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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: AstroSat CZTI detection
  2. Fermi GRB 260428A: Global MASTER-Net observations report
  3. EP260416a: Mondy and Terskol optical upper limits
  4. GRB 260424B: Glowbug gamma-ray detection of a short burst
  5. GRB 260424B: COLIBRÍ optical upper limit
  6. Konus-Wind detection of GRB 260424B
  7. GRB 260428A: Fermi GBM Final Real-time Localization
  8. Fermi-LAT Gamma-ray Observations of IceCube-260425A
  9. GRB 260424C: Fermi GBM Final Localization
  10. EP260321a/SN 2026gzf: spectroscopy at Mondy observatory
  11. IPN triangulation of GRB 260424B (short)
  12. GRB 260424B: SVOM/GRM detection of a short burst
  13. IceCube-260425A - IceCube observation of a high-energy neutrino candidate track-like event
  14. GRB 260305A: likely detection by Fermi-LAT and the LAT gamma-ray position
  15. IceCube Alert 260425A: Global MASTER-Net observations report
  16. Fermi trigger No 798737427: Global MASTER-Net observations report
  17. GRB 260401A: cubesat Avion detection
  18. GRB 260424A: AstroSat CZTI detection of a long burst
  19. EP260321a: Upper limits from ATCA radio observations
  20. GRB 260421B: Kilonova-Catcher optical afterglow detection
  21. GRB 260421B: Insight-HXMT/HE detection
  22. The EP-WXT trigger 01709258652: Mondy optical observations
  23. GRB 250328A: VLT host galaxy discovery and redshift z = 1.250
  24. EP260416a: Mondy optical observations
  25. GRB 260421B: SVOM/ECLAIRs refined analysis
  26. GRB 260421B: 3.6m DOT optical observation
  27. EP260416a: ZTSh R band observations
  28. EP-WXT trigger 01709260362: FRAM-ORM optical observations confirm flaring star G 151-9
  29. IceCube-Cascade 260418A: Upper limits from a search for additional neutrino events in IceCube
  30. EP250512a / GRB 250512B: VLT/X-shooter host galaxy identification and redshift z = 1.773
  31. GRB 250530A: VLT/X-shooter host galaxy redshift z = 1.486
  32. GRB 260419A: AstroSat CZTI detection
  33. GRB 260421B: SVOM/GRM observation
  34. GRB260421B: J band upper limit by SYSU 80cm infrared telescope
  35. GRB 260421B: EP-FXT follow-up observation
  36. The EP-WXT trigger 01709260362 is likely a flaring star
  37. GOTO26djh/AT2026jpw: ATCA radio detection
  38. GRB 260421B: J-band upper limit with WINTER
  39. GRB 260421B: LCO optical counterpart detection
  40. GRB 260421B: Fermi GBM Observation
  41. Fermi Gamma-ray Burst Monitor trigger 798482368/260421694 is not a GRB
  42. GRB 260421A: AstroSat CZTI detection
  43. GOTO26djh/AT2026jpw: radio detection at 15GHz
  44. GRB 260412A: SVOM/ECLAIRs refined analysis
  45. GRB 260421B: SVOM/VT optical observations
  46. EP260416a: J band upper limit by SYSU 80cm infrared telescope
  47. GRB 260310A: Late-time Chandra X-ray Detection
  48. GRB 260418A: Insight-HXMT/HE detection
  49. EP260416a: 1.3m DFOT optical observation
  50. GRB 260415A: CALET Gamma-Ray Burst Monitor detection
  51. GRB 260415B: CALET Gamma-Ray Burst Monitor detection
  52. Fermi GRB 260421C: Global MASTER-Net observations report
  53. GRB 260421C: Fermi GBM Final Real-time Localization
  54. GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
  55. Fermi GRB 260421B: Global MASTER-Net observations report
  56. GRB 260421B: BOOTES-7 early optical afterglow detection
  57. GRB 260421B: LCO optical afterglow confirmation
  58. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  59. GRB 260421B: TRT optical counterpart detection
  60. GRB 260421B: SVOM detection of a long burst
  61. GRB 260421B: BALROG localization (Fermi Trigger 798437606 / GRB 260421176)
  62. GRB 260421B: Fermi GBM Final Real-time Localization
  63. Fermi GRB 260421A: Global MASTER-Net observations report
  64. GRB 260421A: Fermi GBM Final Real-time Localization
  65. EP260321a: VLA radio follow-up
  66. GRB 260412A: LCOGT Optical Upper Limits
  67. The EP-WXT trigger 01709260314 is likely a flaring star
  68. EP260416a: Optical follow-up observations with Kinder
  69. GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient
  70. EP-WXT trigger 01709260303: KAIT optical observations
  71. EP260416a: 1.5m OSN and 2.2m CAHA optical monitoring
  72. The EP-WXT trigger 01709260303 is likely a flaring star
  73. GRB 260417A: SVOM/GRM observation
  74. EP260321A/AT2026gzf: Optical observation from 1.3m DFOT
  75. GRB 260419B: Fermi GBM Final Real-time Localization
  76. GRB 260419A: Fermi GBM Final Real-time Localization
  77. Fermi trigger No 798275385: Global MASTER-Net observations report
  78. EP260417a: GROWTH-India Telescope optical upper limit
  79. Fermi GRB 260417B: Global MASTER-Net observations report
  80. EP260417b: GROWTH-India Telescope optical upper limit
  81. EP260416a: Ondrejov D50 optical detection
  82. GRB 260418B: Fermi GBM Final Real-time Localization
  83. EP260416a: VLT/FORS2 spectroscopic redshift confirmation
  84. EP260417a: Global MASTER-Net observations report
  85. EP260417a/GRB 260417A: refined analysis of the EP-WXT and follow-up EP-FXT observations
  86. EP260416a: NOT tentative spectroscopic redshift of z =1.909
  87. GRB 260418A: Fermi GBM Final Real-time Localization
  88. EP260416a: GMG Optical Observation
  89. Fermi GRB 260417A: Global MASTER-Net observations report
  90. Konus-Wind detection of GRB 260411B
  91. GRB 260417B: Fermi GBM Final Real-time Localization
  92. GRB 260417A: AstroSat CZTI detection
  93. IPN triangulation of GRB 260411B
  94. EP260416a: LCO observations confirm end of flaring phase
  95. EP260324a / AT2026hir: Further multiband optical follow-up with the PKU 60cm Telescope
  96. EP260417a: TRT optical counterpart detection
  97. EP260417a: Einstein Probe detection of an X-ray transient
  98. EP260416a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  99. EP260417b: Einstein Probe detection of a fast X-ray transient
  100. EP-WXT trigger 01709259586: KAIT optical observations

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