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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. Fermi-LAT Gamma-ray Observations of IceCube-260425A
  2. GRB 260424B: Fermi GBM Final Localization
  3. EP260321a/SN 2026gzf: spectroscopy at Mondy observatory
  4. IPN triangulation of GRB 260424B (short)
  5. GRB 260424B: SVOM/GRM detection of a short burst
  6. IceCube-260425A - IceCube observation of a high-energy neutrino candidate track-like event
  7. GRB 260305A: likely detection by Fermi-LAT and the LAT gamma-ray position
  8. IceCube Alert 260425A: Global MASTER-Net observations report
  9. Fermi trigger No 798737427: Global MASTER-Net observations report
  10. GRB 260401A: cubesat Avion detection
  11. GRB 260424A: AstroSat CZTI detection of a long burst
  12. EP260321a: Upper limits from ATCA radio observations
  13. GRB 260421B: Kilonova-Catcher optical afterglow detection
  14. GRB 260421B: Insight-HXMT/HE detection
  15. The EP-WXT trigger 01709258652: Mondy optical observations
  16. GRB 250328A: VLT host galaxy discovery and redshift z = 1.250
  17. EP260416a: Mondy optical observations
  18. GRB 260421B: SVOM/ECLAIRs refined analysis
  19. GRB 260421B: 3.6m DOT optical observation
  20. EP260416a: ZTSh R band observations
  21. EP-WXT trigger 01709260362: FRAM-ORM optical observations confirm flaring star G 151-9
  22. IceCube-Cascade 260418A: Upper limits from a search for additional neutrino events in IceCube
  23. EP250512a / GRB 250512B: VLT/X-shooter host galaxy identification and redshift z = 1.773
  24. GRB 250530A: VLT/X-shooter host galaxy redshift z = 1.486
  25. GRB 260419A: AstroSat CZTI detection
  26. GRB 260421B: SVOM/GRM observation
  27. GRB260421B: J band upper limit by SYSU 80cm infrared telescope
  28. GRB 260421B: EP-FXT follow-up observation
  29. The EP-WXT trigger 01709260362 is likely a flaring star
  30. GOTO26djh/AT2026jpw: ATCA radio detection
  31. GRB 260421B: J-band upper limit with WINTER
  32. GRB 260421B: LCO optical counterpart detection
  33. GRB 260421B: Fermi GBM Observation
  34. Fermi Gamma-ray Burst Monitor trigger 798482368/260421694 is not a GRB
  35. GRB 260421A: AstroSat CZTI detection
  36. GOTO26djh/AT2026jpw: radio detection at 15GHz
  37. GRB 260412A: SVOM/ECLAIRs refined analysis
  38. GRB 260421B: SVOM/VT optical observations
  39. EP260416a: J band upper limit by SYSU 80cm infrared telescope
  40. GRB 260310A: Late-time Chandra X-ray Detection
  41. GRB 260418A: Insight-HXMT/HE detection
  42. EP260416a: 1.3m DFOT optical observation
  43. GRB 260415A: CALET Gamma-Ray Burst Monitor detection
  44. GRB 260415B: CALET Gamma-Ray Burst Monitor detection
  45. Fermi GRB 260421C: Global MASTER-Net observations report
  46. GRB 260421C: Fermi GBM Final Real-time Localization
  47. GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
  48. Fermi GRB 260421B: Global MASTER-Net observations report
  49. GRB 260421B: BOOTES-7 early optical afterglow detection
  50. GRB 260421B: LCO optical afterglow confirmation
  51. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  52. GRB 260421B: TRT optical counterpart detection
  53. GRB 260421B: SVOM detection of a long burst
  54. GRB 260421B: BALROG localization (Fermi Trigger 798437606 / GRB 260421176)
  55. GRB 260421B: Fermi GBM Final Real-time Localization
  56. Fermi GRB 260421A: Global MASTER-Net observations report
  57. GRB 260421A: Fermi GBM Final Real-time Localization
  58. EP260321a: VLA radio follow-up
  59. GRB 260412A: LCOGT Optical Upper Limits
  60. The EP-WXT trigger 01709260314 is likely a flaring star
  61. EP260416a: Optical follow-up observations with Kinder
  62. GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient
  63. EP-WXT trigger 01709260303: KAIT optical observations
  64. EP260416a: 1.5m OSN and 2.2m CAHA optical monitoring
  65. The EP-WXT trigger 01709260303 is likely a flaring star
  66. GRB 260417A: SVOM/GRM observation
  67. EP260321A/AT2026gzf: Optical observation from 1.3m DFOT
  68. GRB 260419B: Fermi GBM Final Real-time Localization
  69. GRB 260419A: Fermi GBM Final Real-time Localization
  70. Fermi trigger No 798275385: Global MASTER-Net observations report
  71. EP260417a: GROWTH-India Telescope optical upper limit
  72. Fermi GRB 260417B: Global MASTER-Net observations report
  73. EP260417b: GROWTH-India Telescope optical upper limit
  74. EP260416a: Ondrejov D50 optical detection
  75. GRB 260418B: Fermi GBM Final Real-time Localization
  76. EP260416a: VLT/FORS2 spectroscopic redshift confirmation
  77. EP260417a: Global MASTER-Net observations report
  78. EP260417a/GRB 260417A: refined analysis of the EP-WXT and follow-up EP-FXT observations
  79. EP260416a: NOT tentative spectroscopic redshift of z =1.909
  80. GRB 260418A: Fermi GBM Final Real-time Localization
  81. EP260416a: GMG Optical Observation
  82. Fermi GRB 260417A: Global MASTER-Net observations report
  83. Konus-Wind detection of GRB 260411B
  84. GRB 260417B: Fermi GBM Final Real-time Localization
  85. GRB 260417A: AstroSat CZTI detection
  86. IPN triangulation of GRB 260411B
  87. EP260416a: LCO observations confirm end of flaring phase
  88. EP260324a / AT2026hir: Further multiband optical follow-up with the PKU 60cm Telescope
  89. EP260417a: TRT optical counterpart detection
  90. EP260417a: Einstein Probe detection of an X-ray transient
  91. EP260416a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  92. EP260417b: Einstein Probe detection of a fast X-ray transient
  93. EP-WXT trigger 01709259586: KAIT optical observations
  94. EP260416a: KAIT optical upper limit
  95. GRB 260414A: Insight-HXMT/HE detection
  96. EP260416a: COLIBRÍ confirmation of the optical rebrightening
  97. EP260416a: WFST optical observations and rebrightening
  98. GRB 260417A: Fermi GBM Final Real-time Localization
  99. GOTO26djh/AT2026jpw: ZTSh R,I bands observations of the transient
  100. EP260416a: SVOM/VT optical observation

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