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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"

36736 results found.

  1. GRB 260310A / AT 2026fgk: COLIBRÍ optical observations
  2. GRB 260310A / AT2026fgk: CAHA 1.23m telescope optical observations
  3. GRB 260310A / AT2026fgk : MASTER OT rebrightening during 7h observations
  4. GRB260310A / AT2026fgk: P200 Spectroscopy
  5. GRB 260312B: Glowbug gamma-ray detection
  6. GRB 260310A: Fermi GBM Observation
  7. GRB 260310A: potential optical counterpart
  8. Fermi GRB 260312B: Global MASTER-Net observations report
  9. Fermi GRB 260311B: Global MASTER-Net observations report
  10. Swift BAT trigger 1500148: A solar flare
  11. GRB 260312B: BALROG localization (Fermi Trigger 795001611 / GRB 260312407)
  12. GRB 260312B: Fermi GBM Final Real-time Localization
  13. GRB 260310B: GECAM-B observation of a burst
  14. Retraction of GCN 43965: GRB is actually solar flare
  15. GRB 260312A: Swift detection of a burst
  16. GRB 260311B: Fermi GBM Final Real-time Localization
  17. GRB 260131A/B: radio detection with the VLA
  18. GRB260307A: GECAM-B observation of a burst
  19. GRB 260308A: SVOM/GRM observation of a short GRB
  20. EP260306a: Mondy optical upper limit
  21. GRB 260310A: AstroSat CZTI detection of a long burst
  22. GRB 260311A: Fermi GBM Final Real-time Localization
  23. Fermi GRB 260310B: Global MASTER-Net observations report
  24. GRB 260310B: Fermi GBM Final Real-time Localization
  25. Fermi GRB 260310A: Global MASTER-Net observations report
  26. GRB 260307B: SVOM/ECLAIRs refined analysis
  27. GRB 260208A: radio detection with the VLA
  28. GRB 260310A: Fermi GBM Final Real-time Localization
  29. GRB 260307A: Glowbug gamma-ray detection
  30. GRB 260308A: Fermi GBM Final Real-time Localization
  31. Fermi GBM Sub-Threshold Detection of GRB 260307B
  32. GRB 260307B: Mephisto optical upper limits
  33. GRB 260307B: possible NOT optical counterpart
  34. GRB 260307B: SVOM/VT upper limit with X band data analysis
  35. Fermi GRB 260307A: Global MASTER-Net observations report
  36. GRB 260307B: SVOM/VT optical candidate
  37. GRB 260307B: SVOM/C-GFT upper limit
  38. GRB 260307B: SVOM detection of a burst
  39. GRB 260307A: Fermi GBM Final Localization
  40. GRB 260211A: late-time NOT i-band observations consistent with archival flux
  41. GRB 260207A: TESS Detection and Possible VLA Counterpart
  42. EP260302a: Optical afterglow rebrightening
  43. GRB 260228A: further EP-FXT observations and X-ray afterglow confirmation
  44. GRB 260303A: 1.3m DFOT optical upper limit (duplicate submission)
  45. GRB 260303A: 1.3m DFOT optical upper limit
  46. GRB 260211A: SVOM/VT optical rebrightening at 20 days after the burst, SN candidate
  47. GRB 260303A: SVOM/ECLAIRs refined analysis
  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 260304A: AstroSat CZTI detection of a long burst
  52. GRB 260303A: SVOM/VT optical observations
  53. GRB 260303A: J-band observations with WINTER
  54. GRB 260303B: NuSTAR detection of prompt emission
  55. Fermi GRB 260303B: Global MASTER-Net observations report
  56. GRB 260228A: SVOM/ECLAIRs refined analysis
  57. GRB 260225A: SVOM/ECLAIRs refined analysis
  58. GRB 260303B: BALROG localization (Fermi Trigger 794237065 / GRB 260303559)
  59. GRB 260303B: Fermi GBM Final Real-time Localization
  60. GRB 260303A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  61. GRB 260303A: SVOM detection of a burst
  62. GRB 260228A: EP-FXT follow-up observation
  63. GRB 251130B: TERI Gamma-ray detection
  64. GRB 260208A: TERI Gamma-ray detection
  65. GRB 260302A: Fermi GBM Final Real-time Localization
  66. EP260227a: Mondy optical observations
  67. GRB 260228A: CAHA 2.2m telescope optical upper limit
  68. GRB 260228A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  69. GRID detection of GRB 260225D
  70. GRB 260228A: SVOM/VT optical upper limits
  71. GRB 260225D: SVOM/GRM observation
  72. GRB 260225B: SVOM/GRM observation
  73. GRB 260228A: SVOM detection of a burst
  74. GRB 260226A: Asiago r-band upper limit
  75. GRB 260225A: SVOM/VT optical continued observations and upper limit
  76. GRID detection of GRB 260223A
  77. GRB 260226A: Insight-HXMT/HE detection of the very bright burst
  78. Konus-Wind detection of GRB 260226A
  79. GRB 260223A: 7DT detection and Medium-band SED of Afterglow
  80. GRB 260225A: WINTER J-band upper limit
  81. GRB 260226A: CALET Gamma-Ray Burst Monitor detection
  82. GRB 260226A: COLIBRÍ optical upper limits
  83. GRB 260226A: LCOGT Optical Upper Limit
  84. GRB 260225D: Glowbug gamma-ray detection of a likely short burst
  85. GRB 260226A: Glowbug gamma-ray detection
  86. GRB 260226A: NuSTAR detection of bright prompt emission
  87. GRB 260226A : GROWTH-India Telescope optical observations
  88. GRB 260226A: LAST optical upper limit
  89. GRB 260226A: Fermi GBM observation
  90. GRB 260226A: Fermi-LAT refined analysis
  91. Fermi GRB 260226A: Global MASTER-Net observations report
  92. GRB 260226A: AstroSat CZTI detection of bright long burst
  93. GRB 260226A: Fermi-LAT detection of a bright burst
  94. GRB 260226A???: BALROG localization (Fermi Trigger 793795080 / GRB 260226443)
  95. GRB260225A: SVOM/ECLAIRs refined position
  96. GRB 260226A: Fermi GBM Final Real-time Localization
  97. GRB 260225A: EP-FXT follow-up observation
  98. GRB 260225A: SVOM/VT optical observation
  99. GRB 260225A: SVOM/COLIBRÍ (FM-GFT) Detection of an Optical Counterpart Candidate
  100. GRB 260225C: Fermi GBM Final Real-time Localization

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