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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"

25840 results found.

  1. EP260403a: LCO optical counterpart detection
  2. EP260403a: COLIBRÍ optical counterpart candidate
  3. GRB 260330B: SVOM/VT optical candidate
  4. EP260403a: Einstein Probe detection of an X-ray transient
  5. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  6. GRB 260403A: AstroSat CZTI detection
  7. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  8. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  9. GRB 260402C: AstroSat CZTI detection of a long burst
  10. EP260324A / AT 2026hir: COLIBRÍ optical observations
  11. GRB 260402B: Fermi GBM Final Real-time Localization
  12. GRB 260402A: WINTER J-band upper limit
  13. GRB260402A: GROWTH-India Telescope optical upper limit
  14. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  15. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  16. GRB 260401A: SVOM/GRM observation
  17. GRB 260401A: GECAM-B observation
  18. EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
  19. GRB 260402A: Kilonova-Catcher optical upper limit
  20. GRB 260402A: MASTER optical observations
  21. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  22. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  23. GRB 260402A: SVOM detection of a burst
  24. GRB 260401A: Fermi GBM Observation
  25. EP260329b: Mondy and Assy-Turgen optical upper limits
  26. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  27. EP260321a :Xinglong optical observations
  28. EP260327a: Xinglong optical upper limit
  29. GRB 260330B: SVOM/VT optical upper limits
  30. Konus-Wind detection of GRB 260320A
  31. GRB 260321A: SVOM/ECLAIRs refined analysis
  32. EP260329b: J-band upper limits with WINTER
  33. EP260329a: J-band upper limit with WINTER
  34. GRB 260330A: Glowbug gamma-ray detection
  35. GRB 260310A: VLA Multi-frequency Radio Observations
  36. GRB 260330B: LCO optical upper limits
  37. GRB 260330B: SVOM detection of a burst
  38. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  39. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  40. EP260329a: COLIBRÍ optical upper limit
  41. EP260329a: EP-FXT follow up observation
  42. EP260329a: NOT optical counterpart candidate
  43. EP260329b: Optical follow-up with Kinder observations
  44. EP 260329b: COLIBRÍ optical observations
  45. EP260329a: Optical upper limit with Kinder observations
  46. EP260329b: LCO optical observations of the counterpart
  47. EP260329b: Einstein Probe detection of an X-ray transient
  48. EP260329a: Einstein Probe detection of an X-ray transient
  49. EP-WXT trigger 01709259209: TRT optical counterpart detection
  50. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  51. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  52. EP260327a: SVOM/VT optical upper limits
  53. EP260327a: WINTER J-band upper limit
  54. EP260327a: COLIBRÍ optical upper limits
  55. EP260327a: Gemini-North optical upper limits
  56. EP260324a: GROWTH-India Telescope optical observation
  57. EP260327a: Einstein Probe detection of an X-ray transient
  58. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  59. The EP-WXT trigger 01709259173 is likely a flaring star
  60. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  61. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  62. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  63. GRB 260326A: Fermi GBM Detection
  64. EP260321a: JinShan near-infrared observations
  65. EP260321a: Upper limits from a neutrino search with IceCube
  66. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  67. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  68. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  69. The EP-WXT trigger 01709259112 is likely a flaring star
  70. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  71. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  72. GRB 260320A: Glowbug gamma-ray detection
  73. EP260321a: COLIBRÍ further optical observations and brightening
  74. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  75. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  76. The EP-WXT trigger 01709259045 is likely a flaring star
  77. EP260321a: GOTO detection of blue variable source
  78. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  79. EP260321a: further Kinder optical observations
  80. GRB 260321A: SVOM/VT optical upper limits
  81. EP260321a: Las Cumbres upper limit
  82. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  83. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  84. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  85. EP260321a: SVOM/VT optical upper limit
  86. GRB 260321A: SVOM detection of a burst
  87. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  88. EP260321a: Einstein Probe detection of an X-ray transient
  89. GRB 260318A: Glowbug gamma-ray detection
  90. GRB 260310A / AT 2026fgk: KAIT optical observations
  91. GRB 260310A / AT2026fgk: NuSTAR follow-up detection
  92. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
  93. GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening
  94. NOEMA Detection of GRB 260310A / AT 2026fgk
  95. GRB 260318A: SVOM/GRM observation
  96. The EP-WXT trigger 01709258989 is likely a flaring star
  97. GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90
  98. GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT
  99. GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
  100. GRB 260310A / AT 2026fgk: radio detection with the VLA

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