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

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