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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. IceCube-250831A: Upper limits from a search for additional neutrino events in IceCube
  2. GRB 250830B: Swift-XRT afterglow detection
  3. LIGO/Virgo/KAGRA S250902av: 1 counterpart neutrino candidate event from an IceCube neutrino search
  4. LIGO/Virgo/KAGRA S250901cb: Updated Sky localization
  5. EP250827b: Liverpool Telescope observations
  6. GRB 250831A (SVOM trigger sb25083102): confirmation of a stellar flare by SVOM/VT
  7. GRB 250902A: SVOM/GRM observation
  8. EP250828a: Early near-infrared follow-up with MIRAGE on the MDM 1.3m telescope
  9. EP250901a: refined analysis of the EP-WXT and EP-FXT observations
  10. GRB 250901A: EP-FXT follow-up observation
  11. GRB 250901A: NOT optical observations
  12. GRB 250902A: Fermi GBM Final Real-time Localization
  13. IceCube-Cascade 250828A: Upper limits from a search for additional neutrino events in IceCube
  14. GRB 250901A: SVOM/VT optical afterglow with VHF data
  15. GRB 250901A: Swift-XRT afterglow detection
  16. EP250901a: Swift-XRT observations
  17. LIGO/Virgo/KAGRA S250830bp: DECam GW-MMADS candidates
  18. GRB 250901A: LCO optical upper limit
  19. EP250827b: Swift observations of AT 2025wkm
  20. LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 1 Candidates
  21. EP250827b: Gemini Spectroscopy of AT 2025wkm
  22. LIGO/Virgo/KAGRA S250901cb: Identification of a GW compact binary merger candidate
  23. EP250831a: NOT optical observations and tentative afterglow candidate
  24. EP250827b: FTW Observations of AT 2025wkm
  25. EP250827b: Contemporaneous detection of EP X-ray flare EP250827b and ZTF transient ZTF25abmpngy/AT2025wkm
  26. GRB 250901A: SVOM detection of a burst
  27. GRB 250831B: SVOM/GRM observation
  28. GRB 250830C: Insight-HXMT detection
  29. EP250901a: Mephisto optical upper limits
  30. GRB 250830C: GECAM-B detection
  31. EP250901a: Global MASTER-Net observations report
  32. GRB 250830C: AstroSat CZTI detection of a long burst
  33. EP250901a: Einstein Probe detection of an X-ray transient
  34. LIGO/Virgo/KAGRA S250830m: Updated Sky localization
  35. EP250831a: EP-FXT follow-up observation
  36. EP250831a: Swift-XRT observations
  37. LIGO/Virgo/KAGRA S250831cc: Coverage and upper limits from MAXI/GSC observations
  38. IceCube Alert 250831.75: Global MASTER-Net observations report
  39. EP250831a: Global MASTER-Net observations report
  40. IceCube-250831A - IceCube observation of a high-energy neutrino candidate track-like event
  41. EP250831a: EP-WXT detection of a fast X-ray transient
  42. GRB 250831A (SVOM trigger sb25083102) is likely an outburst from star G 272-61
  43. GRB 250831A: Swift-XRT counterpart detection
  44. GRB 250831A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  45. GRB 250831A: SVOM/VT upper limit with VHF data
  46. GRB 250831A: SVOM detection of a soft burst
  47. GRB 250830B: Swift-XRT observations
  48. EP250830a: Global MASTER-Net observations report
  49. EP250830a/GRB 250830B: Einstein Probe detection of an X-ray transient and Swift/XRT follow-up
  50. LIGO/Virgo/KAGRA S250830bp: Coverage and upper limits from MAXI/GSC observations
  51. LIGO/Virgo/KAGRA S250830bp GLADEnet Completeness: Potential Host Galaxies in the 90% Credible Volume
  52. LIGO/Virgo/KAGRA S250830bp: NED Galaxies in the 4-Update Localization Volume
  53. LIGO/Virgo/KAGRA S250830bp: Updated Sky localization, EM Bright Classification, and Source Classification
  54. LIGO/Virgo/KAGRA S250830bp: Identification of a GW compact binary merger candidate
  55. EP-WXT trigger 01709200994: Liverpool Telescope upper limits
  56. GRB 250830B: Swift ToO observations
  57. EP-WXT trigger 01709200994: confirmation of a stellar flare by BOOTES-6
  58. GRB 250830B: MAXI/GSC detection
  59. LIGO/Virgo/KAGRA S250830m: Identification of a GW compact binary merger candidate
  60. GRB 250830A / MAXI J0853+337: MAXI/GSC detection
  61. The EP-WXT trigger 01709200994 is likely a flaring star
  62. GRB 250828B: Swift-BAT refined analysis
  63. EP250821a: SOAR observations
  64. EP250827a: very early ATLAS detections, starting 43 sec after the EP trigger
  65. LIGO/Virgo/KAGRA S250725j: Observations with the NSF-DOE Vera C. Rubin Observatory
  66. LIGO/Virgo/KAGRA S250818k: MeerKAT detection of an increase in radio flux from AT2025ulz
  67. GRB 250808B: SVOM detection of a burst through offline search
  68. EP250828a: refined analysis of the EP-WXT and EP-FXT observations
  69. EP250828a: Optical counterpart detection with Kinder observations
  70. EP250828a: Liverpool Telescope upper limits
  71. Swift GRB 250828B: Global MASTER-Net observations report
  72. EP250828a: Global MASTER-Net observations report
  73. EP-WXT trigger 01709200800 : KAIT optical observations
  74. EP250828a: KAIT optical upper limit
  75. EP250827a: Swift/UVOT Detection
  76. EP250828a: NOT optical counterpart confirmation
  77. EP250828a: SVOM/VT optical candidate
  78. EP250828a: Seimei/TriCCS optical counterpart detection
  79. GRB 250828B: Swift detection of a burst
  80. EP250827a: STEP/T80S Confirmation of fading optical counterpart
  81. EP250828a: Optical upper limit with Kinder observations
  82. LIGO/Virgo/KAGRA S250827fo: Updated Sky localization
  83. LIGO/Virgo/KAGRA S250818k: uGMRT 1.3 GHz observations of AT2025ulz
  84. EP250827a: LCO observations show fading optical counterpart
  85. GRB 250828A: Fermi GBM Final Localization
  86. EP250828a: Einstein Probe detection of an X-ray transient
  87. EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations
  88. GRID detection of GRB 250824A
  89. LIGO/Virgo/KAGRA S250827fo: Identification of a GW compact binary merger candidate
  90. EP250827A: VLT/X-shooter redshift confirmation
  91. Fermi GRB 250827A: Global MASTER-Net observations report
  92. EP250827a: confirmation of optical rebrightening with LCO
  93. EP250827a: GOTO observation of the optical afterglow
  94. GRB 250826A: SVOM/GRM observation
  95. GRB 250827A: Fermi GBM Final Real-time Localization
  96. EP250827A: An optical rebrightening was detected by LCO.
  97. EP250827a: Swift-XRT counterpart detection
  98. LIGO/Virgo/KAGRA S250827l: Updated Sky localization
  99. The EP-WXT trigger 01709200800 is likely a flaring star
  100. EP250827a: TRT optical observations

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