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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 260428A: SVOM/GRM observation of a possible short burst with extended emission
  2. GRB 260428A: GECAM-B detection of a possible long duration Type I burst
  3. IceCube-260425A: Upper limits from a search for additional neutrino events in IceCube
  4. GRB 260428A: AstroSat CZTI detection
  5. Fermi GRB 260428A: Global MASTER-Net observations report
  6. EP260416a: Mondy and Terskol optical upper limits
  7. GRB 260424B: Glowbug gamma-ray detection of a short burst
  8. GRB 260424B: COLIBRÍ optical upper limit
  9. Konus-Wind detection of GRB 260424B
  10. GRB 260428A: Fermi GBM Final Real-time Localization
  11. Fermi-LAT Gamma-ray Observations of IceCube-260425A
  12. GRB 260424C: Fermi GBM Final Localization
  13. EP260321a/SN 2026gzf: spectroscopy at Mondy observatory
  14. IPN triangulation of GRB 260424B (short)
  15. GRB 260424B: SVOM/GRM detection of a short burst
  16. IceCube-260425A - IceCube observation of a high-energy neutrino candidate track-like event
  17. GRB 260305A: likely detection by Fermi-LAT and the LAT gamma-ray position
  18. IceCube Alert 260425A: Global MASTER-Net observations report
  19. Fermi trigger No 798737427: Global MASTER-Net observations report
  20. GRB 260401A: cubesat Avion detection
  21. GRB 260424A: AstroSat CZTI detection of a long burst
  22. EP260321a: Upper limits from ATCA radio observations
  23. GRB 260421B: Kilonova-Catcher optical afterglow detection
  24. GRB 260421B: Insight-HXMT/HE detection
  25. The EP-WXT trigger 01709258652: Mondy optical observations
  26. GRB 250328A: VLT host galaxy discovery and redshift z = 1.250
  27. EP260416a: Mondy optical observations
  28. GRB 260421B: SVOM/ECLAIRs refined analysis
  29. GRB 260421B: 3.6m DOT optical observation
  30. EP260416a: ZTSh R band observations
  31. EP-WXT trigger 01709260362: FRAM-ORM optical observations confirm flaring star G 151-9
  32. IceCube-Cascade 260418A: Upper limits from a search for additional neutrino events in IceCube
  33. EP250512a / GRB 250512B: VLT/X-shooter host galaxy identification and redshift z = 1.773
  34. GRB 250530A: VLT/X-shooter host galaxy redshift z = 1.486
  35. GRB 260419A: AstroSat CZTI detection
  36. GRB 260421B: SVOM/GRM observation
  37. GRB260421B: J band upper limit by SYSU 80cm infrared telescope
  38. GRB 260421B: EP-FXT follow-up observation
  39. The EP-WXT trigger 01709260362 is likely a flaring star
  40. GOTO26djh/AT2026jpw: ATCA radio detection
  41. GRB 260421B: J-band upper limit with WINTER
  42. GRB 260421B: LCO optical counterpart detection
  43. GRB 260421B: Fermi GBM Observation
  44. Fermi Gamma-ray Burst Monitor trigger 798482368/260421694 is not a GRB
  45. GRB 260421A: AstroSat CZTI detection
  46. GOTO26djh/AT2026jpw: radio detection at 15GHz
  47. GRB 260412A: SVOM/ECLAIRs refined analysis
  48. GRB 260421B: SVOM/VT optical observations
  49. EP260416a: J band upper limit by SYSU 80cm infrared telescope
  50. GRB 260310A: Late-time Chandra X-ray Detection
  51. GRB 260418A: Insight-HXMT/HE detection
  52. EP260416a: 1.3m DFOT optical observation
  53. GRB 260415A: CALET Gamma-Ray Burst Monitor detection
  54. GRB 260415B: CALET Gamma-Ray Burst Monitor detection
  55. Fermi GRB 260421C: Global MASTER-Net observations report
  56. GRB 260421C: Fermi GBM Final Real-time Localization
  57. GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
  58. Fermi GRB 260421B: Global MASTER-Net observations report
  59. GRB 260421B: BOOTES-7 early optical afterglow detection
  60. GRB 260421B: LCO optical afterglow confirmation
  61. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  62. GRB 260421B: TRT optical counterpart detection
  63. GRB 260421B: SVOM detection of a long burst
  64. GRB 260421B: BALROG localization (Fermi Trigger 798437606 / GRB 260421176)
  65. GRB 260421B: Fermi GBM Final Real-time Localization
  66. Fermi GRB 260421A: Global MASTER-Net observations report
  67. GRB 260421A: Fermi GBM Final Real-time Localization
  68. EP260321a: VLA radio follow-up
  69. GRB 260412A: LCOGT Optical Upper Limits
  70. The EP-WXT trigger 01709260314 is likely a flaring star
  71. EP260416a: Optical follow-up observations with Kinder
  72. GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient
  73. EP-WXT trigger 01709260303: KAIT optical observations
  74. EP260416a: 1.5m OSN and 2.2m CAHA optical monitoring
  75. The EP-WXT trigger 01709260303 is likely a flaring star
  76. GRB 260417A: SVOM/GRM observation
  77. EP260321A/AT2026gzf: Optical observation from 1.3m DFOT
  78. GRB 260419B: Fermi GBM Final Real-time Localization
  79. GRB 260419A: Fermi GBM Final Real-time Localization
  80. Fermi trigger No 798275385: Global MASTER-Net observations report
  81. EP260417a: GROWTH-India Telescope optical upper limit
  82. Fermi GRB 260417B: Global MASTER-Net observations report
  83. EP260417b: GROWTH-India Telescope optical upper limit
  84. EP260416a: Ondrejov D50 optical detection
  85. GRB 260418B: Fermi GBM Final Real-time Localization
  86. EP260416a: VLT/FORS2 spectroscopic redshift confirmation
  87. EP260417a: Global MASTER-Net observations report
  88. EP260417a/GRB 260417A: refined analysis of the EP-WXT and follow-up EP-FXT observations
  89. EP260416a: NOT tentative spectroscopic redshift of z =1.909
  90. GRB 260418A: Fermi GBM Final Real-time Localization
  91. EP260416a: GMG Optical Observation
  92. Fermi GRB 260417A: Global MASTER-Net observations report
  93. Konus-Wind detection of GRB 260411B
  94. GRB 260417B: Fermi GBM Final Real-time Localization
  95. GRB 260417A: AstroSat CZTI detection
  96. IPN triangulation of GRB 260411B
  97. EP260416a: LCO observations confirm end of flaring phase
  98. EP260324a / AT2026hir: Further multiband optical follow-up with the PKU 60cm Telescope
  99. EP260417a: TRT optical counterpart detection
  100. EP260417a: Einstein Probe detection of an X-ray transient

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