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

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