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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. EP260502a: Einstein Probe detection of an X-ray transient
  2. GRB 260429A: SVOM/GRM observation of a short burst
  3. SN 2026kid: Optical follow-up with small-aperture telescopes in Spain and China
  4. EP260429a: Global MASTER-Net observations report
  5. EP260430a: refined analysis of the EP-WXT and follow-up EP-FXT observations
  6. GRB 260424B: AstroSat CZTI detection
  7. GRB 260429B / EP260429a: COLIBRÍ optical upper limit
  8. EP260429a: LCO optical upper limits
  9. EP260430a: LCO optical upper limits
  10. GRB 260430A / EP260430a: COLIBRÍ optical upper limit
  11. GRB 260429A: Fermi GBM Detection
  12. Fermi GRB 260429A: Global MASTER-Net observations report
  13. EP260430a: Global MASTER-Net observations report
  14. EP260430a: Einstein Probe detection of an X-ray transient
  15. EP260429a: EP-WXT detection of a fast X-ray transient
  16. GRB 260429A: Fermi GBM Final Real-time Localization
  17. GRB 260428A: SVOM/GRM observation of a possible short burst with extended emission
  18. GRB 260428A: GECAM-B detection of a possible long duration Type I burst
  19. IceCube-260425A: Upper limits from a search for additional neutrino events in IceCube
  20. GRB 260428A: AstroSat CZTI detection
  21. Fermi GRB 260428A: Global MASTER-Net observations report
  22. EP260416a: Mondy and Terskol optical upper limits
  23. GRB 260424B: Glowbug gamma-ray detection of a short burst
  24. GRB 260424B: COLIBRÍ optical upper limit
  25. Konus-Wind detection of GRB 260424B
  26. GRB 260428A: Fermi GBM Final Real-time Localization
  27. Fermi-LAT Gamma-ray Observations of IceCube-260425A
  28. GRB 260424C: Fermi GBM Final Localization
  29. EP260321a/SN 2026gzf: spectroscopy at Mondy observatory
  30. IPN triangulation of GRB 260424B (short)
  31. GRB 260424B: SVOM/GRM detection of a short burst
  32. IceCube-260425A - IceCube observation of a high-energy neutrino candidate track-like event
  33. GRB 260305A: likely detection by Fermi-LAT and the LAT gamma-ray position
  34. IceCube Alert 260425A: Global MASTER-Net observations report
  35. Fermi trigger No 798737427: Global MASTER-Net observations report
  36. GRB 260401A: cubesat Avion detection
  37. GRB 260424A: AstroSat CZTI detection of a long burst
  38. EP260321a: Upper limits from ATCA radio observations
  39. GRB 260421B: Kilonova-Catcher optical afterglow detection
  40. GRB 260421B: Insight-HXMT/HE detection
  41. The EP-WXT trigger 01709258652: Mondy optical observations
  42. GRB 250328A: VLT host galaxy discovery and redshift z = 1.250
  43. EP260416a: Mondy optical observations
  44. GRB 260421B: SVOM/ECLAIRs refined analysis
  45. GRB 260421B: 3.6m DOT optical observation
  46. EP260416a: ZTSh R band observations
  47. EP-WXT trigger 01709260362: FRAM-ORM optical observations confirm flaring star G 151-9
  48. IceCube-Cascade 260418A: Upper limits from a search for additional neutrino events in IceCube
  49. EP250512a / GRB 250512B: VLT/X-shooter host galaxy identification and redshift z = 1.773
  50. GRB 250530A: VLT/X-shooter host galaxy redshift z = 1.486
  51. GRB 260419A: AstroSat CZTI detection
  52. GRB 260421B: SVOM/GRM observation
  53. GRB260421B: J band upper limit by SYSU 80cm infrared telescope
  54. GRB 260421B: EP-FXT follow-up observation
  55. The EP-WXT trigger 01709260362 is likely a flaring star
  56. GOTO26djh/AT2026jpw: ATCA radio detection
  57. GRB 260421B: J-band upper limit with WINTER
  58. GRB 260421B: LCO optical counterpart detection
  59. GRB 260421B: Fermi GBM Observation
  60. Fermi Gamma-ray Burst Monitor trigger 798482368/260421694 is not a GRB
  61. GRB 260421A: AstroSat CZTI detection
  62. GOTO26djh/AT2026jpw: radio detection at 15GHz
  63. GRB 260412A: SVOM/ECLAIRs refined analysis
  64. GRB 260421B: SVOM/VT optical observations
  65. EP260416a: J band upper limit by SYSU 80cm infrared telescope
  66. GRB 260310A: Late-time Chandra X-ray Detection
  67. GRB 260418A: Insight-HXMT/HE detection
  68. EP260416a: 1.3m DFOT optical observation
  69. GRB 260415A: CALET Gamma-Ray Burst Monitor detection
  70. GRB 260415B: CALET Gamma-Ray Burst Monitor detection
  71. Fermi GRB 260421C: Global MASTER-Net observations report
  72. GRB 260421C: Fermi GBM Final Real-time Localization
  73. GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
  74. Fermi GRB 260421B: Global MASTER-Net observations report
  75. GRB 260421B: BOOTES-7 early optical afterglow detection
  76. GRB 260421B: LCO optical afterglow confirmation
  77. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  78. GRB 260421B: TRT optical counterpart detection
  79. GRB 260421B: SVOM detection of a long burst
  80. GRB 260421B: BALROG localization (Fermi Trigger 798437606 / GRB 260421176)
  81. GRB 260421B: Fermi GBM Final Real-time Localization
  82. Fermi GRB 260421A: Global MASTER-Net observations report
  83. GRB 260421A: Fermi GBM Final Real-time Localization
  84. EP260321a: VLA radio follow-up
  85. GRB 260412A: LCOGT Optical Upper Limits
  86. The EP-WXT trigger 01709260314 is likely a flaring star
  87. EP260416a: Optical follow-up observations with Kinder
  88. GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient
  89. EP-WXT trigger 01709260303: KAIT optical observations
  90. EP260416a: 1.5m OSN and 2.2m CAHA optical monitoring
  91. The EP-WXT trigger 01709260303 is likely a flaring star
  92. GRB 260417A: SVOM/GRM observation
  93. EP260321A/AT2026gzf: Optical observation from 1.3m DFOT
  94. GRB 260419B: Fermi GBM Final Real-time Localization
  95. GRB 260419A: Fermi GBM Final Real-time Localization
  96. Fermi trigger No 798275385: Global MASTER-Net observations report
  97. EP260417a: GROWTH-India Telescope optical upper limit
  98. Fermi GRB 260417B: Global MASTER-Net observations report
  99. EP260417b: GROWTH-India Telescope optical upper limit
  100. EP260416a: Ondrejov D50 optical detection

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