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

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