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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"

27080 results found.

  1. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  2. The EP-WXT trigger 01709259586 is likely a flaring star
  3. GRB 260330B: SVOM/VT further optical observation
  4. EP260403a: LCO optical observations of the counterpart
  5. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  6. EP260403a: LCO optical counterpart detection
  7. EP260403a: COLIBRÍ optical counterpart candidate
  8. GRB 260330B: SVOM/VT optical candidate
  9. EP260403a: Einstein Probe detection of an X-ray transient
  10. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  11. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  12. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  13. GRB 260402C: NuSTAR detection of prompt emission
  14. GRB 260402C: AstroSat CZTI detection of a long burst
  15. EP260324A / AT 2026hir: COLIBRÍ optical observations
  16. GRB 260402A: WINTER J-band upper limit
  17. GRB260402A: GROWTH-India Telescope optical upper limit
  18. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  19. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  20. GRB 260401A: SVOM/GRM observation
  21. EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
  22. GRB 260402A: Kilonova-Catcher optical upper limit
  23. GRB 260402A: MASTER optical observations
  24. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  25. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  26. GRB 260402A: SVOM detection of a burst
  27. Fermi GRB 260401A: Global MASTER-Net observations report
  28. GRB 260401A: Fermi GBM Observation
  29. GRB 260401A: NuSTAR detection of prompt emission
  30. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  31. GRB 260401A: MAXI/GSC detection
  32. GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
  33. GRB 260401A: Fermi GBM Final Real-time Localization
  34. EP260329b: Mondy and Assy-Turgen optical upper limits
  35. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  36. EP260321a :Xinglong optical observations
  37. EP260327a: Xinglong optical upper limit
  38. GRB 260330B: SVOM/VT optical upper limits
  39. Konus-Wind detection of GRB 260320A
  40. GRB 260321A: SVOM/ECLAIRs refined analysis
  41. EP260329b: J-band upper limits with WINTER
  42. EP260329a: J-band upper limit with WINTER
  43. GRB 260330A: Glowbug gamma-ray detection
  44. Fermi GBM Sub-Threshold Detection of GRB 260330B
  45. GRB 260330B: LCO optical upper limits
  46. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  47. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  48. EP260329a: COLIBRÍ optical upper limit
  49. EP260329a: EP-FXT follow up observation
  50. EP260329a: NOT optical counterpart candidate
  51. EP260329b: Global MASTER-Net observations report
  52. Fermi trigger No 796485221: Global MASTER-Net observations report
  53. GRB 260327A: Insight-HXMT/HE detection
  54. EP260329b: Optical follow-up with Kinder observations
  55. EP 260329b: COLIBRÍ optical observations
  56. EP260329a: Optical upper limit with Kinder observations
  57. EP260329b: LCO optical observations of the counterpart
  58. GRB 260326A: Insight-HXMT/HE detection
  59. EP260329b: Einstein Probe detection of an X-ray transient
  60. EP260329a: Einstein Probe detection of an X-ray transient
  61. EP-WXT trigger 01709259209: TRT optical counterpart detection
  62. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  63. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  64. EP260327a: SVOM/VT optical upper limits
  65. EP260327a: WINTER J-band upper limit
  66. EP260327a: COLIBRÍ optical upper limits
  67. EP260327a: Gemini-North optical upper limits
  68. EP260324a: GROWTH-India Telescope optical observation
  69. EP260327a: Global MASTER-Net observations report
  70. EP260327a: Einstein Probe detection of an X-ray transient
  71. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  72. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  73. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  74. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  75. GRB 260326A: Fermi GBM Detection
  76. EP260321a: JinShan near-infrared observations
  77. EP260321a: Upper limits from a neutrino search with IceCube
  78. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  79. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  80. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  81. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  82. Fermi GRB 260323A: Global MASTER-Net observations report
  83. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  84. GRB 260320A: Glowbug gamma-ray detection
  85. EP260321a: COLIBRÍ further optical observations and brightening
  86. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  87. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  88. GRB 260321A: EP-FXT follow-up observation
  89. EP260321a: GOTO detection of blue variable source
  90. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  91. EP260321a: further Kinder optical observations
  92. GRB 260321A: SVOM/VT optical upper limits
  93. EP260321a: Las Cumbres upper limit
  94. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  95. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  96. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  97. EP260321a: SVOM/VT optical upper limit
  98. Fermi GBM Sub-Threshold Detection of GRB 260321A
  99. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  100. EP260321a: Global MASTER-Net observations report

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