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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"

27065 results found.

  1. GRB 260402A: WINTER J-band upper limit
  2. GRB260402A: GROWTH-India Telescope optical upper limit
  3. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  4. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  5. GRB 260401A: SVOM/GRM observation
  6. EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
  7. GRB 260402A: Kilonova-Catcher optical upper limit
  8. GRB 260402A: MASTER optical observations
  9. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  10. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  11. GRB 260402A: SVOM detection of a burst
  12. Fermi GRB 260401A: Global MASTER-Net observations report
  13. GRB 260401A: Fermi GBM Observation
  14. GRB 260401A: NuSTAR detection of prompt emission
  15. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  16. GRB 260401A: MAXI/GSC detection
  17. GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
  18. GRB 260401A: Fermi GBM Final Real-time Localization
  19. EP260329b: Mondy and Assy-Turgen optical upper limits
  20. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  21. EP260321a :Xinglong optical observations
  22. EP260327a: Xinglong optical upper limit
  23. GRB 260330B: SVOM/VT optical upper limits
  24. Konus-Wind detection of GRB 260320A
  25. GRB 260321A: SVOM/ECLAIRs refined analysis
  26. EP260329b: J-band upper limits with WINTER
  27. EP260329a: J-band upper limit with WINTER
  28. GRB 260330A: Glowbug gamma-ray detection
  29. Fermi GBM Sub-Threshold Detection of GRB 260330B
  30. GRB 260330B: LCO optical upper limits
  31. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  32. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  33. EP260329a: COLIBRÍ optical upper limit
  34. EP260329a: EP-FXT follow up observation
  35. EP260329a: NOT optical counterpart candidate
  36. EP260329b: Global MASTER-Net observations report
  37. Fermi trigger No 796485221: Global MASTER-Net observations report
  38. GRB 260327A: Insight-HXMT/HE detection
  39. EP260329b: Optical follow-up with Kinder observations
  40. EP 260329b: COLIBRÍ optical observations
  41. EP260329a: Optical upper limit with Kinder observations
  42. EP260329b: LCO optical observations of the counterpart
  43. GRB 260326A: Insight-HXMT/HE detection
  44. EP260329b: Einstein Probe detection of an X-ray transient
  45. EP260329a: Einstein Probe detection of an X-ray transient
  46. EP-WXT trigger 01709259209: TRT optical counterpart detection
  47. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  48. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  49. EP260327a: SVOM/VT optical upper limits
  50. EP260327a: WINTER J-band upper limit
  51. EP260327a: COLIBRÍ optical upper limits
  52. EP260327a: Gemini-North optical upper limits
  53. EP260324a: GROWTH-India Telescope optical observation
  54. EP260327a: Global MASTER-Net observations report
  55. EP260327a: Einstein Probe detection of an X-ray transient
  56. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  57. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  58. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  59. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  60. GRB 260326A: Fermi GBM Detection
  61. EP260321a: JinShan near-infrared observations
  62. EP260321a: Upper limits from a neutrino search with IceCube
  63. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  64. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  65. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  66. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  67. Fermi GRB 260323A: Global MASTER-Net observations report
  68. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  69. GRB 260320A: Glowbug gamma-ray detection
  70. EP260321a: COLIBRÍ further optical observations and brightening
  71. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  72. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  73. GRB 260321A: EP-FXT follow-up observation
  74. EP260321a: GOTO detection of blue variable source
  75. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  76. EP260321a: further Kinder optical observations
  77. GRB 260321A: SVOM/VT optical upper limits
  78. EP260321a: Las Cumbres upper limit
  79. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  80. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  81. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  82. EP260321a: SVOM/VT optical upper limit
  83. Fermi GBM Sub-Threshold Detection of GRB 260321A
  84. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  85. EP260321a: Global MASTER-Net observations report
  86. EP260321a: Einstein Probe detection of an X-ray transient
  87. GRB 260318A: Glowbug gamma-ray detection
  88. GRB 260310A / AT 2026fgk: KAIT optical observations
  89. GRB 260320A: NuSTAR detection of prompt emission
  90. EP-WXT trigger 01709258989: KAIT confirmation of a stellar flare
  91. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
  92. GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening
  93. EP-WXT trigger 01709258989: confirmation of a stellar flare by BOOTES-7
  94. GRB 260318A: SVOM/GRM observation
  95. GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90
  96. GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT
  97. Fermi GRB 260318A: Global MASTER-Net observations report
  98. GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
  99. GRB 260310A / AT 2026fgk: radio detection with the VLA
  100. GRB 260310A / AT2026fgk: SVOM/VT optical observations

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