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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 260802A: LCO optical upper limits
  2. GRB 260802B: Fermi GBM Final Localization
  3. GRB 260802A / EP J223759.5+531421: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  4. The EP-WXT trigger 01709277420 is likely a flaring star
  5. GRB 260802A/EP J223759.5+531421: SVOM detection of a possible magnetar burst
  6. GRB 260727A: EP-FXT further follow-up observations and candidate afterglow
  7. GRB 260618B: SVOM/VT continued optical observations indicated a steeper and redder decay
  8. GRB 260731A: AstroSat CZTI detection of a long burst
  9. Fermi-LAT Gamma-ray Observations of IceCube-260722A
  10. GRB 260730B: AstroSat CZTI detection
  11. EP260731a: COLIBRÍ optical upper limit
  12. EP260731a: NOT optical upper limit
  13. GRB 260730B: NuSTAR detection of prompt emission
  14. EP260731a: Einstein Probe detection of an X-ray transient
  15. GRB 260727A: SVOM/ECLAIRs refined analysis
  16. GRB 260726A: SVOM/ECLAIRs refined analysis
  17. GRB260730A: Fermi GBM Final Localization
  18. EP260728a: COLIBRÍ optical upper limit
  19. EP260727a: VLT/X-shooter spectroscopic redshift z = 2.817
  20. The EP-WXT trigger 01709277130 (EP260729a): refined EP-WXT analysis and association with a flaring star
  21. EP 260729a: Ondrejov D50 optical detection supports stellar flare origin
  22. EP260729a: Einstein Probe detection of an X-ray transient
  23. EP260727a: SAO RAS optical observations
  24. GRB 260727A: AbAO and SAO RAS optical observations
  25. EP260728a: EP-FXT follow-up observation
  26. GRB 260726A: EP-FXT follow-up observations
  27. EP260728a: Einstein Probe detection of a fast X-ray transient
  28. GRB 260727A: SVOM/GRM observation
  29. GRB 260726A: Fermi GBM Observation
  30. EP260727a: 1.5m OSN optical counterpart detection
  31. EP260727a:refined analysis of the EP-WXT and EP-FXT observation
  32. EP260727a: OHP/T193 optical observations
  33. Konus-Wind detection of GRB 260727A
  34. GRB 260726A: Liverpool Telescope optical observations
  35. GRB 260727A: Liverpool Telescope optical upper limits
  36. EP260727a: Liverpool Telescope confirmation of optical counterpart
  37. EP260727a: NUTTELA-TAO Early Optical Limits
  38. GRB 260728A: Fermi GBM Final Localization
  39. GRB 260727A: EP/FXT follow-up observations
  40. EP260727a: Einstein Probe detection of an X-ray transient
  41. The EP-WXT trigger 01709276927 (EP260727a?): NOT likely optical counterpart
  42. GRB 260727A: Glowbug gamma-ray detection
  43. GRB 260726A: J-band upper limit with WINTER
  44. GRB 260727A: J-band upper limit with WINTER
  45. GRB 260726A: SVOM/VT optical candidate
  46. GRB 260726A: SVOM ECLAIRs improved position and MXT possible detection of a counterpart
  47. GRB 260727A / SVOM sb26072702: RAPAS optical non-detection
  48. EP260723a: SVOM/ECLAIRs Upper Limit
  49. GRB 260727A: GOTO early optical upper limit
  50. GRB 260727A: AstroSat CZTI detection
  51. GRB 260727A: Kilonova-Catcher optical upper limit
  52. GRB 260727A: LCO optical upper limits
  53. GRB 260727B: Fermi GBM Final Real-time Localization
  54. Fermi GRB 260726A: Global MASTER-Net observations report
  55. GRB 260727A: SVOM detection of a bright long burst
  56. GRB 260726A: SVOM detection of a burst
  57. GRB 260726A: Fermi GBM Final Real-time Localization
  58. IceCube-260722A: Classification of ZTF26abjbxfs/SN 2026vts as a Type Ia Supernova
  59. EP260723a: further EP-FXT follow-up observation
  60. EP260725a: EP-FXT follow-up observation and association with a bright flaring star
  61. EP260725a: EP-WXT detection of an X-ray transient
  62. GRB 260616A: cubesat Avion detection
  63. EP260723a: Continued Liverpool Telescope observations suggest hours long optical plateau or rebrightening
  64. GRB 260602B: cubesat Avion detection
  65. GRB 260601A: cubesat Avion detection
  66. EP260723a: EP-FXT follow-up observation
  67. IPN triangulation of GRB 260706B
  68. GRB 260718A: SVOM/ECLAIRs refined analysis
  69. Fermi Gamma-ray Burst Monitor trigger 806592752 / 260724564 is not a GRB
  70. EP260723a: SVOM/VT optical observation
  71. EP260723a: COLIBRÍ optical observations
  72. EP260723a: NOT optical conterpart confirmation
  73. EP260723a: Liverpool Telescope likely optical counterpart
  74. EP260723a: EP-WXT detection of a fast X-ray transient
  75. GRB 260723A: Fermi GBM Final Localization
  76. IceCube-260722A: Upper limits from a search for additional neutrino events in IceCube
  77. IceCube-260722A: One candidate from the Zwicky Transient Facility (ZTF)
  78. IceCube Alert 260722A: Global MASTER-Net observations report
  79. Konus-Wind detection of GRB 260721A
  80. GRB 260722A: Fermi GBM Final Real-time Localization
  81. IceCube-260722A - IceCube observation of a high-energy neutrino candidate track-like event
  82. Fermi GBM trigger 806384210/260722151 is not a GRB
  83. GRB 260721A: NuSTAR detection of prompt emission
  84. Konus-Wind detection of GRB 260714B
  85. SVOM trigger sb26071506: SVOM/VT confirmation of a stellar flare
  86. GRB 260705A: Retraction of optical counterpart
  87. GRB 260714B: Insight-HXMT/HE detection
  88. GRB 260718A: EP-FXT follow-up observation
  89. Fermi trigger No 806104130: Global MASTER-Net observations report
  90. Fermi GRB 260718A: Global MASTER-Net observations report
  91. GRB 260718A: LCO optical upper limits
  92. GRB 260711A: SVOM/GRM observation
  93. GRB 260710A: SVOM/GRM observation
  94. GRB 260718A: Fermi GBM Observation
  95. GRB 260718A : GRANDMA and KNC upper limits
  96. GRB 260718A: SVOM/VT optical upper limits
  97. GRB 260718A: SVOM/VT optical upper limits from VHF data
  98. GRB 260718A: SVOM detection of a burst
  99. GRB 260714B: SVOM/GRM observation
  100. GRB 260310A / AT2026fgk: Late-time Chandra Detection

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