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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 250903A: VLT X-shooter spectroscopic redshift z = 1.590
  2. The EP-WXT trigger 01709201209 is likely a flaring star
  3. LIGO/Virgo/KAGRA S250904ae: Identification of a GW compact binary merger candidate
  4. GRB 250903A: EP-FXT counterpart detection
  5. GRB 250902A: GECAM-B detection
  6. GRB 250903A: LCO optical observation
  7. GRB 250903A: LCO optical afterglow detection
  8. GRB 250903A: SVOM/VT optical confirmation with VHF data
  9. EP250903a: SVOM/VT optical confirmation
  10. EP250901a: Mondy, Assy and SAO RAS optical limits
  11. Subject GRB 250903A: SVOM/MXT afterglow detection
  12. EP250903a: LCO candidate counterpart discovery
  13. GRB 250903A: TRT optical counterpart detection
  14. GRB 250902B: AstroSat CZTI detection
  15. GRB 250903A: SVOM detection of a burst
  16. EP250903a: Global MASTER-Net observations report
  17. EP250903a: TRT optical observations
  18. EP250903a: Einstein Probe detection of an X-ray transient
  19. EP 250827B: Detection of supernova counterpart by LCO.
  20. EP/WXT01709201159: GOTO optical follow-up
  21. EP250827b / AT 2025wkm: TRT optical observations
  22. EP250827b: NOT spectroscopic observations and AT 2025wkm classification as a broad-lined type-Ic supernova
  23. EP250827b: continued Liverpool Telescope observations
  24. GRB 250902B: SVOM/GRM observation
  25. EP250827b: SVOM/VT observation of AT 2025wkm
  26. LIGO/VIRGO/KAGRA S250818k: No evidence for radio variability of AT2025ulz in MeerKAT 3 GHz data
  27. GRB 250831A (SVOM trigger sb25083102): KAIT confirmation of stellar flare
  28. Fermi GRB 250902B: Global MASTER-Net observations report
  29. Fermi-LAT Gamma-ray Observations of IceCube-250831A
  30. GRB 250902A: Fermi GBM Detection
  31. GRB 250901A: Swift/UVOT Upper Limit
  32. GRB 250902B: Fermi GBM Final Real-time Localization
  33. IceCube-250831A: Upper limits from a search for additional neutrino events in IceCube
  34. GRB 250830B: Swift-XRT afterglow detection
  35. LIGO/Virgo/KAGRA S250902av: 1 counterpart neutrino candidate event from an IceCube neutrino search
  36. LIGO/Virgo/KAGRA S250901cb: Updated Sky localization
  37. EP250827b: Liverpool Telescope observations
  38. GRB 250831A (SVOM trigger sb25083102): confirmation of a stellar flare by SVOM/VT
  39. GRB 250902A: SVOM/GRM observation
  40. EP250828a: Early near-infrared follow-up with MIRAGE on the MDM 1.3m telescope
  41. EP250901a: refined analysis of the EP-WXT and EP-FXT observations
  42. GRB 250901A: EP-FXT follow-up observation
  43. GRB 250901A: NOT optical observations
  44. GRB 250902A: Fermi GBM Final Real-time Localization
  45. IceCube-Cascade 250828A: Upper limits from a search for additional neutrino events in IceCube
  46. GRB 250901A: SVOM/VT optical afterglow with VHF data
  47. GRB 250901A: Swift-XRT afterglow detection
  48. EP250901a: Swift-XRT observations
  49. LIGO/Virgo/KAGRA S250830bp: DECam GW-MMADS candidates
  50. GRB 250901A: LCO optical upper limit
  51. EP250827b: Swift observations of AT 2025wkm
  52. LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 1 Candidates
  53. EP250827b: Gemini Spectroscopy of AT 2025wkm
  54. LIGO/Virgo/KAGRA S250901cb: Identification of a GW compact binary merger candidate
  55. EP250831a: NOT optical observations and tentative afterglow candidate
  56. EP250827b: FTW Observations of AT 2025wkm
  57. EP250827b: Contemporaneous detection of EP X-ray flare EP250827b and ZTF transient ZTF25abmpngy/AT2025wkm
  58. GRB 250901A: SVOM detection of a burst
  59. GRB 250831B: SVOM/GRM observation
  60. GRB 250830C: Insight-HXMT detection
  61. EP250901a: Mephisto optical upper limits
  62. GRB 250830C: GECAM-B detection
  63. EP250901a: Global MASTER-Net observations report
  64. GRB 250830C: AstroSat CZTI detection of a long burst
  65. EP250901a: Einstein Probe detection of an X-ray transient
  66. LIGO/Virgo/KAGRA S250830m: Updated Sky localization
  67. EP250831a: EP-FXT follow-up observation
  68. EP250831a: Swift-XRT observations
  69. LIGO/Virgo/KAGRA S250831cc: Coverage and upper limits from MAXI/GSC observations
  70. IceCube Alert 250831.75: Global MASTER-Net observations report
  71. EP250831a: Global MASTER-Net observations report
  72. IceCube-250831A - IceCube observation of a high-energy neutrino candidate track-like event
  73. EP250831a: EP-WXT detection of a fast X-ray transient
  74. GRB 250831A (SVOM trigger sb25083102) is likely an outburst from star G 272-61
  75. GRB 250831A: Swift-XRT counterpart detection
  76. GRB 250831A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  77. GRB 250831A: SVOM/VT upper limit with VHF data
  78. GRB 250831A: SVOM detection of a soft burst
  79. GRB 250830B: Swift-XRT observations
  80. EP250830a: Global MASTER-Net observations report
  81. EP250830a/GRB 250830B: Einstein Probe detection of an X-ray transient and Swift/XRT follow-up
  82. LIGO/Virgo/KAGRA S250830bp: Coverage and upper limits from MAXI/GSC observations
  83. LIGO/Virgo/KAGRA S250830bp GLADEnet Completeness: Potential Host Galaxies in the 90% Credible Volume
  84. LIGO/Virgo/KAGRA S250830bp: NED Galaxies in the 4-Update Localization Volume
  85. LIGO/Virgo/KAGRA S250830bp: Updated Sky localization, EM Bright Classification, and Source Classification
  86. LIGO/Virgo/KAGRA S250830bp: Identification of a GW compact binary merger candidate
  87. EP-WXT trigger 01709200994: Liverpool Telescope upper limits
  88. GRB 250830B: Swift ToO observations
  89. EP-WXT trigger 01709200994: confirmation of a stellar flare by BOOTES-6
  90. GRB 250830B: MAXI/GSC detection
  91. LIGO/Virgo/KAGRA S250830m: Identification of a GW compact binary merger candidate
  92. GRB 250830A / MAXI J0853+337: MAXI/GSC detection
  93. The EP-WXT trigger 01709200994 is likely a flaring star
  94. GRB 250828B: Swift-BAT refined analysis
  95. EP250821a: SOAR observations
  96. EP250827a: very early ATLAS detections, starting 43 sec after the EP trigger
  97. LIGO/Virgo/KAGRA S250725j: Observations with the NSF-DOE Vera C. Rubin Observatory
  98. LIGO/Virgo/KAGRA S250818k: MeerKAT detection of an increase in radio flux from AT2025ulz
  99. GRB 250808B: SVOM detection of a burst through offline search
  100. EP250828a: refined analysis of the EP-WXT and EP-FXT observations

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