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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 260429B / EP260429a: AstroSat CZTI detection
  2. EP260502a: BOOTES-7: early optical upper limit
  3. EP260502a: Las Cumbres upper limit
  4. EP260502a: Einstein Probe detection of an X-ray transient
  5. GRB 260429A: SVOM/GRM observation of a short burst
  6. SN 2026kid: Optical follow-up with small-aperture telescopes in Spain and China
  7. EP260429a: Global MASTER-Net observations report
  8. EP260430a: refined analysis of the EP-WXT and follow-up EP-FXT observations
  9. GRB 260424B: AstroSat CZTI detection
  10. GRB 260429B / EP260429a: COLIBRÍ optical upper limit
  11. EP260429a: LCO optical upper limits
  12. EP260430a: LCO optical upper limits
  13. GRB 260430A / EP260430a: COLIBRÍ optical upper limit
  14. GRB 260429A: Fermi GBM Detection
  15. Fermi GRB 260429A: Global MASTER-Net observations report
  16. EP260430a: Global MASTER-Net observations report
  17. EP260430a: Einstein Probe detection of an X-ray transient
  18. EP260429a: EP-WXT detection of a fast X-ray transient
  19. GRB 260429A: Fermi GBM Final Real-time Localization
  20. GRB 260428A: SVOM/GRM observation of a possible short burst with extended emission
  21. GRB 260428A: GECAM-B detection of a possible long duration Type I burst
  22. IceCube-260425A: Upper limits from a search for additional neutrino events in IceCube
  23. GRB 260428A: AstroSat CZTI detection
  24. Fermi GRB 260428A: Global MASTER-Net observations report
  25. EP260416a: Mondy and Terskol optical upper limits
  26. GRB 260424B: Glowbug gamma-ray detection of a short burst
  27. GRB 260424B: COLIBRÍ optical upper limit
  28. Konus-Wind detection of GRB 260424B
  29. GRB 260428A: Fermi GBM Final Real-time Localization
  30. Fermi-LAT Gamma-ray Observations of IceCube-260425A
  31. GRB 260424C: Fermi GBM Final Localization
  32. EP260321a/SN 2026gzf: spectroscopy at Mondy observatory
  33. IPN triangulation of GRB 260424B (short)
  34. GRB 260424B: SVOM/GRM detection of a short burst
  35. IceCube-260425A - IceCube observation of a high-energy neutrino candidate track-like event
  36. GRB 260305A: likely detection by Fermi-LAT and the LAT gamma-ray position
  37. IceCube Alert 260425A: Global MASTER-Net observations report
  38. Fermi trigger No 798737427: Global MASTER-Net observations report
  39. GRB 260401A: cubesat Avion detection
  40. GRB 260424A: AstroSat CZTI detection of a long burst
  41. EP260321a: Upper limits from ATCA radio observations
  42. GRB 260421B: Kilonova-Catcher optical afterglow detection
  43. GRB 260421B: Insight-HXMT/HE detection
  44. The EP-WXT trigger 01709258652: Mondy optical observations
  45. GRB 250328A: VLT host galaxy discovery and redshift z = 1.250
  46. EP260416a: Mondy optical observations
  47. GRB 260421B: SVOM/ECLAIRs refined analysis
  48. GRB 260421B: 3.6m DOT optical observation
  49. EP260416a: ZTSh R band observations
  50. EP-WXT trigger 01709260362: FRAM-ORM optical observations confirm flaring star G 151-9
  51. IceCube-Cascade 260418A: Upper limits from a search for additional neutrino events in IceCube
  52. EP250512a / GRB 250512B: VLT/X-shooter host galaxy identification and redshift z = 1.773
  53. GRB 250530A: VLT/X-shooter host galaxy redshift z = 1.486
  54. GRB 260419A: AstroSat CZTI detection
  55. GRB 260421B: SVOM/GRM observation
  56. GRB260421B: J band upper limit by SYSU 80cm infrared telescope
  57. GRB 260421B: EP-FXT follow-up observation
  58. The EP-WXT trigger 01709260362 is likely a flaring star
  59. GOTO26djh/AT2026jpw: ATCA radio detection
  60. GRB 260421B: J-band upper limit with WINTER
  61. GRB 260421B: LCO optical counterpart detection
  62. GRB 260421B: Fermi GBM Observation
  63. Fermi Gamma-ray Burst Monitor trigger 798482368/260421694 is not a GRB
  64. GRB 260421A: AstroSat CZTI detection
  65. GOTO26djh/AT2026jpw: radio detection at 15GHz
  66. GRB 260412A: SVOM/ECLAIRs refined analysis
  67. GRB 260421B: SVOM/VT optical observations
  68. EP260416a: J band upper limit by SYSU 80cm infrared telescope
  69. GRB 260310A: Late-time Chandra X-ray Detection
  70. GRB 260418A: Insight-HXMT/HE detection
  71. EP260416a: 1.3m DFOT optical observation
  72. GRB 260415A: CALET Gamma-Ray Burst Monitor detection
  73. GRB 260415B: CALET Gamma-Ray Burst Monitor detection
  74. Fermi GRB 260421C: Global MASTER-Net observations report
  75. GRB 260421C: Fermi GBM Final Real-time Localization
  76. GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
  77. Fermi GRB 260421B: Global MASTER-Net observations report
  78. GRB 260421B: BOOTES-7 early optical afterglow detection
  79. GRB 260421B: LCO optical afterglow confirmation
  80. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  81. GRB 260421B: TRT optical counterpart detection
  82. GRB 260421B: SVOM detection of a long burst
  83. GRB 260421B: BALROG localization (Fermi Trigger 798437606 / GRB 260421176)
  84. GRB 260421B: Fermi GBM Final Real-time Localization
  85. Fermi GRB 260421A: Global MASTER-Net observations report
  86. GRB 260421A: Fermi GBM Final Real-time Localization
  87. EP260321a: VLA radio follow-up
  88. GRB 260412A: LCOGT Optical Upper Limits
  89. The EP-WXT trigger 01709260314 is likely a flaring star
  90. EP260416a: Optical follow-up observations with Kinder
  91. GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient
  92. EP-WXT trigger 01709260303: KAIT optical observations
  93. EP260416a: 1.5m OSN and 2.2m CAHA optical monitoring
  94. The EP-WXT trigger 01709260303 is likely a flaring star
  95. GRB 260417A: SVOM/GRM observation
  96. EP260321A/AT2026gzf: Optical observation from 1.3m DFOT
  97. GRB 260419B: Fermi GBM Final Real-time Localization
  98. GRB 260419A: Fermi GBM Final Real-time Localization
  99. Fermi trigger No 798275385: Global MASTER-Net observations report
  100. EP260417a: GROWTH-India Telescope optical upper limit

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