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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"

32513 results found.

  1. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  2. GRB 260402B: GECAM-B observation
  3. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  4. GRB 260402C: NuSTAR detection of prompt emission
  5. EP260324A / AT 2026hir: COLIBRÍ optical observations
  6. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  7. GRB 260402A: WINTER J-band upper limit
  8. GRB260402A: GROWTH-India Telescope optical upper limit
  9. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  10. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  11. GRB 260401A: SVOM/GRM observation
  12. GRB 260401A: GECAM-B observation
  13. EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
  14. GRB 260402A: Kilonova-Catcher optical upper limit
  15. GRB 260402A: MASTER optical observations
  16. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  17. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  18. Fermi GRB 260401A: Global MASTER-Net observations report
  19. GRB 260401A: Fermi GBM Observation
  20. GRB 260401A: NuSTAR detection of prompt emission
  21. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  22. GRB 260401A: MAXI/GSC detection
  23. EP260329b: Mondy and Assy-Turgen optical upper limits
  24. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  25. EP260321a :Xinglong optical observations
  26. EP260327a: Xinglong optical upper limit
  27. EP260329b: GOTO detection of optical counterpart
  28. GRB 260330B: SVOM/VT optical upper limits
  29. Konus-Wind detection of GRB 260320A
  30. Konus-Wind detection of GRB 260316B (duplicate submission)
  31. Konus-Wind detection of GRB 260316B
  32. GRB 260321A: SVOM/ECLAIRs refined analysis
  33. EP260329b: J-band upper limits with WINTER
  34. EP260329a: J-band upper limit with WINTER
  35. GRB 260330A: Glowbug gamma-ray detection
  36. GRB 260310A: VLA Multi-frequency Radio Observations
  37. Fermi GBM Sub-Threshold Detection of GRB 260330B
  38. GRB 260330B: LCO optical upper limits
  39. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  40. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  41. EP260329a: COLIBRÍ optical upper limit
  42. EP260329a: EP-FXT follow up observation
  43. EP260329a: NOT optical counterpart candidate
  44. EP260329b: Global MASTER-Net observations report
  45. GRB 260327A: Insight-HXMT/HE detection
  46. EP260329b: Optical follow-up with Kinder observations
  47. EP 260329b: COLIBRÍ optical observations
  48. EP260329a: Optical upper limit with Kinder observations
  49. EP260329b: LCO optical observations of the counterpart
  50. GRB 260326A: Insight-HXMT/HE detection
  51. EP260329b: Einstein Probe detection of an X-ray transient
  52. EP-WXT trigger 01709259209: TRT optical counterpart detection
  53. GRID detection of GRB 260326A
  54. GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
  55. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  56. EP260327a: SVOM/VT optical upper limits
  57. SMA Detection of GRB 260310A / AT 2026fgk
  58. GRB 260307B: ATCA Radio Upper Limits
  59. EP260327a: WINTER J-band upper limit
  60. EP260327a: COLIBRÍ optical upper limits
  61. EP260327a: Gemini-North optical upper limits
  62. EP260324a: GROWTH-India Telescope optical observation
  63. EP260327a: Global MASTER-Net observations report
  64. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  65. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  66. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  67. IPN triangulation of GRB 260320A
  68. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  69. GRB 260326A: Fermi GBM Detection
  70. EP260321a: JinShan near-infrared observations
  71. EP260321a: Upper limits from a neutrino search with IceCube
  72. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  73. IPN triangulation of GRB 260316B
  74. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  75. GRID detection of GRB 260320A
  76. EP260321a: Gemini-South confirmation of a supernova (duplicate submission)
  77. EP260321a: Gemini-South confirmation of a supernova
  78. EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
  79. GRB 260310A: LBT optical observations
  80. EP260321A: Mondy optical observations
  81. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  82. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  83. GRB 260316B: CALET Gamma-Ray Burst Monitor detection
  84. Fermi GRB 260323A: Global MASTER-Net observations report
  85. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  86. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  87. GRB 260320A: Glowbug gamma-ray detection
  88. EP260321a / AT2026gzf: VLT/X-shooter detection of supernova-like spectral features at z = 0.0344
  89. EP260321a: COLIBRÍ further optical observations and brightening
  90. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  91. EP260214b: ATCA 6 GHz detection
  92. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  93. GRB 260321A: EP-FXT follow-up observation
  94. EP260321a: ZTF and Rubin detections of the candidate optical counterpart to EP260321a
  95. EP260321a: GOTO detection of blue variable source
  96. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  97. EP260321a: further Kinder optical observations
  98. GRB 260321A: SVOM/VT optical upper limits
  99. EP260321a: Las Cumbres upper limit
  100. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit

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