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

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