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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 260310A: classification as long GRB based on Eiso, Ep, and T_90
  2. GRB 260318A: GECAM-B observation
  3. GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT
  4. Fermi GRB 260318A: Global MASTER-Net observations report
  5. GRB 260318A: Fermi GBM Final Real-time Localization
  6. IceCube-260315A: No Candidate Transients from the Zwicky Transient Facility
  7. Fermi Gamma-ray Burst Monitor trigger 795096033/260312500 (GRB 260313A) is unlikely to be a GRB
  8. GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
  9. GRB 260310A / AT 2026fgk: radio detection with the VLA
  10. GRB 260310A / AT2026fgk: SVOM/VT optical observations
  11. GRB 260310A / AT2026fgk: LCO optical observations
  12. IceCube-260315A/AT2026fpm: EP-FXT follow-up observation
  13. GRB 260317A: Fermi GBM Final Localization
  14. GRB 260316B: GECAM-B observation
  15. GRB 260316B: SVOM/GRM observation
  16. EP260316a / GRB 260316A: SVOM/VT optical upper limits
  17. EP260316a: COLIBRÍ faint optical counterpart candidate
  18. Fermi-LAT Gamma-ray Observations of IceCube-260315A
  19. GRB 260316B: AstroSat CZTI detection
  20. EP260316a: refined analysis of the EP-WXT and EP-FXT observations
  21. IceCube-260315A: Upper limits from a search for additional neutrino events in IceCube
  22. EP260316a: Xinglong optical upper limit
  23. GRB 260316B: Fermi GBM Final Real-time Localization
  24. EP260316a: optical upper limit with Kinder observations
  25. EP260316a / GRB 260316A : Fermi-GBM Sub-Threshold Detection
  26. GRB 260314A: Glowbug gamma-ray detection
  27. The EP-WXT trigger 00199258890 (EP260316a): a correction to the trigger time and FXT automatic follow-up
  28. IceCube-260315A: COLIBRÍ optical observations
  29. EP260314a: Xinglong optical upper limit
  30. EP260314a: optical upper limit with Kinder observations
  31. IceCube Alert-260315A/AT2026fpm Automatic MASTER optical blue counterpart candidate
  32. GRB 260310A / AT2026fgk: 1.3m DFOT optical observations
  33. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS optical observations
  34. GRB 260310A / AT 2026fgk: iTelescope optical observations
  35. EP260314a: COLIBRÍ optical upper limit
  36. GRID detection of GRB 260312B
  37. IceCube-260315A - IceCube observation of a high-energy neutrino candidate track-like event
  38. EP260314a: refined analysis of the EP-WXT and EP-FXT observations
  39. EP260314a: BOOTES-6/DPR optical upper limits at early times
  40. EP260314a: Global MASTER-Net observations report
  41. EP260314a: SVOM/VT optical candidate
  42. Fermi trigger No 795185313: Global MASTER-Net observations report
  43. IceCube Alert 260315A: Global MASTER-Net observations report
  44. EP260314a: Einstein Probe detection of an X-ray transient
  45. The EP-WXT trigger 01709258851: Las Cumbres upper limit
  46. GRB 260314A: GECAM-B observation of a burst
  47. Fermi Gamma-ray Burst Monitor trigger 795185313/260314534 is not a GRB
  48. GRB 260310A / AT2026fgk: SAO RAS optical observations
  49. GRB 260310A/AT2026fgk: radio detection at 15GHz
  50. GRB 260310A / AT2026fgk: TNG NIR detection
  51. GRB 260310A / AT2026fgk: OASDG optical observations
  52. GRB 260310A / AT2026fgk: Multiband optical follow-up with Kinder observations
  53. GRB 260310A / AT 2026fgk: COLIBRÍ continuing optical observations
  54. GRB 260310A / AT2026fgk: further CAHA 1.23m telescope optical observations suggest shallow decay
  55. Fermi GRB 260314A: Global MASTER-Net observations report
  56. Fermi GRB 260313A: Global MASTER-Net observations report
  57. GRB 260314A: Fermi GBM Final Real-time Localization
  58. GRB 260310A/AT 2026fgk: WINTER NIR Detections
  59. GRB 260313A: A Correction to the Fermi GBM Final Localization
  60. GRB 260310A: Einstein Probe Follow-up X-ray Telescope (FXT) Detection
  61. GRB 260310A/AT 2026fgk: J-band observations by the SYSU 80 cm infrared telescope
  62. GRB 260310B: Insight-HXMT/HE detection
  63. GRB 260310A/AT 2026fgk: DDOTI Optical Detection
  64. GRB 260310A: NOT optical polarimetry
  65. GRB 260312B: AstroSat CZTI detection
  66. Swift BAT trigger 1500295: A solar flare
  67. GRB 260313A: Fermi GBM Final Real-time Localization
  68. GRB 260310A/AT 2026fgk: Bok spectroscopic observation
  69. Swift BAT trigger 1500287: A solar flare
  70. GRB 260310A / AT2026fgk: OSIRIS+/GTC spectroscopy confirms redshift z = 0.153
  71. GRB 260308A: Insight-HXMT/HE detection
  72. GRB 260307A: CALET Gamma-Ray Burst Monitor detection
  73. GRB 260310A / AT 2026fgk: Location in the Epeak - Eiso diagram
  74. GRB 260310A / AT 2026fgk: COLIBRÍ optical observations
  75. GRB 260310A / AT2026fgk: CAHA 1.23m telescope optical observations
  76. GRB 260310A / AT2026fgk : MASTER OT rebrightening during 7h observations
  77. GRB260310A / AT2026fgk: P200 Spectroscopy
  78. GRB 260312B: Glowbug gamma-ray detection
  79. GRB 260310A: Fermi GBM Observation
  80. GRB 260310A: potential optical counterpart
  81. Fermi GRB 260312B: Global MASTER-Net observations report
  82. Fermi GRB 260311B: Global MASTER-Net observations report
  83. Swift BAT trigger 1500148: A solar flare
  84. GRB 260312B: BALROG localization (Fermi Trigger 795001611 / GRB 260312407)
  85. GRB 260312B: Fermi GBM Final Real-time Localization
  86. The EP-WXT trigger 01709258843 is not a real source
  87. GRB 260310B: GECAM-B observation of a burst
  88. Retraction of GCN 43965: GRB is actually solar flare
  89. GRB 260312A: Swift detection of a burst
  90. GRB 260311B: Fermi GBM Final Real-time Localization
  91. GRB 260131A/B: radio detection with the VLA
  92. EP260302a: MeerKAT radio counterpart
  93. GRB260307A: GECAM-B observation of a burst
  94. GRB 260308A: SVOM/GRM observation of a short GRB
  95. EP260306a: Mondy optical upper limit
  96. GRB 260310A: AstroSat CZTI detection of a long burst
  97. GRB 260311A: Fermi GBM Final Real-time Localization
  98. Fermi GRB 260310B: Global MASTER-Net observations report
  99. GRB 260310B: Fermi GBM Final Real-time Localization
  100. Fermi GRB 260310A: Global MASTER-Net observations report

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