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

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