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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. Swift GRB 250920C: Global MASTER-Net observations report
  2. GRB 250920B: Swift/UVOT Detection
  3. GRB 250920B: FTW optical and NIR observations of the counterpart
  4. GRB 250920C: Optical counterpart detection by LCO
  5. GRB 250920A: SVOM/GRM observation
  6. GRB250920C: LCOGT Optical Detection
  7. GRB 250920B: Enhanced Swift-XRT position
  8. GRB 250920B: Swift-XRT refined Analysis
  9. GRB 250920B: SVOM/C-GFT optical observations
  10. GRB 250920C: GOTO optical counterpart candidate
  11. GRB 250919A / EP250919a: LCO optical observation
  12. Konus-Wind detection of GRB 250919A
  13. GRB 250920C: Swift detection of a burst
  14. GRB 250920C: Fermi GBM Final Real-time Localization
  15. LIGO/Virgo/KAGRA S250920bq: Coverage and upper limits from MAXI/GSC observations
  16. Swift GRB 250920B: Global MASTER-Net observations report
  17. GRB 250919A / EP250919a: Insight-HXMT detection
  18. GRB 250920A: AstroSat CZTI detection
  19. GRB 250920B: Swift detection of a burst with a bright optical counterpart.
  20. GRB 250920B: Fermi GBM Final Real-time Localization
  21. GRB 250920A: BALROG localization (Fermi Trigger 780029651 / GRB 250920121)
  22. GRB 250920A: Fermi GBM Final Localization
  23. GRB 250919A/EP250919a: SVOM/VT optical observation
  24. GRB 250919A / EP250919a: MASTER bright afterglow detection 24h after GRB time
  25. GRB 250916A: Mondy R-band optical observations
  26. GRB 250919A: Glowbug gamma-ray detection
  27. GRB 250919A: Fermi GBM Observation
  28. Fermi GRB 250918A: Global MASTER-Net observations report
  29. GRB 250919A / EP250919a: NuSTAR detection of bright prompt emission
  30. GRB 250918A: SVOM/GRM observation
  31. GRB 250919A/EP250919A: Swift/UVOT afterglow detection
  32. GRB 250919A: Swift-XRT afterglow detection
  33. GRB 250919A: Fermi-LAT detection
  34. EP250919a/GRB 250919A: Gemini/GMOS-S spectroscopic redshift z = 1.145
  35. GRB 250919A: SVOM/GRM observation of a very bright GRB
  36. GRB 250919A: BALROG localization (Fermi Trigger 779934537 / GRB 250919020)
  37. EP250919a: Global MASTER-Net observations report
  38. EP250919a: Einstein Probe detection of an X-ray transient
  39. Correction for GCN 41877: EP-WXT ID is 01709243841
  40. The EP-WXT trigger 01709243841: Las Cumbres discovery of the optical counterpart
  41. GRB 250916A: Fermi GBM Observation
  42. Fermi GRB 250919A: Global MASTER-Net observations report
  43. GRB 250919A: Fermi GBM Final Real-time Localization
  44. GRB 250916A: KAIT optical observations
  45. GRB 250917B: VLT/HAWK-I near-infrared observations
  46. GRB 250916A: NuSTAR detection of the prompt emission
  47. GRB 250916A: further SAO RAS optical observations
  48. GRB 250912A: SVOM/ECLAIRs refined analysis
  49. GRB 250917B: Swift-BAT refined analysis
  50. LIGO/Virgo/KAGRA S250918aw: 1 counterpart neutrino candidate event from an IceCube neutrino search
  51. GRB 250918A: BALROG localization (Fermi Trigger 779891543 / GRB 250918522)
  52. GRB 250918A: Fermi GBM Final Real-time Localization
  53. GRB 250917B: Swift/UVOT Upper Limits
  54. GRB 250916A: OSIRIS+/GTC redshift z = 2.015
  55. GRB 250916A: Swift-XRT observations
  56. EP250916a: EP-FXT follow-up observation
  57. GRB 250916A: MAO/AZT-22 optical observations
  58. GRB 250916A: SAO RAS optical observations
  59. GRB 250916A : GIT optical observations
  60. LIGO/Virgo/KAGRA S250917aq: Three counterpart neutrino candidates from IceCube neutrino searches
  61. LIGO/Virgo/KAGRA S250917aq: Updated Sky localization
  62. GRB 250916A: Glowbug gamma-ray detection
  63. GRB250917B: WFST optical observations
  64. GRB 250916A: Swift ToO observations
  65. GRB 250917B: Fermi GBM Observation
  66. GRB 250917B: Swift-XRT observations
  67. LIGO/Virgo/KAGRA S250917aq: Identification of a GW compact binary merger candidate
  68. Fermi GRB 250917B: Global MASTER-Net observations report
  69. GRB 250917B: Swift detection of a short burst
  70. GRB 250916A: GOTO optical counterpart candidate
  71. GRB 250917B: Fermi GBM Final Real-time Localization
  72. GRB 250917A: Fermi GBM Final Real-time Localization
  73. The EP-WXT trigger 01709241037 is likely a flaring star
  74. GRB 250916A: AstroSat CZTI detection of a bright long burst
  75. GRB 250910A: SVOM/ECLAIRs refined analysis
  76. EP250916a: Einstein Probe detection of an X-ray transient
  77. Fermi GRB 250916A: Global MASTER-Net observations report
  78. GRB 250916A: Fermi GBM Final Real-time Localization
  79. EP250827b: VLA Observations
  80. LIGO/Virgo/KAGRA S250818k: HCT optical follow-up
  81. SVOM/sb25091517: Confirmation of a stellar flare by SVOM/VT
  82. SVOM/sb25091517: FRAM-ORM stellar flare - transient observation
  83. SVOM/sb25091517: SVOM detection of an X-ray transient
  84. GRB 250912A: Swift/BAT-GUANO localization skymap of a possibly short burst
  85. GRB 250912A: SVOM/COLIBRÍ (FM-GFT) optical observations
  86. GRB 250912A: Swift-XRT observations
  87. GRB250912A: VLT/HAWK-I follow-up observations
  88. GRB 250912A: VLT observations
  89. GRB 250912A: Fermi GBM Observation
  90. GRB 250911A: Insight-HXMT detection
  91. GRB 250912A: SVOM/GRM analysis suggests a possible short GRB with extended emission
  92. GRB 250912A:SVOM/VT optical upper limit
  93. GRB 250912A: LCO optical upper limit
  94. The EP-WXT trigger 01709240768 is likely a flaring star
  95. Fermi GRB 250912A: Global MASTER-Net observations report
  96. EP250911a: Global MASTER-Net observations report
  97. GRB 250912A: SVOM detection of a burst
  98. GRB 250912A: Fermi GBM Final Real-time Localization
  99. IceCube-Cascade 250911A: Upper limits from a search for additional neutrino events in IceCube
  100. LIGO/Virgo/KAGRA S250912s: 2 counterpart neutrino candidate events from an IceCube neutrino search

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