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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"

16154 results found.

  1. EP260416a: LCO observations confirm end of flaring phase
  2. EP260324a / AT2026hir: Further multiband optical follow-up with the PKU 60cm Telescope
  3. EP260417a: TRT optical counterpart detection
  4. EP260416a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  5. EP-WXT trigger 01709259586: KAIT optical observations
  6. EP260416a: KAIT optical upper limit
  7. EP260416a: COLIBRÍ confirmation of the optical rebrightening
  8. EP260416a: WFST optical observations and rebrightening
  9. GOTO26djh/AT2026jpw: ZTSh R,I bands observations of the transient
  10. EP260416a: SVOM/VT optical observation
  11. GOTO26djh/AT2026jpw: SVOM/VT optical observation
  12. EP260416a: COLIBRÍ optical counterpart candidate
  13. COLIBRI optical observations of the transient GOTO26djh/AT2026jpw
  14. GOTO26djh/AT2026jpw : MASTER OT observation
  15. GOTO26djh/AT2026jpw transient: SAO RAS optical observations
  16. NOT r-band observations of the transient GOTO26djh/AT2026jpw
  17. GOTO discovery of fast-fading transient GOTO26djh/AT2026jpw, a candidate orphan afterglow
  18. EP260321a: SVOM/VT optical observations and color changes around peak
  19. GRB 260411B: Fermi-LAT detection
  20. GRB 260412A: SVOM detection of a long burst
  21. GRB 260411B: COLIBRÍ optical observations
  22. GRB 260411B: Ondrejov D50 optical afterglow detection
  23. GRB260411B: 3.6m DOT optical observation
  24. GRB 260411A: SVOM/GRM observation
  25. GRB 260411B: SVOM/GRM observation of a long burst
  26. GRB 260411B: Fermi GBM Detection
  27. GRB 260411B: GOTO optical counterpart candidate
  28. EP260409a: Gemini/FLAMINGOS2 J-band counterpart
  29. GRB 260410A: COLIBRÍ optical upper limit
  30. EP-WXT01709259790: Optical Upper limits with kinder observations
  31. EP-WXT01709259790: Xinglong optical upper limit
  32. EP260409a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  33. GRB 260310A/AT2026fgk: Kilonova-Catcher SN peak identification
  34. EP260409a: SVOM/VT optical upper limits
  35. EP260409a: COLIBRÍ optical upper limits
  36. GRB 260310A: Continued VLA Multi-frequency Radio Observations
  37. GRB 260310A / AT2026fgk: X-ray rebrightening
  38. EP260402a / GRB 260402A: Mephisto optical upper limits
  39. EP-WXT01709259586: Xinglong optical upper limit
  40. EP260403a: Mephisto optical upper limits
  41. EP260402a/GRB 260402A: Xinglong optical upper limit
  42. EP260321a: Upper limits from VLA radio observations
  43. EP260321a: uGMRT observations
  44. EP260405a: GMOS-N optical upper limits
  45. EP260405a: SVOM/VT optical upper limits
  46. EP260405a / EP-WXT 11900672904: COLIBRÍ optical upper limits
  47. EP260324A / AT 2026hir: COLIBRÍ further optical observations
  48. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  49. GRB 260330B: SVOM/VT further optical observation
  50. EP260403a: LCO optical observations of the counterpart
  51. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  52. EP260403a: LCO optical counterpart detection
  53. EP260403a: COLIBRÍ optical counterpart candidate
  54. GRB 260330B: SVOM/VT optical candidate
  55. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  56. EP260324A / AT 2026hir: COLIBRÍ optical observations
  57. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  58. GRB 260402A: WINTER J-band upper limit
  59. GRB260402A: GROWTH-India Telescope optical upper limit
  60. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  61. GRB 260401A: SVOM/GRM observation
  62. GRB 260402A: Kilonova-Catcher optical upper limit
  63. GRB 260402A: MASTER optical observations
  64. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  65. EP260329b: Mondy and Assy-Turgen optical upper limits
  66. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  67. EP260321a :Xinglong optical observations
  68. EP260327a: Xinglong optical upper limit
  69. EP260329b: GOTO detection of optical counterpart
  70. GRB 260330B: SVOM/VT optical upper limits
  71. GRB 260321A: SVOM/ECLAIRs refined analysis
  72. EP260329b: J-band upper limits with WINTER
  73. EP260329a: J-band upper limit with WINTER
  74. GRB 260330B: LCO optical upper limits
  75. GRB 260330B: SVOM detection of a burst
  76. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  77. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  78. EP260329a: COLIBRÍ optical upper limit
  79. EP260329a: EP-FXT follow up observation
  80. EP260329a: NOT optical counterpart candidate
  81. EP260329b: Optical follow-up with Kinder observations
  82. EP 260329b: COLIBRÍ optical observations
  83. EP260329a: Optical upper limit with Kinder observations
  84. EP260329b: LCO optical observations of the counterpart
  85. EP260329b: Einstein Probe detection of an X-ray transient
  86. EP-WXT trigger 01709259209: TRT optical counterpart detection
  87. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  88. GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
  89. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  90. EP260327a: SVOM/VT optical upper limits
  91. EP260327a: WINTER J-band upper limit
  92. EP260327a: COLIBRÍ optical upper limits
  93. EP260327a: Gemini-North optical upper limits
  94. EP260324a: GROWTH-India Telescope optical observation
  95. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  96. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  97. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  98. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  99. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  100. EP260321a: JinShan near-infrared observations

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