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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 250918A: BALROG localization (Fermi Trigger 779891543 / GRB 250918522)
  2. GRB 250918A: Fermi GBM Final Real-time Localization
  3. GRB 250917B: Swift/UVOT Upper Limits
  4. GRB 250916A: OSIRIS+/GTC redshift z = 2.015
  5. GRB 250916A: Swift-XRT observations
  6. EP250916a: EP-FXT follow-up observation
  7. GRB 250916A: MAO/AZT-22 optical observations
  8. GRB 250916A: SAO RAS optical observations
  9. GRB 250916A : GIT optical observations
  10. LIGO/Virgo/KAGRA S250917aq: Three counterpart neutrino candidates from IceCube neutrino searches
  11. LIGO/Virgo/KAGRA S250917aq: Updated Sky localization
  12. GRB 250916A: Glowbug gamma-ray detection
  13. GRB250917B: WFST optical observations
  14. GRB 250916A: Swift ToO observations
  15. GRB 250917B: Fermi GBM Observation
  16. GRB 250917B: Swift-XRT observations
  17. LIGO/Virgo/KAGRA S250917aq: Identification of a GW compact binary merger candidate
  18. Fermi GRB 250917B: Global MASTER-Net observations report
  19. GRB 250917B: Swift detection of a short burst
  20. GRB 250916A: GOTO optical counterpart candidate
  21. GRB 250917B: Fermi GBM Final Real-time Localization
  22. GRB 250917A: Fermi GBM Final Real-time Localization
  23. The EP-WXT trigger 01709241037 is likely a flaring star
  24. GRB 250916A: AstroSat CZTI detection of a bright long burst
  25. GRB 250910A: SVOM/ECLAIRs refined analysis
  26. EP250916a: Einstein Probe detection of an X-ray transient
  27. Fermi GRB 250916A: Global MASTER-Net observations report
  28. GRB 250916A: Fermi GBM Final Real-time Localization
  29. EP250827b: VLA Observations
  30. LIGO/Virgo/KAGRA S250818k: HCT optical follow-up
  31. SVOM/sb25091517: Confirmation of a stellar flare by SVOM/VT
  32. SVOM/sb25091517: FRAM-ORM stellar flare - transient observation
  33. SVOM/sb25091517: SVOM detection of an X-ray transient
  34. GRB 250912A: Swift/BAT-GUANO localization skymap of a possibly short burst
  35. GRB 250912A: SVOM/COLIBRÍ (FM-GFT) optical observations
  36. GRB 250912A: Swift-XRT observations
  37. GRB250912A: VLT/HAWK-I follow-up observations
  38. GRB 250912A: VLT observations
  39. GRB 250912A: Fermi GBM Observation
  40. GRB 250911A: Insight-HXMT detection
  41. GRB 250912A: SVOM/GRM analysis suggests a possible short GRB with extended emission
  42. GRB 250912A:SVOM/VT optical upper limit
  43. GRB 250912A: LCO optical upper limit
  44. The EP-WXT trigger 01709240768 is likely a flaring star
  45. Fermi GRB 250912A: Global MASTER-Net observations report
  46. EP250911a: Global MASTER-Net observations report
  47. GRB 250912A: SVOM detection of a burst
  48. GRB 250912A: Fermi GBM Final Real-time Localization
  49. IceCube-Cascade 250911A: Upper limits from a search for additional neutrino events in IceCube
  50. LIGO/Virgo/KAGRA S250912s: 2 counterpart neutrino candidate events from an IceCube neutrino search
  51. EP250908c: tentative VLT/FORS2 redshift z = 2.87
  52. EP250911a: Upper limit from Fermi-GBM Observations
  53. LIGO/Virgo/KAGRA S250912f: Updated Sky localization
  54. GRB 250911A: GECAM-B detection
  55. GRB 250911A: Swift-BAT refined analysis
  56. EP250911a: GTC/OSIRIS+ spectroscopic redshift z = 3.84
  57. LIGO/Virgo/KAGRA S250912f: Identification of a GW compact binary merger candidate
  58. EP250911a: refined analysis of the EP-WXT and EP-FXT observations
  59. GRB 250910B: SVOM/GRM observation
  60. EP250911a: SVOM/VT optical observation
  61. GRB 250911A: MASTER optical counterpart observations
  62. EP250911a: SAO RAS optical observations
  63. GRB 250911A: Swift-XRT refined Analysis
  64. GRB 250910C: Fermi GBM Final Localization Correction
  65. EP250911a: Swift-XRT observations
  66. EP250911a: Optical detection with Kinder observations
  67. GRB 250911A: Swift/UVOT Detection
  68. GRB 250910A / EP250910a: Swift-XRT afterglow detection
  69. GRB 250910A / EP250910a: SVOM/VT afterglow confirmation
  70. GRB 250909B: Insight-HXMT detection
  71. GRB 250909B: SVOM/GRM observation
  72. LIGO/Virgo/KAGRA S250911ac: Updated Sky localization and Source Classification
  73. GRB 250910A / EP250910a : VLT/HAWK-I NIR counterpart discovery
  74. EP250911a: COLIBRÍ optical observations
  75. LIGO/Virgo/KAGRA S250908y: Updated Sky localization
  76. Fermi GRB 250910B: Global MASTER-Net observations report
  77. EP250911a: LCO optical counterpart discovery
  78. EP250910a: Global MASTER-Net observations report
  79. EP250911a: Einstein Probe detection of an X-ray transient
  80. GRB 250404A / EP250404a: spectroscopic redshift at z = 1.88 (correction to GCN 40084)
  81. LIGO/Virgo/KAGRA S250911ac: Identification of a GW compact binary merger candidate
  82. GRB 250903A: SVOM/ECLAIRs refined analysis
  83. GRB 250911A: Enhanced Swift-XRT position
  84. GRB 250911A: Swift-XRT observations
  85. GRB 250911A: COLIBRÍ optical counterpart candidate
  86. GRB 250911A: Swift detection of a burst
  87. LIGO/Virgo/KAGRA S250906ca: Updated Sky localization
  88. GRB 250910B: BALROG localization (Fermi Trigger 779223130 / GRB 250910786)
  89. GRB 250910B: Fermi GBM Final Real-time Localization
  90. GRB 250910A / EP250910a: VLT/HAWK-I near-infrared observations
  91. EP250910a/GRB 250910A: EP-WXT detection of a fast X-ray transient
  92. GRB 250909B: AstroSat CZTI detection of a long burst
  93. GRB 250910A: SVOM/VT optical upper limit
  94. EP250908C: GROND observation of the fading optical counterpart
  95. GRB 250910A: LCO optical upper limit
  96. GRB 250909A: AstroSat CZTI detection
  97. GRB 250910A: SVOM/MXT possible afterglow detection
  98. GRB 250910A: SVOM detection of a faint burst
  99. LIGO/Virgo/KAGRA S250910b: Retraction of GW compact binary merger candidate
  100. GRB 250702B: Late time Chandra observations

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