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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"

32494 results found.

  1. GRB 250909B: Insight-HXMT detection
  2. GRB 250909B: SVOM/GRM observation
  3. LIGO/Virgo/KAGRA S250911ac: Updated Sky localization and Source Classification
  4. GRB 250910A / EP250910a : VLT/HAWK-I NIR counterpart discovery
  5. EP250911a: COLIBRÍ optical observations
  6. LIGO/Virgo/KAGRA S250908y: Updated Sky localization
  7. Fermi GRB 250910B: Global MASTER-Net observations report
  8. EP250911a: LCO optical counterpart discovery
  9. EP250910a: Global MASTER-Net observations report
  10. GRB 250404A / EP250404a: spectroscopic redshift at z = 1.88 (correction to GCN 40084)
  11. LIGO/Virgo/KAGRA S250911ac: Identification of a GW compact binary merger candidate
  12. GRB 250903A: SVOM/ECLAIRs refined analysis
  13. GRB 250911A: COLIBRÍ optical counterpart candidate
  14. LIGO/Virgo/KAGRA S250906ca: Updated Sky localization
  15. GRB 250910A / EP250910a: VLT/HAWK-I near-infrared observations
  16. EP250910a/GRB 250910A: EP-WXT detection of a fast X-ray transient
  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 250702B: Late time Chandra observations
  23. EP250908b/EP#01709240653: Swift/UVOT Detection
  24. EP250908c: refined analysis of the EP-WXT and EP-FXT observations
  25. GRB 250907A: CALET Gamma-Ray Burst Monitor detection
  26. EP250908c: SVOM/VT optical observation
  27. EP250908c: VLT/FORS2 optical counterpart identification
  28. EP250908b: SVOM/VT optical candidate (Coordinate supplement for GCN 41758)
  29. EP250908b: SVOM/VT optical candidate
  30. EP250908c: Global MASTER-Net observations report
  31. Fermi GRB 250909A: Global MASTER-Net observations report
  32. LIGO/Virgo/KAGRA S250908y: Identification of a GW compact binary merger candidate
  33. GRB 250905A: Swift-BAT refined analysis
  34. Fermi-LAT Gamma-ray Observations of IceCube-250905A
  35. GRB 250903A: Swift-XRT afterglow detection
  36. LIGO/Virgo/KAGRA S250906ca: Identification of a GW compact binary merger candidate
  37. IceCube-250905A: Upper limits from a search for additional neutrino events in IceCube
  38. EP250905a: Liverpool Telescope i-band upper limits
  39. LIGO/Virgo/KAGRA S250830bp: DECam/SOAR GW-MMADS updates
  40. EP250905b: EP-FXT follow-up observation
  41. LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 2 Candidates
  42. EP250905a: Liverpool Telescope observations
  43. EP250905a: refined analysis of the EP-WXT and EP-FXT observations
  44. EP250905b: Global MASTER-Net observations report
  45. EP250905a: FTW one optical and multiple NIR counterpart candidates
  46. EP250905a: JinShan likely optical counterpart detection
  47. GRB 250904A: Swift-BAT refined analysis
  48. GRB 250905A: Swift/UVOT Upper Limits
  49. EP250905a: Global MASTER-Net observations report
  50. GRB 250901A - SVOM/ECLAIRs refined analysis
  51. GRB250904A: Liverpool Telescope upper limits
  52. GRB 250904A: Swift/UVOT Detection
  53. GRB 250903A: Swift/UVOT detection
  54. LIGO/Virgo/KAGRA S250904cv: Updated Sky localization
  55. LIGO/Virgo/KAGRA S250904br: Updated Sky localization
  56. GRB 250905A: KAIT optical upper limit
  57. Swift GRB 250904A: Global MASTER-Net observations report
  58. GRB 250904A: TRT optical counterpart detection
  59. EP250827a and EP250827b: Upper limit from Fermi-GBM Observations
  60. GRB 250902B: CALET Gamma-Ray Burst Monitor detection
  61. EP250827b: Gemini Spectroscopic Confirmation of AT2025wkm as a Ic-BL Supernova
  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. LIGO/Virgo/KAGRA S250904ae: Identification of a GW compact binary merger candidate
  76. GRB 250903A: EP-FXT counterpart detection
  77. GRB 250902A: GECAM-B detection
  78. GRB 250903A: LCO optical observation
  79. GRB 250903A: LCO optical afterglow detection
  80. GRB 250903A: SVOM/VT optical confirmation with VHF data
  81. EP250903a: SVOM/VT optical confirmation
  82. EP250901a: Mondy, Assy and SAO RAS optical limits
  83. Subject GRB 250903A: SVOM/MXT afterglow detection
  84. EP250903a: LCO candidate counterpart discovery
  85. GRB 250903A: TRT optical counterpart detection
  86. GRB 250902B: AstroSat CZTI detection
  87. EP250903a: Global MASTER-Net observations report
  88. EP250903a: TRT optical observations
  89. EP250903a: Einstein Probe detection of an X-ray transient
  90. EP 250827B: Detection of supernova counterpart by LCO.
  91. EP250827b / AT 2025wkm: TRT optical observations
  92. EP250827b: NOT spectroscopic observations and AT 2025wkm classification as a broad-lined type-Ic supernova
  93. EP250827b: continued Liverpool Telescope observations
  94. GRB 250902B: SVOM/GRM observation
  95. EP250827b: SVOM/VT observation of AT 2025wkm
  96. LIGO/VIRGO/KAGRA S250818k: No evidence for radio variability of AT2025ulz in MeerKAT 3 GHz data
  97. GRB 250831A (SVOM trigger sb25083102): KAIT confirmation of stellar flare
  98. Fermi GRB 250902B: Global MASTER-Net observations report
  99. Fermi-LAT Gamma-ray Observations of IceCube-250831A
  100. GRB 250902A: Fermi GBM Detection

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