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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: GOTO optical counterpart candidate
  2. GRB 250919A / EP250919a: LCO optical observation
  3. Konus-Wind detection of GRB 250919A
  4. GRB 250920C: Swift detection of a burst
  5. GRB 250920C: Fermi GBM Final Real-time Localization
  6. LIGO/Virgo/KAGRA S250920bq: Coverage and upper limits from MAXI/GSC observations
  7. Swift GRB 250920B: Global MASTER-Net observations report
  8. GRB 250919A / EP250919a: Insight-HXMT detection
  9. GRB 250920A: AstroSat CZTI detection
  10. GRB 250920B: Swift detection of a burst with a bright optical counterpart.
  11. GRB 250920B: Fermi GBM Final Real-time Localization
  12. GRB 250920A: BALROG localization (Fermi Trigger 780029651 / GRB 250920121)
  13. GRB 250920A: Fermi GBM Final Localization
  14. GRB 250919A/EP250919a: SVOM/VT optical observation
  15. GRB 250919A / EP250919a: MASTER bright afterglow detection 24h after GRB time
  16. GRB 250916A: Mondy R-band optical observations
  17. GRB 250919A: Glowbug gamma-ray detection
  18. GRB 250919A: Fermi GBM Observation
  19. Fermi GRB 250918A: Global MASTER-Net observations report
  20. GRB 250919A / EP250919a: NuSTAR detection of bright prompt emission
  21. GRB 250918A: SVOM/GRM observation
  22. GRB 250919A/EP250919A: Swift/UVOT afterglow detection
  23. GRB 250919A: Swift-XRT afterglow detection
  24. GRB 250919A: Fermi-LAT detection
  25. EP250919a/GRB 250919A: Gemini/GMOS-S spectroscopic redshift z = 1.145
  26. GRB 250919A: SVOM/GRM observation of a very bright GRB
  27. GRB 250919A: BALROG localization (Fermi Trigger 779934537 / GRB 250919020)
  28. EP250919a: Global MASTER-Net observations report
  29. EP250919a: Einstein Probe detection of an X-ray transient
  30. Correction for GCN 41877: EP-WXT ID is 01709243841
  31. The EP-WXT trigger 01709243841: Las Cumbres discovery of the optical counterpart
  32. GRB 250916A: Fermi GBM Observation
  33. Fermi GRB 250919A: Global MASTER-Net observations report
  34. GRB 250919A: Fermi GBM Final Real-time Localization
  35. GRB 250916A: KAIT optical observations
  36. GRB 250917B: VLT/HAWK-I near-infrared observations
  37. GRB 250916A: NuSTAR detection of the prompt emission
  38. GRB 250916A: further SAO RAS optical observations
  39. GRB 250912A: SVOM/ECLAIRs refined analysis
  40. GRB 250917B: Swift-BAT refined analysis
  41. LIGO/Virgo/KAGRA S250918aw: 1 counterpart neutrino candidate event from an IceCube neutrino search
  42. GRB 250918A: BALROG localization (Fermi Trigger 779891543 / GRB 250918522)
  43. GRB 250918A: Fermi GBM Final Real-time Localization
  44. GRB 250917B: Swift/UVOT Upper Limits
  45. GRB 250916A: OSIRIS+/GTC redshift z = 2.015
  46. GRB 250916A: Swift-XRT observations
  47. EP250916a: EP-FXT follow-up observation
  48. GRB 250916A: MAO/AZT-22 optical observations
  49. GRB 250916A: SAO RAS optical observations
  50. GRB 250916A : GIT optical observations
  51. LIGO/Virgo/KAGRA S250917aq: Three counterpart neutrino candidates from IceCube neutrino searches
  52. LIGO/Virgo/KAGRA S250917aq: Updated Sky localization
  53. GRB 250916A: Glowbug gamma-ray detection
  54. GRB250917B: WFST optical observations
  55. GRB 250916A: Swift ToO observations
  56. GRB 250917B: Fermi GBM Observation
  57. GRB 250917B: Swift-XRT observations
  58. LIGO/Virgo/KAGRA S250917aq: Identification of a GW compact binary merger candidate
  59. Fermi GRB 250917B: Global MASTER-Net observations report
  60. GRB 250917B: Swift detection of a short burst
  61. GRB 250916A: GOTO optical counterpart candidate
  62. GRB 250917B: Fermi GBM Final Real-time Localization
  63. GRB 250917A: Fermi GBM Final Real-time Localization
  64. The EP-WXT trigger 01709241037 is likely a flaring star
  65. GRB 250916A: AstroSat CZTI detection of a bright long burst
  66. GRB 250910A: SVOM/ECLAIRs refined analysis
  67. EP250916a: Einstein Probe detection of an X-ray transient
  68. Fermi GRB 250916A: Global MASTER-Net observations report
  69. GRB 250916A: Fermi GBM Final Real-time Localization
  70. EP250827b: VLA Observations
  71. LIGO/Virgo/KAGRA S250818k: HCT optical follow-up
  72. SVOM/sb25091517: Confirmation of a stellar flare by SVOM/VT
  73. SVOM/sb25091517: FRAM-ORM stellar flare - transient observation
  74. SVOM/sb25091517: SVOM detection of an X-ray transient
  75. GRB 250912A: Swift/BAT-GUANO localization skymap of a possibly short burst
  76. GRB 250912A: SVOM/COLIBRÍ (FM-GFT) optical observations
  77. GRB 250912A: Swift-XRT observations
  78. GRB250912A: VLT/HAWK-I follow-up observations
  79. GRB 250912A: VLT observations
  80. GRB 250912A: Fermi GBM Observation
  81. GRB 250911A: Insight-HXMT detection
  82. GRB 250912A: SVOM/GRM analysis suggests a possible short GRB with extended emission
  83. GRB 250912A:SVOM/VT optical upper limit
  84. GRB 250912A: LCO optical upper limit
  85. The EP-WXT trigger 01709240768 is likely a flaring star
  86. Fermi GRB 250912A: Global MASTER-Net observations report
  87. EP250911a: Global MASTER-Net observations report
  88. GRB 250912A: SVOM detection of a burst
  89. GRB 250912A: Fermi GBM Final Real-time Localization
  90. IceCube-Cascade 250911A: Upper limits from a search for additional neutrino events in IceCube
  91. LIGO/Virgo/KAGRA S250912s: 2 counterpart neutrino candidate events from an IceCube neutrino search
  92. EP250908c: tentative VLT/FORS2 redshift z = 2.87
  93. EP250911a: Upper limit from Fermi-GBM Observations
  94. LIGO/Virgo/KAGRA S250912f: Updated Sky localization
  95. GRB 250911A: GECAM-B detection
  96. GRB 250911A: Swift-BAT refined analysis
  97. EP250911a: GTC/OSIRIS+ spectroscopic redshift z = 3.84
  98. LIGO/Virgo/KAGRA S250912f: Identification of a GW compact binary merger candidate
  99. EP250911a: refined analysis of the EP-WXT and EP-FXT observations
  100. GRB 250910B: SVOM/GRM observation

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