRB 260526A: GECAM-B observation
  78. Konus-Wind detection of GRB 260527A (short/hard) ~4 min before EP260527a
  79. EP260526a: EP-FXT follow-up observation
  80. EP260527a: SVOM/VT optical observation
  81. EP260527a: COLIBRÍ optical detection
  82. EP260527a: Einstein Probe detection of a fast X-ray transient
  83. The EP-WXT trigger 01709266172 is likely a flaring star
  84. The EP-WXT trigger 01709266147 is likely a flaring star
  85. Fermi trigger No 801580882: Global MASTER-Net observations report
  86. GRB 260524A: SVOM/ECLAIRs detection of a burst through on-ground search
  87. EP260526a: LCO optical upper limits
  88. EP260526a: Einstein Probe detection of a fast X-ray transient
  89. GRB 260525A: AstroSat CZTI detection
  90. EP260526.405: COLIBRÍ optical upper limits
  91. The EP-WXT trigger 01709266106 is not a real source
  92. Fermi GRB 260526A: Global MASTER-Net observations report
  93. GRB 260526A: Fermi GBM Final Real-time Localization
  94. EP01709266106 (EP260526a?): Liverpool Telescope upper limits
  95. EP-WXT 01709266106: NOT optical upper limits
  96. Fermi GRB 260525A: Global MASTER-Net observations report
  97. GRB 260525A: Fermi GBM Final Real-time Localization
  98. GRB 260523B: AstroSat CZTI detection
  99. GRB 260523B: GECAM-B observation
  100. Fermi GRB 260523A: Global MASTER-Net observations report

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