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

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