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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. EP250911a: LCO optical counterpart discovery
  2. EP250910a: Global MASTER-Net observations report
  3. EP250911a: Einstein Probe detection of an X-ray transient
  4. GRB 250404A / EP250404a: spectroscopic redshift at z = 1.88 (correction to GCN 40084)
  5. LIGO/Virgo/KAGRA S250911ac: Identification of a GW compact binary merger candidate
  6. GRB 250903A: SVOM/ECLAIRs refined analysis
  7. GRB 250911A: Enhanced Swift-XRT position
  8. GRB 250911A: Swift-XRT observations
  9. GRB 250911A: COLIBRÍ optical counterpart candidate
  10. GRB 250911A: Swift detection of a burst
  11. LIGO/Virgo/KAGRA S250906ca: Updated Sky localization
  12. GRB 250910B: BALROG localization (Fermi Trigger 779223130 / GRB 250910786)
  13. GRB 250910B: Fermi GBM Final Real-time Localization
  14. GRB 250910A / EP250910a: VLT/HAWK-I near-infrared observations
  15. EP250910a/GRB 250910A: EP-WXT detection of a fast X-ray transient
  16. GRB 250909B: AstroSat CZTI detection of a long burst
  17. GRB 250910A: SVOM/VT optical upper limit
  18. EP250908C: GROND observation of the fading optical counterpart
  19. GRB 250910A: LCO optical upper limit
  20. GRB 250909A: AstroSat CZTI detection
  21. GRB 250910A: SVOM/MXT possible afterglow detection
  22. GRB 250910A: SVOM detection of a faint burst
  23. LIGO/Virgo/KAGRA S250910b: Retraction of GW compact binary merger candidate
  24. GRB 250702B: Late time Chandra observations
  25. EP250908b/EP#01709240653: Swift/UVOT Detection
  26. EP#01709240653: Swift-XRT observations
  27. The EP-WXT trigger 01709240674 is triggered by the known source SS Cyg
  28. EP250908c: refined analysis of the EP-WXT and EP-FXT observations
  29. GRB 250907A: CALET Gamma-Ray Burst Monitor detection
  30. EP250908c: SVOM/VT optical observation
  31. EP250908c: VLT/FORS2 optical counterpart identification
  32. EP250908b: SVOM/VT optical candidate (Coordinate supplement for GCN 41758)
  33. EP250908b: SVOM/VT optical candidate
  34. The EP-WXT trigger EP250908a/01709240652 is not a real source
  35. EP250908c: Global MASTER-Net observations report
  36. Fermi GRB 250909A: Global MASTER-Net observations report
  37. EP250908c: Einstein Probe detection of an X-ray transient
  38. GRB 250909A: Fermi GBM Final Real-time Localization
  39. EP250908b: EP-WXT detection of a fast X-ray transient and EP-FXT observation
  40. EP#01709240652 (possibly EP250908a): FTW optical and NIR observations
  41. LIGO/Virgo/KAGRA S250908y: Identification of a GW compact binary merger candidate
  42. GRB 250907A: GECAM-B detection
  43. GRB 250905A: Swift-BAT refined analysis
  44. Fermi-LAT Gamma-ray Observations of IceCube-250905A
  45. GRB 250903A: Swift-XRT afterglow detection
  46. LIGO/Virgo/KAGRA S250906ca: Identification of a GW compact binary merger candidate
  47. IceCube-250905A: Upper limits from a search for additional neutrino events in IceCube
  48. SVOM/sb25090605: detection of an X-ray transient from the LMXB 4U 0513-40
  49. EP250905a: Liverpool Telescope i-band upper limits
  50. LIGO/Virgo/KAGRA S250830bp: DECam/SOAR GW-MMADS updates
  51. EP250905b: EP-FXT follow-up observation
  52. LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 2 Candidates
  53. EP250905a: Liverpool Telescope observations
  54. EP250905a: refined analysis of the EP-WXT and EP-FXT observations
  55. EP250905b: Global MASTER-Net observations report
  56. EP250905b: EP-WXT detection of a fast X-ray transient
  57. EP250905a: FTW one optical and multiple NIR counterpart candidates
  58. GRB 250905A: Swift-XRT refined Analysis
  59. EP250905a: JinShan likely optical counterpart detection
  60. IceCube-250905A - IceCube observation of a high-energy neutrino candidate track-like event
  61. GRB 250904A: Swift-BAT refined analysis
  62. IceCube Alert 250905.84: Global MASTER-Net observations report
  63. GRB 250905A: Swift/UVOT Upper Limits
  64. EP250905a: Global MASTER-Net observations report
  65. GRB 250901A - SVOM/ECLAIRs refined analysis
  66. EP250905a: Einstein Probe detection of an X-ray transient
  67. GRB 250905B: Fermi GBM Final Localization
  68. GRB250904A: Liverpool Telescope upper limits
  69. GRB 250905A: Enhanced Swift-XRT position
  70. GRB 250904A: Swift/UVOT Detection
  71. GRB 250903A: Swift/UVOT detection
  72. GRB 250904A: Swift-XRT refined Analysis
  73. LIGO/Virgo/KAGRA S250904cv: Updated Sky localization
  74. LIGO/Virgo/KAGRA S250904br: Updated Sky localization
  75. EP detected a brightening of LMXB 1ES 1735-26.9
  76. GRB 250905A: KAIT optical upper limit
  77. GRB 250905A: Swift detection of a burst
  78. Swift GRB250905.09: Global MASTER-Net observations report
  79. Swift GRB 250904A: Global MASTER-Net observations report
  80. GRB 250904A: Enhanced Swift-XRT position
  81. IceCube-Cascade 250903A: Upper limits from a search for additional neutrino events in IceCube
  82. GRB 250904A: TRT optical counterpart detection
  83. EP250827a and EP250827b: Upper limit from Fermi-GBM Observations
  84. GRB 250902B: CALET Gamma-Ray Burst Monitor detection
  85. GRB 250904A: Prompt enhanced Swift-XRT position
  86. EP250827b: Gemini Spectroscopic Confirmation of AT2025wkm as a Ic-BL Supernova
  87. GRB 250904A: Swift detection of a burst
  88. GRB 250902A: CALET Gamma-Ray Burst Monitor detection
  89. LIGO/Virgo/KAGRA S250904ae: Updated Sky localization
  90. GRB 250902A: VZLUSAT-2 detection
  91. LIGO/Virgo/KAGRA S250904cv: Identification of a GW compact binary merger candidate
  92. GRB 250903A: Swift-XRT observations
  93. EP250903a: Swift-XRT observations
  94. EP#01709201209: Swift-XRT observations
  95. EP250903a: retraction of the LCO candidate, and discovery of the likely counterpart
  96. EP-WXT trigger 01709201209: Liverpool Telescope upper limits
  97. GRB 250830C: VZLUSAT-2 detection
  98. EP250903a: refined analysis of the EP-WXT and EP-FXT observations
  99. LIGO/Virgo/KAGRA S250904br: Identification of a GW compact binary merger candidate
  100. GRB 250903A: VLT X-shooter spectroscopic redshift z = 1.590

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