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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"

41579 results found.

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

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