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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"

27032 results found.

  1. EP260430a: LCO optical upper limits
  2. GRB 260430A / EP260430a: COLIBRÍ optical upper limit
  3. GRB 260429A: Fermi GBM Detection
  4. Fermi GRB 260429A: Global MASTER-Net observations report
  5. EP260430a: Global MASTER-Net observations report
  6. EP260430a: Einstein Probe detection of an X-ray transient
  7. EP260429a: EP-WXT detection of a fast X-ray transient
  8. GRB 260429A: Fermi GBM Final Real-time Localization
  9. GRB 260428A: SVOM/GRM observation of a possible short burst with extended emission
  10. GRB 260428A: GECAM-B detection of a possible long duration Type I burst
  11. Fermi GRB 260428A: Global MASTER-Net observations report
  12. GRB 260424B: COLIBRÍ optical upper limit
  13. GRB 260428A: Fermi GBM Final Real-time Localization
  14. GRB 260424C: Fermi GBM Final Localization
  15. GRB 260424B: SVOM/GRM detection of a short burst
  16. GRB 260305A: likely detection by Fermi-LAT and the LAT gamma-ray position
  17. IceCube Alert 260425A: Global MASTER-Net observations report
  18. Fermi trigger No 798737427: Global MASTER-Net observations report
  19. GRB 260421B: Kilonova-Catcher optical afterglow detection
  20. The EP-WXT trigger 01709258652: Mondy optical observations
  21. GRB 250328A: VLT host galaxy discovery and redshift z = 1.250
  22. GRB 260421B: SVOM/ECLAIRs refined analysis
  23. GRB 260421B: 3.6m DOT optical observation
  24. EP-WXT trigger 01709260362: FRAM-ORM optical observations confirm flaring star G 151-9
  25. GRB 250530A: VLT/X-shooter host galaxy redshift z = 1.486
  26. GRB 260421B: SVOM/GRM observation
  27. GRB260421B: J band upper limit by SYSU 80cm infrared telescope
  28. GRB 260421B: EP-FXT follow-up observation
  29. The EP-WXT trigger 01709260362 is likely a flaring star
  30. GRB 260421B: J-band upper limit with WINTER
  31. GRB 260421B: LCO optical counterpart detection
  32. GRB 260421B: Fermi GBM Observation
  33. Fermi Gamma-ray Burst Monitor trigger 798482368/260421694 is not a GRB
  34. GRB 260412A: SVOM/ECLAIRs refined analysis
  35. GRB 260421B: SVOM/VT optical observations
  36. EP260416a: J band upper limit by SYSU 80cm infrared telescope
  37. GRB 260310A: Late-time Chandra X-ray Detection
  38. EP260416a: 1.3m DFOT optical observation
  39. GRB 260415A: CALET Gamma-Ray Burst Monitor detection
  40. GRB 260415B: CALET Gamma-Ray Burst Monitor detection
  41. Fermi GRB 260421C: Global MASTER-Net observations report
  42. GRB 260421C: Fermi GBM Final Real-time Localization
  43. GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
  44. Fermi GRB 260421B: Global MASTER-Net observations report
  45. GRB 260421B: LCO optical afterglow confirmation
  46. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  47. GRB 260421B: SVOM detection of a long burst
  48. GRB 260421B: BALROG localization (Fermi Trigger 798437606 / GRB 260421176)
  49. GRB 260421B: Fermi GBM Final Real-time Localization
  50. Fermi GRB 260421A: Global MASTER-Net observations report
  51. GRB 260421A: Fermi GBM Final Real-time Localization
  52. EP260321a: VLA radio follow-up
  53. GRB 260412A: LCOGT Optical Upper Limits
  54. The EP-WXT trigger 01709260314 is likely a flaring star
  55. EP-WXT trigger 01709260303: KAIT optical observations
  56. EP260416a: 1.5m OSN and 2.2m CAHA optical monitoring
  57. The EP-WXT trigger 01709260303 is likely a flaring star
  58. GRB 260417A: SVOM/GRM observation
  59. EP260321A/AT2026gzf: Optical observation from 1.3m DFOT
  60. GRB 260419B: Fermi GBM Final Real-time Localization
  61. GRB 260419A: Fermi GBM Final Real-time Localization
  62. Fermi trigger No 798275385: Global MASTER-Net observations report
  63. EP260417a: GROWTH-India Telescope optical upper limit
  64. Fermi GRB 260417B: Global MASTER-Net observations report
  65. EP260417b: GROWTH-India Telescope optical upper limit
  66. EP260416a: Ondrejov D50 optical detection
  67. GRB 260418B: Fermi GBM Final Real-time Localization
  68. EP260416a: VLT/FORS2 spectroscopic redshift confirmation
  69. EP260417a: Global MASTER-Net observations report
  70. EP260417a/GRB 260417A: refined analysis of the EP-WXT and follow-up EP-FXT observations
  71. GRB 260418A: Fermi GBM Final Real-time Localization
  72. EP260416a: GMG Optical Observation
  73. Fermi GRB 260417A: Global MASTER-Net observations report
  74. GRB 260417B: Fermi GBM Final Real-time Localization
  75. EP260416a: LCO observations confirm end of flaring phase
  76. EP260324a / AT2026hir: Further multiband optical follow-up with the PKU 60cm Telescope
  77. EP260417a: TRT optical counterpart detection
  78. EP260417a: Einstein Probe detection of an X-ray transient
  79. EP260416a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  80. EP260417b: Einstein Probe detection of a fast X-ray transient
  81. EP-WXT trigger 01709259586: KAIT optical observations
  82. EP260416a: COLIBRÍ confirmation of the optical rebrightening
  83. EP260416a: WFST optical observations and rebrightening
  84. GRB 260417A: Fermi GBM Final Real-time Localization
  85. EP260416a: SVOM/VT optical observation
  86. GOTO26djh/AT2026jpw: SVOM/VT optical observation
  87. GRB 260415B: Glowbug gamma-ray detection
  88. EP260416a: COLIBRÍ optical counterpart candidate
  89. COLIBRI optical observations of the transient GOTO26djh/AT2026jpw
  90. EP260416a: Global MASTER-Net observations report
  91. EP260416a: Einstein Probe detection of an X-ray transient
  92. GRB 260415B: NuSTAR detection of long prompt emission
  93. GRB 260415B: Fermi GBM Final Localization
  94. GRB 260415A: Fermi GBM Final Real-time Localization
  95. Fermi trigger No 797912738: Global MASTER-Net observations report
  96. EP260409a: Early NIR limits from MIRAGE on the MDM 1.3m telescope
  97. GRB 260414A: Fermi GBM Final Real-time Localization
  98. The EP-WXT trigger 01709260122 is likely a flaring star
  99. Fermi GRB 260413A: Global MASTER-Net observations report
  100. GRB 260413A: Fermi GBM Final Real-time Localization

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