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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"

25885 results found.

  1. GRB 251003A: LAST optical observations
  2. GRB 251002A: LAST optical observations
  3. GRB 251005​C: Swift/UVOT Upper Limits
  4. GRB 250902A: MSU cubesats detection
  5. GRB 251005C: Swift-XRT refined Analysis
  6. GRB 251005C: Enhanced Swift-XRT position
  7. GRB 251005C: Swift detection of a burst
  8. GRB 251002A: Mondy/AZT-33IK optical observations
  9. EP251003a: Einstein Probe detection of an X-ray transient
  10. GRB 251003A: J-band detection with WINTER
  11. GRB 251002A: NIR observations with WINTER
  12. Fermi GBM Sub-Threshold Detection of GRB 250910A
  13. GRB 251003A: Swift-BAT refined analysis
  14. GRB 251001B: NIR observations with WINTER
  15. GRB 251002A: Calapai Observatory, Massa S. Giorgio (Messina), optical observation.
  16. GRB 251003A: Swift/UVOT Upper Limits
  17. GRB 251002A: Swift/UVOT detection
  18. GRB 251001A: AstroSat CZTI detection
  19. GRB 251001B: COLIBRÍ further observations and evidence of a multi-wavelength shallow decay
  20. GRB 251003A: Swift-XRT refined Analysis
  21. GRB 251003A: COLIBRÍ photometric redshift
  22. GRB 251002A: Fermi GBM Observation
  23. GRB 251002A: GOTO detection of optical counterpart
  24. GRB 251001C: SVOM/GRM observation
  25. EP250821a: iTelescope T-59 possible detection of the optical counterpart
  26. GRB 251003A: Enhanced Swift-XRT position
  27. GRB 251002A: AKO Early Optical Afterglow Detection
  28. GRB 251003A: Kilonova-Catcher optical afterglow detection
  29. GRB 251002A: Swift-XRT afterglow detection
  30. GRB 251001B: AbAO optical upper limit
  31. GRB 251002A: Kilonova-Catcher optical afterglow detection
  32. GRB 251002A: AbAO optical observations
  33. GRB 251002A: SVOM/COLIBRÍ (FM-GFT) optical observations
  34. GRB 251001C: CALET Gamma-Ray Burst Monitor detection
  35. GRB 251002A: J band observations by SYSU 80cm infrared telescope
  36. GRB 251002A: OHP/T193 MISTRAL optical afterglow detection
  37. GRB 251002A: EP-FXT counterpart detection
  38. GRB 251003A: LCOGT Optical Detection
  39. GRB 251003A: COLIBRÍ optical detection of the fading afterglow
  40. GRB 251003A: Swift detection of a burst
  41. Fermi/SVOM GRB 251002A : MASTER OT earlier detection in 2 polarization filters
  42. GRB 251002A: SAO RAS optical observations
  43. GRB 251002A: ULL-ASTRO-MASTER early detection of the optical afterglow with the LCO 40-cm telescope at Sutherland Observatory
  44. GRB 251002A: LCO optical observation
  45. GRB 251002A: SVOM/VT optical observation
  46. GRB 251002A: SVOM detection of a burst
  47. GRB 251001B: Swift-BAT refined analysis
  48. GRB 251001A: SVOM/GRM observation
  49. GRB 251001B: Swift/UVOT Detection
  50. GRB 251001B: COLIBRÍ optical observations
  51. GRB 251001B: Swift-XRT refined Analysis
  52. GRB 251001B: SVOM/VT optical observation
  53. GRB 251001B: NOT optical observations
  54. GRB 251001C: Glowbug gamma-ray detection
  55. GRB 251001B: Fermi GBM Observation
  56. GRB 251001B: Enhanced Swift-XRT position
  57. GRB 251001B: LCOGT Optical Observations
  58. GRB 250930A: SVOM/GRM observation
  59. GRB 251001B: TRT optical afterglow detection and potential host galaxy
  60. GRB 251001B: Swift detection of a burst
  61. GRB 251001B: Fermi GBM Final Real-time Localization
  62. GRB 251001A: Fermi GBM Detection
  63. GRB 250910A / EP250910a: VLT limits on the possible associated supernova
  64. GRB 251001A: BALROG localization (Fermi Trigger 780979261 / GRB 251001112)
  65. GRB 251001A: Fermi GBM Final Real-time Localization
  66. LIGO/Virgo/KAGRA S250818k: further MeerKAT monitoring
  67. GRB 250925A: MAO/AZT-22 optical observations
  68. LIGO/Virgo/KAGRA S250929c: Updated Sky localization
  69. GRB 250925A: Mondy I-band optical observations
  70. LIGO/Virgo/KAGRA S250929c: Identification of a GW compact binary merger candidate
  71. LIGO/Virgo/KAGRA S250927cy: Updated Sky localization
  72. LIGO/Virgo/KAGRA S250927ck: Updated Sky localization
  73. Fermi-LAT Gamma-ray Observations of IceCube-250926A
  74. GRB 250926A: triangulation location with Insight-HXMT/HE and Fermi/GBM
  75. GRB 250924A: SVOM/GRM observation
  76. GRB 250925A: Swift-XRT refined Analysis
  77. LIGO/Virgo/KAGRA S250927cy: Identification of a GW compact binary merger candidate
  78. LIGO/Virgo/KAGRA S250927ck: Identification of a GW compact binary merger candidate
  79. IceCube-250926A: Upper limits from a search for additional neutrino events in IceCube
  80. GRB 250920C: ULL-ASTRO-MASTER early detection of the optical afterglow with LCO 40-cm telescope at Siding Spring Observatory
  81. GRB 250926A: AstroSat CZTI detection
  82. GRB 250925A: Swift-BAT refined analysis
  83. GRB 250925A: Mondy and AbAO optical observations
  84. GRB 250925A: COLIBRÍ photometric redshift
  85. GRB 250925A: SVOM/GWAC-F60A upper limit
  86. GRB 250925A/EP250925a: EP-WXT detection
  87. GRB 250926A: DDOTI Optical Observations and Spatial Coincidence with the Orion Nebula
  88. GRB 250925A : MITSuME Akeno optical upper limits
  89. GRB 250925A: JinShan optical observations
  90. GRB 250919A / EP250919a: Global MASTER Net before, during and after trigger optical observations
  91. GRB 250925A: COLIBRÍ optical photometry of the afterglow
  92. GRB250925A: Liverpool Telescope optical observations
  93. GRB 250925A: NOT optical afterglow candidate
  94. GRB 250925A: Leavitt Observatory optical upper limit
  95. GRB 250925A: Enhanced Swift-XRT position
  96. GRB 250924A: Swift-BAT refined analysis
  97. GRB 250925A: GROWTH-India Telescope Upper Limits
  98. GRB 250925A: Swift detection of a burst
  99. GRB 250922A: SVOM/GRM observation
  100. GRB 250924A: 1.6m Mephisto optical upper limits

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