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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 250901A: SVOM/VT optical afterglow with VHF data
  2. GRB 250901A: Swift-XRT afterglow detection
  3. EP250901a: Swift-XRT observations
  4. LIGO/Virgo/KAGRA S250830bp: DECam GW-MMADS candidates
  5. GRB 250901A: LCO optical upper limit
  6. EP250827b: Swift observations of AT 2025wkm
  7. LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 1 Candidates
  8. EP250827b: Gemini Spectroscopy of AT 2025wkm
  9. LIGO/Virgo/KAGRA S250901cb: Identification of a GW compact binary merger candidate
  10. EP250831a: NOT optical observations and tentative afterglow candidate
  11. EP250827b: FTW Observations of AT 2025wkm
  12. EP250827b: Contemporaneous detection of EP X-ray flare EP250827b and ZTF transient ZTF25abmpngy/AT2025wkm
  13. GRB 250901A: SVOM detection of a burst
  14. GRB 250831B: SVOM/GRM observation
  15. GRB 250830C: Insight-HXMT detection
  16. EP250901a: Mephisto optical upper limits
  17. GRB 250830C: GECAM-B detection
  18. EP250901a: Global MASTER-Net observations report
  19. GRB 250830C: AstroSat CZTI detection of a long burst
  20. EP250901a: Einstein Probe detection of an X-ray transient
  21. LIGO/Virgo/KAGRA S250830m: Updated Sky localization
  22. EP250831a: EP-FXT follow-up observation
  23. EP250831a: Swift-XRT observations
  24. LIGO/Virgo/KAGRA S250831cc: Coverage and upper limits from MAXI/GSC observations
  25. IceCube Alert 250831.75: Global MASTER-Net observations report
  26. EP250831a: Global MASTER-Net observations report
  27. IceCube-250831A - IceCube observation of a high-energy neutrino candidate track-like event
  28. EP250831a: EP-WXT detection of a fast X-ray transient
  29. GRB 250831A (SVOM trigger sb25083102) is likely an outburst from star G 272-61
  30. GRB 250831A: Swift-XRT counterpart detection
  31. GRB 250831A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  32. GRB 250831A: SVOM/VT upper limit with VHF data
  33. GRB 250831A: SVOM detection of a soft burst
  34. GRB 250830B: Swift-XRT observations
  35. EP250830a: Global MASTER-Net observations report
  36. EP250830a/GRB 250830B: Einstein Probe detection of an X-ray transient and Swift/XRT follow-up
  37. LIGO/Virgo/KAGRA S250830bp: Coverage and upper limits from MAXI/GSC observations
  38. LIGO/Virgo/KAGRA S250830bp GLADEnet Completeness: Potential Host Galaxies in the 90% Credible Volume
  39. LIGO/Virgo/KAGRA S250830bp: NED Galaxies in the 4-Update Localization Volume
  40. LIGO/Virgo/KAGRA S250830bp: Updated Sky localization, EM Bright Classification, and Source Classification
  41. LIGO/Virgo/KAGRA S250830bp: Identification of a GW compact binary merger candidate
  42. EP-WXT trigger 01709200994: Liverpool Telescope upper limits
  43. GRB 250830B: Swift ToO observations
  44. EP-WXT trigger 01709200994: confirmation of a stellar flare by BOOTES-6
  45. GRB 250830B: MAXI/GSC detection
  46. LIGO/Virgo/KAGRA S250830m: Identification of a GW compact binary merger candidate
  47. GRB 250830A / MAXI J0853+337: MAXI/GSC detection
  48. The EP-WXT trigger 01709200994 is likely a flaring star
  49. GRB 250828B: Swift-BAT refined analysis
  50. EP250821a: SOAR observations
  51. EP250827a: very early ATLAS detections, starting 43 sec after the EP trigger
  52. LIGO/Virgo/KAGRA S250725j: Observations with the NSF-DOE Vera C. Rubin Observatory
  53. LIGO/Virgo/KAGRA S250818k: MeerKAT detection of an increase in radio flux from AT2025ulz
  54. GRB 250808B: SVOM detection of a burst through offline search
  55. EP250828a: refined analysis of the EP-WXT and EP-FXT observations
  56. EP250828a: Optical counterpart detection with Kinder observations
  57. EP250828a: Liverpool Telescope upper limits
  58. Swift GRB 250828B: Global MASTER-Net observations report
  59. EP250828a: Global MASTER-Net observations report
  60. EP-WXT trigger 01709200800 : KAIT optical observations
  61. EP250828a: KAIT optical upper limit
  62. EP250827a: Swift/UVOT Detection
  63. EP250828a: NOT optical counterpart confirmation
  64. EP250828a: SVOM/VT optical candidate
  65. EP250828a: Seimei/TriCCS optical counterpart detection
  66. GRB 250828B: Swift detection of a burst
  67. EP250827a: STEP/T80S Confirmation of fading optical counterpart
  68. EP250828a: Optical upper limit with Kinder observations
  69. LIGO/Virgo/KAGRA S250827fo: Updated Sky localization
  70. LIGO/Virgo/KAGRA S250818k: uGMRT 1.3 GHz observations of AT2025ulz
  71. EP250827a: LCO observations show fading optical counterpart
  72. GRB 250828A: Fermi GBM Final Localization
  73. EP250828a: Einstein Probe detection of an X-ray transient
  74. EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations
  75. GRID detection of GRB 250824A
  76. LIGO/Virgo/KAGRA S250827fo: Identification of a GW compact binary merger candidate
  77. EP250827A: VLT/X-shooter redshift confirmation
  78. Fermi GRB 250827A: Global MASTER-Net observations report
  79. EP250827a: confirmation of optical rebrightening with LCO
  80. EP250827a: GOTO observation of the optical afterglow
  81. GRB 250826A: SVOM/GRM observation
  82. GRB 250827A: Fermi GBM Final Real-time Localization
  83. EP250827A: An optical rebrightening was detected by LCO.
  84. EP250827a: Swift-XRT counterpart detection
  85. LIGO/Virgo/KAGRA S250827l: Updated Sky localization
  86. The EP-WXT trigger 01709200800 is likely a flaring star
  87. EP250827a: TRT optical observations
  88. EP250827a: BOOTES-7 early optical dectection
  89. EP250827a / GRB 250827A: MASTER-OAFA OT observation
  90. EP250827a: Gemini-South redshift z = 1.613
  91. EP250827a: Global MASTER-Net observations report
  92. EP250827a: Las Cumbres independent detection of the optical counterpart
  93. EP250827a: Gemini-South optical counterpart detection
  94. EP250827a: Einstein Probe detection of an X-ray transient
  95. LIGO/Virgo/KAGRA S250827l: Identification of a GW compact binary merger candidate
  96. Fermi GRB 250826A: Global MASTER-Net observations report
  97. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  98. EP250821a: Gemini GMOS Redshift Confirmation
  99. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  100. Fermi trigger No 777883624: Global MASTER-Net observations report

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