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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 260120B: Fermi GBM Observation
  2. EP260105a: GTC/HiPERCAM optical observations
  3. GRB 260120B: Swift/UVOT Detection
  4. GRB 260120B: COLIBRÍ optical upper limits
  5. SVOM GRB260121.06: Global MASTER-Net observations report
  6. GRB 260120B: Enhanced Swift-XRT position
  7. GRB 260120B: SVOM/C-GFT optical counterpart detection
  8. GRB 260120C: Fermi GBM Final Real-time Localization
  9. GRB 260101A: 239Alferov CubeSat detection
  10. EP260116a: COLIBRÍ observations of a tentative optical rebrightening
  11. GRB 260120B: Swift detection of a burst
  12. Swift GRB260120B: Global MASTER-Net observations report
  13. GRB 260120B: Fermi GBM Final Real-time Localization
  14. EP260119A: Mondy I-Band Observations
  15. Fermi trigger No 790601190: Global MASTER-Net observations report
  16. Fermi trigger No 790570272: Global MASTER-Net observations report
  17. GRB 260114A: Swift/UVOT Upper Limits
  18. EP260119a: Liverpool Telescope optical follow-up observations
  19. GRB 251202A: further radio observations with the VLA
  20. Trigger 1442421: Swift detection of HMXB 1A 1118-61
  21. EP260119A: GTC/OSIRIS+ spectroscopic redshift z = 5.47
  22. EP260119a: KAIT optical observations
  23. GRB 260120A: Fermi GBM Final Real-time Localization
  24. EP260119a: SVOM/VT optical observation
  25. EP260119a: update of EP-FXT follow-up observation
  26. EP260119a: NOT optical observations
  27. EP260119a: SAO RAS optical observations
  28. SVOM GRB260119.92: Global MASTER-Net observations report
  29. SVOM GRB260119.92: Global MASTER-Net observations report
  30. SVOM GRB260119.90: Global MASTER-Net observations report
  31. EP260116a: COLIBRÍ detection of a fading optical source
  32. GRB 251208D: SVOM/ECLAIRs refined analysis
  33. GRB 251208D: SVOM/ECLAIRs refined analysis
  34. GRB 260117A: Swift-XRT afterglow detection
  35. EP260119a: COLIBRÍ photometric redshift z ≈ 5.6
  36. EP260119a: Global MASTER-Net observations report
  37. GRB 260115A: AstroSat CZTI detection
  38. EP260119a: LCO optical observations
  39. GRB 260117A: ZTSh optical upper limit
  40. EP260119a: COLIBRÍ optical counterpart candidate
  41. EP260119a: preliminary result from the EP-FXT observation
  42. GRB 260110A: SVOM detection of a burst through offline search
  43. EP260119a: EP-WXT detection of a fast X-ray transient
  44. Swift GRB260118.48: Global MASTER-Net observations report
  45. GRB 260117A: SVOM/COLIBRÍ (FM-GFT) optical observations
  46. SVOM GRB260117.82: Global MASTER-Net observations report
  47. Fermi-LAT Gamma-ray Observations of IceCube-260115A
  48. Swift trigger on the HMXB 1A 1118-61
  49. GRB 260117A: SVOM/VT optical candidate
  50. GRB 260117A: SVOM/C-GFT upper limit
  51. GRB 260117A: Swift-XRT observations
  52. GRB 260117A: Swift ToO observations
  53. GRB 260117A: SVOM detection of a long faint burst
  54. EP 260116a: COLIBRÍ optical upper limit
  55. Swift triggered on the HMXB 1A 1118-61
  56. GRB 260115A: GECAM-B observation
  57. FRB 20251229A: COLIBRÍ further inspection of the updated localization
  58. EP260116a: Liverpool Telescope upper limits
  59. FRB 20251229A: Updated CHIME/FRB Baseband Localization of FRB 20251229A
  60. EP260116A: 1.3m DFOT optical upper limit
  61. GRB 260114A: VLT/MUSE spectroscopic observations
  62. IceCube-260115A: Upper limits from a search for additional neutrino events in IceCube
  63. EP260116a: Global MASTER-Net observations report
  64. GRB 260111A: COLIBRÍ fading of the optical counterpart candidate
  65. EP260116a: Xinglong optical upper limit
  66. EP260116a: Einstein Probe detection of an X-ray transient
  67. GRB 260114A: VLT/HAWK-I further near-infrared upper limits
  68. IceCube Alert 260115.73: Global MASTER-Net observations report
  69. IceCube-260115A - IceCube observation of a high-energy neutrino candidate track-like event
  70. GRB 260115A: BALROG localization (Fermi Trigger 790192010 / GRB 260115741)
  71. IceCube: GCN Notices for high-energy track alerts now streamed via Kafka
  72. Fermi GRB 260115A: Global MASTER-Net observations report
  73. GRB 260115A: Fermi GBM Final Real-time Localization
  74. GRB260114A: STEP/T80S optical limits
  75. GRB 251222A: radio detection with the VLA
  76. GRB 260114A: VLT/HAWK-I near-infrared upper limits
  77. Konus-Wind detection of GRB 260114A
  78. GRB 260114A: Swift-XRT refined Analysis
  79. GRB 260114A: 6 GHz VLA observations
  80. GRB 260114A: VLT/X-shooter redshift of the putative host galaxy
  81. GRB 260114A : MITSuME Akeno optical upper limits
  82. GRB 260114A: COLIBRÍ optical upper limits
  83. GRB 260114A: TNG NIR upper limit
  84. GRB 260114A: NOT optical observations
  85. Konus-Wind detection of GRB 251230A / EP251230a
  86. GRB 260114A: SVOM/GRM observation of a short burst
  87. Swift GRB 260114A: Global MASTER-Net observations report
  88. GRB 260114A: GECAM-B observation of a short burst
  89. GRB 260114A: Mondy optical observations
  90. GRB 260114A: Fermi GBM observation
  91. GRB 260112B: GECAM-B observation
  92. GRB 260114A: GMG Optical Observation
  93. Fermi-LAT Gamma-ray Observations of IceCube-260111A
  94. GRB 260114A: Swift detection of a short burst
  95. GRB 260114A: Fermi GBM Final Real-time Localization
  96. EP-WXT trigger 01709251266: SVOM/C-GFT confirmation of a stellar flare
  97. IceCube-260111A: Upper limits from a search for additional neutrino events in IceCube
  98. Swift GRB260113.43: Global MASTER-Net observations report
  99. EP260110a: NOT and GTC Optical and Near-Infrared Observations
  100. EP260110a: TRT optical upper limits

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