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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"

27030 results found.

  1. GRB 260429A: Fermi GBM Detection
  2. Fermi GRB 260429A: Global MASTER-Net observations report
  3. EP260430a: Global MASTER-Net observations report
  4. EP260430a: Einstein Probe detection of an X-ray transient
  5. EP260429a: EP-WXT detection of a fast X-ray transient
  6. GRB 260429A: Fermi GBM Final Real-time Localization
  7. GRB 260428A: SVOM/GRM observation of a possible short burst with extended emission
  8. GRB 260428A: GECAM-B detection of a possible long duration Type I burst
  9. Fermi GRB 260428A: Global MASTER-Net observations report
  10. GRB 260424B: COLIBRÍ optical upper limit
  11. GRB 260428A: Fermi GBM Final Real-time Localization
  12. GRB 260424C: Fermi GBM Final Localization
  13. GRB 260424B: SVOM/GRM detection of a short burst
  14. GRB 260305A: likely detection by Fermi-LAT and the LAT gamma-ray position
  15. IceCube Alert 260425A: Global MASTER-Net observations report
  16. Fermi trigger No 798737427: Global MASTER-Net observations report
  17. GRB 260421B: Kilonova-Catcher optical afterglow detection
  18. The EP-WXT trigger 01709258652: Mondy optical observations
  19. GRB 250328A: VLT host galaxy discovery and redshift z = 1.250
  20. GRB 260421B: SVOM/ECLAIRs refined analysis
  21. GRB 260421B: 3.6m DOT optical observation
  22. EP-WXT trigger 01709260362: FRAM-ORM optical observations confirm flaring star G 151-9
  23. GRB 250530A: VLT/X-shooter host galaxy redshift z = 1.486
  24. GRB 260421B: SVOM/GRM observation
  25. GRB260421B: J band upper limit by SYSU 80cm infrared telescope
  26. GRB 260421B: EP-FXT follow-up observation
  27. The EP-WXT trigger 01709260362 is likely a flaring star
  28. GRB 260421B: J-band upper limit with WINTER
  29. GRB 260421B: LCO optical counterpart detection
  30. GRB 260421B: Fermi GBM Observation
  31. Fermi Gamma-ray Burst Monitor trigger 798482368/260421694 is not a GRB
  32. GRB 260412A: SVOM/ECLAIRs refined analysis
  33. GRB 260421B: SVOM/VT optical observations
  34. EP260416a: J band upper limit by SYSU 80cm infrared telescope
  35. GRB 260310A: Late-time Chandra X-ray Detection
  36. EP260416a: 1.3m DFOT optical observation
  37. GRB 260415A: CALET Gamma-Ray Burst Monitor detection
  38. GRB 260415B: CALET Gamma-Ray Burst Monitor detection
  39. Fermi GRB 260421C: Global MASTER-Net observations report
  40. GRB 260421C: Fermi GBM Final Real-time Localization
  41. GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
  42. Fermi GRB 260421B: Global MASTER-Net observations report
  43. GRB 260421B: LCO optical afterglow confirmation
  44. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  45. GRB 260421B: SVOM detection of a long burst
  46. GRB 260421B: BALROG localization (Fermi Trigger 798437606 / GRB 260421176)
  47. GRB 260421B: Fermi GBM Final Real-time Localization
  48. Fermi GRB 260421A: Global MASTER-Net observations report
  49. GRB 260421A: Fermi GBM Final Real-time Localization
  50. EP260321a: VLA radio follow-up
  51. GRB 260412A: LCOGT Optical Upper Limits
  52. The EP-WXT trigger 01709260314 is likely a flaring star
  53. EP-WXT trigger 01709260303: KAIT optical observations
  54. EP260416a: 1.5m OSN and 2.2m CAHA optical monitoring
  55. The EP-WXT trigger 01709260303 is likely a flaring star
  56. GRB 260417A: SVOM/GRM observation
  57. EP260321A/AT2026gzf: Optical observation from 1.3m DFOT
  58. GRB 260419B: Fermi GBM Final Real-time Localization
  59. GRB 260419A: Fermi GBM Final Real-time Localization
  60. Fermi trigger No 798275385: Global MASTER-Net observations report
  61. EP260417a: GROWTH-India Telescope optical upper limit
  62. Fermi GRB 260417B: Global MASTER-Net observations report
  63. EP260417b: GROWTH-India Telescope optical upper limit
  64. EP260416a: Ondrejov D50 optical detection
  65. GRB 260418B: Fermi GBM Final Real-time Localization
  66. EP260416a: VLT/FORS2 spectroscopic redshift confirmation
  67. EP260417a: Global MASTER-Net observations report
  68. EP260417a/GRB 260417A: refined analysis of the EP-WXT and follow-up EP-FXT observations
  69. GRB 260418A: Fermi GBM Final Real-time Localization
  70. EP260416a: GMG Optical Observation
  71. Fermi GRB 260417A: Global MASTER-Net observations report
  72. GRB 260417B: Fermi GBM Final Real-time Localization
  73. EP260416a: LCO observations confirm end of flaring phase
  74. EP260324a / AT2026hir: Further multiband optical follow-up with the PKU 60cm Telescope
  75. EP260417a: TRT optical counterpart detection
  76. EP260417a: Einstein Probe detection of an X-ray transient
  77. EP260416a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  78. EP260417b: Einstein Probe detection of a fast X-ray transient
  79. EP-WXT trigger 01709259586: KAIT optical observations
  80. EP260416a: COLIBRÍ confirmation of the optical rebrightening
  81. EP260416a: WFST optical observations and rebrightening
  82. GRB 260417A: Fermi GBM Final Real-time Localization
  83. EP260416a: SVOM/VT optical observation
  84. GOTO26djh/AT2026jpw: SVOM/VT optical observation
  85. GRB 260415B: Glowbug gamma-ray detection
  86. EP260416a: COLIBRÍ optical counterpart candidate
  87. COLIBRI optical observations of the transient GOTO26djh/AT2026jpw
  88. EP260416a: Global MASTER-Net observations report
  89. EP260416a: Einstein Probe detection of an X-ray transient
  90. GRB 260415B: NuSTAR detection of long prompt emission
  91. GRB 260415B: Fermi GBM Final Localization
  92. GRB 260415A: Fermi GBM Final Real-time Localization
  93. Fermi trigger No 797912738: Global MASTER-Net observations report
  94. EP260409a: Early NIR limits from MIRAGE on the MDM 1.3m telescope
  95. GRB 260414A: Fermi GBM Final Real-time Localization
  96. The EP-WXT trigger 01709260122 is likely a flaring star
  97. Fermi GRB 260413A: Global MASTER-Net observations report
  98. GRB 260413A: Fermi GBM Final Real-time Localization
  99. GRB 260411B: GECAM-B observation of a long burst
  100. EP260321a: SVOM/VT optical observations and color changes around peak

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