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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 251001A: Fermi GBM Final Real-time Localization
  2. LIGO/Virgo/KAGRA S250830bp: SOAR spectroscopy of two DESGW candidates
  3. LIGO/Virgo/KAGRA S250818k: further MeerKAT monitoring
  4. GRB 250910A / EP250910a: VLT/X-shooter host galaxy redshift z = 0.592
  5. GRB 250925A: MAO/AZT-22 optical observations
  6. Fermi GRB 250929A: Global MASTER-Net observations report
  7. GRB 250929A: Fermi GBM Final Real-time Localization
  8. GRB 250926A: CALET Gamma-Ray Burst Monitor detection
  9. LIGO/Virgo/KAGRA S250929c: Updated Sky localization
  10. GRB 250925A: Mondy I-band optical observations
  11. GRB 250916A: SVOM/VT optical observation
  12. LIGO/Virgo/KAGRA S250929c: Identification of a GW compact binary merger candidate
  13. LIGO/Virgo/KAGRA S250927cy: Updated Sky localization
  14. LIGO/Virgo/KAGRA S250927ck: Updated Sky localization
  15. Fermi-LAT Gamma-ray Observations of IceCube-250926A
  16. GRB 250926A: triangulation location with Insight-HXMT/HE and Fermi/GBM
  17. GRB 250924A: SVOM/GRM observation
  18. GRB 250925A: Swift-XRT refined Analysis
  19. LIGO/Virgo/KAGRA S250927cy: Identification of a GW compact binary merger candidate
  20. LIGO/Virgo/KAGRA S250927ck: Identification of a GW compact binary merger candidate
  21. IceCube-250926A: Upper limits from a search for additional neutrino events in IceCube
  22. GRB 250926A: Insight-HXMT detection
  23. GRB 250926B: Fermi GBM Final Localization
  24. Fermi trigger No 780609036: Global MASTER-Net observations report
  25. IceCube Alert 250926.52: Global MASTER-Net observations report
  26. GRB 250920C: ULL-ASTRO-MASTER early detection of the optical afterglow with LCO 40-cm telescope at Siding Spring Observatory
  27. GRB 250926A: AstroSat CZTI detection
  28. GRB 250925A: Swift/UVOT Upper Limits
  29. GRB 250925A: Swift-BAT refined analysis
  30. GRB 250925A: Mondy and AbAO optical observations
  31. GRB 250925A: COLIBRÍ photometric redshift
  32. IceCube-250926A - IceCube observation of a high-energy neutrino candidate track-like event
  33. GRB 250925A: SVOM/GWAC-F60A upper limit
  34. GRB 250925A/EP250925a: EP-WXT detection
  35. GRB 250926A: DDOTI Optical Observations and Spatial Coincidence with the Orion Nebula
  36. GRB 250925A : MITSuME Akeno optical upper limits
  37. GRB 250925A: JinShan optical observations
  38. GRB 250925A: 1.5m OSN optical detection and redshift with the 10.4m GTC/OSIRIS+
  39. GRB 250919A / EP250919a: Global MASTER Net before, during and after trigger optical observations
  40. GRB 250925A: COLIBRÍ optical photometry of the afterglow
  41. Fermi GRB 250926A: Global MASTER-Net observations report
  42. GRB 250926A: Fermi GBM Final Real-time Localization
  43. GRB 250925A: Optical Observations via Virtual Telescope Project, Italy
  44. GRB250925A: Liverpool Telescope optical observations
  45. GRB 250925A: NOT optical afterglow candidate
  46. GRB 250925A: Leavitt Observatory optical upper limit
  47. GRB 250925A: Enhanced Swift-XRT position
  48. GRB 250924A: Swift-BAT refined analysis
  49. GRB 250925A: GROWTH-India Telescope Upper Limits
  50. GRB 250925A: Swift detection of a burst
  51. Swift GRB 250925A: Global MASTER-Net observations report
  52. GRB 250922A: SVOM/GRM observation
  53. GRB 250924A: 1.6m Mephisto optical upper limits
  54. GRB 250924A: SAO RAS optical observations
  55. GRB 250924A: NOT optical observations
  56. GRB 250924A: AstroSat CZTI detection
  57. GRB 250914A: AstroSat CZTI detection
  58. GRB 250920B: AstroSat CZTI detection
  59. GRB 250924A: SVOM/VT optical observation
  60. GRB 250924A: Swift/UVOT Detection
  61. GRB 250924A: Swift-XRT refined Analysis
  62. GRB 250924A: Enhanced Swift-XRT position
  63. GRB 250924A: J-band detection with WINTER
  64. GRB 250924A: GROWTH-India Telescope Upper Limits
  65. GRB 250924A: KAIT optical observations
  66. GRB 250924A: Mondy optical observations, afterglow fading
  67. GRB 250924A: Kilonova-Catcher optical afterglow detection
  68. GRB 250920C: Kilonova-Catcher optical afterglow detection
  69. GRB 250922B: SVOM/GRM observation
  70. GRB 250920C: TRT optical observation
  71. GRB 250924B: Fermi GBM Final Localization
  72. GRB 250924A: COLIBRÍ optical observations
  73. Swift GRB 250924A: Global MASTER-Net observations report
  74. GRB 250919A / EP250919a: further LCO optical observation
  75. GRB 250924A: DDOTI Detection of the Optical Counterpart
  76. GRB 250924A: Swift detection of a burst with an optical counterpart
  77. GRB 250920B: AbAO optical upper limits
  78. Konus-Wind detection of GRB 250920C
  79. GRB 250920C: KAIT optical observations
  80. GRB 250920C: VLT redshift confirmation z = 1.399
  81. EP250911a: e-MERLIN radio observations
  82. GRB 250920B: CrAO ZTSH optical observations
  83. GRB 250920C: SALT redshift confirmation
  84. GRB 250920C: COLIBRÍ optical observations
  85. GRB 250922C: AstroSat CZTI detection of a short burst
  86. Fermi GRB 250922B: Global MASTER-Net observations report
  87. GRB 250920B: SAO RAS optical observations
  88. GRB 250920C: NIR observations with WINTER
  89. GRB 250920B: NIR observations with WINTER
  90. Fermi trigger No 780156732: Global MASTER-Net observations report
  91. GRB 250922B: Fermi GBM Final Real-time Localization
  92. GRB 250920C: PRIME near-infrared detection
  93. Konus-Wind detection of GRB 250920B
  94. Konus-Wind detection of GRB 250920A
  95. IPN triangulation of GRB 250920A (long/bright)
  96. Konus-Wind detection of GRB 250911A
  97. GRB 250916A: Swift/UVOT Detection
  98. GRB 250920B: Glowbug gamma-ray detection
  99. GRB 250916A: CrAO ZTSh R-band optical observations
  100. GRB 250920C: Swift-XRT refined Analysis

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