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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 251006A (short): Glowbug gamma-ray detection
  2. GRB 251005C: COLIBRÍ optical observations
  3. Fermi GRB 251006A: Global MASTER-Net observations report
  4. GRB 251005C: VLT/X-shooter Imaging
  5. GRB 251003A: LAST optical observations
  6. GRB 251002A: LAST optical observations
  7. GRB 251006A: Fermi GBM Final Real-time Localization
  8. GRB 251005C: SVOM/VT optical candidate
  9. GRB 251005C: AstroSat CZTI detection
  10. GRB 251005C: Swift/UVOT Upper Limits
  11. GRB 250902A: MSU cubesats detection
  12. GRB 251005C: Swift-XRT refined Analysis
  13. GRB 251005C: Fermi GBM Observation
  14. Swift GRB 251005A: Global MASTER-Net observations report
  15. GRB 251005C: Enhanced Swift-XRT position
  16. GRB 251005C: GOTO optical upper limits
  17. Fermi trigger No 781367244: Global MASTER-Net observations report
  18. GRB 251005C: Swift detection of a burst
  19. GRB 251005B: Fermi GBM Final Real-time Localization
  20. GRB 251005A: Fermi GBM Final Localization
  21. GRB 251002A: Mondy/AZT-33IK optical observations
  22. GRB 251002A: Insight-HXMT detection
  23. GRB 251002A: Insight-HXMT detection
  24. EP251003a: Einstein Probe detection of an X-ray transient
  25. GRB 251003A: J-band detection with WINTER
  26. GRB 251002A: NIR observations with WINTER
  27. Fermi GBM Sub-Threshold Detection of GRB 250910A
  28. GRB 251003A: Swift-BAT refined analysis
  29. GRB 251001B: NIR observations with WINTER
  30. GRB 251002A: Calapai Observatory, Massa S. Giorgio (Messina), optical observation.
  31. GRB 251003A: Swift/UVOT Upper Limits
  32. GRB 251002A: Swift/UVOT detection
  33. GRB 251001A: AstroSat CZTI detection
  34. GRB 251001B: COLIBRÍ further observations and evidence of a multi-wavelength shallow decay
  35. GRB 251003A: Swift-XRT refined Analysis
  36. GRB 251003A: COLIBRÍ photometric redshift
  37. GRB 251003A: GOTO detection of the optical counterpart
  38. GRB 251002A: Fermi GBM Observation
  39. LIGO/Virgo/KAGRA S251003at: Retraction of GW compact binary merger candidate
  40. GRB 251002A: GOTO detection of optical counterpart
  41. GRB 251001C: SVOM/GRM observation
  42. EP250821a: iTelescope T-59 possible detection of the optical counterpart
  43. GRB 251003A: Enhanced Swift-XRT position
  44. GRB 251002A: AKO Early Optical Afterglow Detection
  45. GRB 251003A: GTC/OSIRIS+ spectroscopic redshift z = 4.412
  46. GRB 251003A: Kilonova-Catcher optical afterglow detection
  47. GRB 251002A: Swift-XRT afterglow detection
  48. GRB 251001B: AbAO optical upper limit
  49. GRB 251002A: Kilonova-Catcher optical afterglow detection
  50. GRB 251002A: AbAO optical observations
  51. GRB 251002A: SVOM/COLIBRÍ (FM-GFT) optical observations
  52. GRB 251001C: CALET Gamma-Ray Burst Monitor detection
  53. GRB 251002A: J band observations by SYSU 80cm infrared telescope
  54. GRB 251002A: OHP/T193 MISTRAL optical afterglow detection
  55. GRB 251002A: VLT/X-shooter spectroscopic redshift z = 2.178
  56. GRB 251002A: EP-FXT counterpart detection
  57. GRB 251003A: LCOGT Optical Detection
  58. GRB 251003A: COLIBRÍ optical detection of the fading afterglow
  59. GRB 251003A: 1.5m OSN afterglow candidate
  60. GRB 251003A: Prompt enhanced Swift-XRT position
  61. GRB 251003A: Swift detection of a burst
  62. GRB 251003A: Fermi GBM Final Real-time Localization
  63. Swift GRB251003A: Global MASTER-Net observations report
  64. Fermi/SVOM GRB 251002A : MASTER OT earlier detection in 2 polarization filters
  65. GRB 251002A: BOOTES-6 early optical detection
  66. GRB 251002A: SAO RAS optical observations
  67. GRB 251002A: ULL-ASTRO-MASTER early detection of the optical afterglow with the LCO 40-cm telescope at Sutherland Observatory
  68. GRB 251002A: FRAM-ORM afterglow detection
  69. GRB 251002A: LCO optical observation
  70. GRB 251002A: SVOM/VT optical observation
  71. GRB 251002A: SVOM detection of a burst
  72. Fermi GRB 251002A: Global MASTER-Net observations report
  73. GRB 251001B: Swift-BAT refined analysis
  74. GRB 251001A: SVOM/GRM observation
  75. GRB 251001A: Insight-HXMT detection
  76. GRB 251001B: Swift/UVOT Detection
  77. GRB 251001B: COLIBRÍ optical observations
  78. GRB 251001B: GTC/OSIRIS+ spectroscopic redshift z = 2.162
  79. GRB 251001B: Swift-XRT refined Analysis
  80. GRB 251001B: SVOM/VT optical observation
  81. GRB 251001B: NOT optical observations
  82. GRB 251001C: Glowbug gamma-ray detection
  83. Swift GRB 251001B: Global MASTER-Net observations report
  84. GRB 251001B: Fermi GBM Observation
  85. GRB 251001B: Further GOTO observations of optical counterpart.
  86. GRB 251001B: Enhanced Swift-XRT position
  87. GRB 250930A: Fermi GBM Final Localization
  88. GRB 251001B: LCOGT Optical Observations
  89. GRB 250930A: SVOM/GRM observation
  90. GRB 251001B: TRT optical afterglow detection and potential host galaxy
  91. GRB 251001B: GOTO optical counterpart detection
  92. GRB 251001B: Swift detection of a burst
  93. GRB 251001B: Fermi GBM Final Real-time Localization
  94. GRB 251001A: Fermi GBM Detection
  95. GRB 250910A / EP250910a: VLT limits on the possible associated supernova
  96. GRB 251001A: BALROG localization (Fermi Trigger 780979261 / GRB 251001112)
  97. GRB 251001A: Fermi GBM Final Real-time Localization
  98. LIGO/Virgo/KAGRA S250830bp: SOAR spectroscopy of two DESGW candidates
  99. LIGO/Virgo/KAGRA S250818k: further MeerKAT monitoring
  100. GRB 250910A / EP250910a: VLT/X-shooter host galaxy redshift z = 0.592

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