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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 251003A: Swift-XRT refined Analysis
  2. GRB 251003A: COLIBRÍ photometric redshift
  3. GRB 251003A: GOTO detection of the optical counterpart
  4. GRB 251002A: Fermi GBM Observation
  5. LIGO/Virgo/KAGRA S251003at: Retraction of GW compact binary merger candidate
  6. GRB 251002A: GOTO detection of optical counterpart
  7. GRB 251001C: SVOM/GRM observation
  8. EP250821a: iTelescope T-59 possible detection of the optical counterpart
  9. GRB 251003A: Enhanced Swift-XRT position
  10. GRB 251002A: AKO Early Optical Afterglow Detection
  11. GRB 251003A: GTC/OSIRIS+ spectroscopic redshift z = 4.412
  12. GRB 251003A: Kilonova-Catcher optical afterglow detection
  13. GRB 251002A: Swift-XRT afterglow detection
  14. GRB 251001B: AbAO optical upper limit
  15. GRB 251002A: Kilonova-Catcher optical afterglow detection
  16. GRB 251002A: AbAO optical observations
  17. GRB 251002A: SVOM/COLIBRÍ (FM-GFT) optical observations
  18. GRB 251001C: CALET Gamma-Ray Burst Monitor detection
  19. GRB 251002A: J band observations by SYSU 80cm infrared telescope
  20. GRB 251002A: OHP/T193 MISTRAL optical afterglow detection
  21. GRB 251002A: VLT/X-shooter spectroscopic redshift z = 2.178
  22. GRB 251002A: EP-FXT counterpart detection
  23. GRB 251003A: LCOGT Optical Detection
  24. GRB 251003A: COLIBRÍ optical detection of the fading afterglow
  25. GRB 251003A: 1.5m OSN afterglow candidate
  26. GRB 251003A: Prompt enhanced Swift-XRT position
  27. GRB 251003A: Swift detection of a burst
  28. GRB 251003A: Fermi GBM Final Real-time Localization
  29. Swift GRB251003A: Global MASTER-Net observations report
  30. Fermi/SVOM GRB 251002A : MASTER OT earlier detection in 2 polarization filters
  31. GRB 251002A: BOOTES-6 early optical detection
  32. GRB 251002A: SAO RAS optical observations
  33. GRB 251002A: ULL-ASTRO-MASTER early detection of the optical afterglow with the LCO 40-cm telescope at Sutherland Observatory
  34. GRB 251002A: FRAM-ORM afterglow detection
  35. GRB 251002A: LCO optical observation
  36. GRB 251002A: SVOM/VT optical observation
  37. GRB 251002A: SVOM detection of a burst
  38. Fermi GRB 251002A: Global MASTER-Net observations report
  39. GRB 251001B: Swift-BAT refined analysis
  40. GRB 251001A: SVOM/GRM observation
  41. GRB 251001A: Insight-HXMT detection
  42. GRB 251001B: Swift/UVOT Detection
  43. GRB 251001B: COLIBRÍ optical observations
  44. GRB 251001B: GTC/OSIRIS+ spectroscopic redshift z = 2.162
  45. GRB 251001B: Swift-XRT refined Analysis
  46. GRB 251001B: SVOM/VT optical observation
  47. GRB 251001B: NOT optical observations
  48. GRB 251001C: Glowbug gamma-ray detection
  49. Swift GRB 251001B: Global MASTER-Net observations report
  50. GRB 251001B: Fermi GBM Observation
  51. GRB 251001B: Further GOTO observations of optical counterpart.
  52. GRB 251001B: Enhanced Swift-XRT position
  53. GRB 250930A: Fermi GBM Final Localization
  54. GRB 251001B: LCOGT Optical Observations
  55. GRB 250930A: SVOM/GRM observation
  56. GRB 251001B: TRT optical afterglow detection and potential host galaxy
  57. GRB 251001B: GOTO optical counterpart detection
  58. GRB 251001B: Swift detection of a burst
  59. GRB 251001B: Fermi GBM Final Real-time Localization
  60. GRB 251001A: Fermi GBM Detection
  61. GRB 250910A / EP250910a: VLT limits on the possible associated supernova
  62. GRB 251001A: BALROG localization (Fermi Trigger 780979261 / GRB 251001112)
  63. GRB 251001A: Fermi GBM Final Real-time Localization
  64. LIGO/Virgo/KAGRA S250830bp: SOAR spectroscopy of two DESGW candidates
  65. LIGO/Virgo/KAGRA S250818k: further MeerKAT monitoring
  66. GRB 250910A / EP250910a: VLT/X-shooter host galaxy redshift z = 0.592
  67. GRB 250925A: MAO/AZT-22 optical observations
  68. Fermi GRB 250929A: Global MASTER-Net observations report
  69. GRB 250929A: Fermi GBM Final Real-time Localization
  70. GRB 250926A: CALET Gamma-Ray Burst Monitor detection
  71. LIGO/Virgo/KAGRA S250929c: Updated Sky localization
  72. GRB 250925A: Mondy I-band optical observations
  73. GRB 250916A: SVOM/VT optical observation
  74. LIGO/Virgo/KAGRA S250929c: Identification of a GW compact binary merger candidate
  75. LIGO/Virgo/KAGRA S250927cy: Updated Sky localization
  76. LIGO/Virgo/KAGRA S250927ck: Updated Sky localization
  77. Fermi-LAT Gamma-ray Observations of IceCube-250926A
  78. GRB 250926A: triangulation location with Insight-HXMT/HE and Fermi/GBM
  79. GRB 250924A: SVOM/GRM observation
  80. GRB 250925A: Swift-XRT refined Analysis
  81. LIGO/Virgo/KAGRA S250927cy: Identification of a GW compact binary merger candidate
  82. LIGO/Virgo/KAGRA S250927ck: Identification of a GW compact binary merger candidate
  83. IceCube-250926A: Upper limits from a search for additional neutrino events in IceCube
  84. GRB 250926A: Insight-HXMT detection
  85. GRB 250926B: Fermi GBM Final Localization
  86. Fermi trigger No 780609036: Global MASTER-Net observations report
  87. IceCube Alert 250926.52: Global MASTER-Net observations report
  88. GRB 250920C: ULL-ASTRO-MASTER early detection of the optical afterglow with LCO 40-cm telescope at Siding Spring Observatory
  89. GRB 250926A: AstroSat CZTI detection
  90. GRB 250925A: Swift/UVOT Upper Limits
  91. GRB 250925A: Swift-BAT refined analysis
  92. GRB 250925A: Mondy and AbAO optical observations
  93. GRB 250925A: COLIBRÍ photometric redshift
  94. IceCube-250926A - IceCube observation of a high-energy neutrino candidate track-like event
  95. GRB 250925A: SVOM/GWAC-F60A upper limit
  96. GRB 250925A/EP250925a: EP-WXT detection
  97. GRB 250926A: DDOTI Optical Observations and Spatial Coincidence with the Orion Nebula
  98. GRB 250925A : MITSuME Akeno optical upper limits
  99. GRB 250925A: JinShan optical observations
  100. GRB 250925A: 1.5m OSN optical detection and redshift with the 10.4m GTC/OSIRIS+

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