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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. EP260806a: SVOM/VT optical observation
  2. EP260806a: Liverpool Telescope observations of the counterpart show a blue colour
  3. EP260806a: OSIRIS+/GTC redshift z=0.089
  4. EP260731a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  5. EP260806a: LCO likely optical counterpart
  6. EP260806a: Einstein Probe detection of an X-ray transient
  7. GRB 260715A: cubesat Avion detection
  8. GRB 260709A: cubesat Avion detection
  9. GRB 260708A: cubesat Avion detection
  10. SN 2026stf / GRB 260708A: ATLAS forced photometry
  11. IceCube-260805A - IceCube observation of a high-energy neutrino candidate track-like event
  12. GRB 260730B: Glowbug gamma-ray detection
  13. GRB 260805C: Glowbug gamma-ray detection
  14. GRB 260805B: Glowbug gamma-ray detection
  15. Fermi GRB 260805A: Global MASTER-Net observations report
  16. GRB 260805B: Fermi GBM Final Localization
  17. GRB 260804A: Glowbug gamma-ray detection
  18. GRB 260805B: BALROG localization (Fermi Trigger 807622617 / GRB 260805484)
  19. GRB 260805A: Fermi GBM Final Localization
  20. AT 2026wki: EP/FXT follow-up observations
  21. GRB 260730B: CALET Gamma-Ray Burst Monitor detection
  22. GRB 260708A / SN 2026stf: Spectroscopic host redshift z = 0.055 and confirmation of an associated type Ic-BL supernova
  23. IceCube-Cascade 260801A: Upper limits from a search for additional neutrino events in IceCube
  24. GRB 260804A: Fermi GBM Final Real-time Localization
  25. GRB 260708A: LCO further optical observations show supernova features
  26. GRB 260803A: Fermi GBM Final Real-time Localization
  27. Fermi GRB 260802B: Global MASTER-Net observations report
  28. GRB 260802A / EP J223759.5+521421: EP-FXT follow-up observation
  29. GRB 260802A / EP J223759.5+531421: SVOM/VT optical upper limit
  30. GRB 260802A: SVOM/VT optical upper limits from VHF data
  31. GRB 260802A: LCO optical upper limits
  32. GRB 260802B: Fermi GBM Final Localization
  33. GRB 260802A / EP J223759.5+531421: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  34. The EP-WXT trigger 01709277420 is likely a flaring star
  35. GRB 260802A/EP J223759.5+531421: SVOM detection of a possible magnetar burst
  36. GRB 260727A: EP-FXT further follow-up observations and candidate afterglow
  37. GRB 260618B: SVOM/VT continued optical observations indicated a steeper and redder decay
  38. GRB 260731A: AstroSat CZTI detection of a long burst
  39. Fermi-LAT Gamma-ray Observations of IceCube-260722A
  40. GRB 260730B: AstroSat CZTI detection
  41. EP260731a: COLIBRÍ optical upper limit
  42. EP260731a: NOT optical upper limit
  43. GRB 260730B: NuSTAR detection of prompt emission
  44. EP260731a: Einstein Probe detection of an X-ray transient
  45. GRB 260727A: SVOM/ECLAIRs refined analysis
  46. GRB 260726A: SVOM/ECLAIRs refined analysis
  47. GRB260730A: Fermi GBM Final Localization
  48. EP260728a: COLIBRÍ optical upper limit
  49. EP260727a: VLT/X-shooter spectroscopic redshift z = 2.817
  50. The EP-WXT trigger 01709277130 (EP260729a): refined EP-WXT analysis and association with a flaring star
  51. EP 260729a: Ondrejov D50 optical detection supports stellar flare origin
  52. EP260729a: Einstein Probe detection of an X-ray transient
  53. EP260727a: SAO RAS optical observations
  54. GRB 260727A: AbAO and SAO RAS optical observations
  55. EP260728a: EP-FXT follow-up observation
  56. GRB 260726A: EP-FXT follow-up observations
  57. EP260728a: Einstein Probe detection of a fast X-ray transient
  58. GRB 260727A: SVOM/GRM observation
  59. GRB 260726A: Fermi GBM Observation
  60. EP260727a: 1.5m OSN optical counterpart detection
  61. EP260727a:refined analysis of the EP-WXT and EP-FXT observation
  62. EP260727a: OHP/T193 optical observations
  63. Konus-Wind detection of GRB 260727A
  64. GRB 260726A: Liverpool Telescope optical observations
  65. GRB 260727A: Liverpool Telescope optical upper limits
  66. EP260727a: Liverpool Telescope confirmation of optical counterpart
  67. EP260727a: NUTTELA-TAO Early Optical Limits
  68. GRB 260728A: Fermi GBM Final Localization
  69. GRB 260727A: EP/FXT follow-up observations
  70. EP260727a: Einstein Probe detection of an X-ray transient
  71. The EP-WXT trigger 01709276927 (EP260727a?): NOT likely optical counterpart
  72. GRB 260727A: Glowbug gamma-ray detection
  73. GRB 260726A: J-band upper limit with WINTER
  74. GRB 260727A: J-band upper limit with WINTER
  75. GRB 260726A: SVOM/VT optical candidate
  76. GRB 260726A: SVOM ECLAIRs improved position and MXT possible detection of a counterpart
  77. GRB 260727A / SVOM sb26072702: RAPAS optical non-detection
  78. EP260723a: SVOM/ECLAIRs Upper Limit
  79. GRB 260727A: GOTO early optical upper limit
  80. GRB 260727A: AstroSat CZTI detection
  81. GRB 260727A: Kilonova-Catcher optical upper limit
  82. GRB 260727A: LCO optical upper limits
  83. GRB 260727B: Fermi GBM Final Real-time Localization
  84. Fermi GRB 260726A: Global MASTER-Net observations report
  85. GRB 260727A: SVOM detection of a bright long burst
  86. GRB 260726A: SVOM detection of a burst
  87. GRB 260726A: Fermi GBM Final Real-time Localization
  88. IceCube-260722A: Classification of ZTF26abjbxfs/SN 2026vts as a Type Ia Supernova
  89. EP260723a: further EP-FXT follow-up observation
  90. EP260725a: EP-FXT follow-up observation and association with a bright flaring star
  91. EP260725a: EP-WXT detection of an X-ray transient
  92. GRB 260616A: cubesat Avion detection
  93. EP260723a: Continued Liverpool Telescope observations suggest hours long optical plateau or rebrightening
  94. GRB 260602B: cubesat Avion detection
  95. GRB 260601A: cubesat Avion detection
  96. EP260723a: EP-FXT follow-up observation
  97. IPN triangulation of GRB 260706B
  98. GRB 260718A: SVOM/ECLAIRs refined analysis
  99. Fermi Gamma-ray Burst Monitor trigger 806592752 / 260724564 is not a GRB
  100. EP260723a: SVOM/VT optical observation

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