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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 260808B: GTC/OSIRIS+ spectroscopic redshift z = 1.295
  2. GRB 260813A: BALROG localization (Fermi Trigger 808341387 / GRB 260813803)
  3. GRB 260813A: Fermi GBM Final Real-time Localization
  4. EP260812a: NOT and Liverpool Telescope upper limits:
  5. EP260812b: Liverpool Telescope observations
  6. EP260812b: GOTO detection of the optical counterpart
  7. EP260812a: refined analysis of the EP-WXT and autonomous EP-FXT observation
  8. EP260812a: SVOM/C-GFT optical upper limit
  9. EP260812b: COLIBRÍ optical observations
  10. EP260812b: SVOM/VT optical observation
  11. GRB 260808A: SVOM/GRM observation
  12. EP260812b: Einstein Probe detection of an X-ray transient
  13. EP trigger #01709278129 (EP260812b?): NOT optical counterpart
  14. Fermi GBM Sub-Threshold Detection of GRB 260809A
  15. GRB 260810A: Glowbug gamma-ray detection
  16. GRB 260808B: SVOM/COLIBRÍ (FM-GFT) confirmation of the optical rebrightening
  17. GRB 260810A: AstroSat CZTI detection of a long burst
  18. EP260812a: Einstein Probe detection of an X-ray transient
  19. GRB 260809A: SAO RAS optical observations
  20. GRB 260808B: SAO RAS optical observations
  21. GRB 260808B: SVOM/VT optical re-brightening at day 3
  22. GRB 260317A: SVOM/ECLAIRs detection through offline targeted search and its possible association to magnetar 1E 1841-04.5
  23. GRB 260806A: CALET Gamma-Ray Burst Monitor detection
  24. GRB 260808A: GECAM-B observation
  25. GRB 260807A: SVOM/ECLAIRs refined analysis
  26. EP260806a: MAO/AZT-22 optical observations
  27. IceCube-260807A: Upper limits from a search for additional neutrino events in IceCube
  28. GRB260808B: MAO/AZT-22 optical observations
  29. GRB 250607A: SVOM/ECLAIRs detection through offline targeted search
  30. GRB 260809A: J-band upper limit with WINTER
  31. EP260809a: VLT/X-shooter spectroscopic redshift z = 3.07
  32. GRB 260806A: Glowbug gamma-ray detection
  33. GRB 260808A: CALET Gamma-Ray Burst Monitor detection
  34. GRB 260805C: CALET Gamma-Ray Burst Monitor detection
  35. GRB 260804A: CALET Gamma-Ray Burst Monitor detection
  36. GRB260809A/EPF_J234751.2+210212: EP-FXT follow-up observation
  37. The EP-WXT trigger 01709278015 is likely a flaring star
  38. GRB 260809A: SVOM/COLIBRÍ (FM-GFT) optical observation
  39. GRB 260808B: SVOM/COLIBRÍ (FM-GFT) optical observation
  40. GRB 260809A: NOT optical observations
  41. GRB260809A: MAO/AZT-22 optical observations
  42. GRB260809A: OHP/T193 optical observations
  43. IceCube-260805A: Upper limits from a search for additional neutrino events in IceCube
  44. GRB 260809A: SVOM/VT optical counterpart
  45. EP260809a: J-band upper limit with WINTER
  46. GRB 260808B: J-band upper limit with WINTER
  47. GRB 260808B: SVOM/ECLAIRs refined analysis
  48. EP260809a:refined analysis of the EP-WXT and autonomous EP-FXT observation
  49. GRB 260809A: SVOM detection of a faint burst
  50. GRB 260808B: Liverpool Telescope optical observations
  51. GRB 260808B: NOT optical observations
  52. GRB 260808B: LCO optical observations
  53. GRB 260808A: NuSTAR detection of prompt emission
  54. EP260809a: COLIBRÍ optical observations
  55. EP260809a: LCO optical observation
  56. EP260809a: OHP/T193 optical observations
  57. GRB260808B: OHP/T193 optical observations
  58. GRB 260808B / EPF_J230056.0+082842: EP-FXT follow-up observation
  59. EP260809a: Einstein Probe detection of an X-ray transient
  60. GRB 260808B: SVOM/VT optical afterglow confirmation
  61. GRB 260808C: Fermi GBM Final Real-time Localization
  62. GRB 260808B: SVOM/VT optical candidate from VHF data ( localization correction for GCN 45317 )
  63. GRB 260808B: SVOM/VT optical candidate from VHF data
  64. GRB 260808B: SVOM detection of a faint burst
  65. GRB 260808A: BALROG localization (Fermi Trigger 807850307 / GRB 260808119)
  66. Fermi GRB 260808A: Global MASTER-Net observations report
  67. GRB 260808A: Fermi GBM Final Real-time Localization
  68. EP260806a: ZTF serendipitous detection of ZTF26abmjjnm / AT 2026yeh
  69. IceCube Alert 260807A: Global MASTER-Net observations report
  70. IceCube-260805A: One candidate from the Zwicky Transient Facility
  71. GRB 260807A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  72. GRB 260807A: SVOM possible detection of a faint burst
  73. IceCube-260807A - IceCube observation of a high-energy neutrino candidate track-like event
  74. EP260806a: COLIBRÍ optical observations
  75. EP260806a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  76. EP260806a: SVOM/VT optical observation
  77. EP260806a: Liverpool Telescope observations of the counterpart show a blue colour
  78. EP260806a: OSIRIS+/GTC redshift z=0.089
  79. EP260731a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  80. EP260806a: LCO likely optical counterpart
  81. EP260806a: Einstein Probe detection of an X-ray transient
  82. GRB 260715A: cubesat Avion detection
  83. GRB 260709A: cubesat Avion detection
  84. GRB 260708A: cubesat Avion detection
  85. SN 2026stf / GRB 260708A: ATLAS forced photometry
  86. IceCube-260805A - IceCube observation of a high-energy neutrino candidate track-like event
  87. GRB 260730B: Glowbug gamma-ray detection
  88. GRB 260805C: Glowbug gamma-ray detection
  89. GRB 260805B: Glowbug gamma-ray detection
  90. Fermi GRB 260805A: Global MASTER-Net observations report
  91. GRB 260805B: Fermi GBM Final Localization
  92. GRB 260804A: Glowbug gamma-ray detection
  93. GRB 260805B: BALROG localization (Fermi Trigger 807622617 / GRB 260805484)
  94. GRB 260805A: Fermi GBM Final Localization
  95. AT 2026wki: EP/FXT follow-up observations
  96. GRB 260730B: CALET Gamma-Ray Burst Monitor detection
  97. GRB 260708A / SN 2026stf: Spectroscopic host redshift z = 0.055 and confirmation of an associated type Ic-BL supernova
  98. IceCube-Cascade 260801A: Upper limits from a search for additional neutrino events in IceCube
  99. GRB 260804A: Fermi GBM Final Real-time Localization
  100. GRB 260708A: LCO further optical observations show supernova features

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