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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. LIGO/Virgo/KAGRA S250904cv: Updated Sky localization
  2. LIGO/Virgo/KAGRA S250904br: Updated Sky localization
  3. EP detected a brightening of LMXB 1ES 1735-26.9
  4. GRB 250905A: KAIT optical upper limit
  5. GRB 250905A: Swift detection of a burst
  6. Swift GRB250905.09: Global MASTER-Net observations report
  7. Swift GRB 250904A: Global MASTER-Net observations report
  8. GRB 250904A: Enhanced Swift-XRT position
  9. IceCube-Cascade 250903A: Upper limits from a search for additional neutrino events in IceCube
  10. GRB 250904A: TRT optical counterpart detection
  11. EP250827a and EP250827b: Upper limit from Fermi-GBM Observations
  12. GRB 250902B: CALET Gamma-Ray Burst Monitor detection
  13. GRB 250904A: Prompt enhanced Swift-XRT position
  14. EP250827b: Gemini Spectroscopic Confirmation of AT2025wkm as a Ic-BL Supernova
  15. GRB 250904A: Swift detection of a burst
  16. GRB 250902A: CALET Gamma-Ray Burst Monitor detection
  17. LIGO/Virgo/KAGRA S250904ae: Updated Sky localization
  18. GRB 250902A: VZLUSAT-2 detection
  19. LIGO/Virgo/KAGRA S250904cv: Identification of a GW compact binary merger candidate
  20. GRB 250903A: Swift-XRT observations
  21. EP250903a: Swift-XRT observations
  22. EP#01709201209: Swift-XRT observations
  23. EP250903a: retraction of the LCO candidate, and discovery of the likely counterpart
  24. EP-WXT trigger 01709201209: Liverpool Telescope upper limits
  25. GRB 250830C: VZLUSAT-2 detection
  26. EP250903a: refined analysis of the EP-WXT and EP-FXT observations
  27. LIGO/Virgo/KAGRA S250904br: Identification of a GW compact binary merger candidate
  28. GRB 250903A: VLT X-shooter spectroscopic redshift z = 1.590
  29. The EP-WXT trigger 01709201209 is likely a flaring star
  30. LIGO/Virgo/KAGRA S250904ae: Identification of a GW compact binary merger candidate
  31. GRB 250903A: EP-FXT counterpart detection
  32. GRB 250902A: GECAM-B detection
  33. GRB 250903A: LCO optical observation
  34. GRB 250903A: LCO optical afterglow detection
  35. GRB 250903A: SVOM/VT optical confirmation with VHF data
  36. EP250903a: SVOM/VT optical confirmation
  37. EP250901a: Mondy, Assy and SAO RAS optical limits
  38. Subject GRB 250903A: SVOM/MXT afterglow detection
  39. EP250903a: LCO candidate counterpart discovery
  40. GRB 250903A: TRT optical counterpart detection
  41. GRB 250902B: AstroSat CZTI detection
  42. GRB 250903A: SVOM detection of a burst
  43. EP250903a: Global MASTER-Net observations report
  44. EP250903a: TRT optical observations
  45. EP250903a: Einstein Probe detection of an X-ray transient
  46. EP 250827B: Detection of supernova counterpart by LCO.
  47. EP/WXT01709201159: GOTO optical follow-up
  48. EP250827b / AT 2025wkm: TRT optical observations
  49. EP250827b: NOT spectroscopic observations and AT 2025wkm classification as a broad-lined type-Ic supernova
  50. EP250827b: continued Liverpool Telescope observations
  51. GRB 250902B: SVOM/GRM observation
  52. EP250827b: SVOM/VT observation of AT 2025wkm
  53. LIGO/VIRGO/KAGRA S250818k: No evidence for radio variability of AT2025ulz in MeerKAT 3 GHz data
  54. GRB 250831A (SVOM trigger sb25083102): KAIT confirmation of stellar flare
  55. Fermi GRB 250902B: Global MASTER-Net observations report
  56. Fermi-LAT Gamma-ray Observations of IceCube-250831A
  57. GRB 250902A: Fermi GBM Detection
  58. GRB 250901A: Swift/UVOT Upper Limit
  59. GRB 250902B: Fermi GBM Final Real-time Localization
  60. IceCube-250831A: Upper limits from a search for additional neutrino events in IceCube
  61. GRB 250830B: Swift-XRT afterglow detection
  62. LIGO/Virgo/KAGRA S250902av: 1 counterpart neutrino candidate event from an IceCube neutrino search
  63. LIGO/Virgo/KAGRA S250901cb: Updated Sky localization
  64. EP250827b: Liverpool Telescope observations
  65. GRB 250831A (SVOM trigger sb25083102): confirmation of a stellar flare by SVOM/VT
  66. GRB 250902A: SVOM/GRM observation
  67. EP250828a: Early near-infrared follow-up with MIRAGE on the MDM 1.3m telescope
  68. EP250901a: refined analysis of the EP-WXT and EP-FXT observations
  69. GRB 250901A: EP-FXT follow-up observation
  70. GRB 250901A: NOT optical observations
  71. GRB 250902A: Fermi GBM Final Real-time Localization
  72. IceCube-Cascade 250828A: Upper limits from a search for additional neutrino events in IceCube
  73. GRB 250901A: SVOM/VT optical afterglow with VHF data
  74. GRB 250901A: Swift-XRT afterglow detection
  75. EP250901a: Swift-XRT observations
  76. LIGO/Virgo/KAGRA S250830bp: DECam GW-MMADS candidates
  77. GRB 250901A: LCO optical upper limit
  78. EP250827b: Swift observations of AT 2025wkm
  79. LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 1 Candidates
  80. EP250827b: Gemini Spectroscopy of AT 2025wkm
  81. LIGO/Virgo/KAGRA S250901cb: Identification of a GW compact binary merger candidate
  82. EP250831a: NOT optical observations and tentative afterglow candidate
  83. EP250827b: FTW Observations of AT 2025wkm
  84. EP250827b: Contemporaneous detection of EP X-ray flare EP250827b and ZTF transient ZTF25abmpngy/AT2025wkm
  85. GRB 250901A: SVOM detection of a burst
  86. GRB 250831B: SVOM/GRM observation
  87. GRB 250830C: Insight-HXMT detection
  88. EP250901a: Mephisto optical upper limits
  89. GRB 250830C: GECAM-B detection
  90. EP250901a: Global MASTER-Net observations report
  91. GRB 250830C: AstroSat CZTI detection of a long burst
  92. EP250901a: Einstein Probe detection of an X-ray transient
  93. LIGO/Virgo/KAGRA S250830m: Updated Sky localization
  94. EP250831a: EP-FXT follow-up observation
  95. EP250831a: Swift-XRT observations
  96. LIGO/Virgo/KAGRA S250831cc: Coverage and upper limits from MAXI/GSC observations
  97. IceCube Alert 250831.75: Global MASTER-Net observations report
  98. EP250831a: Global MASTER-Net observations report
  99. IceCube-250831A - IceCube observation of a high-energy neutrino candidate track-like event
  100. EP250831a: EP-WXT detection of a fast X-ray transient

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