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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. EP250827a and EP250827b: Upper limit from Fermi-GBM Observations
  2. GRB 250902B: CALET Gamma-Ray Burst Monitor detection
  3. GRB 250904A: Prompt enhanced Swift-XRT position
  4. EP250827b: Gemini Spectroscopic Confirmation of AT2025wkm as a Ic-BL Supernova
  5. GRB 250904A: Swift detection of a burst
  6. GRB 250902A: CALET Gamma-Ray Burst Monitor detection
  7. LIGO/Virgo/KAGRA S250904ae: Updated Sky localization
  8. GRB 250902A: VZLUSAT-2 detection
  9. LIGO/Virgo/KAGRA S250904cv: Identification of a GW compact binary merger candidate
  10. GRB 250903A: Swift-XRT observations
  11. EP250903a: Swift-XRT observations
  12. EP#01709201209: Swift-XRT observations
  13. EP250903a: retraction of the LCO candidate, and discovery of the likely counterpart
  14. EP-WXT trigger 01709201209: Liverpool Telescope upper limits
  15. GRB 250830C: VZLUSAT-2 detection
  16. EP250903a: refined analysis of the EP-WXT and EP-FXT observations
  17. LIGO/Virgo/KAGRA S250904br: Identification of a GW compact binary merger candidate
  18. GRB 250903A: VLT X-shooter spectroscopic redshift z = 1.590
  19. The EP-WXT trigger 01709201209 is likely a flaring star
  20. LIGO/Virgo/KAGRA S250904ae: Identification of a GW compact binary merger candidate
  21. GRB 250903A: EP-FXT counterpart detection
  22. GRB 250902A: GECAM-B detection
  23. GRB 250903A: LCO optical observation
  24. GRB 250903A: LCO optical afterglow detection
  25. GRB 250903A: SVOM/VT optical confirmation with VHF data
  26. EP250903a: SVOM/VT optical confirmation
  27. EP250901a: Mondy, Assy and SAO RAS optical limits
  28. Subject GRB 250903A: SVOM/MXT afterglow detection
  29. EP250903a: LCO candidate counterpart discovery
  30. GRB 250903A: TRT optical counterpart detection
  31. GRB 250902B: AstroSat CZTI detection
  32. GRB 250903A: SVOM detection of a burst
  33. EP250903a: Global MASTER-Net observations report
  34. EP250903a: TRT optical observations
  35. EP250903a: Einstein Probe detection of an X-ray transient
  36. EP 250827B: Detection of supernova counterpart by LCO.
  37. EP/WXT01709201159: GOTO optical follow-up
  38. EP250827b / AT 2025wkm: TRT optical observations
  39. EP250827b: NOT spectroscopic observations and AT 2025wkm classification as a broad-lined type-Ic supernova
  40. EP250827b: continued Liverpool Telescope observations
  41. GRB 250902B: SVOM/GRM observation
  42. EP250827b: SVOM/VT observation of AT 2025wkm
  43. LIGO/VIRGO/KAGRA S250818k: No evidence for radio variability of AT2025ulz in MeerKAT 3 GHz data
  44. GRB 250831A (SVOM trigger sb25083102): KAIT confirmation of stellar flare
  45. Fermi GRB 250902B: Global MASTER-Net observations report
  46. Fermi-LAT Gamma-ray Observations of IceCube-250831A
  47. GRB 250902A: Fermi GBM Detection
  48. GRB 250901A: Swift/UVOT Upper Limit
  49. GRB 250902B: Fermi GBM Final Real-time Localization
  50. IceCube-250831A: Upper limits from a search for additional neutrino events in IceCube
  51. GRB 250830B: Swift-XRT afterglow detection
  52. LIGO/Virgo/KAGRA S250902av: 1 counterpart neutrino candidate event from an IceCube neutrino search
  53. LIGO/Virgo/KAGRA S250901cb: Updated Sky localization
  54. EP250827b: Liverpool Telescope observations
  55. GRB 250831A (SVOM trigger sb25083102): confirmation of a stellar flare by SVOM/VT
  56. GRB 250902A: SVOM/GRM observation
  57. EP250828a: Early near-infrared follow-up with MIRAGE on the MDM 1.3m telescope
  58. EP250901a: refined analysis of the EP-WXT and EP-FXT observations
  59. GRB 250901A: EP-FXT follow-up observation
  60. GRB 250901A: NOT optical observations
  61. GRB 250902A: Fermi GBM Final Real-time Localization
  62. IceCube-Cascade 250828A: Upper limits from a search for additional neutrino events in IceCube
  63. GRB 250901A: SVOM/VT optical afterglow with VHF data
  64. GRB 250901A: Swift-XRT afterglow detection
  65. EP250901a: Swift-XRT observations
  66. LIGO/Virgo/KAGRA S250830bp: DECam GW-MMADS candidates
  67. GRB 250901A: LCO optical upper limit
  68. EP250827b: Swift observations of AT 2025wkm
  69. LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 1 Candidates
  70. EP250827b: Gemini Spectroscopy of AT 2025wkm
  71. LIGO/Virgo/KAGRA S250901cb: Identification of a GW compact binary merger candidate
  72. EP250831a: NOT optical observations and tentative afterglow candidate
  73. EP250827b: FTW Observations of AT 2025wkm
  74. EP250827b: Contemporaneous detection of EP X-ray flare EP250827b and ZTF transient ZTF25abmpngy/AT2025wkm
  75. GRB 250901A: SVOM detection of a burst
  76. GRB 250831B: SVOM/GRM observation
  77. GRB 250830C: Insight-HXMT detection
  78. EP250901a: Mephisto optical upper limits
  79. GRB 250830C: GECAM-B detection
  80. EP250901a: Global MASTER-Net observations report
  81. GRB 250830C: AstroSat CZTI detection of a long burst
  82. EP250901a: Einstein Probe detection of an X-ray transient
  83. LIGO/Virgo/KAGRA S250830m: Updated Sky localization
  84. EP250831a: EP-FXT follow-up observation
  85. EP250831a: Swift-XRT observations
  86. LIGO/Virgo/KAGRA S250831cc: Coverage and upper limits from MAXI/GSC observations
  87. IceCube Alert 250831.75: Global MASTER-Net observations report
  88. EP250831a: Global MASTER-Net observations report
  89. IceCube-250831A - IceCube observation of a high-energy neutrino candidate track-like event
  90. EP250831a: EP-WXT detection of a fast X-ray transient
  91. GRB 250831A (SVOM trigger sb25083102) is likely an outburst from star G 272-61
  92. GRB 250831A: Swift-XRT counterpart detection
  93. GRB 250831A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  94. GRB 250831A: SVOM/VT upper limit with VHF data
  95. GRB 250831A: SVOM detection of a soft burst
  96. GRB 250830B: Swift-XRT observations
  97. EP250830a: Global MASTER-Net observations report
  98. EP250830a/GRB 250830B: Einstein Probe detection of an X-ray transient and Swift/XRT follow-up
  99. LIGO/Virgo/KAGRA S250830bp: Coverage and upper limits from MAXI/GSC observations
  100. LIGO/Virgo/KAGRA S250830bp GLADEnet Completeness: Potential Host Galaxies in the 90% Credible Volume

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