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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"

21784 results found.

  1. GRB 260424B: COLIBRÍ optical upper limit
  2. Fermi-LAT Gamma-ray Observations of IceCube-260425A
  3. EP260321a/SN 2026gzf: spectroscopy at Mondy observatory
  4. IceCube Alert 260425A: Global MASTER-Net observations report
  5. Fermi trigger No 798737427: Global MASTER-Net observations report
  6. EP260321a: Upper limits from ATCA radio observations
  7. GRB 260421B: Kilonova-Catcher optical afterglow detection
  8. The EP-WXT trigger 01709258652: Mondy optical observations
  9. GRB 250328A: VLT host galaxy discovery and redshift z = 1.250
  10. EP260416a: Mondy optical observations
  11. GRB 260421B: SVOM/ECLAIRs refined analysis
  12. GRB 260421B: 3.6m DOT optical observation
  13. EP260416a: ZTSh R band observations
  14. EP-WXT trigger 01709260362: FRAM-ORM optical observations confirm flaring star G 151-9
  15. EP250512a / GRB 250512B: VLT/X-shooter host galaxy identification and redshift z = 1.773
  16. GRB 250530A: VLT/X-shooter host galaxy redshift z = 1.486
  17. GRB260421B: J band upper limit by SYSU 80cm infrared telescope
  18. GOTO26djh/AT2026jpw: ATCA radio detection
  19. GRB 260421B: J-band upper limit with WINTER
  20. GRB 260421B: LCO optical counterpart detection
  21. GOTO26djh/AT2026jpw: radio detection at 15GHz
  22. GRB 260412A: SVOM/ECLAIRs refined analysis
  23. GRB 260421B: SVOM/VT optical observations
  24. EP260416a: J band upper limit by SYSU 80cm infrared telescope
  25. GRB 260310A: Late-time Chandra X-ray Detection
  26. EP260416a: 1.3m DFOT optical observation
  27. Fermi GRB 260421C: Global MASTER-Net observations report
  28. Fermi GRB 260421B: Global MASTER-Net observations report
  29. GRB 260421B: LCO optical afterglow confirmation
  30. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  31. Fermi GRB 260421A: Global MASTER-Net observations report
  32. EP260321a: VLA radio follow-up
  33. EP260416a: Optical follow-up observations with Kinder
  34. GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient
  35. EP-WXT trigger 01709260303: KAIT optical observations
  36. EP260321A/AT2026gzf: Optical observation from 1.3m DFOT
  37. Fermi trigger No 798275385: Global MASTER-Net observations report
  38. Fermi GRB 260417B: Global MASTER-Net observations report
  39. EP260417a: Global MASTER-Net observations report
  40. EP260417a/GRB 260417A: refined analysis of the EP-WXT and follow-up EP-FXT observations
  41. EP260416a: NOT tentative spectroscopic redshift of z =1.909
  42. Fermi GRB 260417A: Global MASTER-Net observations report
  43. EP260416a: LCO observations confirm end of flaring phase
  44. EP260324a / AT2026hir: Further multiband optical follow-up with the PKU 60cm Telescope
  45. EP260416a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  46. EP-WXT trigger 01709259586: KAIT optical observations
  47. EP260416a: WFST optical observations and rebrightening
  48. GOTO26djh/AT2026jpw: ZTSh R,I bands observations of the transient
  49. EP260416a: COLIBRÍ optical counterpart candidate
  50. COLIBRI optical observations of the transient GOTO26djh/AT2026jpw
  51. EP260416a: Global MASTER-Net observations report
  52. GOTO26djh/AT2026jpw : MASTER OT observation
  53. GOTO26djh/AT2026jpw: EP-FXT X-ray counterpart detection
  54. GOTO26djh/AT2026jpw transient: SAO RAS optical observations
  55. NOT r-band observations of the transient GOTO26djh/AT2026jpw
  56. GOTO discovery of fast-fading transient GOTO26djh/AT2026jpw, a candidate orphan afterglow
  57. Fermi trigger No 797912738: Global MASTER-Net observations report
  58. EP260409a: Early NIR limits from MIRAGE on the MDM 1.3m telescope
  59. EP260321a: CMO SAI J,K observations
  60. Fermi GRB 260413A: Global MASTER-Net observations report
  61. EP260321a: SVOM/VT optical observations and color changes around peak
  62. Fermi GRB 260412A: Global MASTER-Net observations report
  63. GRB 260310A / AT2026fgk: NuSTAR detection of the rebrightening
  64. GRB 260411B: COLIBRÍ optical observations
  65. GRB260411B: 3.6m DOT optical observation
  66. GRB 260411B: GOTO optical counterpart candidate
  67. EP260409a: Gemini/FLAMINGOS2 J-band counterpart
  68. EP-WXT01709259790: Optical Upper limits with kinder observations
  69. EP260409a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  70. EP260321a: Chandra X-ray Non-detection
  71. GRB 260310A/AT2026fgk: Kilonova-Catcher SN peak identification
  72. EP260409a: SVOM/VT optical upper limits
  73. EP260409a: Global MASTER-Net observations report
  74. EP260321a: VLA radio detection
  75. GRB 260402A: SVOM/ECLAIRs refined analysis
  76. GRB 260310A: Continued VLA Multi-frequency Radio Observations
  77. GRB 260310A / AT2026fgk: X-ray rebrightening
  78. EP260402a / GRB 260402A: Mephisto optical upper limits
  79. EP260403a: Mephisto optical upper limits
  80. EP260321a: Upper limits from VLA radio observations
  81. EP260321a: uGMRT observations
  82. EP260405a: SVOM/VT optical upper limits
  83. EP260405a: Global MASTER-Net observations report
  84. EP260405a / EP-WXT 11900672904: COLIBRÍ optical upper limits
  85. Fermi trigger No 797039833: Global MASTER-Net observations report
  86. EP260324A / AT 2026hir: COLIBRÍ further optical observations
  87. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  88. GRB 260330B: SVOM/VT further optical observation
  89. GRB 260330B: SVOM/ECLAIRs refined analysis
  90. EP260403a: LCO optical observations of the counterpart
  91. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  92. EP260403a: LCO optical counterpart detection
  93. EP260403a: COLIBRÍ optical counterpart candidate
  94. GRB 260330B: SVOM/VT optical candidate
  95. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  96. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  97. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  98. EP260324A / AT 2026hir: COLIBRÍ optical observations
  99. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  100. GRB 260402A: WINTER J-band upper limit

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