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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"

27354 results found.

  1. GRB 260401A: NuSTAR detection of prompt emission
  2. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  3. GRB 260401A: MAXI/GSC detection
  4. GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
  5. GRB 260401A: Fermi GBM Final Real-time Localization
  6. EP260329b: Mondy and Assy-Turgen optical upper limits
  7. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  8. EP260321a :Xinglong optical observations
  9. EP260327a: Xinglong optical upper limit
  10. GRB 260330B: SVOM/VT optical upper limits
  11. Konus-Wind detection of GRB 260320A
  12. GRB 260321A: SVOM/ECLAIRs refined analysis
  13. EP260329b: J-band upper limits with WINTER
  14. EP260329a: J-band upper limit with WINTER
  15. GRB 260330A: Glowbug gamma-ray detection
  16. Fermi GBM Sub-Threshold Detection of GRB 260330B
  17. GRB 260330B: LCO optical upper limits
  18. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  19. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  20. EP260329a: COLIBRÍ optical upper limit
  21. EP260329a: EP-FXT follow up observation
  22. EP260329a: NOT optical counterpart candidate
  23. EP260329b: Global MASTER-Net observations report
  24. Fermi trigger No 796485221: Global MASTER-Net observations report
  25. GRB 260327A: Insight-HXMT/HE detection
  26. EP260329b: Optical follow-up with Kinder observations
  27. EP 260329b: COLIBRÍ optical observations
  28. EP260329a: Optical upper limit with Kinder observations
  29. EP260329b: LCO optical observations of the counterpart
  30. GRB 260326A: Insight-HXMT/HE detection
  31. EP260329b: Einstein Probe detection of an X-ray transient
  32. EP260329a: Einstein Probe detection of an X-ray transient
  33. EP-WXT trigger 01709259209: TRT optical counterpart detection
  34. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  35. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  36. EP260327a: SVOM/VT optical upper limits
  37. EP260327a: WINTER J-band upper limit
  38. EP260327a: COLIBRÍ optical upper limits
  39. EP260327a: Gemini-North optical upper limits
  40. EP260324a: GROWTH-India Telescope optical observation
  41. EP260327a: Global MASTER-Net observations report
  42. EP260327a: Einstein Probe detection of an X-ray transient
  43. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  44. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  45. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  46. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  47. GRB 260326A: Fermi GBM Detection
  48. EP260321a: JinShan near-infrared observations
  49. EP260321a: Upper limits from a neutrino search with IceCube
  50. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  51. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  52. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  53. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  54. Fermi GRB 260323A: Global MASTER-Net observations report
  55. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  56. GRB 260320A: Glowbug gamma-ray detection
  57. EP260321a: COLIBRÍ further optical observations and brightening
  58. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  59. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  60. GRB 260321A: EP-FXT follow-up observation
  61. EP260321a: GOTO detection of blue variable source
  62. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  63. EP260321a: further Kinder optical observations
  64. GRB 260321A: SVOM/VT optical upper limits
  65. EP260321a: Las Cumbres upper limit
  66. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  67. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  68. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  69. EP260321a: SVOM/VT optical upper limit
  70. Fermi GBM Sub-Threshold Detection of GRB 260321A
  71. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  72. EP260321a: Global MASTER-Net observations report
  73. EP260321a: Einstein Probe detection of an X-ray transient
  74. GRB 260318A: Glowbug gamma-ray detection
  75. GRB 260310A / AT 2026fgk: KAIT optical observations
  76. GRB 260320A: NuSTAR detection of prompt emission
  77. EP-WXT trigger 01709258989: KAIT confirmation of a stellar flare
  78. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
  79. GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening
  80. EP-WXT trigger 01709258989: confirmation of a stellar flare by BOOTES-7
  81. GRB 260318A: SVOM/GRM observation
  82. GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90
  83. GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT
  84. Fermi GRB 260318A: Global MASTER-Net observations report
  85. GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
  86. GRB 260310A / AT 2026fgk: radio detection with the VLA
  87. GRB 260310A / AT2026fgk: SVOM/VT optical observations
  88. GRB 260310A / AT2026fgk: LCO optical observations
  89. GRB 260316B: SVOM/GRM observation
  90. EP260316a / GRB 260316A: SVOM/VT optical upper limits
  91. EP260316a: COLIBRÍ faint optical counterpart candidate
  92. Fermi-LAT Gamma-ray Observations of IceCube-260315A
  93. EP260316a: refined analysis of the EP-WXT and EP-FXT observations
  94. IceCube-260315A: Upper limits from a search for additional neutrino events in IceCube
  95. EP260316a: Xinglong optical upper limit
  96. EP260316a: optical upper limit with Kinder observations
  97. EP260316a / GRB 260316A : Fermi-GBM Sub-Threshold Detection
  98. GRB 260314A: Glowbug gamma-ray detection
  99. The EP-WXT trigger 00199258890 (EP260316a): a correction to the trigger time and FXT automatic follow-up
  100. IceCube-260315A: COLIBRÍ optical observations

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