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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"

21801 results found.

  1. EP260405a / EP-WXT 11900672904: COLIBRÍ optical upper limits
  2. Fermi trigger No 797039833: Global MASTER-Net observations report
  3. EP260324A / AT 2026hir: COLIBRÍ further optical observations
  4. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  5. GRB 260330B: SVOM/VT further optical observation
  6. GRB 260330B: SVOM/ECLAIRs refined analysis
  7. EP260403a: LCO optical observations of the counterpart
  8. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  9. EP260403a: LCO optical counterpart detection
  10. EP260403a: COLIBRÍ optical counterpart candidate
  11. GRB 260330B: SVOM/VT optical candidate
  12. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  13. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  14. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  15. EP260324A / AT 2026hir: COLIBRÍ optical observations
  16. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  17. GRB 260402A: WINTER J-band upper limit
  18. GRB260402A: GROWTH-India Telescope optical upper limit
  19. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  20. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  21. GRB 260402A: Kilonova-Catcher optical upper limit
  22. GRB 260402A: MASTER optical observations
  23. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  24. Fermi GRB 260401A: Global MASTER-Net observations report
  25. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  26. EP260321a :Xinglong optical observations
  27. EP260329b: GOTO detection of optical counterpart
  28. GRB 260330B: SVOM/VT optical upper limits
  29. GRB 260321A: SVOM/ECLAIRs refined analysis
  30. EP260329b: J-band upper limits with WINTER
  31. EP260329a: J-band upper limit with WINTER
  32. GRB 260310A: VLA Multi-frequency Radio Observations
  33. Fermi GBM Sub-Threshold Detection of GRB 260330B
  34. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  35. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  36. EP260329a: EP-FXT follow up observation
  37. EP260329b: Global MASTER-Net observations report
  38. Fermi trigger No 796485221: Global MASTER-Net observations report
  39. EP260329b: Optical follow-up with Kinder observations
  40. EP 260329b: COLIBRÍ optical observations
  41. EP260329a: Optical upper limit with Kinder observations
  42. EP260329b: LCO optical observations of the counterpart
  43. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  44. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  45. EP260327a: SVOM/VT optical upper limits
  46. SMA Detection of GRB 260310A / AT 2026fgk
  47. GRB 260307B: ATCA Radio Upper Limits
  48. EP260327a: WINTER J-band upper limit
  49. EP260327a: COLIBRÍ optical upper limits
  50. EP260327a: Gemini-North optical upper limits
  51. EP260324a: GROWTH-India Telescope optical observation
  52. EP260327a: Global MASTER-Net observations report
  53. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  54. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  55. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  56. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  57. EP260321a: JinShan near-infrared observations
  58. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  59. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  60. EP260321a: Gemini-South confirmation of a supernova
  61. EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
  62. GRB 260310A: LBT optical observations
  63. EP260321A: Mondy optical observations
  64. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  65. Fermi GRB 260323A: Global MASTER-Net observations report
  66. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  67. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  68. EP260321a / AT2026gzf: VLT/X-shooter detection of supernova-like spectral features at z = 0.0344
  69. EP260321a: COLIBRÍ further optical observations and brightening
  70. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  71. EP260214b: ATCA 6 GHz detection
  72. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  73. EP260321a: ZTF and Rubin detections of the candidate optical counterpart to EP260321a
  74. EP260321a: GOTO detection of blue variable source
  75. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  76. EP260321a: further Kinder optical observations
  77. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  78. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  79. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  80. EP260321a: SVOM/VT optical upper limit
  81. GRB 260310A: continued optical observation at Mondy
  82. Fermi GBM Sub-Threshold Detection of GRB 260321A
  83. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  84. EP260321a: Global MASTER-Net observations report
  85. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS new optical observations
  86. GRB 260310A / AT 2026fgk: KAIT optical observations
  87. GRB 260310A / AT 2026fgk: FTW optical and NIR observations show no rebrightening
  88. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
  89. GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening
  90. GRB 260310A/AT2026fgk: LBT near-infrared observations
  91. NOEMA Detection of GRB 260310A / AT 2026fgk
  92. EP-WXT trigger 01709258989: confirmation of a stellar flare by BOOTES-7
  93. GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT
  94. Fermi GRB 260318A: Global MASTER-Net observations report
  95. IceCube-260315A: No Candidate Transients from the Zwicky Transient Facility
  96. GRB 260310A / AT 2026fgk: radio detection with the VLA
  97. GRB 260310A / AT2026fgk: SVOM/VT optical observations
  98. GRB 260310A / AT2026fgk: LCO optical observations
  99. EP260316a: COLIBRÍ faint optical counterpart candidate
  100. Fermi-LAT Gamma-ray Observations of IceCube-260315A

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