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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. EP260430a: refined analysis of the EP-WXT and follow-up EP-FXT observations
  2. GRB 260424B: AstroSat CZTI detection
  3. GRB 260429B / EP260429a: COLIBRÍ optical upper limit
  4. EP260429a: LCO optical upper limits
  5. EP260430a: LCO optical upper limits
  6. GRB 260430A / EP260430a: COLIBRÍ optical upper limit
  7. GRB 260429A: Fermi GBM Detection
  8. Fermi GRB 260429A: Global MASTER-Net observations report
  9. EP260430a: Global MASTER-Net observations report
  10. EP260430a: Einstein Probe detection of an X-ray transient
  11. EP260429a: EP-WXT detection of a fast X-ray transient
  12. GRB 260429A: Fermi GBM Final Real-time Localization
  13. GRB 260428A: SVOM/GRM observation of a possible short burst with extended emission
  14. GRB 260428A: GECAM-B detection of a possible long duration Type I burst
  15. IceCube-260425A: Upper limits from a search for additional neutrino events in IceCube
  16. GRB 260428A: AstroSat CZTI detection
  17. Fermi GRB 260428A: Global MASTER-Net observations report
  18. EP260416a: Mondy and Terskol optical upper limits
  19. GRB 260424B: Glowbug gamma-ray detection of a short burst
  20. GRB 260424B: COLIBRÍ optical upper limit
  21. Konus-Wind detection of GRB 260424B
  22. GRB 260428A: Fermi GBM Final Real-time Localization
  23. Fermi-LAT Gamma-ray Observations of IceCube-260425A
  24. GRB 260424C: Fermi GBM Final Localization
  25. EP260321a/SN 2026gzf: spectroscopy at Mondy observatory
  26. IPN triangulation of GRB 260424B (short)
  27. GRB 260424B: SVOM/GRM detection of a short burst
  28. IceCube-260425A - IceCube observation of a high-energy neutrino candidate track-like event
  29. GRB 260305A: likely detection by Fermi-LAT and the LAT gamma-ray position
  30. IceCube Alert 260425A: Global MASTER-Net observations report
  31. Fermi trigger No 798737427: Global MASTER-Net observations report
  32. GRB 260401A: cubesat Avion detection
  33. GRB 260424A: AstroSat CZTI detection of a long burst
  34. EP260321a: Upper limits from ATCA radio observations
  35. GRB 260421B: Kilonova-Catcher optical afterglow detection
  36. GRB 260421B: Insight-HXMT/HE detection
  37. The EP-WXT trigger 01709258652: Mondy optical observations
  38. GRB 250328A: VLT host galaxy discovery and redshift z = 1.250
  39. EP260416a: Mondy optical observations
  40. GRB 260421B: SVOM/ECLAIRs refined analysis
  41. GRB 260421B: 3.6m DOT optical observation
  42. EP260416a: ZTSh R band observations
  43. EP-WXT trigger 01709260362: FRAM-ORM optical observations confirm flaring star G 151-9
  44. IceCube-Cascade 260418A: Upper limits from a search for additional neutrino events in IceCube
  45. EP250512a / GRB 250512B: VLT/X-shooter host galaxy identification and redshift z = 1.773
  46. GRB 250530A: VLT/X-shooter host galaxy redshift z = 1.486
  47. GRB 260419A: AstroSat CZTI detection
  48. GRB 260421B: SVOM/GRM observation
  49. GRB260421B: J band upper limit by SYSU 80cm infrared telescope
  50. GRB 260421B: EP-FXT follow-up observation
  51. The EP-WXT trigger 01709260362 is likely a flaring star
  52. GOTO26djh/AT2026jpw: ATCA radio detection
  53. GRB 260421B: J-band upper limit with WINTER
  54. GRB 260421B: LCO optical counterpart detection
  55. GRB 260421B: Fermi GBM Observation
  56. Fermi Gamma-ray Burst Monitor trigger 798482368/260421694 is not a GRB
  57. GRB 260421A: AstroSat CZTI detection
  58. GOTO26djh/AT2026jpw: radio detection at 15GHz
  59. GRB 260412A: SVOM/ECLAIRs refined analysis
  60. GRB 260421B: SVOM/VT optical observations
  61. EP260416a: J band upper limit by SYSU 80cm infrared telescope
  62. GRB 260310A: Late-time Chandra X-ray Detection
  63. GRB 260418A: Insight-HXMT/HE detection
  64. EP260416a: 1.3m DFOT optical observation
  65. GRB 260415A: CALET Gamma-Ray Burst Monitor detection
  66. GRB 260415B: CALET Gamma-Ray Burst Monitor detection
  67. Fermi GRB 260421C: Global MASTER-Net observations report
  68. GRB 260421C: Fermi GBM Final Real-time Localization
  69. GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
  70. Fermi GRB 260421B: Global MASTER-Net observations report
  71. GRB 260421B: BOOTES-7 early optical afterglow detection
  72. GRB 260421B: LCO optical afterglow confirmation
  73. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  74. GRB 260421B: TRT optical counterpart detection
  75. GRB 260421B: SVOM detection of a long burst
  76. GRB 260421B: BALROG localization (Fermi Trigger 798437606 / GRB 260421176)
  77. GRB 260421B: Fermi GBM Final Real-time Localization
  78. Fermi GRB 260421A: Global MASTER-Net observations report
  79. GRB 260421A: Fermi GBM Final Real-time Localization
  80. EP260321a: VLA radio follow-up
  81. GRB 260412A: LCOGT Optical Upper Limits
  82. The EP-WXT trigger 01709260314 is likely a flaring star
  83. EP260416a: Optical follow-up observations with Kinder
  84. GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient
  85. EP-WXT trigger 01709260303: KAIT optical observations
  86. EP260416a: 1.5m OSN and 2.2m CAHA optical monitoring
  87. The EP-WXT trigger 01709260303 is likely a flaring star
  88. GRB 260417A: SVOM/GRM observation
  89. EP260321A/AT2026gzf: Optical observation from 1.3m DFOT
  90. GRB 260419B: Fermi GBM Final Real-time Localization
  91. GRB 260419A: Fermi GBM Final Real-time Localization
  92. Fermi trigger No 798275385: Global MASTER-Net observations report
  93. EP260417a: GROWTH-India Telescope optical upper limit
  94. Fermi GRB 260417B: Global MASTER-Net observations report
  95. EP260417b: GROWTH-India Telescope optical upper limit
  96. EP260416a: Ondrejov D50 optical detection
  97. GRB 260418B: Fermi GBM Final Real-time Localization
  98. EP260416a: VLT/FORS2 spectroscopic redshift confirmation
  99. EP260417a: Global MASTER-Net observations report
  100. EP260417a/GRB 260417A: refined analysis of the EP-WXT and follow-up EP-FXT observations

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