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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 251001B: COLIBRÍ optical observations
  2. GRB 251001B: GTC/OSIRIS+ spectroscopic redshift z = 2.162
  3. GRB 251001B: Swift-XRT refined Analysis
  4. GRB 251001B: SVOM/VT optical observation
  5. GRB 251001B: NOT optical observations
  6. GRB 251001C: Glowbug gamma-ray detection
  7. Swift GRB 251001B: Global MASTER-Net observations report
  8. GRB 251001B: Fermi GBM Observation
  9. GRB 251001B: Further GOTO observations of optical counterpart.
  10. GRB 251001B: Enhanced Swift-XRT position
  11. GRB 250930A: Fermi GBM Final Localization
  12. GRB 251001B: LCOGT Optical Observations
  13. GRB 250930A: SVOM/GRM observation
  14. GRB 251001B: TRT optical afterglow detection and potential host galaxy
  15. GRB 251001B: GOTO optical counterpart detection
  16. GRB 251001B: Swift detection of a burst
  17. GRB 251001B: Fermi GBM Final Real-time Localization
  18. GRB 251001A: Fermi GBM Detection
  19. GRB 250910A / EP250910a: VLT limits on the possible associated supernova
  20. GRB 251001A: BALROG localization (Fermi Trigger 780979261 / GRB 251001112)
  21. GRB 251001A: Fermi GBM Final Real-time Localization
  22. LIGO/Virgo/KAGRA S250830bp: SOAR spectroscopy of two DESGW candidates
  23. LIGO/Virgo/KAGRA S250818k: further MeerKAT monitoring
  24. GRB 250910A / EP250910a: VLT/X-shooter host galaxy redshift z = 0.592
  25. GRB 250925A: MAO/AZT-22 optical observations
  26. Fermi GRB 250929A: Global MASTER-Net observations report
  27. GRB 250929A: Fermi GBM Final Real-time Localization
  28. GRB 250926A: CALET Gamma-Ray Burst Monitor detection
  29. LIGO/Virgo/KAGRA S250929c: Updated Sky localization
  30. GRB 250925A: Mondy I-band optical observations
  31. GRB 250916A: SVOM/VT optical observation
  32. LIGO/Virgo/KAGRA S250929c: Identification of a GW compact binary merger candidate
  33. LIGO/Virgo/KAGRA S250927cy: Updated Sky localization
  34. LIGO/Virgo/KAGRA S250927ck: Updated Sky localization
  35. Fermi-LAT Gamma-ray Observations of IceCube-250926A
  36. GRB 250926A: triangulation location with Insight-HXMT/HE and Fermi/GBM
  37. GRB 250924A: SVOM/GRM observation
  38. GRB 250925A: Swift-XRT refined Analysis
  39. LIGO/Virgo/KAGRA S250927cy: Identification of a GW compact binary merger candidate
  40. LIGO/Virgo/KAGRA S250927ck: Identification of a GW compact binary merger candidate
  41. IceCube-250926A: Upper limits from a search for additional neutrino events in IceCube
  42. GRB 250926A: Insight-HXMT detection
  43. GRB 250926B: Fermi GBM Final Localization
  44. Fermi trigger No 780609036: Global MASTER-Net observations report
  45. IceCube Alert 250926.52: Global MASTER-Net observations report
  46. GRB 250920C: ULL-ASTRO-MASTER early detection of the optical afterglow with LCO 40-cm telescope at Siding Spring Observatory
  47. GRB 250926A: AstroSat CZTI detection
  48. GRB 250925A: Swift/UVOT Upper Limits
  49. GRB 250925A: Swift-BAT refined analysis
  50. GRB 250925A: Mondy and AbAO optical observations
  51. GRB 250925A: COLIBRÍ photometric redshift
  52. IceCube-250926A - IceCube observation of a high-energy neutrino candidate track-like event
  53. GRB 250925A: SVOM/GWAC-F60A upper limit
  54. GRB 250925A/EP250925a: EP-WXT detection
  55. GRB 250926A: DDOTI Optical Observations and Spatial Coincidence with the Orion Nebula
  56. GRB 250925A : MITSuME Akeno optical upper limits
  57. GRB 250925A: JinShan optical observations
  58. GRB 250925A: 1.5m OSN optical detection and redshift with the 10.4m GTC/OSIRIS+
  59. GRB 250919A / EP250919a: Global MASTER Net before, during and after trigger optical observations
  60. GRB 250925A: COLIBRÍ optical photometry of the afterglow
  61. Fermi GRB 250926A: Global MASTER-Net observations report
  62. GRB 250926A: Fermi GBM Final Real-time Localization
  63. GRB 250925A: Optical Observations via Virtual Telescope Project, Italy
  64. GRB250925A: Liverpool Telescope optical observations
  65. GRB 250925A: NOT optical afterglow candidate
  66. GRB 250925A: Leavitt Observatory optical upper limit
  67. GRB 250925A: Enhanced Swift-XRT position
  68. GRB 250924A: Swift-BAT refined analysis
  69. GRB 250925A: GROWTH-India Telescope Upper Limits
  70. GRB 250925A: Swift detection of a burst
  71. Swift GRB 250925A: Global MASTER-Net observations report
  72. GRB 250922A: SVOM/GRM observation
  73. GRB 250924A: 1.6m Mephisto optical upper limits
  74. GRB 250924A: SAO RAS optical observations
  75. GRB 250924A: NOT optical observations
  76. GRB 250924A: AstroSat CZTI detection
  77. GRB 250914A: AstroSat CZTI detection
  78. GRB 250920B: AstroSat CZTI detection
  79. GRB 250924A: SVOM/VT optical observation
  80. GRB 250924A: Swift/UVOT Detection
  81. GRB 250924A: Swift-XRT refined Analysis
  82. GRB 250924A: Enhanced Swift-XRT position
  83. GRB 250924A: J-band detection with WINTER
  84. GRB 250924A: GROWTH-India Telescope Upper Limits
  85. GRB 250924A: KAIT optical observations
  86. GRB 250924A: Mondy optical observations, afterglow fading
  87. GRB 250924A: Kilonova-Catcher optical afterglow detection
  88. GRB 250920C: Kilonova-Catcher optical afterglow detection
  89. GRB 250922B: SVOM/GRM observation
  90. GRB 250920C: TRT optical observation
  91. GRB 250924B: Fermi GBM Final Localization
  92. GRB 250924A: COLIBRÍ optical observations
  93. Swift GRB 250924A: Global MASTER-Net observations report
  94. GRB 250919A / EP250919a: further LCO optical observation
  95. GRB 250924A: DDOTI Detection of the Optical Counterpart
  96. GRB 250924A: Swift detection of a burst with an optical counterpart
  97. GRB 250920B: AbAO optical upper limits
  98. Konus-Wind detection of GRB 250920C
  99. GRB 250920C: KAIT optical observations
  100. GRB 250920C: VLT redshift confirmation z = 1.399

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