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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. EP260430a: Einstein Probe detection of an X-ray transient
  2. EP260429a: EP-WXT detection of a fast X-ray transient
  3. GRB 260429A: Fermi GBM Final Real-time Localization
  4. GRB 260428A: SVOM/GRM observation of a possible short burst with extended emission
  5. GRB 260428A: GECAM-B detection of a possible long duration Type I burst
  6. IceCube-260425A: Upper limits from a search for additional neutrino events in IceCube
  7. GRB 260428A: AstroSat CZTI detection
  8. Fermi GRB 260428A: Global MASTER-Net observations report
  9. EP260416a: Mondy and Terskol optical upper limits
  10. GRB 260424B: Glowbug gamma-ray detection of a short burst
  11. GRB 260424B: COLIBRÍ optical upper limit
  12. Konus-Wind detection of GRB 260424B
  13. GRB 260428A: Fermi GBM Final Real-time Localization
  14. Fermi-LAT Gamma-ray Observations of IceCube-260425A
  15. GRB 260424C: Fermi GBM Final Localization
  16. EP260321a/SN 2026gzf: spectroscopy at Mondy observatory
  17. IPN triangulation of GRB 260424B (short)
  18. GRB 260424B: SVOM/GRM detection of a short burst
  19. IceCube-260425A - IceCube observation of a high-energy neutrino candidate track-like event
  20. GRB 260305A: likely detection by Fermi-LAT and the LAT gamma-ray position
  21. IceCube Alert 260425A: Global MASTER-Net observations report
  22. Fermi trigger No 798737427: Global MASTER-Net observations report
  23. GRB 260401A: cubesat Avion detection
  24. GRB 260424A: AstroSat CZTI detection of a long burst
  25. EP260321a: Upper limits from ATCA radio observations
  26. GRB 260421B: Kilonova-Catcher optical afterglow detection
  27. GRB 260421B: Insight-HXMT/HE detection
  28. The EP-WXT trigger 01709258652: Mondy optical observations
  29. GRB 250328A: VLT host galaxy discovery and redshift z = 1.250
  30. EP260416a: Mondy optical observations
  31. GRB 260421B: SVOM/ECLAIRs refined analysis
  32. GRB 260421B: 3.6m DOT optical observation
  33. EP260416a: ZTSh R band observations
  34. EP-WXT trigger 01709260362: FRAM-ORM optical observations confirm flaring star G 151-9
  35. IceCube-Cascade 260418A: Upper limits from a search for additional neutrino events in IceCube
  36. EP250512a / GRB 250512B: VLT/X-shooter host galaxy identification and redshift z = 1.773
  37. GRB 250530A: VLT/X-shooter host galaxy redshift z = 1.486
  38. GRB 260419A: AstroSat CZTI detection
  39. GRB 260421B: SVOM/GRM observation
  40. GRB260421B: J band upper limit by SYSU 80cm infrared telescope
  41. GRB 260421B: EP-FXT follow-up observation
  42. The EP-WXT trigger 01709260362 is likely a flaring star
  43. GOTO26djh/AT2026jpw: ATCA radio detection
  44. GRB 260421B: J-band upper limit with WINTER
  45. GRB 260421B: LCO optical counterpart detection
  46. GRB 260421B: Fermi GBM Observation
  47. Fermi Gamma-ray Burst Monitor trigger 798482368/260421694 is not a GRB
  48. GRB 260421A: AstroSat CZTI detection
  49. GOTO26djh/AT2026jpw: radio detection at 15GHz
  50. GRB 260412A: SVOM/ECLAIRs refined analysis
  51. GRB 260421B: SVOM/VT optical observations
  52. EP260416a: J band upper limit by SYSU 80cm infrared telescope
  53. GRB 260310A: Late-time Chandra X-ray Detection
  54. GRB 260418A: Insight-HXMT/HE detection
  55. EP260416a: 1.3m DFOT optical observation
  56. GRB 260415A: CALET Gamma-Ray Burst Monitor detection
  57. GRB 260415B: CALET Gamma-Ray Burst Monitor detection
  58. Fermi GRB 260421C: Global MASTER-Net observations report
  59. GRB 260421C: Fermi GBM Final Real-time Localization
  60. GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
  61. Fermi GRB 260421B: Global MASTER-Net observations report
  62. GRB 260421B: BOOTES-7 early optical afterglow detection
  63. GRB 260421B: LCO optical afterglow confirmation
  64. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  65. GRB 260421B: TRT optical counterpart detection
  66. GRB 260421B: SVOM detection of a long burst
  67. GRB 260421B: BALROG localization (Fermi Trigger 798437606 / GRB 260421176)
  68. GRB 260421B: Fermi GBM Final Real-time Localization
  69. Fermi GRB 260421A: Global MASTER-Net observations report
  70. GRB 260421A: Fermi GBM Final Real-time Localization
  71. EP260321a: VLA radio follow-up
  72. GRB 260412A: LCOGT Optical Upper Limits
  73. The EP-WXT trigger 01709260314 is likely a flaring star
  74. EP260416a: Optical follow-up observations with Kinder
  75. GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient
  76. EP-WXT trigger 01709260303: KAIT optical observations
  77. EP260416a: 1.5m OSN and 2.2m CAHA optical monitoring
  78. The EP-WXT trigger 01709260303 is likely a flaring star
  79. GRB 260417A: SVOM/GRM observation
  80. EP260321A/AT2026gzf: Optical observation from 1.3m DFOT
  81. GRB 260419B: Fermi GBM Final Real-time Localization
  82. GRB 260419A: Fermi GBM Final Real-time Localization
  83. Fermi trigger No 798275385: Global MASTER-Net observations report
  84. EP260417a: GROWTH-India Telescope optical upper limit
  85. Fermi GRB 260417B: Global MASTER-Net observations report
  86. EP260417b: GROWTH-India Telescope optical upper limit
  87. EP260416a: Ondrejov D50 optical detection
  88. GRB 260418B: Fermi GBM Final Real-time Localization
  89. EP260416a: VLT/FORS2 spectroscopic redshift confirmation
  90. EP260417a: Global MASTER-Net observations report
  91. EP260417a/GRB 260417A: refined analysis of the EP-WXT and follow-up EP-FXT observations
  92. EP260416a: NOT tentative spectroscopic redshift of z =1.909
  93. GRB 260418A: Fermi GBM Final Real-time Localization
  94. EP260416a: GMG Optical Observation
  95. Fermi GRB 260417A: Global MASTER-Net observations report
  96. Konus-Wind detection of GRB 260411B
  97. GRB 260417B: Fermi GBM Final Real-time Localization
  98. GRB 260417A: AstroSat CZTI detection
  99. IPN triangulation of GRB 260411B
  100. EP260416a: LCO observations confirm end of flaring phase

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