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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"

12272 results found.

  1. GRB 260310A / AT 2026fgk: COLIBRÍ continuing optical observations
  2. GRB 260310A / AT2026fgk: further CAHA 1.23m telescope optical observations suggest shallow decay
  3. Fermi GRB 260314A: Global MASTER-Net observations report
  4. Fermi GRB 260313A: Global MASTER-Net observations report
  5. GRB 260314A: Fermi GBM Final Real-time Localization
  6. GRB 260310A/AT 2026fgk: WINTER NIR Detections
  7. GRB 260313A: A Correction to the Fermi GBM Final Localization
  8. GRB 260310A: Einstein Probe Follow-up X-ray Telescope (FXT) Detection
  9. GRB 260310A/AT 2026fgk: J-band observations by the SYSU 80 cm infrared telescope
  10. GRB 260310B: Insight-HXMT/HE detection
  11. GRB 260310A/AT 2026fgk: DDOTI Optical Detection
  12. GRB 260312B: AstroSat CZTI detection
  13. GRB 260313A: Fermi GBM Final Real-time Localization
  14. GRB 260308A: Insight-HXMT/HE detection
  15. GRB 260307A: CALET Gamma-Ray Burst Monitor detection
  16. GRB 260310A / AT 2026fgk: Location in the Epeak - Eiso diagram
  17. GRB 260310A / AT 2026fgk: COLIBRÍ optical observations
  18. GRB 260310A / AT2026fgk: CAHA 1.23m telescope optical observations
  19. GRB 260310A / AT2026fgk : MASTER OT rebrightening during 7h observations
  20. GRB260310A / AT2026fgk: P200 Spectroscopy
  21. GRB 260312B: Glowbug gamma-ray detection
  22. GRB 260310A: Fermi GBM Observation
  23. GRB 260310A: potential optical counterpart
  24. Fermi GRB 260312B: Global MASTER-Net observations report
  25. Fermi GRB 260311B: Global MASTER-Net observations report
  26. GRB 260312B: BALROG localization (Fermi Trigger 795001611 / GRB 260312407)
  27. GRB 260312B: Fermi GBM Final Real-time Localization
  28. GRB 260310B: GECAM-B observation of a burst
  29. GRB 260311B: Fermi GBM Final Real-time Localization
  30. GRB 260131A/B: radio detection with the VLA
  31. GRB260307A: GECAM-B observation of a burst
  32. GRB 260308A: SVOM/GRM observation of a short GRB
  33. GRB 260310A: AstroSat CZTI detection of a long burst
  34. GRB 260311A: Fermi GBM Final Real-time Localization
  35. Fermi GRB 260310B: Global MASTER-Net observations report
  36. GRB 260310B: Fermi GBM Final Real-time Localization
  37. Fermi GRB 260310A: Global MASTER-Net observations report
  38. GRB 260307B: SVOM/ECLAIRs refined analysis
  39. GRB 260208A: radio detection with the VLA
  40. GRB 260310A: Fermi GBM Final Real-time Localization
  41. GRB 260307A: Glowbug gamma-ray detection
  42. GRB 260308A: Fermi GBM Final Real-time Localization
  43. Fermi GBM Sub-Threshold Detection of GRB 260307B
  44. Fermi GRB 260307A: Global MASTER-Net observations report
  45. GRB 260307A: Fermi GBM Final Localization
  46. GRB 260207A: TESS Detection and Possible VLA Counterpart
  47. GRB 260211A: SVOM/VT optical rebrightening at 20 days after the burst, SN candidate
  48. Fermi GRB 260305A: Global MASTER-Net observations report
  49. GRB 260305A: Fermi GBM Final Real-time Localization
  50. GRB 260303B: AstroSat CZTI detection
  51. GRB 260303B: NuSTAR detection of prompt emission
  52. Fermi GRB 260303B: Global MASTER-Net observations report
  53. IceCube-260217A: No Candidate Transients from the Zwicky Transient Facility
  54. GRB 260303B: BALROG localization (Fermi Trigger 794237065 / GRB 260303559)
  55. GRB 260303B: Fermi GBM Final Real-time Localization
  56. GRB 251130B: TERI Gamma-ray detection
  57. GRB 260208A: TERI Gamma-ray detection
  58. GRB 260302A: Fermi GBM Final Real-time Localization
  59. GRB 260225B: SVOM/GRM observation
  60. GRB 260226A: Asiago r-band upper limit
  61. GRID detection of GRB 260223A
  62. IceCube cascade alert 142200_1517143 retraction
  63. GRB 260226A: Insight-HXMT/HE detection of the very bright burst
  64. Konus-Wind detection of GRB 260226A
  65. GRB 260223A: 7DT detection and Medium-band SED of Afterglow
  66. GRB 260226A: CALET Gamma-Ray Burst Monitor detection
  67. GRB 260226A: COLIBRÍ optical upper limits
  68. GRB 260226A: LCOGT Optical Upper Limit
  69. GRB 260226A: Glowbug gamma-ray detection
  70. GRB 260226A: NuSTAR detection of bright prompt emission
  71. GRB 260226A : GROWTH-India Telescope optical observations
  72. GRB 260226A: LAST optical upper limit
  73. GRB 260226A: Fermi GBM observation
  74. GRB 260226A: Fermi-LAT refined analysis
  75. Fermi GRB 260226A: Global MASTER-Net observations report
  76. GRB 260226A: AstroSat CZTI detection of bright long burst
  77. GRB 260226A: Fermi-LAT detection of a bright burst
  78. GRB 260226A???: BALROG localization (Fermi Trigger 793795080 / GRB 260226443)
  79. GRB 260226A: Fermi GBM Final Real-time Localization
  80. GRB 260225C: Fermi GBM Final Real-time Localization
  81. GRB 260223A: Fermi GBM Observation
  82. GRB 260225B: Fermi GBM Final Real-time Localization
  83. GRB 260223A: Glowbug gamma-ray detection
  84. GRB 260223A: COLIBRÍ optical afterglow decay confirmation
  85. GRB 260223A: SVOM/VT optical observation
  86. GRB 260223A: SVOM/GRM observation
  87. GRB 260223A: COLIBRÍ further optical observations and a brightening
  88. GRB 260223A: COLIBRÍ optical observations
  89. GRB 260223A: DDOTI Optical Candidate
  90. GRB 260223A: BALROG localization (Fermi Trigger 793512674 / GRB 260223174)
  91. Fermi GRB 260223A: Global MASTER-Net observations report
  92. GRB 260223A: Fermi GBM Final Real-time Localization
  93. GRB 260222A: Fermi GBM Final Real-time Localization
  94. Fermi GRB 260221B: Global MASTER-Net observations report
  95. GRB 260221B: Fermi GBM Final Real-time Localization
  96. Fermi GRB 260221A: Global MASTER-Net observations report
  97. GRB 260221A: Fermi GBM Final Real-time Localization
  98. GRB 260219A: AstroSat CZTI detection
  99. IceCube-260217A: Upper limits from a search for additional neutrino events in IceCube
  100. GRB 260219A: GECAM-B observation of a long burst

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