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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. Swift GRB 250904A: Global MASTER-Net observations report
  2. GRB 250904A: Enhanced Swift-XRT position
  3. IceCube-Cascade 250903A: Upper limits from a search for additional neutrino events in IceCube
  4. GRB 250904A: TRT optical counterpart detection
  5. EP250827a and EP250827b: Upper limit from Fermi-GBM Observations
  6. GRB 250902B: CALET Gamma-Ray Burst Monitor detection
  7. GRB 250904A: Prompt enhanced Swift-XRT position
  8. EP250827b: Gemini Spectroscopic Confirmation of AT2025wkm as a Ic-BL Supernova
  9. GRB 250904A: Swift detection of a burst
  10. GRB 250902A: CALET Gamma-Ray Burst Monitor detection
  11. LIGO/Virgo/KAGRA S250904ae: Updated Sky localization
  12. GRB 250902A: VZLUSAT-2 detection
  13. LIGO/Virgo/KAGRA S250904cv: Identification of a GW compact binary merger candidate
  14. GRB 250903A: Swift-XRT observations
  15. EP250903a: Swift-XRT observations
  16. EP#01709201209: Swift-XRT observations
  17. EP250903a: retraction of the LCO candidate, and discovery of the likely counterpart
  18. EP-WXT trigger 01709201209: Liverpool Telescope upper limits
  19. GRB 250830C: VZLUSAT-2 detection
  20. EP250903a: refined analysis of the EP-WXT and EP-FXT observations
  21. LIGO/Virgo/KAGRA S250904br: Identification of a GW compact binary merger candidate
  22. GRB 250903A: VLT X-shooter spectroscopic redshift z = 1.590
  23. The EP-WXT trigger 01709201209 is likely a flaring star
  24. LIGO/Virgo/KAGRA S250904ae: Identification of a GW compact binary merger candidate
  25. GRB 250903A: EP-FXT counterpart detection
  26. GRB 250902A: GECAM-B detection
  27. GRB 250903A: LCO optical observation
  28. GRB 250903A: LCO optical afterglow detection
  29. GRB 250903A: SVOM/VT optical confirmation with VHF data
  30. EP250903a: SVOM/VT optical confirmation
  31. EP250901a: Mondy, Assy and SAO RAS optical limits
  32. Subject GRB 250903A: SVOM/MXT afterglow detection
  33. EP250903a: LCO candidate counterpart discovery
  34. GRB 250903A: TRT optical counterpart detection
  35. GRB 250902B: AstroSat CZTI detection
  36. GRB 250903A: SVOM detection of a burst
  37. EP250903a: Global MASTER-Net observations report
  38. EP250903a: TRT optical observations
  39. EP250903a: Einstein Probe detection of an X-ray transient
  40. EP 250827B: Detection of supernova counterpart by LCO.
  41. EP/WXT01709201159: GOTO optical follow-up
  42. EP250827b / AT 2025wkm: TRT optical observations
  43. EP250827b: NOT spectroscopic observations and AT 2025wkm classification as a broad-lined type-Ic supernova
  44. EP250827b: continued Liverpool Telescope observations
  45. GRB 250902B: SVOM/GRM observation
  46. EP250827b: SVOM/VT observation of AT 2025wkm
  47. LIGO/VIRGO/KAGRA S250818k: No evidence for radio variability of AT2025ulz in MeerKAT 3 GHz data
  48. GRB 250831A (SVOM trigger sb25083102): KAIT confirmation of stellar flare
  49. Fermi GRB 250902B: Global MASTER-Net observations report
  50. Fermi-LAT Gamma-ray Observations of IceCube-250831A
  51. GRB 250902A: Fermi GBM Detection
  52. GRB 250901A: Swift/UVOT Upper Limit
  53. GRB 250902B: Fermi GBM Final Real-time Localization
  54. IceCube-250831A: Upper limits from a search for additional neutrino events in IceCube
  55. GRB 250830B: Swift-XRT afterglow detection
  56. LIGO/Virgo/KAGRA S250902av: 1 counterpart neutrino candidate event from an IceCube neutrino search
  57. LIGO/Virgo/KAGRA S250901cb: Updated Sky localization
  58. EP250827b: Liverpool Telescope observations
  59. GRB 250831A (SVOM trigger sb25083102): confirmation of a stellar flare by SVOM/VT
  60. GRB 250902A: SVOM/GRM observation
  61. EP250828a: Early near-infrared follow-up with MIRAGE on the MDM 1.3m telescope
  62. EP250901a: refined analysis of the EP-WXT and EP-FXT observations
  63. GRB 250901A: EP-FXT follow-up observation
  64. GRB 250901A: NOT optical observations
  65. GRB 250902A: Fermi GBM Final Real-time Localization
  66. IceCube-Cascade 250828A: Upper limits from a search for additional neutrino events in IceCube
  67. GRB 250901A: SVOM/VT optical afterglow with VHF data
  68. GRB 250901A: Swift-XRT afterglow detection
  69. EP250901a: Swift-XRT observations
  70. LIGO/Virgo/KAGRA S250830bp: DECam GW-MMADS candidates
  71. GRB 250901A: LCO optical upper limit
  72. EP250827b: Swift observations of AT 2025wkm
  73. LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 1 Candidates
  74. EP250827b: Gemini Spectroscopy of AT 2025wkm
  75. LIGO/Virgo/KAGRA S250901cb: Identification of a GW compact binary merger candidate
  76. EP250831a: NOT optical observations and tentative afterglow candidate
  77. EP250827b: FTW Observations of AT 2025wkm
  78. EP250827b: Contemporaneous detection of EP X-ray flare EP250827b and ZTF transient ZTF25abmpngy/AT2025wkm
  79. GRB 250901A: SVOM detection of a burst
  80. GRB 250831B: SVOM/GRM observation
  81. GRB 250830C: Insight-HXMT detection
  82. EP250901a: Mephisto optical upper limits
  83. GRB 250830C: GECAM-B detection
  84. EP250901a: Global MASTER-Net observations report
  85. GRB 250830C: AstroSat CZTI detection of a long burst
  86. EP250901a: Einstein Probe detection of an X-ray transient
  87. LIGO/Virgo/KAGRA S250830m: Updated Sky localization
  88. EP250831a: EP-FXT follow-up observation
  89. EP250831a: Swift-XRT observations
  90. LIGO/Virgo/KAGRA S250831cc: Coverage and upper limits from MAXI/GSC observations
  91. IceCube Alert 250831.75: Global MASTER-Net observations report
  92. EP250831a: Global MASTER-Net observations report
  93. IceCube-250831A - IceCube observation of a high-energy neutrino candidate track-like event
  94. EP250831a: EP-WXT detection of a fast X-ray transient
  95. GRB 250831A (SVOM trigger sb25083102) is likely an outburst from star G 272-61
  96. GRB 250831A: Swift-XRT counterpart detection
  97. GRB 250831A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  98. GRB 250831A: SVOM/VT upper limit with VHF data
  99. GRB 250831A: SVOM detection of a soft burst
  100. GRB 250830B: Swift-XRT observations

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