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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 250830C: Insight-HXMT detection
  2. EP250901a: Mephisto optical upper limits
  3. GRB 250830C: GECAM-B detection
  4. EP250901a: Global MASTER-Net observations report
  5. GRB 250830C: AstroSat CZTI detection of a long burst
  6. EP250901a: Einstein Probe detection of an X-ray transient
  7. LIGO/Virgo/KAGRA S250830m: Updated Sky localization
  8. EP250831a: EP-FXT follow-up observation
  9. EP250831a: Swift-XRT observations
  10. LIGO/Virgo/KAGRA S250831cc: Coverage and upper limits from MAXI/GSC observations
  11. IceCube Alert 250831.75: Global MASTER-Net observations report
  12. EP250831a: Global MASTER-Net observations report
  13. IceCube-250831A - IceCube observation of a high-energy neutrino candidate track-like event
  14. EP250831a: EP-WXT detection of a fast X-ray transient
  15. GRB 250831A (SVOM trigger sb25083102) is likely an outburst from star G 272-61
  16. GRB 250831A: Swift-XRT counterpart detection
  17. GRB 250831A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  18. GRB 250831A: SVOM/VT upper limit with VHF data
  19. GRB 250831A: SVOM detection of a soft burst
  20. GRB 250830B: Swift-XRT observations
  21. EP250830a: Global MASTER-Net observations report
  22. EP250830a/GRB 250830B: Einstein Probe detection of an X-ray transient and Swift/XRT follow-up
  23. LIGO/Virgo/KAGRA S250830bp: Coverage and upper limits from MAXI/GSC observations
  24. LIGO/Virgo/KAGRA S250830bp GLADEnet Completeness: Potential Host Galaxies in the 90% Credible Volume
  25. LIGO/Virgo/KAGRA S250830bp: NED Galaxies in the 4-Update Localization Volume
  26. LIGO/Virgo/KAGRA S250830bp: Updated Sky localization, EM Bright Classification, and Source Classification
  27. LIGO/Virgo/KAGRA S250830bp: Identification of a GW compact binary merger candidate
  28. EP-WXT trigger 01709200994: Liverpool Telescope upper limits
  29. GRB 250830B: Swift ToO observations
  30. EP-WXT trigger 01709200994: confirmation of a stellar flare by BOOTES-6
  31. GRB 250830B: MAXI/GSC detection
  32. LIGO/Virgo/KAGRA S250830m: Identification of a GW compact binary merger candidate
  33. GRB 250830A / MAXI J0853+337: MAXI/GSC detection
  34. The EP-WXT trigger 01709200994 is likely a flaring star
  35. GRB 250828B: Swift-BAT refined analysis
  36. EP250821a: SOAR observations
  37. EP250827a: very early ATLAS detections, starting 43 sec after the EP trigger
  38. LIGO/Virgo/KAGRA S250725j: Observations with the NSF-DOE Vera C. Rubin Observatory
  39. LIGO/Virgo/KAGRA S250818k: MeerKAT detection of an increase in radio flux from AT2025ulz
  40. GRB 250808B: SVOM detection of a burst through offline search
  41. EP250828a: refined analysis of the EP-WXT and EP-FXT observations
  42. EP250828a: Optical counterpart detection with Kinder observations
  43. EP250828a: Liverpool Telescope upper limits
  44. Swift GRB 250828B: Global MASTER-Net observations report
  45. EP250828a: Global MASTER-Net observations report
  46. EP-WXT trigger 01709200800 : KAIT optical observations
  47. EP250828a: KAIT optical upper limit
  48. EP250827a: Swift/UVOT Detection
  49. EP250828a: NOT optical counterpart confirmation
  50. EP250828a: SVOM/VT optical candidate
  51. EP250828a: Seimei/TriCCS optical counterpart detection
  52. GRB 250828B: Swift detection of a burst
  53. EP250827a: STEP/T80S Confirmation of fading optical counterpart
  54. EP250828a: Optical upper limit with Kinder observations
  55. LIGO/Virgo/KAGRA S250827fo: Updated Sky localization
  56. LIGO/Virgo/KAGRA S250818k: uGMRT 1.3 GHz observations of AT2025ulz
  57. EP250827a: LCO observations show fading optical counterpart
  58. GRB 250828A: Fermi GBM Final Localization
  59. EP250828a: Einstein Probe detection of an X-ray transient
  60. EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations
  61. GRID detection of GRB 250824A
  62. LIGO/Virgo/KAGRA S250827fo: Identification of a GW compact binary merger candidate
  63. EP250827A: VLT/X-shooter redshift confirmation
  64. Fermi GRB 250827A: Global MASTER-Net observations report
  65. EP250827a: confirmation of optical rebrightening with LCO
  66. EP250827a: GOTO observation of the optical afterglow
  67. GRB 250826A: SVOM/GRM observation
  68. GRB 250827A: Fermi GBM Final Real-time Localization
  69. EP250827A: An optical rebrightening was detected by LCO.
  70. EP250827a: Swift-XRT counterpart detection
  71. LIGO/Virgo/KAGRA S250827l: Updated Sky localization
  72. The EP-WXT trigger 01709200800 is likely a flaring star
  73. EP250827a: TRT optical observations
  74. EP250827a: BOOTES-7 early optical dectection
  75. EP250827a / GRB 250827A: MASTER-OAFA OT observation
  76. EP250827a: Gemini-South redshift z = 1.613
  77. EP250827a: Global MASTER-Net observations report
  78. EP250827a: Las Cumbres independent detection of the optical counterpart
  79. EP250827a: Gemini-South optical counterpart detection
  80. EP250827a: Einstein Probe detection of an X-ray transient
  81. LIGO/Virgo/KAGRA S250827l: Identification of a GW compact binary merger candidate
  82. Fermi GRB 250826A: Global MASTER-Net observations report
  83. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  84. EP250821a: Gemini GMOS Redshift Confirmation
  85. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  86. Fermi trigger No 777883624: Global MASTER-Net observations report
  87. Fermi Gamma-ray Burst Monitor trigger 777883624/250826283 is not a GRB
  88. GRB 250826A: Fermi GBM Final Real-time Localization
  89. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Confirmation of Rebrightening of AT2025ulz
  90. Fermi GRB 250824B: Global MASTER-Net observations report
  91. LIGO/Virgo/KAGRA S250818k: VLA upper limits on AT2025ulz
  92. LIGO/Virgo/KAGRA S250818k: nature of the AT2025ulz/ZTF25abjmnnps OT
  93. LIGO/Virgo/KAGRA S250818k: Pan-STARRS imaging confirms re-brightening of SN2025ulz
  94. GRB 250823A: Swift-BAT refined analysis
  95. LIGO/Virgo/KAGRA S250818k: Continued Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  96. GRB 250821B: AstroSat CZTI detection
  97. GRB 250819A: AstroSat CZTI detection
  98. LIGO/Virgo/KAGRA S250818k: FTW Observations Show Continued Reddening of AT 2025ulz
  99. LIGO/Virgo/KAGRA S250818k: MASTER predicovery limits of the AT2025ulz/ZTF25abjmnps KN candidate
  100. GRB 250821B: Insight-HXMT detection

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