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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"
  1. EP260321a: Las Cumbres upper limit
  2. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  3. GRB 260320A: Insight-HXMT/HE detection
  4. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  5. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  6. EP260321a: SVOM/VT optical upper limit
  7. GRB 260310A: continued optical observation at Mondy
  8. Fermi GBM Sub-Threshold Detection of GRB 260321A
  9. GRB 260321A: SVOM detection of a burst
  10. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  11. EP260321a: Global MASTER-Net observations report
  12. EP260321a: Einstein Probe detection of an X-ray transient
  13. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS new optical observations
  14. GRB 260318A: Glowbug gamma-ray detection
  15. GRB 260310A / AT 2026fgk: KAIT optical observations
  16. GRB 260320A: NuSTAR detection of prompt emission
  17. GRB 260310A / AT2026fgk: NuSTAR follow-up detection
  18. EP-WXT trigger 01709258989: KAIT confirmation of a stellar flare
  19. GRB 260310A / AT 2026fgk: FTW optical and NIR observations show no rebrightening
  20. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
  21. GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening
  22. GRB 260310A/AT2026fgk: LBT near-infrared observations
  23. NOEMA Detection of GRB 260310A / AT 2026fgk
  24. EP-WXT trigger 01709258989: confirmation of a stellar flare by BOOTES-7
  25. GRB 260318A: SVOM/GRM observation
  26. The EP-WXT trigger 01709258989 is likely a flaring star
  27. GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90
  28. GRB 260318A: GECAM-B observation
  29. GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT
  30. Fermi GRB 260318A: Global MASTER-Net observations report
  31. GRB 260318A: Fermi GBM Final Real-time Localization
  32. IceCube-260315A: No Candidate Transients from the Zwicky Transient Facility
  33. Fermi Gamma-ray Burst Monitor trigger 795096033/260312500 (GRB 260313A) is unlikely to be a GRB
  34. GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
  35. GRB 260310A / AT 2026fgk: radio detection with the VLA
  36. GRB 260310A / AT2026fgk: SVOM/VT optical observations
  37. GRB 260310A / AT2026fgk: LCO optical observations
  38. IceCube-260315A/AT2026fpm: EP-FXT follow-up observation
  39. GRB 260317A: Fermi GBM Final Localization
  40. GRB 260316B: GECAM-B observation
  41. GRB 260316B: SVOM/GRM observation
  42. EP260316a / GRB 260316A: SVOM/VT optical upper limits
  43. EP260316a: COLIBRÍ faint optical counterpart candidate
  44. Fermi-LAT Gamma-ray Observations of IceCube-260315A
  45. GRB 260316B: AstroSat CZTI detection
  46. EP260316a: refined analysis of the EP-WXT and EP-FXT observations
  47. IceCube-260315A: Upper limits from a search for additional neutrino events in IceCube
  48. EP260316a: Xinglong optical upper limit
  49. GRB 260316B: Fermi GBM Final Real-time Localization
  50. EP260316a: optical upper limit with Kinder observations
  51. EP260316a / GRB 260316A : Fermi-GBM Sub-Threshold Detection
  52. GRB 260314A: Glowbug gamma-ray detection
  53. The EP-WXT trigger 00199258890 (EP260316a): a correction to the trigger time and FXT automatic follow-up
  54. IceCube-260315A: COLIBRÍ optical observations
  55. EP260314a: Xinglong optical upper limit
  56. EP260314a: optical upper limit with Kinder observations
  57. IceCube Alert-260315A/AT2026fpm Automatic MASTER optical blue counterpart candidate
  58. GRB 260310A / AT2026fgk: 1.3m DFOT optical observations
  59. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS optical observations
  60. GRB 260310A / AT 2026fgk: iTelescope optical observations
  61. EP260314a: COLIBRÍ optical upper limit
  62. GRID detection of GRB 260312B
  63. IceCube-260315A - IceCube observation of a high-energy neutrino candidate track-like event
  64. EP260314a: refined analysis of the EP-WXT and EP-FXT observations
  65. EP260314a: BOOTES-6/DPR optical upper limits at early times
  66. EP260314a: Global MASTER-Net observations report
  67. EP260314a: SVOM/VT optical candidate
  68. Fermi trigger No 795185313: Global MASTER-Net observations report
  69. IceCube Alert 260315A: Global MASTER-Net observations report
  70. EP260314a: Einstein Probe detection of an X-ray transient
  71. The EP-WXT trigger 01709258851: Las Cumbres upper limit
  72. GRB 260314A: GECAM-B observation of a burst
  73. Fermi Gamma-ray Burst Monitor trigger 795185313/260314534 is not a GRB
  74. GRB 260310A / AT2026fgk: SAO RAS optical observations
  75. GRB 260310A/AT2026fgk: radio detection at 15GHz
  76. GRB 260310A / AT2026fgk: TNG NIR detection
  77. GRB 260310A / AT2026fgk: OASDG optical observations
  78. GRB 260310A / AT2026fgk: Multiband optical follow-up with Kinder observations
  79. GRB 260310A / AT 2026fgk: COLIBRÍ continuing optical observations
  80. GRB 260310A / AT2026fgk: further CAHA 1.23m telescope optical observations suggest shallow decay
  81. Fermi GRB 260314A: Global MASTER-Net observations report
  82. Fermi GRB 260313A: Global MASTER-Net observations report
  83. GRB 260314A: Fermi GBM Final Real-time Localization
  84. GRB 260310A/AT 2026fgk: WINTER NIR Detections
  85. GRB 260313A: A Correction to the Fermi GBM Final Localization
  86. GRB 260310A: Einstein Probe Follow-up X-ray Telescope (FXT) Detection
  87. GRB 260310A/AT 2026fgk: J-band observations by the SYSU 80 cm infrared telescope
  88. GRB 260310B: Insight-HXMT/HE detection
  89. GRB 260310A/AT 2026fgk: DDOTI Optical Detection
  90. GRB 260310A: NOT optical polarimetry
  91. GRB 260312B: AstroSat CZTI detection
  92. Swift BAT trigger 1500295: A solar flare
  93. GRB 260313A: Fermi GBM Final Real-time Localization
  94. GRB 260310A/AT 2026fgk: Bok spectroscopic observation
  95. Swift BAT trigger 1500287: A solar flare
  96. GRB 260310A / AT2026fgk: OSIRIS+/GTC spectroscopy confirms redshift z = 0.153
  97. GRB 260308A: Insight-HXMT/HE detection
  98. GRB 260307A: CALET Gamma-Ray Burst Monitor detection
  99. GRB 260310A / AT 2026fgk: Location in the Epeak - Eiso diagram
  100. GRB 260310A / AT 2026fgk: COLIBRÍ optical observations

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