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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. The EP-WXT trigger 01709240674 is triggered by the known source SS Cyg
  2. EP250908c: refined analysis of the EP-WXT and EP-FXT observations
  3. GRB 250907A: CALET Gamma-Ray Burst Monitor detection
  4. EP250908c: SVOM/VT optical observation
  5. EP250908c: VLT/FORS2 optical counterpart identification
  6. EP250908b: SVOM/VT optical candidate (Coordinate supplement for GCN 41758)
  7. EP250908b: SVOM/VT optical candidate
  8. The EP-WXT trigger EP250908a/01709240652 is not a real source
  9. EP250908c: Global MASTER-Net observations report
  10. Fermi GRB 250909A: Global MASTER-Net observations report
  11. EP250908c: Einstein Probe detection of an X-ray transient
  12. GRB 250909A: Fermi GBM Final Real-time Localization
  13. EP250908b: EP-WXT detection of a fast X-ray transient and EP-FXT observation
  14. EP#01709240652 (possibly EP250908a): FTW optical and NIR observations
  15. LIGO/Virgo/KAGRA S250908y: Identification of a GW compact binary merger candidate
  16. GRB 250907A: GECAM-B detection
  17. GRB 250905A: Swift-BAT refined analysis
  18. Fermi-LAT Gamma-ray Observations of IceCube-250905A
  19. GRB 250903A: Swift-XRT afterglow detection
  20. LIGO/Virgo/KAGRA S250906ca: Identification of a GW compact binary merger candidate
  21. IceCube-250905A: Upper limits from a search for additional neutrino events in IceCube
  22. SVOM/sb25090605: detection of an X-ray transient from the LMXB 4U 0513-40
  23. EP250905a: Liverpool Telescope i-band upper limits
  24. LIGO/Virgo/KAGRA S250830bp: DECam/SOAR GW-MMADS updates
  25. EP250905b: EP-FXT follow-up observation
  26. LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 2 Candidates
  27. EP250905a: Liverpool Telescope observations
  28. EP250905a: refined analysis of the EP-WXT and EP-FXT observations
  29. EP250905b: Global MASTER-Net observations report
  30. EP250905b: EP-WXT detection of a fast X-ray transient
  31. EP250905a: FTW one optical and multiple NIR counterpart candidates
  32. GRB 250905A: Swift-XRT refined Analysis
  33. EP250905a: JinShan likely optical counterpart detection
  34. IceCube-250905A - IceCube observation of a high-energy neutrino candidate track-like event
  35. GRB 250904A: Swift-BAT refined analysis
  36. IceCube Alert 250905.84: Global MASTER-Net observations report
  37. GRB 250905A: Swift/UVOT Upper Limits
  38. EP250905a: Global MASTER-Net observations report
  39. GRB 250901A - SVOM/ECLAIRs refined analysis
  40. EP250905a: Einstein Probe detection of an X-ray transient
  41. GRB 250905B: Fermi GBM Final Localization
  42. GRB250904A: Liverpool Telescope upper limits
  43. GRB 250905A: Enhanced Swift-XRT position
  44. GRB 250904A: Swift/UVOT Detection
  45. GRB 250903A: Swift/UVOT detection
  46. GRB 250904A: Swift-XRT refined Analysis
  47. LIGO/Virgo/KAGRA S250904cv: Updated Sky localization
  48. LIGO/Virgo/KAGRA S250904br: Updated Sky localization
  49. EP detected a brightening of LMXB 1ES 1735-26.9
  50. GRB 250905A: KAIT optical upper limit
  51. GRB 250905A: Swift detection of a burst
  52. Swift GRB250905.09: Global MASTER-Net observations report
  53. Swift GRB 250904A: Global MASTER-Net observations report
  54. GRB 250904A: Enhanced Swift-XRT position
  55. IceCube-Cascade 250903A: Upper limits from a search for additional neutrino events in IceCube
  56. GRB 250904A: TRT optical counterpart detection
  57. EP250827a and EP250827b: Upper limit from Fermi-GBM Observations
  58. GRB 250902B: CALET Gamma-Ray Burst Monitor detection
  59. GRB 250904A: Prompt enhanced Swift-XRT position
  60. EP250827b: Gemini Spectroscopic Confirmation of AT2025wkm as a Ic-BL Supernova
  61. GRB 250904A: Swift detection of a burst
  62. GRB 250902A: CALET Gamma-Ray Burst Monitor detection
  63. LIGO/Virgo/KAGRA S250904ae: Updated Sky localization
  64. GRB 250902A: VZLUSAT-2 detection
  65. LIGO/Virgo/KAGRA S250904cv: Identification of a GW compact binary merger candidate
  66. GRB 250903A: Swift-XRT observations
  67. EP250903a: Swift-XRT observations
  68. EP#01709201209: Swift-XRT observations
  69. EP250903a: retraction of the LCO candidate, and discovery of the likely counterpart
  70. EP-WXT trigger 01709201209: Liverpool Telescope upper limits
  71. GRB 250830C: VZLUSAT-2 detection
  72. EP250903a: refined analysis of the EP-WXT and EP-FXT observations
  73. LIGO/Virgo/KAGRA S250904br: Identification of a GW compact binary merger candidate
  74. GRB 250903A: VLT X-shooter spectroscopic redshift z = 1.590
  75. The EP-WXT trigger 01709201209 is likely a flaring star
  76. LIGO/Virgo/KAGRA S250904ae: Identification of a GW compact binary merger candidate
  77. GRB 250903A: EP-FXT counterpart detection
  78. GRB 250902A: GECAM-B detection
  79. GRB 250903A: LCO optical observation
  80. GRB 250903A: LCO optical afterglow detection
  81. GRB 250903A: SVOM/VT optical confirmation with VHF data
  82. EP250903a: SVOM/VT optical confirmation
  83. EP250901a: Mondy, Assy and SAO RAS optical limits
  84. Subject GRB 250903A: SVOM/MXT afterglow detection
  85. EP250903a: LCO candidate counterpart discovery
  86. GRB 250903A: TRT optical counterpart detection
  87. GRB 250902B: AstroSat CZTI detection
  88. GRB 250903A: SVOM detection of a burst
  89. EP250903a: Global MASTER-Net observations report
  90. EP250903a: TRT optical observations
  91. EP250903a: Einstein Probe detection of an X-ray transient
  92. EP 250827B: Detection of supernova counterpart by LCO.
  93. EP/WXT01709201159: GOTO optical follow-up
  94. EP250827b / AT 2025wkm: TRT optical observations
  95. EP250827b: NOT spectroscopic observations and AT 2025wkm classification as a broad-lined type-Ic supernova
  96. EP250827b: continued Liverpool Telescope observations
  97. GRB 250902B: SVOM/GRM observation
  98. EP250827b: SVOM/VT observation of AT 2025wkm
  99. LIGO/VIRGO/KAGRA S250818k: No evidence for radio variability of AT2025ulz in MeerKAT 3 GHz data
  100. GRB 250831A (SVOM trigger sb25083102): KAIT confirmation of stellar flare

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