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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"

21791 results found.

  1. EP260502a: BOOTES-7 observations of a fading catalogued source close to the X-ray position
  2. SN 2026kid: Optical follow-up with small-aperture telescopes in Spain and China
  3. EP260429a: Global MASTER-Net observations report
  4. EP260430a: refined analysis of the EP-WXT and follow-up EP-FXT observations
  5. Fermi GRB 260429A: Global MASTER-Net observations report
  6. EP260430a: Global MASTER-Net observations report
  7. Fermi GRB 260428A: Global MASTER-Net observations report
  8. GRB 260424B: COLIBRÍ optical upper limit
  9. Fermi-LAT Gamma-ray Observations of IceCube-260425A
  10. EP260321a/SN 2026gzf: spectroscopy at Mondy observatory
  11. IceCube Alert 260425A: Global MASTER-Net observations report
  12. Fermi trigger No 798737427: Global MASTER-Net observations report
  13. EP260321a: Upper limits from ATCA radio observations
  14. GRB 260421B: Kilonova-Catcher optical afterglow detection
  15. The EP-WXT trigger 01709258652: Mondy optical observations
  16. GRB 250328A: VLT host galaxy discovery and redshift z = 1.250
  17. EP260416a: Mondy optical observations
  18. GRB 260421B: SVOM/ECLAIRs refined analysis
  19. GRB 260421B: 3.6m DOT optical observation
  20. EP260416a: ZTSh R band observations
  21. EP-WXT trigger 01709260362: FRAM-ORM optical observations confirm flaring star G 151-9
  22. EP250512a / GRB 250512B: VLT/X-shooter host galaxy identification and redshift z = 1.773
  23. GRB 250530A: VLT/X-shooter host galaxy redshift z = 1.486
  24. GRB260421B: J band upper limit by SYSU 80cm infrared telescope
  25. GOTO26djh/AT2026jpw: ATCA radio detection
  26. GRB 260421B: J-band upper limit with WINTER
  27. GRB 260421B: LCO optical counterpart detection
  28. GOTO26djh/AT2026jpw: radio detection at 15GHz
  29. GRB 260412A: SVOM/ECLAIRs refined analysis
  30. GRB 260421B: SVOM/VT optical observations
  31. EP260416a: J band upper limit by SYSU 80cm infrared telescope
  32. GRB 260310A: Late-time Chandra X-ray Detection
  33. EP260416a: 1.3m DFOT optical observation
  34. Fermi GRB 260421C: Global MASTER-Net observations report
  35. Fermi GRB 260421B: Global MASTER-Net observations report
  36. GRB 260421B: LCO optical afterglow confirmation
  37. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  38. Fermi GRB 260421A: Global MASTER-Net observations report
  39. EP260321a: VLA radio follow-up
  40. EP260416a: Optical follow-up observations with Kinder
  41. GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient
  42. EP-WXT trigger 01709260303: KAIT optical observations
  43. EP260321A/AT2026gzf: Optical observation from 1.3m DFOT
  44. Fermi trigger No 798275385: Global MASTER-Net observations report
  45. Fermi GRB 260417B: Global MASTER-Net observations report
  46. EP260417a: Global MASTER-Net observations report
  47. EP260417a/GRB 260417A: refined analysis of the EP-WXT and follow-up EP-FXT observations
  48. EP260416a: NOT tentative spectroscopic redshift of z =1.909
  49. Fermi GRB 260417A: Global MASTER-Net observations report
  50. EP260416a: LCO observations confirm end of flaring phase
  51. EP260324a / AT2026hir: Further multiband optical follow-up with the PKU 60cm Telescope
  52. EP260416a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  53. EP-WXT trigger 01709259586: KAIT optical observations
  54. EP260416a: WFST optical observations and rebrightening
  55. GOTO26djh/AT2026jpw: ZTSh R,I bands observations of the transient
  56. EP260416a: COLIBRÍ optical counterpart candidate
  57. COLIBRI optical observations of the transient GOTO26djh/AT2026jpw
  58. EP260416a: Global MASTER-Net observations report
  59. GOTO26djh/AT2026jpw : MASTER OT observation
  60. GOTO26djh/AT2026jpw: EP-FXT X-ray counterpart detection
  61. GOTO26djh/AT2026jpw transient: SAO RAS optical observations
  62. NOT r-band observations of the transient GOTO26djh/AT2026jpw
  63. GOTO discovery of fast-fading transient GOTO26djh/AT2026jpw, a candidate orphan afterglow
  64. Fermi trigger No 797912738: Global MASTER-Net observations report
  65. EP260409a: Early NIR limits from MIRAGE on the MDM 1.3m telescope
  66. EP260321a: CMO SAI J,K observations
  67. Fermi GRB 260413A: Global MASTER-Net observations report
  68. EP260321a: SVOM/VT optical observations and color changes around peak
  69. Fermi GRB 260412A: Global MASTER-Net observations report
  70. GRB 260310A / AT2026fgk: NuSTAR detection of the rebrightening
  71. GRB 260411B: COLIBRÍ optical observations
  72. GRB260411B: 3.6m DOT optical observation
  73. GRB 260411B: GOTO optical counterpart candidate
  74. EP260409a: Gemini/FLAMINGOS2 J-band counterpart
  75. EP-WXT01709259790: Optical Upper limits with kinder observations
  76. EP260409a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  77. EP260321a: Chandra X-ray Non-detection
  78. GRB 260310A/AT2026fgk: Kilonova-Catcher SN peak identification
  79. EP260409a: SVOM/VT optical upper limits
  80. EP260409a: Global MASTER-Net observations report
  81. EP260321a: VLA radio detection
  82. GRB 260402A: SVOM/ECLAIRs refined analysis
  83. GRB 260310A: Continued VLA Multi-frequency Radio Observations
  84. GRB 260310A / AT2026fgk: X-ray rebrightening
  85. EP260402a / GRB 260402A: Mephisto optical upper limits
  86. EP260403a: Mephisto optical upper limits
  87. EP260321a: Upper limits from VLA radio observations
  88. EP260321a: uGMRT observations
  89. EP260405a: SVOM/VT optical upper limits
  90. EP260405a: Global MASTER-Net observations report
  91. EP260405a / EP-WXT 11900672904: COLIBRÍ optical upper limits
  92. Fermi trigger No 797039833: Global MASTER-Net observations report
  93. EP260324A / AT 2026hir: COLIBRÍ further optical observations
  94. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  95. GRB 260330B: SVOM/VT further optical observation
  96. GRB 260330B: SVOM/ECLAIRs refined analysis
  97. EP260403a: LCO optical observations of the counterpart
  98. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  99. EP260403a: LCO optical counterpart detection
  100. EP260403a: COLIBRÍ optical counterpart candidate

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