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

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