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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"

27474 results found.

  1. GRB 260607B: Fermi GBM Observation
  2. GRB 260604C: Simeiz Zeiss-1000 optical observations of the afterglow
  3. GRB 260604C: OPD1.6m - GRANDMA observations - detection
  4. GRB 260604C: 6 GHz VLA observations
  5. GRB 260604C: SAO RAS optical observations
  6. GRB 260604B: SVOM/GRM detection
  7. EP260605a: Einstein Probe detection of a fast X-ray transient
  8. EP260603a: COLIBRÍ optical upper limit
  9. GRB 260604A: Glowbug gamma-ray detection
  10. GRB 260604C: LCO optical upper limit
  11. EP260602d: EP-FXT follow-up observation
  12. EP260602c: EP-FXT follow-up observation
  13. GRB 260601B / EP260601a: AstroSat CZTI detection
  14. GRB 260527A/EP260527a: 6 GHz VLA observations
  15. GRB 260604C: Kilonova-Catcher optical afterglow detection
  16. GRB 260604C: SVOM/COLIBRÍ (FM-GFT) optical observations
  17. GRB 260604C: Jinshan optical observations
  18. GRB 260604C: Fermi GBM Observation
  19. EP260602d: J-band upper limit with WINTER
  20. EP260602b: J-band upper limit with WINTER
  21. GRB 260604C: LAST detection of optical counterpart candidate
  22. Fermi GRB 260604C: Global MASTER-Net observations report
  23. Fermi GRB 260604C: Global MASTER-Net observations report
  24. SVOM GRB260604.85: Global MASTER-Net observations report
  25. GRB 260603A: Simeiz Zeiss-1000 optical upper limit
  26. GRB 260601A: CALET Gamma-Ray Burst Monitor detection
  27. EP260602a: EP-FXT follow-up observation
  28. EP260603a: Global MASTER-Net observations report
  29. EP260603a: Einstein Probe detection of a fast X-ray transient
  30. EP260602d: Optical Upper limits with kinder observations
  31. EP260602b: Liverpool Telescope observations
  32. EP260602a: Liverpool Telescope optical upper limits
  33. EP260602b: Liverpool Telescope and LCO observations
  34. EP260602a: GTC and Liverpool Telescope optical observations
  35. EP260601a/GRB 260601B: EP-FXT follow-up observation
  36. GRB 260601B / EP260601a: Mondy optical upper limit
  37. EP260602b: EP-FXT follow-up observation
  38. GRB 260601B/EP260601a: Glowbug gamma-ray detection
  39. GRB 260603A: Kilonova-Catcher optical upper limit
  40. GRB 260603A: SVOM/VT optical observations
  41. EP260602a: NOT NIR J-band observations
  42. GRB 260603A: SVOM/COLIBRÍ (FM-GFT) photometric redshift z = 3.57
  43. EP260602d: Einstein Probe detection of a fast X-ray transient
  44. Fermi trigger No 802141998: Global MASTER-Net observations report
  45. GRB 260601A: SVOM/GRM observation of a short burst
  46. EP260602c: Einstein Probe detection of a fast X-ray transient
  47. GRB 260603A: SVOM/COLIBRÍ (GFT-FM) optical counterpart candidate
  48. EP260602a: COLIBRÍ optical observations
  49. GRB260601B/EP260601a: NOT near-infrared observations
  50. SVOM GRB260603.23: Global MASTER-Net observations report
  51. GRB 260603A: SVOM detection of a burst
  52. EP260602b: Einstein Probe detection of a fast X-ray transient
  53. Fermi GRB 260602B: Global MASTER-Net observations report
  54. Fermi GRB 260602B: Global MASTER-Net observations report
  55. EP260530a: Xinglong optical spectroscopy of EP260530a / AT 2026nwl
  56. EP260602a: SVOM/VT optical candidate
  57. EP-WXT trigger 01709266414 (EP260602b): JinShan optical counterpart detection
  58. GRB 260601B/EP260601a: J-band upper limit with WINTER
  59. EP260530a/AT 2026nwl: COLIBRÍ optical follow up
  60. EP260530a/AT 2026nwl: KAIT optical observations
  61. GRB 260601B: CALET Gamma-Ray Burst Monitor detection
  62. EP260602a: Optical upper limits with Kinder observations
  63. GRB 260601B / EP260601a: NuSTAR detection of prompt emission
  64. EP260602a: Einstein Probe detection of a fast X-ray transient
  65. GRB 260601B/EP260601a: SVOM/VT optical observations
  66. GRB 260601B/EP260601a: GECAM-B analysis suggests a possible long duration Type I burst
  67. GRB 260601B: GECAM-B detection of a burst probably associated with EP260601a
  68. EP260601a: Einstein Probe detection of an X-ray transient
  69. EP-WXT trigger 01709266307 (EP260601a): COLIBRÍ optical observations
  70. EP-WXT trigger 01709266307 (EP260601a): JinShan optical counterpart detection
  71. GRB 260601A: Glowbug gamma-ray detection of a short burst
  72. GRB 260531B: Glowbug gamma-ray detection
  73. GRB 260601A: Fermi GBM Observation
  74. EP260530a/AT 2026nwl: COLIBRÍ optical observations
  75. GRB 260527A/EP260527a: Glowbug gamma-ray detection
  76. Fermi GRB 260601A: Global MASTER-Net observations report
  77. GRB 260601A: Fermi GBM Final Real-time Localization
  78. The EP-WXT trigger 01709266272 is likely a flaring star
  79. AT2026nik: EP-FXT X-ray counterpart
  80. Fermi trigger No 801900520: Global MASTER-Net observations report
  81. GRB 260531A: MAXI/GSC detection
  82. AT 2026nuz: COLIBRÍ optical observations
  83. EP260527a/GRB 260527A: optical upper limit with Kinder observations
  84. GRB 260429B / EP260429a: COLIBRÍ optical counterpart candidate
  85. GRB 260527A/EP260527a: VLT/X-shooter tentative redshift
  86. Fermi GRB 260529A: Global MASTER-Net observations report
  87. EP260526a: SVOM/VT optical upper limits
  88. EP260527a / GRB 260527A: VLT detection of the optical and nIR counterpart
  89. EP260527a/GRB 260527A: Infrared J upper limit with MDM/MIRAGE
  90. EP260527a/GRB 260527A: EP-FXT follow-up observation
  91. GRB 260527A: GECAM-B detection of a short burst probably associated with EP260527a
  92. EP260527a: SVOM/VT optical observation
  93. EP260527a: COLIBRÍ optical detection
  94. EP260527a: Einstein Probe detection of a fast X-ray transient
  95. Fermi trigger No 801580882: Global MASTER-Net observations report
  96. EP260526a: LCO optical upper limits
  97. EP260526a: Einstein Probe detection of a fast X-ray transient
  98. EP260526.405: COLIBRÍ optical upper limits
  99. The EP-WXT trigger 01709266106 is not a real source
  100. Fermi GRB 260526A: Global MASTER-Net observations report

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