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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 260604A: Glowbug gamma-ray detection
  2. GRB 260604C: LCO optical upper limit
  3. GRB 260604C: Liverpool Telescope optical detection
  4. The EP-WXT trigger 01709267001 is likely a flaring star
  5. EP260602d: EP-FXT follow-up observation
  6. EP260602c: EP-FXT follow-up observation
  7. GRB 260601B / EP260601a: AstroSat CZTI detection
  8. GRB 260527A/EP260527a: 6 GHz VLA observations
  9. GRB 260604C: GOTO detections of the optical afterglow
  10. GRB 260604C: Correction to GCN 44828
  11. GRB 260604C: Kilonova-Catcher optical afterglow detection
  12. GRB 260604C: SVOM/COLIBRÍ (FM-GFT) optical observations
  13. The EP-WXT trigger 01709266798 is likely a flaring star
  14. GRB 260604C: Jinshan optical observations
  15. GRB 260604C: Fermi GBM Observation
  16. EP260602d: J-band upper limit with WINTER
  17. EP260602b: J-band upper limit with WINTER
  18. GRB 260604C: LAST detection of optical counterpart candidate
  19. GRB 260604C: MASTER OT J145749.59+284903.0 optical counterpart discovery
  20. Fermi GRB 260604C: Global MASTER-Net observations report
  21. Fermi GRB 260604C: Global MASTER-Net observations report
  22. SVOM GRB260604.85: Global MASTER-Net observations report
  23. GRB 260604C: SVOM detection of a long burst
  24. GRB 260604C: Fermi GBM Final Real-time Localization
  25. GRB 260515A: SVOM/VT optical detection at about 18 days post trigger
  26. GRB 260603A: NOT optical observations
  27. GRB 260603A: Simeiz Zeiss-1000 optical upper limit
  28. GRB 260604B: Fermi GBM Final Real-time Localization
  29. GRB 260601A: CALET Gamma-Ray Burst Monitor detection
  30. EP260602a: EP-FXT follow-up observation
  31. EP260603a: Global MASTER-Net observations report
  32. EP260603a: Einstein Probe detection of a fast X-ray transient
  33. EP260602d: Optical Upper limits with kinder observations
  34. GRB 260604A: Fermi GBM Final Real-time Localization
  35. EP260602b: Liverpool Telescope observations
  36. EP260602a: Liverpool Telescope optical upper limits
  37. EP260602b: Liverpool Telescope and LCO observations
  38. GRB 260603B: Fermi GBM Final Localization
  39. EP260602a: GTC and Liverpool Telescope optical observations
  40. Konus-Wind detection of GRB 260601B/EP260601a
  41. GRB 260603A: EP-FXT follow-up observation
  42. EP260601a/GRB 260601B: EP-FXT follow-up observation
  43. GRB 260601B / EP260601a: Mondy optical upper limit
  44. EP260602b: EP-FXT follow-up observation
  45. GRB 260601B/EP260601a: Glowbug gamma-ray detection
  46. GRB 260603A: Kilonova-Catcher optical upper limit
  47. GRB 260603A: SVOM/VT optical observations
  48. EP260602a: NOT NIR J-band observations
  49. GRB 260603A: SVOM/COLIBRÍ (FM-GFT) photometric redshift z = 3.57
  50. EP260602d: Einstein Probe detection of a fast X-ray transient
  51. Fermi trigger No 802141998: Global MASTER-Net observations report
  52. EP260602a: SVOM/VT optical magnitudes correction
  53. GRB 260601A: SVOM/GRM observation of a short burst
  54. EP260602c: Einstein Probe detection of a fast X-ray transient
  55. GRB 260603A: SVOM/COLIBRÍ (GFT-FM) optical counterpart candidate
  56. EP260602a: COLIBRÍ optical observations
  57. GRB260601B/EP260601a: NOT near-infrared observations
  58. SVOM GRB260603.23: Global MASTER-Net observations report
  59. GRB 260603A: SVOM detection of a burst
  60. EP260602b: Einstein Probe detection of a fast X-ray transient
  61. GRB 260601B/EP260601a: Insight-HXMT detection
  62. Fermi GRB 260602B: Global MASTER-Net observations report
  63. Fermi GRB 260602B: Global MASTER-Net observations report
  64. EP260530a: Xinglong optical spectroscopy of EP260530a / AT 2026nwl
  65. EP260602a: SVOM/VT optical candidate
  66. EP-WXT trigger 01709266414 (EP260602b): JinShan optical counterpart detection
  67. GRB 260602B: Fermi GBM Final Localization
  68. GRB 260601A: GECAM-B observation of a short burst
  69. GRB 260601B/EP260601a: J-band upper limit with WINTER
  70. EP260530a/AT 2026nwl: COLIBRÍ optical follow up
  71. EP260530a/AT 2026nwl: KAIT optical observations
  72. GRB 260602A: Fermi GBM Final Real-time Localization
  73. GRB 260601B: CALET Gamma-Ray Burst Monitor detection
  74. EP260602a: Optical upper limits with Kinder observations
  75. GRB 260601B / EP260601a: NuSTAR detection of prompt emission
  76. EP260602a: Einstein Probe detection of a fast X-ray transient
  77. GRB 260601B/EP260601a: SVOM/VT optical observations
  78. GRB 260601B/EP260601a: GECAM-B analysis suggests a possible long duration Type I burst
  79. GRB 260601B: GECAM-B detection of a burst probably associated with EP260601a
  80. EP260601a: Einstein Probe detection of an X-ray transient
  81. EP-WXT trigger 01709266307 (EP260601a): COLIBRÍ optical observations
  82. EP-WXT trigger 01709266307 (EP260601a): JinShan optical counterpart detection
  83. GRB 260601A: Glowbug gamma-ray detection of a short burst
  84. GRB 260531B: Glowbug gamma-ray detection
  85. GRB 260516D: VLA radio detection
  86. GRB 260601A: Fermi GBM Observation
  87. EP260530a/AT 2026nwl: COLIBRÍ optical observations
  88. GRB 260530C: SVOM/ECLAIRs detection of a burst through on-ground search
  89. GRB 260527A/EP260527a: Glowbug gamma-ray detection
  90. Fermi GRB 260601A: Global MASTER-Net observations report
  91. GRB 260601A: Fermi GBM Final Real-time Localization
  92. GRB 260531B: GECAM-B observation
  93. GRB 260518B: SVOM/ECLAIRs detection of a soft burst possibly associated with EP 260518a and AT 2026ndp
  94. The EP-WXT trigger 01709266272 is likely a flaring star
  95. GRB 260531C: Fermi GBM Final Localization Correction
  96. Fermi Gamma-ray Burst Monitor trigger 801900520/260531256 is not a GRB
  97. AT2026nik: EP-FXT X-ray counterpart
  98. Fermi trigger No 801900520: Global MASTER-Net observations report
  99. GRB 260531B: Fermi GBM Final Real-time Localization
  100. GRB 260531A: MAXI/GSC detection

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