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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"
  1. IceCube-260315A/AT2026fpm: EP-FXT follow-up observation
  2. GRB 260317A: Fermi GBM Final Localization
  3. GRB 260316B: GECAM-B observation
  4. GRB 260316B: SVOM/GRM observation
  5. EP260316a / GRB 260316A: SVOM/VT optical upper limits
  6. EP260316a: COLIBRÍ faint optical counterpart candidate
  7. Fermi-LAT Gamma-ray Observations of IceCube-260315A
  8. GRB 260316B: AstroSat CZTI detection
  9. EP260316a: refined analysis of the EP-WXT and EP-FXT observations
  10. IceCube-260315A: Upper limits from a search for additional neutrino events in IceCube
  11. EP260316a: Xinglong optical upper limit
  12. GRB 260316B: Fermi GBM Final Real-time Localization
  13. EP260316a: optical upper limit with Kinder observations
  14. EP260316a / GRB 260316A : Fermi-GBM Sub-Threshold Detection
  15. GRB 260314A: Glowbug gamma-ray detection
  16. The EP-WXT trigger 00199258890 (EP260316a): a correction to the trigger time and FXT automatic follow-up
  17. IceCube-260315A: COLIBRÍ optical observations
  18. EP260314a: Xinglong optical upper limit
  19. EP260314a: optical upper limit with Kinder observations
  20. IceCube Alert-260315A/AT2026fpm Automatic MASTER optical blue counterpart candidate
  21. GRB 260310A / AT2026fgk: 1.3m DFOT optical observations
  22. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS optical observations
  23. GRB 260310A / AT 2026fgk: iTelescope optical observations
  24. EP260314a: COLIBRÍ optical upper limit
  25. GRID detection of GRB 260312B
  26. IceCube-260315A - IceCube observation of a high-energy neutrino candidate track-like event
  27. EP260314a: refined analysis of the EP-WXT and EP-FXT observations
  28. EP260314a: BOOTES-6/DPR optical upper limits at early times
  29. EP260314a: Global MASTER-Net observations report
  30. EP260314a: SVOM/VT optical candidate
  31. Fermi trigger No 795185313: Global MASTER-Net observations report
  32. IceCube Alert 260315A: Global MASTER-Net observations report
  33. EP260314a: Einstein Probe detection of an X-ray transient
  34. The EP-WXT trigger 01709258851: Las Cumbres upper limit
  35. GRB 260314A: GECAM-B observation of a burst
  36. Fermi Gamma-ray Burst Monitor trigger 795185313/260314534 is not a GRB
  37. GRB 260310A / AT2026fgk: SAO RAS optical observations
  38. GRB 260310A/AT2026fgk: radio detection at 15GHz
  39. GRB 260310A / AT2026fgk: TNG NIR detection
  40. GRB 260310A / AT2026fgk: OASDG optical observations
  41. GRB 260310A / AT2026fgk: Multiband optical follow-up with Kinder observations
  42. GRB 260310A / AT 2026fgk: COLIBRÍ continuing optical observations
  43. GRB 260310A / AT2026fgk: further CAHA 1.23m telescope optical observations suggest shallow decay
  44. Fermi GRB 260314A: Global MASTER-Net observations report
  45. Fermi GRB 260313A: Global MASTER-Net observations report
  46. GRB 260314A: Fermi GBM Final Real-time Localization
  47. GRB 260310A/AT 2026fgk: WINTER NIR Detections
  48. GRB 260313A: A Correction to the Fermi GBM Final Localization
  49. GRB 260310A: Einstein Probe Follow-up X-ray Telescope (FXT) Detection
  50. GRB 260310A/AT 2026fgk: J-band observations by the SYSU 80 cm infrared telescope
  51. GRB 260310B: Insight-HXMT/HE detection
  52. GRB 260310A/AT 2026fgk: DDOTI Optical Detection
  53. GRB 260310A: NOT optical polarimetry
  54. GRB 260312B: AstroSat CZTI detection
  55. Swift BAT trigger 1500295: A solar flare
  56. GRB 260313A: Fermi GBM Final Real-time Localization
  57. GRB 260310A/AT 2026fgk: Bok spectroscopic observation
  58. Swift BAT trigger 1500287: A solar flare
  59. GRB 260310A / AT2026fgk: OSIRIS+/GTC spectroscopy confirms redshift z = 0.153
  60. GRB 260308A: Insight-HXMT/HE detection
  61. GRB 260307A: CALET Gamma-Ray Burst Monitor detection
  62. GRB 260310A / AT 2026fgk: Location in the Epeak - Eiso diagram
  63. GRB 260310A / AT 2026fgk: COLIBRÍ optical observations
  64. GRB 260310A / AT2026fgk: CAHA 1.23m telescope optical observations
  65. GRB 260310A / AT2026fgk : MASTER OT rebrightening during 7h observations
  66. GRB260310A / AT2026fgk: P200 Spectroscopy
  67. GRB 260312B: Glowbug gamma-ray detection
  68. GRB 260310A: Fermi GBM Observation
  69. GRB 260310A: potential optical counterpart
  70. Fermi GRB 260312B: Global MASTER-Net observations report
  71. Fermi GRB 260311B: Global MASTER-Net observations report
  72. Swift BAT trigger 1500148: A solar flare
  73. GRB 260312B: BALROG localization (Fermi Trigger 795001611 / GRB 260312407)
  74. GRB 260312B: Fermi GBM Final Real-time Localization
  75. The EP-WXT trigger 01709258843 is not a real source
  76. GRB 260310B: GECAM-B observation of a burst
  77. Retraction of GCN 43965: GRB is actually solar flare
  78. GRB 260312A: Swift detection of a burst
  79. GRB 260311B: Fermi GBM Final Real-time Localization
  80. GRB 260131A/B: radio detection with the VLA
  81. EP260302a: MeerKAT radio counterpart
  82. GRB260307A: GECAM-B observation of a burst
  83. GRB 260308A: SVOM/GRM observation of a short GRB
  84. EP260306a: Mondy optical upper limit
  85. GRB 260310A: AstroSat CZTI detection of a long burst
  86. GRB 260311A: Fermi GBM Final Real-time Localization
  87. Fermi GRB 260310B: Global MASTER-Net observations report
  88. GRB 260310B: Fermi GBM Final Real-time Localization
  89. Fermi GRB 260310A: Global MASTER-Net observations report
  90. GRB 260307B: SVOM/ECLAIRs refined analysis
  91. GRB 260208A: radio detection with the VLA
  92. GRB 260310A: Fermi GBM Final Real-time Localization
  93. GRB 260307A: Glowbug gamma-ray detection
  94. GRB 260308A: Fermi GBM Final Real-time Localization
  95. Fermi GBM Sub-Threshold Detection of GRB 260307B
  96. GRB 260307B: Mephisto optical upper limits
  97. GRB 260307B: possible NOT optical counterpart
  98. GRB 260307B: SVOM/VT upper limit with X band data analysis
  99. Fermi GRB 260307A: Global MASTER-Net observations report
  100. GRB260307B: GROWTH-India Telescope optical upper limit

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