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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 250920C: Optical counterpart detection by LCO
  2. GRB 250920A: SVOM/GRM observation
  3. GRB250920C: LCOGT Optical Detection
  4. GRB 250920B: Enhanced Swift-XRT position
  5. GRB 250920B: Swift-XRT refined Analysis
  6. GRB 250920B: SVOM/C-GFT optical observations
  7. GRB 250920C: GOTO optical counterpart candidate
  8. GRB 250919A / EP250919a: LCO optical observation
  9. Konus-Wind detection of GRB 250919A
  10. GRB 250920C: Swift detection of a burst
  11. GRB 250920C: Fermi GBM Final Real-time Localization
  12. LIGO/Virgo/KAGRA S250920bq: Coverage and upper limits from MAXI/GSC observations
  13. Swift GRB 250920B: Global MASTER-Net observations report
  14. GRB 250919A / EP250919a: Insight-HXMT detection
  15. GRB 250920A: AstroSat CZTI detection
  16. GRB 250920B: Swift detection of a burst with a bright optical counterpart.
  17. GRB 250920B: Fermi GBM Final Real-time Localization
  18. GRB 250920A: BALROG localization (Fermi Trigger 780029651 / GRB 250920121)
  19. GRB 250920A: Fermi GBM Final Localization
  20. GRB 250919A/EP250919a: SVOM/VT optical observation
  21. GRB 250919A / EP250919a: MASTER bright afterglow detection 24h after GRB time
  22. GRB 250916A: Mondy R-band optical observations
  23. GRB 250919A: Glowbug gamma-ray detection
  24. GRB 250919A: Fermi GBM Observation
  25. Fermi GRB 250918A: Global MASTER-Net observations report
  26. GRB 250919A / EP250919a: NuSTAR detection of bright prompt emission
  27. GRB 250918A: SVOM/GRM observation
  28. GRB 250919A/EP250919A: Swift/UVOT afterglow detection
  29. GRB 250919A: Swift-XRT afterglow detection
  30. GRB 250919A: Fermi-LAT detection
  31. EP250919a/GRB 250919A: Gemini/GMOS-S spectroscopic redshift z = 1.145
  32. GRB 250919A: SVOM/GRM observation of a very bright GRB
  33. GRB 250919A: BALROG localization (Fermi Trigger 779934537 / GRB 250919020)
  34. EP250919a: Global MASTER-Net observations report
  35. EP250919a: Einstein Probe detection of an X-ray transient
  36. Correction for GCN 41877: EP-WXT ID is 01709243841
  37. The EP-WXT trigger 01709243841: Las Cumbres discovery of the optical counterpart
  38. GRB 250916A: Fermi GBM Observation
  39. Fermi GRB 250919A: Global MASTER-Net observations report
  40. GRB 250919A: Fermi GBM Final Real-time Localization
  41. GRB 250916A: KAIT optical observations
  42. GRB 250917B: VLT/HAWK-I near-infrared observations
  43. GRB 250916A: NuSTAR detection of the prompt emission
  44. GRB 250916A: further SAO RAS optical observations
  45. GRB 250912A: SVOM/ECLAIRs refined analysis
  46. GRB 250917B: Swift-BAT refined analysis
  47. LIGO/Virgo/KAGRA S250918aw: 1 counterpart neutrino candidate event from an IceCube neutrino search
  48. GRB 250918A: BALROG localization (Fermi Trigger 779891543 / GRB 250918522)
  49. GRB 250918A: Fermi GBM Final Real-time Localization
  50. GRB 250917B: Swift/UVOT Upper Limits
  51. GRB 250916A: OSIRIS+/GTC redshift z = 2.015
  52. GRB 250916A: Swift-XRT observations
  53. EP250916a: EP-FXT follow-up observation
  54. GRB 250916A: MAO/AZT-22 optical observations
  55. GRB 250916A: SAO RAS optical observations
  56. GRB 250916A : GIT optical observations
  57. LIGO/Virgo/KAGRA S250917aq: Three counterpart neutrino candidates from IceCube neutrino searches
  58. LIGO/Virgo/KAGRA S250917aq: Updated Sky localization
  59. GRB 250916A: Glowbug gamma-ray detection
  60. GRB250917B: WFST optical observations
  61. GRB 250916A: Swift ToO observations
  62. GRB 250917B: Fermi GBM Observation
  63. GRB 250917B: Swift-XRT observations
  64. LIGO/Virgo/KAGRA S250917aq: Identification of a GW compact binary merger candidate
  65. Fermi GRB 250917B: Global MASTER-Net observations report
  66. GRB 250917B: Swift detection of a short burst
  67. GRB 250916A: GOTO optical counterpart candidate
  68. GRB 250917B: Fermi GBM Final Real-time Localization
  69. GRB 250917A: Fermi GBM Final Real-time Localization
  70. The EP-WXT trigger 01709241037 is likely a flaring star
  71. GRB 250916A: AstroSat CZTI detection of a bright long burst
  72. GRB 250910A: SVOM/ECLAIRs refined analysis
  73. EP250916a: Einstein Probe detection of an X-ray transient
  74. Fermi GRB 250916A: Global MASTER-Net observations report
  75. GRB 250916A: Fermi GBM Final Real-time Localization
  76. EP250827b: VLA Observations
  77. LIGO/Virgo/KAGRA S250818k: HCT optical follow-up
  78. SVOM/sb25091517: Confirmation of a stellar flare by SVOM/VT
  79. SVOM/sb25091517: FRAM-ORM stellar flare - transient observation
  80. SVOM/sb25091517: SVOM detection of an X-ray transient
  81. GRB 250912A: Swift/BAT-GUANO localization skymap of a possibly short burst
  82. GRB 250912A: SVOM/COLIBRÍ (FM-GFT) optical observations
  83. GRB 250912A: Swift-XRT observations
  84. GRB250912A: VLT/HAWK-I follow-up observations
  85. GRB 250912A: VLT observations
  86. GRB 250912A: Fermi GBM Observation
  87. GRB 250911A: Insight-HXMT detection
  88. GRB 250912A: SVOM/GRM analysis suggests a possible short GRB with extended emission
  89. GRB 250912A:SVOM/VT optical upper limit
  90. GRB 250912A: LCO optical upper limit
  91. The EP-WXT trigger 01709240768 is likely a flaring star
  92. Fermi GRB 250912A: Global MASTER-Net observations report
  93. EP250911a: Global MASTER-Net observations report
  94. GRB 250912A: SVOM detection of a burst
  95. GRB 250912A: Fermi GBM Final Real-time Localization
  96. IceCube-Cascade 250911A: Upper limits from a search for additional neutrino events in IceCube
  97. LIGO/Virgo/KAGRA S250912s: 2 counterpart neutrino candidate events from an IceCube neutrino search
  98. EP250908c: tentative VLT/FORS2 redshift z = 2.87
  99. EP250911a: Upper limit from Fermi-GBM Observations
  100. LIGO/Virgo/KAGRA S250912f: Updated Sky localization

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