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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 260429A: Fermi GBM Final Real-time Localization
  2. GRB 260428A: SVOM/GRM observation of a possible short burst with extended emission
  3. GRB 260428A: GECAM-B detection of a possible long duration Type I burst
  4. IceCube-260425A: Upper limits from a search for additional neutrino events in IceCube
  5. GRB 260428A: AstroSat CZTI detection
  6. Fermi GRB 260428A: Global MASTER-Net observations report
  7. EP260416a: Mondy and Terskol optical upper limits
  8. GRB 260424B: Glowbug gamma-ray detection of a short burst
  9. GRB 260424B: COLIBRÍ optical upper limit
  10. Konus-Wind detection of GRB 260424B
  11. GRB 260428A: Fermi GBM Final Real-time Localization
  12. Fermi-LAT Gamma-ray Observations of IceCube-260425A
  13. GRB 260424C: Fermi GBM Final Localization
  14. EP260321a/SN 2026gzf: spectroscopy at Mondy observatory
  15. IPN triangulation of GRB 260424B (short)
  16. GRB 260424B: SVOM/GRM detection of a short burst
  17. IceCube-260425A - IceCube observation of a high-energy neutrino candidate track-like event
  18. GRB 260305A: likely detection by Fermi-LAT and the LAT gamma-ray position
  19. IceCube Alert 260425A: Global MASTER-Net observations report
  20. Fermi trigger No 798737427: Global MASTER-Net observations report
  21. GRB 260401A: cubesat Avion detection
  22. GRB 260424A: AstroSat CZTI detection of a long burst
  23. EP260321a: Upper limits from ATCA radio observations
  24. GRB 260421B: Kilonova-Catcher optical afterglow detection
  25. GRB 260421B: Insight-HXMT/HE detection
  26. The EP-WXT trigger 01709258652: Mondy optical observations
  27. GRB 250328A: VLT host galaxy discovery and redshift z = 1.250
  28. EP260416a: Mondy optical observations
  29. GRB 260421B: SVOM/ECLAIRs refined analysis
  30. GRB 260421B: 3.6m DOT optical observation
  31. EP260416a: ZTSh R band observations
  32. EP-WXT trigger 01709260362: FRAM-ORM optical observations confirm flaring star G 151-9
  33. IceCube-Cascade 260418A: Upper limits from a search for additional neutrino events in IceCube
  34. EP250512a / GRB 250512B: VLT/X-shooter host galaxy identification and redshift z = 1.773
  35. GRB 250530A: VLT/X-shooter host galaxy redshift z = 1.486
  36. GRB 260419A: AstroSat CZTI detection
  37. GRB 260421B: SVOM/GRM observation
  38. GRB260421B: J band upper limit by SYSU 80cm infrared telescope
  39. GRB 260421B: EP-FXT follow-up observation
  40. The EP-WXT trigger 01709260362 is likely a flaring star
  41. GOTO26djh/AT2026jpw: ATCA radio detection
  42. GRB 260421B: J-band upper limit with WINTER
  43. GRB 260421B: LCO optical counterpart detection
  44. GRB 260421B: Fermi GBM Observation
  45. Fermi Gamma-ray Burst Monitor trigger 798482368/260421694 is not a GRB
  46. GRB 260421A: AstroSat CZTI detection
  47. GOTO26djh/AT2026jpw: radio detection at 15GHz
  48. GRB 260412A: SVOM/ECLAIRs refined analysis
  49. GRB 260421B: SVOM/VT optical observations
  50. EP260416a: J band upper limit by SYSU 80cm infrared telescope
  51. GRB 260310A: Late-time Chandra X-ray Detection
  52. GRB 260418A: Insight-HXMT/HE detection
  53. EP260416a: 1.3m DFOT optical observation
  54. GRB 260415A: CALET Gamma-Ray Burst Monitor detection
  55. GRB 260415B: CALET Gamma-Ray Burst Monitor detection
  56. Fermi GRB 260421C: Global MASTER-Net observations report
  57. GRB 260421C: Fermi GBM Final Real-time Localization
  58. GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
  59. Fermi GRB 260421B: Global MASTER-Net observations report
  60. GRB 260421B: BOOTES-7 early optical afterglow detection
  61. GRB 260421B: LCO optical afterglow confirmation
  62. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  63. GRB 260421B: TRT optical counterpart detection
  64. GRB 260421B: SVOM detection of a long burst
  65. GRB 260421B: BALROG localization (Fermi Trigger 798437606 / GRB 260421176)
  66. GRB 260421B: Fermi GBM Final Real-time Localization
  67. Fermi GRB 260421A: Global MASTER-Net observations report
  68. GRB 260421A: Fermi GBM Final Real-time Localization
  69. EP260321a: VLA radio follow-up
  70. GRB 260412A: LCOGT Optical Upper Limits
  71. The EP-WXT trigger 01709260314 is likely a flaring star
  72. EP260416a: Optical follow-up observations with Kinder
  73. GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient
  74. EP-WXT trigger 01709260303: KAIT optical observations
  75. EP260416a: 1.5m OSN and 2.2m CAHA optical monitoring
  76. The EP-WXT trigger 01709260303 is likely a flaring star
  77. GRB 260417A: SVOM/GRM observation
  78. EP260321A/AT2026gzf: Optical observation from 1.3m DFOT
  79. GRB 260419B: Fermi GBM Final Real-time Localization
  80. GRB 260419A: Fermi GBM Final Real-time Localization
  81. Fermi trigger No 798275385: Global MASTER-Net observations report
  82. EP260417a: GROWTH-India Telescope optical upper limit
  83. Fermi GRB 260417B: Global MASTER-Net observations report
  84. EP260417b: GROWTH-India Telescope optical upper limit
  85. EP260416a: Ondrejov D50 optical detection
  86. GRB 260418B: Fermi GBM Final Real-time Localization
  87. EP260416a: VLT/FORS2 spectroscopic redshift confirmation
  88. EP260417a: Global MASTER-Net observations report
  89. EP260417a/GRB 260417A: refined analysis of the EP-WXT and follow-up EP-FXT observations
  90. EP260416a: NOT tentative spectroscopic redshift of z =1.909
  91. GRB 260418A: Fermi GBM Final Real-time Localization
  92. EP260416a: GMG Optical Observation
  93. Fermi GRB 260417A: Global MASTER-Net observations report
  94. Konus-Wind detection of GRB 260411B
  95. GRB 260417B: Fermi GBM Final Real-time Localization
  96. GRB 260417A: AstroSat CZTI detection
  97. IPN triangulation of GRB 260411B
  98. EP260416a: LCO observations confirm end of flaring phase
  99. EP260324a / AT2026hir: Further multiband optical follow-up with the PKU 60cm Telescope
  100. EP260417a: TRT optical counterpart detection

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