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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"

21265 results found.

  1. GRB 260421B: LCO optical counterpart detection
  2. GOTO26djh/AT2026jpw: radio detection at 15GHz
  3. GRB 260412A: SVOM/ECLAIRs refined analysis
  4. GRB 260421B: SVOM/VT optical observations
  5. EP260416a: J band upper limit by SYSU 80cm infrared telescope
  6. GRB 260310A: Late-time Chandra X-ray Detection
  7. EP260416a: 1.3m DFOT optical observation
  8. Fermi GRB 260421C: Global MASTER-Net observations report
  9. Fermi GRB 260421B: Global MASTER-Net observations report
  10. GRB 260421B: LCO optical afterglow confirmation
  11. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  12. Fermi GRB 260421A: Global MASTER-Net observations report
  13. EP260321a: VLA radio follow-up
  14. EP260416a: Optical follow-up observations with Kinder
  15. GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient
  16. EP-WXT trigger 01709260303: KAIT optical observations
  17. EP260321A/AT2026gzf: Optical observation from 1.3m DFOT
  18. Fermi trigger No 798275385: Global MASTER-Net observations report
  19. Fermi GRB 260417B: Global MASTER-Net observations report
  20. EP260417a: Global MASTER-Net observations report
  21. EP260417a/GRB 260417A: refined analysis of the EP-WXT and follow-up EP-FXT observations
  22. EP260416a: NOT tentative spectroscopic redshift of z =1.909
  23. Fermi GRB 260417A: Global MASTER-Net observations report
  24. EP260416a: LCO observations confirm end of flaring phase
  25. EP260324a / AT2026hir: Further multiband optical follow-up with the PKU 60cm Telescope
  26. EP260416a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  27. EP-WXT trigger 01709259586: KAIT optical observations
  28. EP260416a: WFST optical observations and rebrightening
  29. GOTO26djh/AT2026jpw: ZTSh R,I bands observations of the transient
  30. EP260416a: COLIBRÍ optical counterpart candidate
  31. COLIBRI optical observations of the transient GOTO26djh/AT2026jpw
  32. EP260416a: Global MASTER-Net observations report
  33. GOTO26djh/AT2026jpw : MASTER OT observation
  34. GOTO26djh/AT2026jpw: EP-FXT X-ray counterpart detection
  35. GOTO26djh/AT2026jpw transient: SAO RAS optical observations
  36. NOT r-band observations of the transient GOTO26djh/AT2026jpw
  37. GOTO discovery of fast-fading transient GOTO26djh/AT2026jpw, a candidate orphan afterglow
  38. Fermi trigger No 797912738: Global MASTER-Net observations report
  39. EP260409a: Early NIR limits from MIRAGE on the MDM 1.3m telescope
  40. EP260321a: CMO SAI J,K observations
  41. Fermi GRB 260413A: Global MASTER-Net observations report
  42. EP260321a: SVOM/VT optical observations and color changes around peak
  43. Fermi GRB 260412A: Global MASTER-Net observations report
  44. GRB 260310A / AT2026fgk: NuSTAR detection of the rebrightening
  45. GRB 260411B: COLIBRÍ optical observations
  46. GRB260411B: 3.6m DOT optical observation
  47. GRB 260411B: GOTO optical counterpart candidate
  48. EP260409a: Gemini/FLAMINGOS2 J-band counterpart
  49. EP-WXT01709259790: Optical Upper limits with kinder observations
  50. EP260409a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  51. EP260321a: Chandra X-ray Non-detection
  52. GRB 260310A/AT2026fgk: Kilonova-Catcher SN peak identification
  53. EP260409a: SVOM/VT optical upper limits
  54. EP260409a: Global MASTER-Net observations report
  55. EP260321a: VLA radio detection
  56. GRB 260402A: SVOM/ECLAIRs refined analysis
  57. GRB 260310A: Continued VLA Multi-frequency Radio Observations
  58. GRB 260310A / AT2026fgk: X-ray rebrightening
  59. EP260402a / GRB 260402A: Mephisto optical upper limits
  60. EP260403a: Mephisto optical upper limits
  61. EP260321a: Upper limits from VLA radio observations
  62. EP260321a: uGMRT observations
  63. EP260405a: SVOM/VT optical upper limits
  64. EP260405a: Global MASTER-Net observations report
  65. EP260405a / EP-WXT 11900672904: COLIBRÍ optical upper limits
  66. Fermi trigger No 797039833: Global MASTER-Net observations report
  67. EP260324A / AT 2026hir: COLIBRÍ further optical observations
  68. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  69. GRB 260330B: SVOM/VT further optical observation
  70. GRB 260330B: SVOM/ECLAIRs refined analysis
  71. EP260403a: LCO optical observations of the counterpart
  72. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  73. EP260403a: LCO optical counterpart detection
  74. EP260403a: COLIBRÍ optical counterpart candidate
  75. GRB 260330B: SVOM/VT optical candidate
  76. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  77. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  78. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  79. EP260324A / AT 2026hir: COLIBRÍ optical observations
  80. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  81. GRB 260402A: WINTER J-band upper limit
  82. GRB260402A: GROWTH-India Telescope optical upper limit
  83. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  84. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  85. GRB 260402A: Kilonova-Catcher optical upper limit
  86. GRB 260402A: MASTER optical observations
  87. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  88. Fermi GRB 260401A: Global MASTER-Net observations report
  89. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  90. EP260321a :Xinglong optical observations
  91. EP260329b: GOTO detection of optical counterpart
  92. GRB 260330B: SVOM/VT optical upper limits
  93. GRB 260321A: SVOM/ECLAIRs refined analysis
  94. EP260329b: J-band upper limits with WINTER
  95. EP260329a: J-band upper limit with WINTER
  96. GRB 260310A: VLA Multi-frequency Radio Observations
  97. Fermi GBM Sub-Threshold Detection of GRB 260330B
  98. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  99. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  100. EP260329a: EP-FXT follow up observation

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