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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 250916A: AstroSat CZTI detection of a bright long burst
  2. GRB 250910A: SVOM/ECLAIRs refined analysis
  3. EP250916a: Einstein Probe detection of an X-ray transient
  4. Fermi GRB 250916A: Global MASTER-Net observations report
  5. GRB 250916A: Fermi GBM Final Real-time Localization
  6. EP250827b: VLA Observations
  7. LIGO/Virgo/KAGRA S250818k: HCT optical follow-up
  8. SVOM/sb25091517: Confirmation of a stellar flare by SVOM/VT
  9. SVOM/sb25091517: FRAM-ORM stellar flare - transient observation
  10. SVOM/sb25091517: SVOM detection of an X-ray transient
  11. GRB 250912A: Swift/BAT-GUANO localization skymap of a possibly short burst
  12. GRB 250912A: SVOM/COLIBRÍ (FM-GFT) optical observations
  13. GRB 250912A: Swift-XRT observations
  14. GRB250912A: VLT/HAWK-I follow-up observations
  15. GRB 250912A: VLT observations
  16. GRB 250912A: Fermi GBM Observation
  17. GRB 250911A: Insight-HXMT detection
  18. GRB 250912A: SVOM/GRM analysis suggests a possible short GRB with extended emission
  19. GRB 250912A:SVOM/VT optical upper limit
  20. GRB 250912A: LCO optical upper limit
  21. The EP-WXT trigger 01709240768 is likely a flaring star
  22. Fermi GRB 250912A: Global MASTER-Net observations report
  23. EP250911a: Global MASTER-Net observations report
  24. GRB 250912A: SVOM detection of a burst
  25. GRB 250912A: Fermi GBM Final Real-time Localization
  26. IceCube-Cascade 250911A: Upper limits from a search for additional neutrino events in IceCube
  27. LIGO/Virgo/KAGRA S250912s: 2 counterpart neutrino candidate events from an IceCube neutrino search
  28. EP250908c: tentative VLT/FORS2 redshift z = 2.87
  29. EP250911a: Upper limit from Fermi-GBM Observations
  30. LIGO/Virgo/KAGRA S250912f: Updated Sky localization
  31. GRB 250911A: GECAM-B detection
  32. GRB 250911A: Swift-BAT refined analysis
  33. EP250911a: GTC/OSIRIS+ spectroscopic redshift z = 3.84
  34. LIGO/Virgo/KAGRA S250912f: Identification of a GW compact binary merger candidate
  35. EP250911a: refined analysis of the EP-WXT and EP-FXT observations
  36. GRB 250910B: SVOM/GRM observation
  37. EP250911a: SVOM/VT optical observation
  38. GRB 250911A: MASTER optical counterpart observations
  39. EP250911a: SAO RAS optical observations
  40. GRB 250911A: Swift-XRT refined Analysis
  41. GRB 250910C: Fermi GBM Final Localization Correction
  42. EP250911a: Swift-XRT observations
  43. EP250911a: Optical detection with Kinder observations
  44. GRB 250911A: Swift/UVOT Detection
  45. GRB 250910A / EP250910a: Swift-XRT afterglow detection
  46. GRB 250910A / EP250910a: SVOM/VT afterglow confirmation
  47. GRB 250909B: Insight-HXMT detection
  48. GRB 250909B: SVOM/GRM observation
  49. LIGO/Virgo/KAGRA S250911ac: Updated Sky localization and Source Classification
  50. GRB 250910A / EP250910a : VLT/HAWK-I NIR counterpart discovery
  51. EP250911a: COLIBRÍ optical observations
  52. LIGO/Virgo/KAGRA S250908y: Updated Sky localization
  53. Fermi GRB 250910B: Global MASTER-Net observations report
  54. EP250911a: LCO optical counterpart discovery
  55. EP250910a: Global MASTER-Net observations report
  56. EP250911a: Einstein Probe detection of an X-ray transient
  57. GRB 250404A / EP250404a: spectroscopic redshift at z = 1.88 (correction to GCN 40084)
  58. LIGO/Virgo/KAGRA S250911ac: Identification of a GW compact binary merger candidate
  59. GRB 250903A: SVOM/ECLAIRs refined analysis
  60. GRB 250911A: Enhanced Swift-XRT position
  61. GRB 250911A: Swift-XRT observations
  62. GRB 250911A: COLIBRÍ optical counterpart candidate
  63. GRB 250911A: Swift detection of a burst
  64. LIGO/Virgo/KAGRA S250906ca: Updated Sky localization
  65. GRB 250910B: BALROG localization (Fermi Trigger 779223130 / GRB 250910786)
  66. GRB 250910B: Fermi GBM Final Real-time Localization
  67. GRB 250910A / EP250910a: VLT/HAWK-I near-infrared observations
  68. EP250910a/GRB 250910A: EP-WXT detection of a fast X-ray transient
  69. GRB 250909B: AstroSat CZTI detection of a long burst
  70. GRB 250910A: SVOM/VT optical upper limit
  71. EP250908C: GROND observation of the fading optical counterpart
  72. GRB 250910A: LCO optical upper limit
  73. GRB 250909A: AstroSat CZTI detection
  74. GRB 250910A: SVOM/MXT possible afterglow detection
  75. GRB 250910A: SVOM detection of a faint burst
  76. LIGO/Virgo/KAGRA S250910b: Retraction of GW compact binary merger candidate
  77. GRB 250702B: Late time Chandra observations
  78. EP250908b/EP#01709240653: Swift/UVOT Detection
  79. EP#01709240653: Swift-XRT observations
  80. The EP-WXT trigger 01709240674 is triggered by the known source SS Cyg
  81. EP250908c: refined analysis of the EP-WXT and EP-FXT observations
  82. GRB 250907A: CALET Gamma-Ray Burst Monitor detection
  83. EP250908c: SVOM/VT optical observation
  84. EP250908c: VLT/FORS2 optical counterpart identification
  85. EP250908b: SVOM/VT optical candidate (Coordinate supplement for GCN 41758)
  86. EP250908b: SVOM/VT optical candidate
  87. The EP-WXT trigger EP250908a/01709240652 is not a real source
  88. EP250908c: Global MASTER-Net observations report
  89. Fermi GRB 250909A: Global MASTER-Net observations report
  90. EP250908c: Einstein Probe detection of an X-ray transient
  91. GRB 250909A: Fermi GBM Final Real-time Localization
  92. EP250908b: EP-WXT detection of a fast X-ray transient and EP-FXT observation
  93. EP#01709240652 (possibly EP250908a): FTW optical and NIR observations
  94. LIGO/Virgo/KAGRA S250908y: Identification of a GW compact binary merger candidate
  95. GRB 250907A: GECAM-B detection
  96. GRB 250905A: Swift-BAT refined analysis
  97. Fermi-LAT Gamma-ray Observations of IceCube-250905A
  98. GRB 250903A: Swift-XRT afterglow detection
  99. LIGO/Virgo/KAGRA S250906ca: Identification of a GW compact binary merger candidate
  100. IceCube-250905A: Upper limits from a search for additional neutrino events in IceCube

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