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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. LIGO/Virgo/KAGRA S250901cb: Identification of a GW compact binary merger candidate
  2. EP250831a: NOT optical observations and tentative afterglow candidate
  3. EP250827b: FTW Observations of AT 2025wkm
  4. EP250827b: Contemporaneous detection of EP X-ray flare EP250827b and ZTF transient ZTF25abmpngy/AT2025wkm
  5. GRB 250901A: SVOM detection of a burst
  6. GRB 250831B: SVOM/GRM observation
  7. GRB 250830C: Insight-HXMT detection
  8. EP250901a: Mephisto optical upper limits
  9. GRB 250830C: GECAM-B detection
  10. EP250901a: Global MASTER-Net observations report
  11. GRB 250830C: AstroSat CZTI detection of a long burst
  12. EP250901a: Einstein Probe detection of an X-ray transient
  13. LIGO/Virgo/KAGRA S250830m: Updated Sky localization
  14. EP250831a: EP-FXT follow-up observation
  15. EP250831a: Swift-XRT observations
  16. LIGO/Virgo/KAGRA S250831cc: Coverage and upper limits from MAXI/GSC observations
  17. IceCube Alert 250831.75: Global MASTER-Net observations report
  18. EP250831a: Global MASTER-Net observations report
  19. IceCube-250831A - IceCube observation of a high-energy neutrino candidate track-like event
  20. EP250831a: EP-WXT detection of a fast X-ray transient
  21. GRB 250831A (SVOM trigger sb25083102) is likely an outburst from star G 272-61
  22. GRB 250831A: Swift-XRT counterpart detection
  23. GRB 250831A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  24. GRB 250831A: SVOM/VT upper limit with VHF data
  25. GRB 250831A: SVOM detection of a soft burst
  26. GRB 250830B: Swift-XRT observations
  27. EP250830a: Global MASTER-Net observations report
  28. EP250830a/GRB 250830B: Einstein Probe detection of an X-ray transient and Swift/XRT follow-up
  29. LIGO/Virgo/KAGRA S250830bp: Coverage and upper limits from MAXI/GSC observations
  30. LIGO/Virgo/KAGRA S250830bp GLADEnet Completeness: Potential Host Galaxies in the 90% Credible Volume
  31. LIGO/Virgo/KAGRA S250830bp: NED Galaxies in the 4-Update Localization Volume
  32. LIGO/Virgo/KAGRA S250830bp: Updated Sky localization, EM Bright Classification, and Source Classification
  33. LIGO/Virgo/KAGRA S250830bp: Identification of a GW compact binary merger candidate
  34. EP-WXT trigger 01709200994: Liverpool Telescope upper limits
  35. GRB 250830B: Swift ToO observations
  36. EP-WXT trigger 01709200994: confirmation of a stellar flare by BOOTES-6
  37. GRB 250830B: MAXI/GSC detection
  38. LIGO/Virgo/KAGRA S250830m: Identification of a GW compact binary merger candidate
  39. GRB 250830A / MAXI J0853+337: MAXI/GSC detection
  40. The EP-WXT trigger 01709200994 is likely a flaring star
  41. GRB 250828B: Swift-BAT refined analysis
  42. EP250821a: SOAR observations
  43. EP250827a: very early ATLAS detections, starting 43 sec after the EP trigger
  44. LIGO/Virgo/KAGRA S250725j: Observations with the NSF-DOE Vera C. Rubin Observatory
  45. LIGO/Virgo/KAGRA S250818k: MeerKAT detection of an increase in radio flux from AT2025ulz
  46. GRB 250808B: SVOM detection of a burst through offline search
  47. EP250828a: refined analysis of the EP-WXT and EP-FXT observations
  48. EP250828a: Optical counterpart detection with Kinder observations
  49. EP250828a: Liverpool Telescope upper limits
  50. Swift GRB 250828B: Global MASTER-Net observations report
  51. EP250828a: Global MASTER-Net observations report
  52. EP-WXT trigger 01709200800 : KAIT optical observations
  53. EP250828a: KAIT optical upper limit
  54. EP250827a: Swift/UVOT Detection
  55. EP250828a: NOT optical counterpart confirmation
  56. EP250828a: SVOM/VT optical candidate
  57. EP250828a: Seimei/TriCCS optical counterpart detection
  58. GRB 250828B: Swift detection of a burst
  59. EP250827a: STEP/T80S Confirmation of fading optical counterpart
  60. EP250828a: Optical upper limit with Kinder observations
  61. LIGO/Virgo/KAGRA S250827fo: Updated Sky localization
  62. LIGO/Virgo/KAGRA S250818k: uGMRT 1.3 GHz observations of AT2025ulz
  63. EP250827a: LCO observations show fading optical counterpart
  64. GRB 250828A: Fermi GBM Final Localization
  65. EP250828a: Einstein Probe detection of an X-ray transient
  66. EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations
  67. GRID detection of GRB 250824A
  68. LIGO/Virgo/KAGRA S250827fo: Identification of a GW compact binary merger candidate
  69. EP250827A: VLT/X-shooter redshift confirmation
  70. Fermi GRB 250827A: Global MASTER-Net observations report
  71. EP250827a: confirmation of optical rebrightening with LCO
  72. EP250827a: GOTO observation of the optical afterglow
  73. GRB 250826A: SVOM/GRM observation
  74. GRB 250827A: Fermi GBM Final Real-time Localization
  75. EP250827A: An optical rebrightening was detected by LCO.
  76. EP250827a: Swift-XRT counterpart detection
  77. LIGO/Virgo/KAGRA S250827l: Updated Sky localization
  78. The EP-WXT trigger 01709200800 is likely a flaring star
  79. EP250827a: TRT optical observations
  80. EP250827a: BOOTES-7 early optical dectection
  81. EP250827a / GRB 250827A: MASTER-OAFA OT observation
  82. EP250827a: Gemini-South redshift z = 1.613
  83. EP250827a: Global MASTER-Net observations report
  84. EP250827a: Las Cumbres independent detection of the optical counterpart
  85. EP250827a: Gemini-South optical counterpart detection
  86. EP250827a: Einstein Probe detection of an X-ray transient
  87. LIGO/Virgo/KAGRA S250827l: Identification of a GW compact binary merger candidate
  88. Fermi GRB 250826A: Global MASTER-Net observations report
  89. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  90. EP250821a: Gemini GMOS Redshift Confirmation
  91. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  92. Fermi trigger No 777883624: Global MASTER-Net observations report
  93. Fermi Gamma-ray Burst Monitor trigger 777883624/250826283 is not a GRB
  94. GRB 250826A: Fermi GBM Final Real-time Localization
  95. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Confirmation of Rebrightening of AT2025ulz
  96. Fermi GRB 250824B: Global MASTER-Net observations report
  97. LIGO/Virgo/KAGRA S250818k: VLA upper limits on AT2025ulz
  98. LIGO/Virgo/KAGRA S250818k: nature of the AT2025ulz/ZTF25abjmnnps OT
  99. LIGO/Virgo/KAGRA S250818k: Pan-STARRS imaging confirms re-brightening of SN2025ulz
  100. GRB 250823A: Swift-BAT refined analysis

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