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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"

28056 results found.

  1. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  2. GRB 260402A: SVOM detection of a burst
  3. Fermi GRB 260401A: Global MASTER-Net observations report
  4. GRB 260401A: Fermi GBM Observation
  5. GRB 260401A: NuSTAR detection of prompt emission
  6. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  7. GRB 260401A: MAXI/GSC detection
  8. GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
  9. GRB 260401A: Fermi GBM Final Real-time Localization
  10. EP260329b: Mondy and Assy-Turgen optical upper limits
  11. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  12. EP260321a :Xinglong optical observations
  13. EP260327a: Xinglong optical upper limit
  14. GRB 260330B: SVOM/VT optical upper limits
  15. Konus-Wind detection of GRB 260320A
  16. GRB 260321A: SVOM/ECLAIRs refined analysis
  17. EP260329b: J-band upper limits with WINTER
  18. EP260329a: J-band upper limit with WINTER
  19. GRB 260330A: Glowbug gamma-ray detection
  20. Fermi GBM Sub-Threshold Detection of GRB 260330B
  21. GRB 260330B: LCO optical upper limits
  22. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  23. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  24. EP260329a: COLIBRÍ optical upper limit
  25. EP260329a: EP-FXT follow up observation
  26. EP260329a: NOT optical counterpart candidate
  27. EP260329b: Global MASTER-Net observations report
  28. Fermi trigger No 796485221: Global MASTER-Net observations report
  29. GRB 260327A: Insight-HXMT/HE detection
  30. EP260329b: Optical follow-up with Kinder observations
  31. EP 260329b: COLIBRÍ optical observations
  32. EP260329a: Optical upper limit with Kinder observations
  33. EP260329b: LCO optical observations of the counterpart
  34. GRB 260326A: Insight-HXMT/HE detection
  35. EP260329b: Einstein Probe detection of an X-ray transient
  36. EP260329a: Einstein Probe detection of an X-ray transient
  37. EP-WXT trigger 01709259209: TRT optical counterpart detection
  38. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  39. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  40. EP260327a: SVOM/VT optical upper limits
  41. EP260327a: WINTER J-band upper limit
  42. EP260327a: COLIBRÍ optical upper limits
  43. EP260327a: Gemini-North optical upper limits
  44. EP260324a: GROWTH-India Telescope optical observation
  45. EP260327a: Global MASTER-Net observations report
  46. EP260327a: Einstein Probe detection of an X-ray transient
  47. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  48. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  49. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  50. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  51. GRB 260326A: Fermi GBM Detection
  52. EP260321a: JinShan near-infrared observations
  53. EP260321a: Upper limits from a neutrino search with IceCube
  54. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  55. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  56. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  57. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  58. Fermi GRB 260323A: Global MASTER-Net observations report
  59. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  60. GRB 260320A: Glowbug gamma-ray detection
  61. EP260321a: COLIBRÍ further optical observations and brightening
  62. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  63. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  64. GRB 260321A: EP-FXT follow-up observation
  65. EP260321a: GOTO detection of blue variable source
  66. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  67. EP260321a: further Kinder optical observations
  68. GRB 260321A: SVOM/VT optical upper limits
  69. EP260321a: Las Cumbres upper limit
  70. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  71. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  72. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  73. EP260321a: SVOM/VT optical upper limit
  74. Fermi GBM Sub-Threshold Detection of GRB 260321A
  75. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  76. EP260321a: Global MASTER-Net observations report
  77. EP260321a: Einstein Probe detection of an X-ray transient
  78. GRB 260318A: Glowbug gamma-ray detection
  79. GRB 260310A / AT 2026fgk: KAIT optical observations
  80. GRB 260320A: NuSTAR detection of prompt emission
  81. EP-WXT trigger 01709258989: KAIT confirmation of a stellar flare
  82. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
  83. GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening
  84. EP-WXT trigger 01709258989: confirmation of a stellar flare by BOOTES-7
  85. GRB 260318A: SVOM/GRM observation
  86. GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90
  87. GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT
  88. Fermi GRB 260318A: Global MASTER-Net observations report
  89. GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
  90. GRB 260310A / AT 2026fgk: radio detection with the VLA
  91. GRB 260310A / AT2026fgk: SVOM/VT optical observations
  92. GRB 260310A / AT2026fgk: LCO optical observations
  93. GRB 260316B: SVOM/GRM observation
  94. EP260316a / GRB 260316A: SVOM/VT optical upper limits
  95. EP260316a: COLIBRÍ faint optical counterpart candidate
  96. Fermi-LAT Gamma-ray Observations of IceCube-260315A
  97. EP260316a: refined analysis of the EP-WXT and EP-FXT observations
  98. IceCube-260315A: Upper limits from a search for additional neutrino events in IceCube
  99. EP260316a: Xinglong optical upper limit
  100. EP260316a: optical upper limit with Kinder observations

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