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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"

15697 results found.

  1. EP260429a: LCO optical upper limits
  2. EP260430a: LCO optical upper limits
  3. GRB 260430A / EP260430a: COLIBRÍ optical upper limit
  4. GRB 260428A: SVOM/GRM observation of a possible short burst with extended emission
  5. EP260416a: Mondy and Terskol optical upper limits
  6. GRB 260424B: COLIBRÍ optical upper limit
  7. EP260321a/SN 2026gzf: spectroscopy at Mondy observatory
  8. EP260321a: Upper limits from ATCA radio observations
  9. GRB 260421B: Kilonova-Catcher optical afterglow detection
  10. The EP-WXT trigger 01709258652: Mondy optical observations
  11. GRB 250328A: VLT host galaxy discovery and redshift z = 1.250
  12. EP260416a: Mondy optical observations
  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. EP250512a / GRB 250512B: VLT/X-shooter host galaxy identification and redshift z = 1.773
  17. GRB 250530A: VLT/X-shooter host galaxy redshift z = 1.486
  18. GRB 260421B: SVOM/GRM observation
  19. GRB 260421B: EP-FXT follow-up observation
  20. GRB 260421B: J-band upper limit with WINTER
  21. GRB 260421B: LCO optical counterpart detection
  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. GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
  27. GRB 260421B: BOOTES-7 early optical afterglow detection
  28. GRB 260421B: LCO optical afterglow confirmation
  29. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  30. GRB 260421B: TRT optical counterpart detection
  31. GRB 260412A: LCOGT Optical Upper Limits
  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. GRB 260417A: SVOM/GRM observation
  37. EP260321A/AT2026gzf: Optical observation from 1.3m DFOT
  38. EP260417a: GROWTH-India Telescope optical upper limit
  39. EP260417b: GROWTH-India Telescope optical upper limit
  40. EP260416a: Ondrejov D50 optical detection
  41. EP260416a: VLT/FORS2 spectroscopic redshift confirmation
  42. EP260416a: NOT tentative spectroscopic redshift of z =1.909
  43. EP260416a: GMG Optical Observation
  44. EP260416a: LCO observations confirm end of flaring phase
  45. EP260324a / AT2026hir: Further multiband optical follow-up with the PKU 60cm Telescope
  46. EP260417a: TRT optical counterpart detection
  47. EP260416a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  48. EP-WXT trigger 01709259586: KAIT optical observations
  49. EP260416a: KAIT optical upper limit
  50. EP260416a: COLIBRÍ confirmation of the optical rebrightening
  51. EP260416a: WFST optical observations and rebrightening
  52. GOTO26djh/AT2026jpw: ZTSh R,I bands observations of the transient
  53. EP260416a: SVOM/VT optical observation
  54. GOTO26djh/AT2026jpw: SVOM/VT optical observation
  55. EP260416a: COLIBRÍ optical counterpart candidate
  56. COLIBRI optical observations of the transient GOTO26djh/AT2026jpw
  57. GOTO26djh/AT2026jpw : MASTER OT observation
  58. GOTO26djh/AT2026jpw transient: SAO RAS optical observations
  59. NOT r-band observations of the transient GOTO26djh/AT2026jpw
  60. GOTO discovery of fast-fading transient GOTO26djh/AT2026jpw, a candidate orphan afterglow
  61. EP260321a: SVOM/VT optical observations and color changes around peak
  62. GRB 260411B: Fermi-LAT detection
  63. GRB 260412A: SVOM detection of a long burst
  64. GRB 260411B: COLIBRÍ optical observations
  65. GRB 260411B: Ondrejov D50 optical afterglow detection
  66. GRB260411B: 3.6m DOT optical observation
  67. GRB 260411A: SVOM/GRM observation
  68. GRB 260411B: SVOM/GRM observation of a long burst
  69. GRB 260411B: Fermi GBM Detection
  70. GRB 260411B: GOTO optical counterpart candidate
  71. EP260409a: Gemini/FLAMINGOS2 J-band counterpart
  72. GRB 260410A: COLIBRÍ optical upper limit
  73. EP-WXT01709259790: Optical Upper limits with kinder observations
  74. EP-WXT01709259790: Xinglong optical upper limit
  75. EP260409a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  76. GRB 260310A/AT2026fgk: Kilonova-Catcher SN peak identification
  77. EP260409a: SVOM/VT optical upper limits
  78. EP260409a: COLIBRÍ optical upper limits
  79. GRB 260310A: Continued VLA Multi-frequency Radio Observations
  80. GRB 260310A / AT2026fgk: X-ray rebrightening
  81. EP260402a / GRB 260402A: Mephisto optical upper limits
  82. EP-WXT01709259586: Xinglong optical upper limit
  83. EP260403a: Mephisto optical upper limits
  84. EP260402a/GRB 260402A: Xinglong optical upper limit
  85. EP260321a: Upper limits from VLA radio observations
  86. EP260321a: uGMRT observations
  87. EP260405a: GMOS-N optical upper limits
  88. EP260405a: SVOM/VT optical upper limits
  89. EP260405a / EP-WXT 11900672904: COLIBRÍ optical upper limits
  90. EP260324A / AT 2026hir: COLIBRÍ further optical observations
  91. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  92. GRB 260330B: SVOM/VT further optical observation
  93. EP260403a: LCO optical observations of the counterpart
  94. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  95. EP260403a: LCO optical counterpart detection
  96. EP260403a: COLIBRÍ optical counterpart candidate
  97. GRB 260330B: SVOM/VT optical candidate
  98. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  99. EP260324A / AT 2026hir: COLIBRÍ optical observations
  100. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph

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