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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"

20480 results found.

  1. EP260430a: Global MASTER-Net observations report
  2. Fermi GRB 260428A: Global MASTER-Net observations report
  3. GRB 260424B: COLIBRÍ optical upper limit
  4. Fermi-LAT Gamma-ray Observations of IceCube-260425A
  5. IceCube Alert 260425A: Global MASTER-Net observations report
  6. Fermi trigger No 798737427: Global MASTER-Net observations report
  7. EP260321a: Upper limits from ATCA radio observations
  8. GRB 260421B: Kilonova-Catcher optical afterglow detection
  9. The EP-WXT trigger 01709258652: Mondy optical observations
  10. GRB 250328A: VLT host galaxy discovery and redshift z = 1.250
  11. EP260416a: Mondy optical observations
  12. GRB 260421B: SVOM/ECLAIRs refined analysis
  13. GRB 260421B: 3.6m DOT optical observation
  14. EP260416a: ZTSh R band observations
  15. EP-WXT trigger 01709260362: FRAM-ORM optical observations confirm flaring star G 151-9
  16. GRB260421B: J band upper limit by SYSU 80cm infrared telescope
  17. GOTO26djh/AT2026jpw: ATCA radio detection
  18. GRB 260421B: J-band upper limit with WINTER
  19. GRB 260421B: LCO optical counterpart detection
  20. GOTO26djh/AT2026jpw: radio detection at 15GHz
  21. GRB 260412A: SVOM/ECLAIRs refined analysis
  22. GRB 260421B: SVOM/VT optical observations
  23. EP260416a: J band upper limit by SYSU 80cm infrared telescope
  24. GRB 260310A: Late-time Chandra X-ray Detection
  25. EP260416a: 1.3m DFOT optical observation
  26. Fermi GRB 260421C: Global MASTER-Net observations report
  27. Fermi GRB 260421B: Global MASTER-Net observations report
  28. GRB 260421B: LCO optical afterglow confirmation
  29. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  30. Fermi GRB 260421A: Global MASTER-Net observations report
  31. EP260321a: VLA radio follow-up
  32. EP260416a: Optical follow-up observations with Kinder
  33. GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient
  34. EP-WXT trigger 01709260303: KAIT optical observations
  35. EP260416a: 1.5m OSN and 2.2m CAHA optical monitoring
  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. EP260416a: Ondrejov D50 optical detection
  40. EP260417a: Global MASTER-Net observations report
  41. EP260417a/GRB 260417A: refined analysis of the EP-WXT and follow-up EP-FXT observations
  42. EP260416a: NOT tentative spectroscopic redshift of z =1.909
  43. Fermi GRB 260417A: Global MASTER-Net observations report
  44. EP260416a: LCO observations confirm end of flaring phase
  45. EP260324a / AT2026hir: Further multiband optical follow-up with the PKU 60cm Telescope
  46. EP260416a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  47. EP-WXT trigger 01709259586: KAIT optical observations
  48. EP260416a: WFST optical observations and rebrightening
  49. GOTO26djh/AT2026jpw: ZTSh R,I bands observations of the transient
  50. EP260416a: COLIBRÍ optical counterpart candidate
  51. COLIBRI optical observations of the transient GOTO26djh/AT2026jpw
  52. EP260416a: Global MASTER-Net observations report
  53. GOTO26djh/AT2026jpw : MASTER OT observation
  54. GOTO26djh/AT2026jpw: EP-FXT X-ray counterpart detection
  55. GOTO26djh/AT2026jpw transient: SAO RAS optical observations
  56. NOT r-band observations of the transient GOTO26djh/AT2026jpw
  57. GOTO discovery of fast-fading transient GOTO26djh/AT2026jpw, a candidate orphan afterglow
  58. Fermi trigger No 797912738: Global MASTER-Net observations report
  59. EP260409a: Early NIR limits from MIRAGE on the MDM 1.3m telescope
  60. EP260321a: CMO SAI J,K observations
  61. Fermi GRB 260413A: Global MASTER-Net observations report
  62. EP260321a: SVOM/VT optical observations and color changes around peak
  63. Fermi GRB 260412A: Global MASTER-Net observations report
  64. GRB 260310A / AT2026fgk: NuSTAR detection of the rebrightening
  65. GRB 260411B: COLIBRÍ optical observations
  66. GRB260411B: 3.6m DOT optical observation
  67. GRB 260411B: GOTO optical counterpart candidate
  68. EP260409a: Gemini/FLAMINGOS2 J-band counterpart
  69. EP-WXT01709259790: Optical Upper limits with kinder observations
  70. EP260409a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  71. EP260321a: Chandra X-ray Non-detection
  72. GRB 260310A/AT2026fgk: Kilonova-Catcher SN peak identification
  73. EP260409a: SVOM/VT optical upper limits
  74. EP260409a: Global MASTER-Net observations report
  75. EP260321a: VLA radio detection
  76. GRB 260402A: SVOM/ECLAIRs refined analysis
  77. GRB 260310A: Continued VLA Multi-frequency Radio Observations
  78. GRB 260310A / AT2026fgk: X-ray rebrightening
  79. EP260402a / GRB 260402A: Mephisto optical upper limits
  80. EP260403a: Mephisto optical upper limits
  81. EP260321a: Upper limits from VLA radio observations
  82. EP260321a: uGMRT observations
  83. EP260405a: SVOM/VT optical upper limits
  84. EP260405a: Global MASTER-Net observations report
  85. EP260405a / EP-WXT 11900672904: COLIBRÍ optical upper limits
  86. Fermi trigger No 797039833: Global MASTER-Net observations report
  87. EP260324A / AT 2026hir: COLIBRÍ further optical observations
  88. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  89. GRB 260330B: SVOM/VT further optical observation
  90. GRB 260330B: SVOM/ECLAIRs refined analysis
  91. EP260403a: LCO optical observations of the counterpart
  92. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  93. EP260403a: LCO optical counterpart detection
  94. EP260403a: COLIBRÍ optical counterpart candidate
  95. GRB 260330B: SVOM/VT optical candidate
  96. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  97. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  98. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  99. EP260324A / AT 2026hir: COLIBRÍ optical observations
  100. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph

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