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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"

21793 results found.

  1. EP260403a: LCO optical counterpart detection
  2. EP260403a: COLIBRÍ optical counterpart candidate
  3. GRB 260330B: SVOM/VT optical candidate
  4. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  5. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  6. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  7. EP260324A / AT 2026hir: COLIBRÍ optical observations
  8. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  9. GRB 260402A: WINTER J-band upper limit
  10. GRB260402A: GROWTH-India Telescope optical upper limit
  11. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  12. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  13. GRB 260402A: Kilonova-Catcher optical upper limit
  14. GRB 260402A: MASTER optical observations
  15. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  16. Fermi GRB 260401A: Global MASTER-Net observations report
  17. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  18. EP260321a :Xinglong optical observations
  19. EP260329b: GOTO detection of optical counterpart
  20. GRB 260330B: SVOM/VT optical upper limits
  21. GRB 260321A: SVOM/ECLAIRs refined analysis
  22. EP260329b: J-band upper limits with WINTER
  23. EP260329a: J-band upper limit with WINTER
  24. GRB 260310A: VLA Multi-frequency Radio Observations
  25. Fermi GBM Sub-Threshold Detection of GRB 260330B
  26. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  27. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  28. EP260329a: EP-FXT follow up observation
  29. EP260329b: Global MASTER-Net observations report
  30. Fermi trigger No 796485221: Global MASTER-Net observations report
  31. EP260329b: Optical follow-up with Kinder observations
  32. EP 260329b: COLIBRÍ optical observations
  33. EP260329a: Optical upper limit with Kinder observations
  34. EP260329b: LCO optical observations of the counterpart
  35. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  36. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  37. EP260327a: SVOM/VT optical upper limits
  38. SMA Detection of GRB 260310A / AT 2026fgk
  39. GRB 260307B: ATCA Radio Upper Limits
  40. EP260327a: WINTER J-band upper limit
  41. EP260327a: COLIBRÍ optical upper limits
  42. EP260327a: Gemini-North optical upper limits
  43. EP260324a: GROWTH-India Telescope optical observation
  44. EP260327a: Global MASTER-Net observations report
  45. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  46. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  47. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  48. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  49. EP260321a: JinShan near-infrared observations
  50. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  51. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  52. EP260321a: Gemini-South confirmation of a supernova
  53. EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
  54. GRB 260310A: LBT optical observations
  55. EP260321A: Mondy optical observations
  56. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  57. Fermi GRB 260323A: Global MASTER-Net observations report
  58. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  59. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  60. EP260321a / AT2026gzf: VLT/X-shooter detection of supernova-like spectral features at z = 0.0344
  61. EP260321a: COLIBRÍ further optical observations and brightening
  62. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  63. EP260214b: ATCA 6 GHz detection
  64. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  65. EP260321a: ZTF and Rubin detections of the candidate optical counterpart to EP260321a
  66. EP260321a: GOTO detection of blue variable source
  67. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  68. EP260321a: further Kinder optical observations
  69. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  70. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  71. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  72. EP260321a: SVOM/VT optical upper limit
  73. GRB 260310A: continued optical observation at Mondy
  74. Fermi GBM Sub-Threshold Detection of GRB 260321A
  75. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  76. EP260321a: Global MASTER-Net observations report
  77. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS new optical observations
  78. GRB 260310A / AT 2026fgk: KAIT optical observations
  79. GRB 260310A / AT 2026fgk: FTW optical and NIR observations show no rebrightening
  80. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
  81. GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening
  82. GRB 260310A/AT2026fgk: LBT near-infrared observations
  83. NOEMA Detection of GRB 260310A / AT 2026fgk
  84. EP-WXT trigger 01709258989: confirmation of a stellar flare by BOOTES-7
  85. GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT
  86. Fermi GRB 260318A: Global MASTER-Net observations report
  87. IceCube-260315A: No Candidate Transients from the Zwicky Transient Facility
  88. GRB 260310A / AT 2026fgk: radio detection with the VLA
  89. GRB 260310A / AT2026fgk: SVOM/VT optical observations
  90. GRB 260310A / AT2026fgk: LCO optical observations
  91. EP260316a: COLIBRÍ faint optical counterpart candidate
  92. Fermi-LAT Gamma-ray Observations of IceCube-260315A
  93. EP260316a: refined analysis of the EP-WXT and EP-FXT observations
  94. EP260316a: optical upper limit with Kinder observations
  95. EP260316a / GRB 260316A : Fermi-GBM Sub-Threshold Detection
  96. IceCube-260315A: COLIBRÍ optical observations
  97. EP260314a: optical upper limit with Kinder observations
  98. IceCube Alert-260315A/AT2026fpm Automatic MASTER optical blue counterpart candidate
  99. GRB 260310A / AT2026fgk: 1.3m DFOT optical observations
  100. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS optical observations

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