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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 260805C: Glowbug gamma-ray detection
  2. GRB 260805B: Glowbug gamma-ray detection
  3. Fermi GRB 260805A: Global MASTER-Net observations report
  4. GRB 260805B: Fermi GBM Final Localization
  5. GRB 260804A: Glowbug gamma-ray detection
  6. GRB 260805B: BALROG localization (Fermi Trigger 807622617 / GRB 260805484)
  7. GRB 260805A: Fermi GBM Final Localization
  8. AT 2026wki: EP/FXT follow-up observations
  9. GRB 260730B: CALET Gamma-Ray Burst Monitor detection
  10. GRB 260708A / SN 2026stf: Spectroscopic host redshift z = 0.055 and confirmation of an associated type Ic-BL supernova
  11. IceCube-Cascade 260801A: Upper limits from a search for additional neutrino events in IceCube
  12. GRB 260804A: Fermi GBM Final Real-time Localization
  13. GRB 260708A: LCO further optical observations show supernova features
  14. GRB 260803A: Fermi GBM Final Real-time Localization
  15. Fermi GRB 260802B: Global MASTER-Net observations report
  16. GRB 260802A / EP J223759.5+521421: EP-FXT follow-up observation
  17. GRB 260802A / EP J223759.5+531421: SVOM/VT optical upper limit
  18. GRB 260802A: SVOM/VT optical upper limits from VHF data
  19. GRB 260802A: LCO optical upper limits
  20. GRB 260802B: Fermi GBM Final Localization
  21. GRB 260802A / EP J223759.5+531421: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  22. The EP-WXT trigger 01709277420 is likely a flaring star
  23. GRB 260802A/EP J223759.5+531421: SVOM detection of a possible magnetar burst
  24. GRB 260727A: EP-FXT further follow-up observations and candidate afterglow
  25. GRB 260618B: SVOM/VT continued optical observations indicated a steeper and redder decay
  26. GRB 260731A: AstroSat CZTI detection of a long burst
  27. Fermi-LAT Gamma-ray Observations of IceCube-260722A
  28. GRB 260730B: AstroSat CZTI detection
  29. EP260731a: COLIBRÍ optical upper limit
  30. EP260731a: NOT optical upper limit
  31. GRB 260730B: NuSTAR detection of prompt emission
  32. EP260731a: Einstein Probe detection of an X-ray transient
  33. GRB 260727A: SVOM/ECLAIRs refined analysis
  34. GRB 260726A: SVOM/ECLAIRs refined analysis
  35. GRB260730A: Fermi GBM Final Localization
  36. EP260728a: COLIBRÍ optical upper limit
  37. EP260727a: VLT/X-shooter spectroscopic redshift z = 2.817
  38. The EP-WXT trigger 01709277130 (EP260729a): refined EP-WXT analysis and association with a flaring star
  39. EP 260729a: Ondrejov D50 optical detection supports stellar flare origin
  40. EP260729a: Einstein Probe detection of an X-ray transient
  41. EP260727a: SAO RAS optical observations
  42. GRB 260727A: AbAO and SAO RAS optical observations
  43. EP260728a: EP-FXT follow-up observation
  44. GRB 260726A: EP-FXT follow-up observations
  45. EP260728a: Einstein Probe detection of a fast X-ray transient
  46. GRB 260727A: SVOM/GRM observation
  47. GRB 260726A: Fermi GBM Observation
  48. EP260727a: 1.5m OSN optical counterpart detection
  49. EP260727a:refined analysis of the EP-WXT and EP-FXT observation
  50. EP260727a: OHP/T193 optical observations
  51. Konus-Wind detection of GRB 260727A
  52. GRB 260726A: Liverpool Telescope optical observations
  53. GRB 260727A: Liverpool Telescope optical upper limits
  54. EP260727a: Liverpool Telescope confirmation of optical counterpart
  55. EP260727a: NUTTELA-TAO Early Optical Limits
  56. GRB 260728A: Fermi GBM Final Localization
  57. GRB 260727A: EP/FXT follow-up observations
  58. EP260727a: Einstein Probe detection of an X-ray transient
  59. The EP-WXT trigger 01709276927 (EP260727a?): NOT likely optical counterpart
  60. GRB 260727A: Glowbug gamma-ray detection
  61. GRB 260726A: J-band upper limit with WINTER
  62. GRB 260727A: J-band upper limit with WINTER
  63. GRB 260726A: SVOM/VT optical candidate
  64. GRB 260726A: SVOM ECLAIRs improved position and MXT possible detection of a counterpart
  65. GRB 260727A / SVOM sb26072702: RAPAS optical non-detection
  66. EP260723a: SVOM/ECLAIRs Upper Limit
  67. GRB 260727A: GOTO early optical upper limit
  68. GRB 260727A: AstroSat CZTI detection
  69. GRB 260727A: Kilonova-Catcher optical upper limit
  70. GRB 260727A: LCO optical upper limits
  71. GRB 260727B: Fermi GBM Final Real-time Localization
  72. Fermi GRB 260726A: Global MASTER-Net observations report
  73. GRB 260727A: SVOM detection of a bright long burst
  74. GRB 260726A: SVOM detection of a burst
  75. GRB 260726A: Fermi GBM Final Real-time Localization
  76. IceCube-260722A: Classification of ZTF26abjbxfs/SN 2026vts as a Type Ia Supernova
  77. EP260723a: further EP-FXT follow-up observation
  78. EP260725a: EP-FXT follow-up observation and association with a bright flaring star
  79. EP260725a: EP-WXT detection of an X-ray transient
  80. GRB 260616A: cubesat Avion detection
  81. EP260723a: Continued Liverpool Telescope observations suggest hours long optical plateau or rebrightening
  82. GRB 260602B: cubesat Avion detection
  83. GRB 260601A: cubesat Avion detection
  84. EP260723a: EP-FXT follow-up observation
  85. IPN triangulation of GRB 260706B
  86. GRB 260718A: SVOM/ECLAIRs refined analysis
  87. Fermi Gamma-ray Burst Monitor trigger 806592752 / 260724564 is not a GRB
  88. EP260723a: SVOM/VT optical observation
  89. EP260723a: COLIBRÍ optical observations
  90. EP260723a: NOT optical conterpart confirmation
  91. EP260723a: Liverpool Telescope likely optical counterpart
  92. EP260723a: EP-WXT detection of a fast X-ray transient
  93. GRB 260723A: Fermi GBM Final Localization
  94. IceCube-260722A: Upper limits from a search for additional neutrino events in IceCube
  95. IceCube-260722A: One candidate from the Zwicky Transient Facility (ZTF)
  96. IceCube Alert 260722A: Global MASTER-Net observations report
  97. Konus-Wind detection of GRB 260721A
  98. GRB 260722A: Fermi GBM Final Real-time Localization
  99. IceCube-260722A - IceCube observation of a high-energy neutrino candidate track-like event
  100. Fermi GBM trigger 806384210/260722151 is not a GRB

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