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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"

20951 results found.

  1. Fermi GRB 260421A: Global MASTER-Net observations report
  2. EP260321a: VLA radio follow-up
  3. EP260416a: Optical follow-up observations with Kinder
  4. GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient
  5. EP-WXT trigger 01709260303: KAIT optical observations
  6. EP260416a: 1.5m OSN and 2.2m CAHA optical monitoring
  7. EP260321A/AT2026gzf: Optical observation from 1.3m DFOT
  8. Fermi trigger No 798275385: Global MASTER-Net observations report
  9. Fermi GRB 260417B: Global MASTER-Net observations report
  10. EP260416a: Ondrejov D50 optical detection
  11. EP260417a: Global MASTER-Net observations report
  12. EP260417a/GRB 260417A: refined analysis of the EP-WXT and follow-up EP-FXT observations
  13. EP260416a: NOT tentative spectroscopic redshift of z =1.909
  14. Fermi GRB 260417A: Global MASTER-Net observations report
  15. EP260416a: LCO observations confirm end of flaring phase
  16. EP260324a / AT2026hir: Further multiband optical follow-up with the PKU 60cm Telescope
  17. EP260416a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  18. EP-WXT trigger 01709259586: KAIT optical observations
  19. EP260416a: WFST optical observations and rebrightening
  20. GOTO26djh/AT2026jpw: ZTSh R,I bands observations of the transient
  21. EP260416a: COLIBRÍ optical counterpart candidate
  22. COLIBRI optical observations of the transient GOTO26djh/AT2026jpw
  23. EP260416a: Global MASTER-Net observations report
  24. GOTO26djh/AT2026jpw : MASTER OT observation
  25. GOTO26djh/AT2026jpw: EP-FXT X-ray counterpart detection
  26. GOTO26djh/AT2026jpw transient: SAO RAS optical observations
  27. NOT r-band observations of the transient GOTO26djh/AT2026jpw
  28. GOTO discovery of fast-fading transient GOTO26djh/AT2026jpw, a candidate orphan afterglow
  29. Fermi trigger No 797912738: Global MASTER-Net observations report
  30. EP260409a: Early NIR limits from MIRAGE on the MDM 1.3m telescope
  31. EP260321a: CMO SAI J,K observations
  32. Fermi GRB 260413A: Global MASTER-Net observations report
  33. EP260321a: SVOM/VT optical observations and color changes around peak
  34. Fermi GRB 260412A: Global MASTER-Net observations report
  35. GRB 260310A / AT2026fgk: NuSTAR detection of the rebrightening
  36. GRB 260411B: COLIBRÍ optical observations
  37. GRB260411B: 3.6m DOT optical observation
  38. GRB 260411B: GOTO optical counterpart candidate
  39. EP260409a: Gemini/FLAMINGOS2 J-band counterpart
  40. EP-WXT01709259790: Optical Upper limits with kinder observations
  41. EP260409a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  42. EP260321a: Chandra X-ray Non-detection
  43. GRB 260310A/AT2026fgk: Kilonova-Catcher SN peak identification
  44. EP260409a: SVOM/VT optical upper limits
  45. EP260409a: Global MASTER-Net observations report
  46. EP260321a: VLA radio detection
  47. GRB 260402A: SVOM/ECLAIRs refined analysis
  48. GRB 260310A: Continued VLA Multi-frequency Radio Observations
  49. GRB 260310A / AT2026fgk: X-ray rebrightening
  50. EP260402a / GRB 260402A: Mephisto optical upper limits
  51. EP260403a: Mephisto optical upper limits
  52. EP260321a: Upper limits from VLA radio observations
  53. EP260321a: uGMRT observations
  54. EP260405a: SVOM/VT optical upper limits
  55. EP260405a: Global MASTER-Net observations report
  56. EP260405a / EP-WXT 11900672904: COLIBRÍ optical upper limits
  57. Fermi trigger No 797039833: Global MASTER-Net observations report
  58. EP260324A / AT 2026hir: COLIBRÍ further optical observations
  59. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  60. GRB 260330B: SVOM/VT further optical observation
  61. GRB 260330B: SVOM/ECLAIRs refined analysis
  62. EP260403a: LCO optical observations of the counterpart
  63. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  64. EP260403a: LCO optical counterpart detection
  65. EP260403a: COLIBRÍ optical counterpart candidate
  66. GRB 260330B: SVOM/VT optical candidate
  67. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  68. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  69. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  70. EP260324A / AT 2026hir: COLIBRÍ optical observations
  71. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  72. GRB 260402A: WINTER J-band upper limit
  73. GRB260402A: GROWTH-India Telescope optical upper limit
  74. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  75. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  76. GRB 260402A: Kilonova-Catcher optical upper limit
  77. GRB 260402A: MASTER optical observations
  78. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  79. Fermi GRB 260401A: Global MASTER-Net observations report
  80. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  81. EP260321a :Xinglong optical observations
  82. EP260329b: GOTO detection of optical counterpart
  83. GRB 260330B: SVOM/VT optical upper limits
  84. GRB 260321A: SVOM/ECLAIRs refined analysis
  85. EP260329b: J-band upper limits with WINTER
  86. EP260329a: J-band upper limit with WINTER
  87. GRB 260310A: VLA Multi-frequency Radio Observations
  88. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  89. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  90. EP260329a: EP-FXT follow up observation
  91. EP260329b: Global MASTER-Net observations report
  92. Fermi trigger No 796485221: Global MASTER-Net observations report
  93. EP260329b: Optical follow-up with Kinder observations
  94. EP 260329b: COLIBRÍ optical observations
  95. EP260329a: Optical upper limit with Kinder observations
  96. EP260329b: LCO optical observations of the counterpart
  97. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  98. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  99. EP260327a: SVOM/VT optical upper limits
  100. SMA Detection of GRB 260310A / AT 2026fgk

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