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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"

20958 results found.

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

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