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

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