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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 260502A: Fermi GBM Final Localization
  2. The EP-WXT trigger 01709261576 is likely a flaring star
  3. GRB 260429B / EP260429a: EP-FXT follow-up observation
  4. EP260502a: BOOTES-7 observations of a fading catalogued source close to the X-ray position
  5. GRB 260429B / EP260429a: AstroSat CZTI detection
  6. GRB EP260502a: BOOTES-7: early optical upper limit
  7. EP260502a: Las Cumbres upper limit
  8. EP260502a: Einstein Probe detection of an X-ray transient
  9. GRB 260429A: SVOM/GRM observation of a short burst
  10. SN 2026kid: Optical follow-up with small-aperture telescopes in Spain and China
  11. EP260429a: Global MASTER-Net observations report
  12. EP260430a: refined analysis of the EP-WXT and follow-up EP-FXT observations
  13. GRB 260424B: AstroSat CZTI detection
  14. GRB 260429B / EP260429a: COLIBRÍ optical upper limit
  15. EP260429a: LCO optical upper limits
  16. EP260430a: LCO optical upper limits
  17. GRB 260430A / EP260430a: COLIBRÍ optical upper limit
  18. GRB 260429A: Fermi GBM Detection
  19. Fermi GRB 260429A: Global MASTER-Net observations report
  20. EP260430a: Global MASTER-Net observations report
  21. EP260430a: Einstein Probe detection of an X-ray transient
  22. EP260429a: EP-WXT detection of a fast X-ray transient
  23. GRB 260429A: Fermi GBM Final Real-time Localization
  24. GRB 260428A: SVOM/GRM observation of a possible short burst with extended emission
  25. GRB 260428A: GECAM-B detection of a possible long duration Type I burst
  26. IceCube-260425A: Upper limits from a search for additional neutrino events in IceCube
  27. GRB 260428A: AstroSat CZTI detection
  28. Fermi GRB 260428A: Global MASTER-Net observations report
  29. EP260416a: Mondy and Terskol optical upper limits
  30. GRB 260424B: Glowbug gamma-ray detection of a short burst
  31. GRB 260424B: COLIBRÍ optical upper limit
  32. Konus-Wind detection of GRB 260424B
  33. GRB 260428A: Fermi GBM Final Real-time Localization
  34. Fermi-LAT Gamma-ray Observations of IceCube-260425A
  35. GRB 260424C: Fermi GBM Final Localization
  36. EP260321a/SN 2026gzf: spectroscopy at Mondy observatory
  37. IPN triangulation of GRB 260424B (short)
  38. GRB 260424B: SVOM/GRM detection of a short burst
  39. IceCube-260425A - IceCube observation of a high-energy neutrino candidate track-like event
  40. GRB 260305A: likely detection by Fermi-LAT and the LAT gamma-ray position
  41. IceCube Alert 260425A: Global MASTER-Net observations report
  42. Fermi trigger No 798737427: Global MASTER-Net observations report
  43. GRB 260401A: cubesat Avion detection
  44. GRB 260424A: AstroSat CZTI detection of a long burst
  45. EP260321a: Upper limits from ATCA radio observations
  46. GRB 260421B: Kilonova-Catcher optical afterglow detection
  47. GRB 260421B: Insight-HXMT/HE detection
  48. The EP-WXT trigger 01709258652: Mondy optical observations
  49. GRB 250328A: VLT host galaxy discovery and redshift z = 1.250
  50. EP260416a: Mondy optical observations
  51. GRB 260421B: SVOM/ECLAIRs refined analysis
  52. GRB 260421B: 3.6m DOT optical observation
  53. EP260416a: ZTSh R band observations
  54. EP-WXT trigger 01709260362: FRAM-ORM optical observations confirm flaring star G 151-9
  55. IceCube-Cascade 260418A: Upper limits from a search for additional neutrino events in IceCube
  56. EP250512a / GRB 250512B: VLT/X-shooter host galaxy identification and redshift z = 1.773
  57. GRB 250530A: VLT/X-shooter host galaxy redshift z = 1.486
  58. GRB 260419A: AstroSat CZTI detection
  59. GRB 260421B: SVOM/GRM observation
  60. GRB260421B: J band upper limit by SYSU 80cm infrared telescope
  61. GRB 260421B: EP-FXT follow-up observation
  62. The EP-WXT trigger 01709260362 is likely a flaring star
  63. GOTO26djh/AT2026jpw: ATCA radio detection
  64. GRB 260421B: J-band upper limit with WINTER
  65. GRB 260421B: LCO optical counterpart detection
  66. GRB 260421B: Fermi GBM Observation
  67. Fermi Gamma-ray Burst Monitor trigger 798482368/260421694 is not a GRB
  68. GRB 260421A: AstroSat CZTI detection
  69. GOTO26djh/AT2026jpw: radio detection at 15GHz
  70. GRB 260412A: SVOM/ECLAIRs refined analysis
  71. GRB 260421B: SVOM/VT optical observations
  72. EP260416a: J band upper limit by SYSU 80cm infrared telescope
  73. GRB 260310A: Late-time Chandra X-ray Detection
  74. GRB 260418A: Insight-HXMT/HE detection
  75. EP260416a: 1.3m DFOT optical observation
  76. GRB 260415A: CALET Gamma-Ray Burst Monitor detection
  77. GRB 260415B: CALET Gamma-Ray Burst Monitor detection
  78. Fermi GRB 260421C: Global MASTER-Net observations report
  79. GRB 260421C: Fermi GBM Final Real-time Localization
  80. GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
  81. Fermi GRB 260421B: Global MASTER-Net observations report
  82. GRB 260421B: BOOTES-7 early optical afterglow detection
  83. GRB 260421B: LCO optical afterglow confirmation
  84. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  85. GRB 260421B: TRT optical counterpart detection
  86. GRB 260421B: SVOM detection of a long burst
  87. GRB 260421B: BALROG localization (Fermi Trigger 798437606 / GRB 260421176)
  88. GRB 260421B: Fermi GBM Final Real-time Localization
  89. Fermi GRB 260421A: Global MASTER-Net observations report
  90. GRB 260421A: Fermi GBM Final Real-time Localization
  91. EP260321a: VLA radio follow-up
  92. GRB 260412A: LCOGT Optical Upper Limits
  93. The EP-WXT trigger 01709260314 is likely a flaring star
  94. EP260416a: Optical follow-up observations with Kinder
  95. GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient
  96. EP-WXT trigger 01709260303: KAIT optical observations
  97. EP260416a: 1.5m OSN and 2.2m CAHA optical monitoring
  98. The EP-WXT trigger 01709260303 is likely a flaring star
  99. GRB 260417A: SVOM/GRM observation
  100. EP260321A/AT2026gzf: Optical observation from 1.3m DFOT

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