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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"

15985 results found.

  1. GRB 260421B: LCO optical afterglow confirmation
  2. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  3. GRB 260421B: TRT optical counterpart detection
  4. GRB 260412A: LCOGT Optical Upper Limits
  5. EP260416a: Optical follow-up observations with Kinder
  6. GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient
  7. EP-WXT trigger 01709260303: KAIT optical observations
  8. EP260416a: 1.5m OSN and 2.2m CAHA optical monitoring
  9. GRB 260417A: SVOM/GRM observation
  10. EP260321A/AT2026gzf: Optical observation from 1.3m DFOT
  11. EP260417a: GROWTH-India Telescope optical upper limit
  12. EP260417b: GROWTH-India Telescope optical upper limit
  13. EP260416a: Ondrejov D50 optical detection
  14. EP260416a: VLT/FORS2 spectroscopic redshift confirmation
  15. EP260416a: NOT tentative spectroscopic redshift of z =1.909
  16. EP260416a: GMG Optical Observation
  17. EP260416a: LCO observations confirm end of flaring phase
  18. EP260324a / AT2026hir: Further multiband optical follow-up with the PKU 60cm Telescope
  19. EP260417a: TRT optical counterpart detection
  20. EP260416a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  21. EP-WXT trigger 01709259586: KAIT optical observations
  22. EP260416a: KAIT optical upper limit
  23. EP260416a: COLIBRÍ confirmation of the optical rebrightening
  24. EP260416a: WFST optical observations and rebrightening
  25. GOTO26djh/AT2026jpw: ZTSh R,I bands observations of the transient
  26. EP260416a: SVOM/VT optical observation
  27. GOTO26djh/AT2026jpw: SVOM/VT optical observation
  28. EP260416a: COLIBRÍ optical counterpart candidate
  29. COLIBRI optical observations of the transient GOTO26djh/AT2026jpw
  30. GOTO26djh/AT2026jpw : MASTER OT observation
  31. GOTO26djh/AT2026jpw transient: SAO RAS optical observations
  32. NOT r-band observations of the transient GOTO26djh/AT2026jpw
  33. GOTO discovery of fast-fading transient GOTO26djh/AT2026jpw, a candidate orphan afterglow
  34. EP260321a: CMO SAI J,K observations
  35. EP260321a: SVOM/VT optical observations and color changes around peak
  36. GRB 260411B: Fermi-LAT detection
  37. GRB 260412A: SVOM detection of a long burst
  38. GRB 260411B: COLIBRÍ optical observations
  39. GRB 260411B: Ondrejov D50 optical afterglow detection
  40. GRB260411B: 3.6m DOT optical observation
  41. GRB 260411A: SVOM/GRM observation
  42. GRB 260411B: SVOM/GRM observation of a long burst
  43. GRB 260411B: Fermi GBM Detection
  44. GRB 260411B: GOTO optical counterpart candidate
  45. EP260409a: Gemini/FLAMINGOS2 J-band counterpart
  46. GRB 260410A: COLIBRÍ optical upper limit
  47. EP-WXT01709259790: Optical Upper limits with kinder observations
  48. EP-WXT01709259790: Xinglong optical upper limit
  49. EP260409a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  50. GRB 260310A/AT2026fgk: Kilonova-Catcher SN peak identification
  51. EP260409a: SVOM/VT optical upper limits
  52. EP260409a: COLIBRÍ optical upper limits
  53. GRB 260310A / AT2026fgk: X-ray rebrightening
  54. EP260402a / GRB 260402A: Mephisto optical upper limits
  55. EP-WXT01709259586: Xinglong optical upper limit
  56. EP260403a: Mephisto optical upper limits
  57. EP260402a/GRB 260402A: Xinglong optical upper limit
  58. EP260321a: Upper limits from VLA radio observations
  59. EP260321a: uGMRT observations
  60. EP260405a: GMOS-N optical upper limits
  61. EP260405a: SVOM/VT optical upper limits
  62. EP260405a / EP-WXT 11900672904: COLIBRÍ optical upper limits
  63. EP260324A / AT 2026hir: COLIBRÍ further optical observations
  64. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  65. GRB 260330B: SVOM/VT further optical observation
  66. EP260403a: LCO optical observations of the counterpart
  67. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  68. EP260403a: LCO optical counterpart detection
  69. EP260403a: COLIBRÍ optical counterpart candidate
  70. GRB 260330B: SVOM/VT optical candidate
  71. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  72. EP260324A / AT 2026hir: COLIBRÍ optical observations
  73. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  74. GRB 260402A: WINTER J-band upper limit
  75. GRB260402A: GROWTH-India Telescope optical upper limit
  76. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  77. GRB 260401A: SVOM/GRM observation
  78. GRB 260402A: Kilonova-Catcher optical upper limit
  79. GRB 260402A: MASTER optical observations
  80. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  81. EP260329b: Mondy and Assy-Turgen optical upper limits
  82. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  83. EP260321a :Xinglong optical observations
  84. EP260327a: Xinglong optical upper limit
  85. EP260329b: GOTO detection of optical counterpart
  86. GRB 260330B: SVOM/VT optical upper limits
  87. GRB 260321A: SVOM/ECLAIRs refined analysis
  88. EP260329b: J-band upper limits with WINTER
  89. EP260329a: J-band upper limit with WINTER
  90. GRB 260330B: LCO optical upper limits
  91. GRB 260330B: SVOM detection of a burst
  92. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  93. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  94. EP260329a: COLIBRÍ optical upper limit
  95. EP260329a: EP-FXT follow up observation
  96. EP260329a: NOT optical counterpart candidate
  97. EP260329b: Optical follow-up with Kinder observations
  98. EP 260329b: COLIBRÍ optical observations
  99. EP260329a: Optical upper limit with Kinder observations
  100. EP260329b: LCO optical observations of the counterpart

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