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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"

41630 results found.

  1. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  2. GRID detection of GRB 260320A
  3. EP260321a: Gemini-South confirmation of a supernova
  4. EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
  5. GRB 260310A: LBT optical observations
  6. EP260321A: Mondy optical observations
  7. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  8. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  9. The EP-WXT trigger 01709259112 is likely a flaring star
  10. Fermi GRB 260323A: Global MASTER-Net observations report
  11. GRB 260323A: Fermi GBM Final Real-time Localization
  12. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  13. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  14. GRB 260322A: Fermi GBM Final Localization
  15. GRB 260320A: Glowbug gamma-ray detection
  16. EP260321a / AT2026gzf: VLT/X-shooter detection of supernova-like spectral features at z = 0.0344
  17. EP260321a: COLIBRÍ further optical observations and brightening
  18. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  19. EP260214b: ATCA 6 GHz detection
  20. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  21. GRB 260321A: EP-FXT follow-up observation
  22. The EP-WXT trigger 01709259045 is likely a flaring star
  23. EP260321a: ZTF and Rubin detections of the candidate optical counterpart to EP260321a
  24. EP260321a: GOTO detection of blue variable source
  25. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  26. EP260321a: further Kinder optical observations
  27. GRB 260321A: SVOM/VT optical upper limits
  28. EP260321a: Las Cumbres upper limit
  29. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  30. GRB 260320A: Insight-HXMT/HE detection
  31. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  32. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  33. EP260321a: SVOM/VT optical upper limit
  34. GRB 260310A: continued optical observation at Mondy
  35. Fermi GBM Sub-Threshold Detection of GRB 260321A
  36. GRB 260321A: SVOM detection of a burst
  37. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  38. EP260321a: Global MASTER-Net observations report
  39. EP260321a: Einstein Probe detection of an X-ray transient
  40. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS new optical observations
  41. GRB 260318A: Glowbug gamma-ray detection
  42. GRB 260310A / AT 2026fgk: KAIT optical observations
  43. GRB 260320A: NuSTAR detection of prompt emission
  44. GRB 260310A / AT2026fgk: NuSTAR follow-up detection
  45. GRB 260310A / AT 2026fgk: FTW optical and NIR observations show no rebrightening
  46. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
  47. GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening
  48. GRB 260310A/AT2026fgk: LBT near-infrared observations
  49. NOEMA Detection of GRB 260310A / AT 2026fgk
  50. EP-WXT trigger 01709258989: confirmation of a stellar flare by BOOTES-7
  51. GRB 260318A: SVOM/GRM observation
  52. The EP-WXT trigger 01709258989 is likely a flaring star
  53. GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90
  54. GRB 260318A: GECAM-B observation
  55. GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT
  56. Fermi GRB 260318A: Global MASTER-Net observations report
  57. GRB 260318A: Fermi GBM Final Real-time Localization
  58. IceCube-260315A: No Candidate Transients from the Zwicky Transient Facility
  59. GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
  60. GRB 260310A / AT 2026fgk: radio detection with the VLA
  61. GRB 260310A / AT2026fgk: SVOM/VT optical observations
  62. GRB 260310A / AT2026fgk: LCO optical observations
  63. IceCube-260315A/AT2026fpm: EP-FXT follow-up observation
  64. GRB 260317A: Fermi GBM Final Localization
  65. GRB 260316B: GECAM-B observation
  66. GRB 260316B: SVOM/GRM observation
  67. EP260316a / GRB 260316A: SVOM/VT optical upper limits
  68. EP260316a: COLIBRÍ faint optical counterpart candidate
  69. Fermi-LAT Gamma-ray Observations of IceCube-260315A
  70. GRB 260316B: AstroSat CZTI detection
  71. EP260316a: refined analysis of the EP-WXT and EP-FXT observations
  72. IceCube-260315A: Upper limits from a search for additional neutrino events in IceCube
  73. EP260316a: Xinglong optical upper limit
  74. GRB 260316B: Fermi GBM Final Real-time Localization
  75. EP260316a: optical upper limit with Kinder observations
  76. EP260316a / GRB 260316A : Fermi-GBM Sub-Threshold Detection
  77. GRB 260314A: Glowbug gamma-ray detection
  78. The EP-WXT trigger 00199258890 (EP260316a): a correction to the trigger time and FXT automatic follow-up
  79. IceCube-260315A: COLIBRÍ optical observations
  80. EP260314a: Xinglong optical upper limit
  81. EP260314a: optical upper limit with Kinder observations
  82. IceCube Alert-260315A/AT2026fpm Automatic MASTER optical blue counterpart candidate
  83. GRB 260310A / AT2026fgk: 1.3m DFOT optical observations
  84. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS optical observations
  85. GRB 260310A / AT 2026fgk: iTelescope optical observations
  86. EP260314a: COLIBRÍ optical upper limit
  87. GRID detection of GRB 260312B
  88. IceCube-260315A - IceCube observation of a high-energy neutrino candidate track-like event
  89. EP260314a: refined analysis of the EP-WXT and EP-FXT observations
  90. EP260314a: BOOTES-6/DPR optical upper limits at early times
  91. EP260314a: Global MASTER-Net observations report
  92. EP260314a: SVOM/VT optical candidate
  93. Fermi trigger No 795185313: Global MASTER-Net observations report
  94. IceCube Alert 260315A: Global MASTER-Net observations report
  95. EP260314a: Einstein Probe detection of an X-ray transient
  96. The EP-WXT trigger 01709258851: Las Cumbres upper limit
  97. GRB 260310A / AT2026fgk: SAO RAS optical observations
  98. GRB 260310A/AT2026fgk: radio detection at 15GHz
  99. GRB 260310A / AT2026fgk: TNG NIR detection
  100. GRB 260310A / AT2026fgk: OASDG optical observations

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