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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 251002A: Insight-HXMT detection
  2. EP251003a: Einstein Probe detection of an X-ray transient
  3. GRB 251003A: J-band detection with WINTER
  4. GRB 251002A: NIR observations with WINTER
  5. Fermi GBM Sub-Threshold Detection of GRB 250910A
  6. GRB 251003A: Swift-BAT refined analysis
  7. GRB 251001B: NIR observations with WINTER
  8. GRB 251002A: Calapai Observatory, Massa S. Giorgio (Messina), optical observation.
  9. GRB 251003A: Swift/UVOT Upper Limits
  10. GRB 251002A: Swift/UVOT detection
  11. GRB 251001A: AstroSat CZTI detection
  12. GRB 251001B: COLIBRÍ further observations and evidence of a multi-wavelength shallow decay
  13. GRB 251003A: Swift-XRT refined Analysis
  14. GRB 251003A: COLIBRÍ photometric redshift
  15. GRB 251003A: GOTO detection of the optical counterpart
  16. GRB 251002A: Fermi GBM Observation
  17. LIGO/Virgo/KAGRA S251003at: Retraction of GW compact binary merger candidate
  18. GRB 251002A: GOTO detection of optical counterpart
  19. GRB 251001C: SVOM/GRM observation
  20. EP250821a: iTelescope T-59 possible detection of the optical counterpart
  21. GRB 251003A: Enhanced Swift-XRT position
  22. GRB 251002A: AKO Early Optical Afterglow Detection
  23. GRB 251003A: GTC/OSIRIS+ spectroscopic redshift z = 4.412
  24. GRB 251003A: Kilonova-Catcher optical afterglow detection
  25. GRB 251002A: Swift-XRT afterglow detection
  26. GRB 251001B: AbAO optical upper limit
  27. GRB 251002A: Kilonova-Catcher optical afterglow detection
  28. GRB 251002A: AbAO optical observations
  29. GRB 251002A: SVOM/COLIBRÍ (FM-GFT) optical observations
  30. GRB 251001C: CALET Gamma-Ray Burst Monitor detection
  31. GRB 251002A: J band observations by SYSU 80cm infrared telescope
  32. GRB 251002A: OHP/T193 MISTRAL optical afterglow detection
  33. GRB 251002A: VLT/X-shooter spectroscopic redshift z = 2.178
  34. GRB 251002A: EP-FXT counterpart detection
  35. GRB 251003A: LCOGT Optical Detection
  36. GRB 251003A: COLIBRÍ optical detection of the fading afterglow
  37. GRB 251003A: 1.5m OSN afterglow candidate
  38. GRB 251003A: Prompt enhanced Swift-XRT position
  39. GRB 251003A: Swift detection of a burst
  40. GRB 251003A: Fermi GBM Final Real-time Localization
  41. Swift GRB251003A: Global MASTER-Net observations report
  42. Fermi/SVOM GRB 251002A : MASTER OT earlier detection in 2 polarization filters
  43. GRB 251002A: BOOTES-6 early optical detection
  44. GRB 251002A: SAO RAS optical observations
  45. GRB 251002A: ULL-ASTRO-MASTER early detection of the optical afterglow with the LCO 40-cm telescope at Sutherland Observatory
  46. GRB 251002A: FRAM-ORM afterglow detection
  47. GRB 251002A: LCO optical observation
  48. GRB 251002A: SVOM/VT optical observation
  49. GRB 251002A: SVOM detection of a burst
  50. Fermi GRB 251002A: Global MASTER-Net observations report
  51. GRB 251001B: Swift-BAT refined analysis
  52. GRB 251001A: SVOM/GRM observation
  53. GRB 251001A: Insight-HXMT detection
  54. GRB 251001B: Swift/UVOT Detection
  55. GRB 251001B: COLIBRÍ optical observations
  56. GRB 251001B: GTC/OSIRIS+ spectroscopic redshift z = 2.162
  57. GRB 251001B: Swift-XRT refined Analysis
  58. GRB 251001B: SVOM/VT optical observation
  59. GRB 251001B: NOT optical observations
  60. GRB 251001C: Glowbug gamma-ray detection
  61. Swift GRB 251001B: Global MASTER-Net observations report
  62. GRB 251001B: Fermi GBM Observation
  63. GRB 251001B: Further GOTO observations of optical counterpart.
  64. GRB 251001B: Enhanced Swift-XRT position
  65. GRB 250930A: Fermi GBM Final Localization
  66. GRB 251001B: LCOGT Optical Observations
  67. GRB 250930A: SVOM/GRM observation
  68. GRB 251001B: TRT optical afterglow detection and potential host galaxy
  69. GRB 251001B: GOTO optical counterpart detection
  70. GRB 251001B: Swift detection of a burst
  71. GRB 251001B: Fermi GBM Final Real-time Localization
  72. GRB 251001A: Fermi GBM Detection
  73. GRB 250910A / EP250910a: VLT limits on the possible associated supernova
  74. GRB 251001A: BALROG localization (Fermi Trigger 780979261 / GRB 251001112)
  75. GRB 251001A: Fermi GBM Final Real-time Localization
  76. LIGO/Virgo/KAGRA S250830bp: SOAR spectroscopy of two DESGW candidates
  77. LIGO/Virgo/KAGRA S250818k: further MeerKAT monitoring
  78. GRB 250910A / EP250910a: VLT/X-shooter host galaxy redshift z = 0.592
  79. GRB 250925A: MAO/AZT-22 optical observations
  80. Fermi GRB 250929A: Global MASTER-Net observations report
  81. GRB 250929A: Fermi GBM Final Real-time Localization
  82. GRB 250926A: CALET Gamma-Ray Burst Monitor detection
  83. LIGO/Virgo/KAGRA S250929c: Updated Sky localization
  84. GRB 250925A: Mondy I-band optical observations
  85. GRB 250916A: SVOM/VT optical observation
  86. LIGO/Virgo/KAGRA S250929c: Identification of a GW compact binary merger candidate
  87. LIGO/Virgo/KAGRA S250927cy: Updated Sky localization
  88. LIGO/Virgo/KAGRA S250927ck: Updated Sky localization
  89. Fermi-LAT Gamma-ray Observations of IceCube-250926A
  90. GRB 250926A: triangulation location with Insight-HXMT/HE and Fermi/GBM
  91. GRB 250924A: SVOM/GRM observation
  92. GRB 250925A: Swift-XRT refined Analysis
  93. LIGO/Virgo/KAGRA S250927cy: Identification of a GW compact binary merger candidate
  94. LIGO/Virgo/KAGRA S250927ck: Identification of a GW compact binary merger candidate
  95. IceCube-250926A: Upper limits from a search for additional neutrino events in IceCube
  96. GRB 250926A: Insight-HXMT detection
  97. GRB 250926B: Fermi GBM Final Localization
  98. Fermi trigger No 780609036: Global MASTER-Net observations report
  99. IceCube Alert 250926.52: Global MASTER-Net observations report
  100. GRB 250920C: ULL-ASTRO-MASTER early detection of the optical afterglow with LCO 40-cm telescope at Siding Spring Observatory

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