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

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