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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-BAT refined analysis
  2. EP250911a: GTC/OSIRIS+ spectroscopic redshift z = 3.84
  3. LIGO/Virgo/KAGRA S250912f: Identification of a GW compact binary merger candidate
  4. EP250911a: refined analysis of the EP-WXT and EP-FXT observations
  5. GRB 250910B: SVOM/GRM observation
  6. EP250911a: SVOM/VT optical observation
  7. GRB 250911A: MASTER optical counterpart observations
  8. EP250911a: SAO RAS optical observations
  9. GRB 250911A: Swift-XRT refined Analysis
  10. GRB 250910C: Fermi GBM Final Localization Correction
  11. EP250911a: Swift-XRT observations
  12. EP250911a: Optical detection with Kinder observations
  13. GRB 250911A: Swift/UVOT Detection
  14. GRB 250910A / EP250910a: Swift-XRT afterglow detection
  15. GRB 250910A / EP250910a: SVOM/VT afterglow confirmation
  16. GRB 250909B: Insight-HXMT detection
  17. GRB 250909B: SVOM/GRM observation
  18. LIGO/Virgo/KAGRA S250911ac: Updated Sky localization and Source Classification
  19. GRB 250910A / EP250910a : VLT/HAWK-I NIR counterpart discovery
  20. EP250911a: COLIBRÍ optical observations
  21. LIGO/Virgo/KAGRA S250908y: Updated Sky localization
  22. Fermi GRB 250910B: Global MASTER-Net observations report
  23. EP250911a: LCO optical counterpart discovery
  24. EP250910a: Global MASTER-Net observations report
  25. EP250911a: Einstein Probe detection of an X-ray transient
  26. GRB 250404A / EP250404a: spectroscopic redshift at z = 1.88 (correction to GCN 40084)
  27. LIGO/Virgo/KAGRA S250911ac: Identification of a GW compact binary merger candidate
  28. GRB 250903A: SVOM/ECLAIRs refined analysis
  29. GRB 250911A: Enhanced Swift-XRT position
  30. GRB 250911A: Swift-XRT observations
  31. GRB 250911A: COLIBRÍ optical counterpart candidate
  32. GRB 250911A: Swift detection of a burst
  33. LIGO/Virgo/KAGRA S250906ca: Updated Sky localization
  34. GRB 250910B: BALROG localization (Fermi Trigger 779223130 / GRB 250910786)
  35. GRB 250910B: Fermi GBM Final Real-time Localization
  36. GRB 250910A / EP250910a: VLT/HAWK-I near-infrared observations
  37. EP250910a/GRB 250910A: EP-WXT detection of a fast X-ray transient
  38. GRB 250909B: AstroSat CZTI detection of a long burst
  39. GRB 250910A: SVOM/VT optical upper limit
  40. EP250908C: GROND observation of the fading optical counterpart
  41. GRB 250910A: LCO optical upper limit
  42. GRB 250909A: AstroSat CZTI detection
  43. GRB 250910A: SVOM/MXT possible afterglow detection
  44. GRB 250910A: SVOM detection of a faint burst
  45. LIGO/Virgo/KAGRA S250910b: Retraction of GW compact binary merger candidate
  46. GRB 250702B: Late time Chandra observations
  47. EP250908b/EP#01709240653: Swift/UVOT Detection
  48. EP#01709240653: Swift-XRT observations
  49. The EP-WXT trigger 01709240674 is triggered by the known source SS Cyg
  50. EP250908c: refined analysis of the EP-WXT and EP-FXT observations
  51. GRB 250907A: CALET Gamma-Ray Burst Monitor detection
  52. EP250908c: SVOM/VT optical observation
  53. EP250908c: VLT/FORS2 optical counterpart identification
  54. EP250908b: SVOM/VT optical candidate (Coordinate supplement for GCN 41758)
  55. EP250908b: SVOM/VT optical candidate
  56. The EP-WXT trigger EP250908a/01709240652 is not a real source
  57. EP250908c: Global MASTER-Net observations report
  58. Fermi GRB 250909A: Global MASTER-Net observations report
  59. EP250908c: Einstein Probe detection of an X-ray transient
  60. GRB 250909A: Fermi GBM Final Real-time Localization
  61. EP250908b: EP-WXT detection of a fast X-ray transient and EP-FXT observation
  62. EP#01709240652 (possibly EP250908a): FTW optical and NIR observations
  63. LIGO/Virgo/KAGRA S250908y: Identification of a GW compact binary merger candidate
  64. GRB 250907A: GECAM-B detection
  65. GRB 250905A: Swift-BAT refined analysis
  66. Fermi-LAT Gamma-ray Observations of IceCube-250905A
  67. GRB 250903A: Swift-XRT afterglow detection
  68. LIGO/Virgo/KAGRA S250906ca: Identification of a GW compact binary merger candidate
  69. IceCube-250905A: Upper limits from a search for additional neutrino events in IceCube
  70. SVOM/sb25090605: detection of an X-ray transient from the LMXB 4U 0513-40
  71. EP250905a: Liverpool Telescope i-band upper limits
  72. LIGO/Virgo/KAGRA S250830bp: DECam/SOAR GW-MMADS updates
  73. EP250905b: EP-FXT follow-up observation
  74. LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 2 Candidates
  75. EP250905a: Liverpool Telescope observations
  76. EP250905a: refined analysis of the EP-WXT and EP-FXT observations
  77. EP250905b: Global MASTER-Net observations report
  78. EP250905b: EP-WXT detection of a fast X-ray transient
  79. EP250905a: FTW one optical and multiple NIR counterpart candidates
  80. GRB 250905A: Swift-XRT refined Analysis
  81. EP250905a: JinShan likely optical counterpart detection
  82. IceCube-250905A - IceCube observation of a high-energy neutrino candidate track-like event
  83. GRB 250904A: Swift-BAT refined analysis
  84. IceCube Alert 250905.84: Global MASTER-Net observations report
  85. GRB 250905A: Swift/UVOT Upper Limits
  86. EP250905a: Global MASTER-Net observations report
  87. GRB 250901A - SVOM/ECLAIRs refined analysis
  88. EP250905a: Einstein Probe detection of an X-ray transient
  89. GRB 250905B: Fermi GBM Final Localization
  90. GRB250904A: Liverpool Telescope upper limits
  91. GRB 250905A: Enhanced Swift-XRT position
  92. GRB 250904A: Swift/UVOT Detection
  93. GRB 250903A: Swift/UVOT detection
  94. GRB 250904A: Swift-XRT refined Analysis
  95. LIGO/Virgo/KAGRA S250904cv: Updated Sky localization
  96. LIGO/Virgo/KAGRA S250904br: Updated Sky localization
  97. EP detected a brightening of LMXB 1ES 1735-26.9
  98. GRB 250905A: KAIT optical upper limit
  99. GRB 250905A: Swift detection of a burst
  100. Swift GRB250905.09: Global MASTER-Net observations report

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