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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 260424B: COLIBRÍ optical upper limit
  2. Konus-Wind detection of GRB 260424B
  3. GRB 260428A: Fermi GBM Final Real-time Localization
  4. Fermi-LAT Gamma-ray Observations of IceCube-260425A
  5. GRB 260424B: Fermi GBM Final Localization
  6. EP260321a/SN 2026gzf: spectroscopy at Mondy observatory
  7. IPN triangulation of GRB 260424B (short)
  8. GRB 260424B: SVOM/GRM detection of a short burst
  9. IceCube-260425A - IceCube observation of a high-energy neutrino candidate track-like event
  10. GRB 260305A: likely detection by Fermi-LAT and the LAT gamma-ray position
  11. IceCube Alert 260425A: Global MASTER-Net observations report
  12. Fermi trigger No 798737427: Global MASTER-Net observations report
  13. GRB 260401A: cubesat Avion detection
  14. GRB 260424A: AstroSat CZTI detection of a long burst
  15. EP260321a: Upper limits from ATCA radio observations
  16. GRB 260421B: Kilonova-Catcher optical afterglow detection
  17. GRB 260421B: Insight-HXMT/HE detection
  18. The EP-WXT trigger 01709258652: Mondy optical observations
  19. GRB 250328A: VLT host galaxy discovery and redshift z = 1.250
  20. EP260416a: Mondy optical observations
  21. GRB 260421B: SVOM/ECLAIRs refined analysis
  22. GRB 260421B: 3.6m DOT optical observation
  23. EP260416a: ZTSh R band observations
  24. EP-WXT trigger 01709260362: FRAM-ORM optical observations confirm flaring star G 151-9
  25. IceCube-Cascade 260418A: Upper limits from a search for additional neutrino events in IceCube
  26. EP250512a / GRB 250512B: VLT/X-shooter host galaxy identification and redshift z = 1.773
  27. GRB 250530A: VLT/X-shooter host galaxy redshift z = 1.486
  28. GRB 260419A: AstroSat CZTI detection
  29. GRB 260421B: SVOM/GRM observation
  30. GRB260421B: J band upper limit by SYSU 80cm infrared telescope
  31. GRB 260421B: EP-FXT follow-up observation
  32. The EP-WXT trigger 01709260362 is likely a flaring star
  33. GOTO26djh/AT2026jpw: ATCA radio detection
  34. GRB 260421B: J-band upper limit with WINTER
  35. GRB 260421B: LCO optical counterpart detection
  36. GRB 260421B: Fermi GBM Observation
  37. Fermi Gamma-ray Burst Monitor trigger 798482368/260421694 is not a GRB
  38. GRB 260421A: AstroSat CZTI detection
  39. GOTO26djh/AT2026jpw: radio detection at 15GHz
  40. GRB 260412A: SVOM/ECLAIRs refined analysis
  41. GRB 260421B: SVOM/VT optical observations
  42. EP260416a: J band upper limit by SYSU 80cm infrared telescope
  43. GRB 260310A: Late-time Chandra X-ray Detection
  44. GRB 260418A: Insight-HXMT/HE detection
  45. EP260416a: 1.3m DFOT optical observation
  46. GRB 260415A: CALET Gamma-Ray Burst Monitor detection
  47. GRB 260415B: CALET Gamma-Ray Burst Monitor detection
  48. Fermi GRB 260421C: Global MASTER-Net observations report
  49. GRB 260421C: Fermi GBM Final Real-time Localization
  50. GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
  51. Fermi GRB 260421B: Global MASTER-Net observations report
  52. GRB 260421B: BOOTES-7 early optical afterglow detection
  53. GRB 260421B: LCO optical afterglow confirmation
  54. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  55. GRB 260421B: TRT optical counterpart detection
  56. GRB 260421B: SVOM detection of a long burst
  57. GRB 260421B: BALROG localization (Fermi Trigger 798437606 / GRB 260421176)
  58. GRB 260421B: Fermi GBM Final Real-time Localization
  59. Fermi GRB 260421A: Global MASTER-Net observations report
  60. GRB 260421A: Fermi GBM Final Real-time Localization
  61. EP260321a: VLA radio follow-up
  62. GRB 260412A: LCOGT Optical Upper Limits
  63. The EP-WXT trigger 01709260314 is likely a flaring star
  64. EP260416a: Optical follow-up observations with Kinder
  65. GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient
  66. EP-WXT trigger 01709260303: KAIT optical observations
  67. EP260416a: 1.5m OSN and 2.2m CAHA optical monitoring
  68. The EP-WXT trigger 01709260303 is likely a flaring star
  69. GRB 260417A: SVOM/GRM observation
  70. EP260321A/AT2026gzf: Optical observation from 1.3m DFOT
  71. GRB 260419B: Fermi GBM Final Real-time Localization
  72. GRB 260419A: Fermi GBM Final Real-time Localization
  73. Fermi trigger No 798275385: Global MASTER-Net observations report
  74. EP260417a: GROWTH-India Telescope optical upper limit
  75. Fermi GRB 260417B: Global MASTER-Net observations report
  76. EP260417b: GROWTH-India Telescope optical upper limit
  77. EP260416a: Ondrejov D50 optical detection
  78. GRB 260418B: Fermi GBM Final Real-time Localization
  79. EP260416a: VLT/FORS2 spectroscopic redshift confirmation
  80. EP260417a: Global MASTER-Net observations report
  81. EP260417a/GRB 260417A: refined analysis of the EP-WXT and follow-up EP-FXT observations
  82. EP260416a: NOT tentative spectroscopic redshift of z =1.909
  83. GRB 260418A: Fermi GBM Final Real-time Localization
  84. EP260416a: GMG Optical Observation
  85. Fermi GRB 260417A: Global MASTER-Net observations report
  86. Konus-Wind detection of GRB 260411B
  87. GRB 260417B: Fermi GBM Final Real-time Localization
  88. GRB 260417A: AstroSat CZTI detection
  89. IPN triangulation of GRB 260411B
  90. EP260416a: LCO observations confirm end of flaring phase
  91. EP260324a / AT2026hir: Further multiband optical follow-up with the PKU 60cm Telescope
  92. EP260417a: TRT optical counterpart detection
  93. EP260417a: Einstein Probe detection of an X-ray transient
  94. EP260416a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  95. EP260417b: Einstein Probe detection of a fast X-ray transient
  96. EP-WXT trigger 01709259586: KAIT optical observations
  97. EP260416a: KAIT optical upper limit
  98. GRB 260414A: Insight-HXMT/HE detection
  99. EP260416a: COLIBRÍ confirmation of the optical rebrightening
  100. EP260416a: WFST optical observations and rebrightening

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