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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. EP-WXT trigger 01709195487: confirmation of a stellar flare by BOOTES-6 & BOOTES-7
  2. GRB 250728A: COLIBRÍ optical upper limit
  3. GRB 250728A: Fermi GBM Observation
  4. Fermi trigger No 775387550: Global MASTER-Net observations report
  5. LIGO/Virgo/KAGRA S250727dc: Updated Sky localization
  6. LIGO/Virgo/KAGRA S250727dc: Swift-UVOT detection of a new source, AT 2025smm
  7. GRB 250728A: Swift ToO observations
  8. GRB 250728A: Swift/BAT-GUANO arcminute localization of a short burst
  9. GRB 250727A: AST3-2 Upper limit
  10. LIGO/Virgo/KAGRA S250727cl: Updated Sky localization
  11. GRB 250727A: EP-FXT counterpart detection
  12. GRB250727A: SVOM/VT optical upper limit
  13. GRB 250727A: Swift-XRT observations
  14. LIGO/Virgo/KAGRA S250727dc: Identification of a GW compact binary merger candidate
  15. LIGO/Virgo/KAGRA S250727cl: Identification of a GW compact binary merger candidate
  16. LIGO/Virgo/KAGRA S250725j: DECam GW-MMADS candidates
  17. GRB 250727A: SVOM detection of a burst
  18. LIGO/Virgo/KAGRA S250725l: Updated Sky localization
  19. LIGO/Virgo/KAGRA S250726ak: Updated Sky localization
  20. The EP-WXT trigger 01709195487 is likely a flaring star
  21. Swift detection of the Soft Gamma Repeater PSR J1647-4552
  22. LIGO/Virgo/KAGRA S250726ak: Identification of a GW compact binary merger candidate
  23. GRB 250725A: Swift-XRT refined Analysis
  24. GRB 250725A: Fermi GBM Observation
  25. LIGO/Virgo/KAGRA S250725j: Updated Sky localization
  26. GRB 250725A: Swift-BAT refined analysis
  27. Konus-Wind detection of GRB 250725A
  28. LIGO/Virgo/KAGRA S250725j: NED Galaxies in the 3-Initial Localization Volume
  29. GRB 250725A: SVOM/GRM observation
  30. GRB 250725A: Global MASTER-Net: First Optical Synchronous Observatios of Short GRB.
  31. GRB 250725A: Swift/UVOT Upper Limits
  32. GRB 250725A: Fermi-LAT detection
  33. GRB 250725A: VLT/FORS2 spectroscopic redshift z = 5.26
  34. GRB 250725A: BOOTES-7 early optical detection
  35. GRB 250725A: SVOM/VT optical candidate
  36. GRB 250725A: MASTER-OAFA optical detection of very fast afterglow
  37. LIGO/Virgo/KAGRA S250725l: Identification of a GW compact binary merger candidate (duplicate submission)
  38. LIGO/Virgo/KAGRA S250725l: Identification of a GW compact binary merger candidate
  39. LIGO/Virgo/KAGRA S250725j: Identification of a GW compact binary merger candidate
  40. GRB 250725A: Enhanced Swift-XRT position
  41. GRB 250725A: Swift detection of a burst
  42. Swift GRB 250725A: Global MASTER-Net OT detection
  43. GRB 250725A: Fermi GBM Final Real-time Localization
  44. Fermi GRB 250725A: Global MASTER-Net observations report
  45. Swift GRB 250725A: Global MASTER-Net observations report
  46. EP250702a/GRB250702 B,E,D: MeerKAT radio observations at 3.06 GHz
  47. SVOM J195836+32283 is not a real source
  48. EP250702a/GRB250702 B,D,E: uGMRT Radio detection in 1.26 GHz
  49. SVOM J195836+32283/sb25072103: Second VT observation
  50. SVOM J195836+32283/sb25072103: Liverpool Telescope detection of an extended source
  51. GRB 250723B: Fermi GBM Final Real-time Localization
  52. GRB 250721A: Fermi GBM Observation
  53. GRB 250723A: Fermi GBM Final Real-time Localization
  54. SVOM J195836+32283/sb25072103: Swift XRT/UVOT upper limits
  55. SVOM J195836+32283/sb25072103: NIR observations with WINTER
  56. Swift-BAT trigger 1334535 is not a GRB
  57. GRB 250721A: Swift-XRT observations
  58. GRB 250722A: Fermi GBM Final Real-time Localization
  59. GRB 250713A : SVOM/ECLAIRs refined analysis
  60. GRB 250717B: SVOM/GRM observation
  61. LIGO/Virgo/KAGRA S250711q: Updated Sky localization
  62. The SVOM alert sb25072103 is not due to a GRB, but to a new galactic transient SVOM J195836+32283.
  63. GRB 250721A: Tiled Swift observations
  64. GRB 250721A: MAXI/GSC detection
  65. GRB 250721A: Fermi GBM Final Localization
  66. GRB 250720B: Fermi GBM Final Localization Correction
  67. GRB 250720A: Fermi GBM Final Localization
  68. Fermi trigger No 774730635: Global MASTER-Net observations report
  69. LIGO/Virgo/KAGRA S250720j: Retraction of GW compact binary merger candidate
  70. Fermi Gamma-ray Burst Monitor trigger 774670514/250720094 is not a GRB
  71. EP250702a/GRB250702B,D,E: SVOM/VT optical upper limit
  72. GRB 250717B: COLIBRÍ optical upper limit
  73. LIGO/Virgo/KAGRA S250711q: Upper limits from Swift/BAT-GUANO
  74. GRB 250717B: Swift-XRT observations
  75. GRB 250718B: Fermi GBM Final Localization Correction
  76. GRB 250718B: Fermi GBM Final Real-time Localization
  77. Swift Trigger 1334535 / GRB 250718A: COLIBRÍ optical upper limits
  78. Swift Trigger 1334535: a possible GRB 250718A
  79. Swift GRB250718.01: Global MASTER-Net observations report
  80. GRB 250717B: Swift ToO observations
  81. GRB 270713A: Kitab and AbAO Optical Observations
  82. GRB 250717B: Fermi GBM Observation
  83. GRB 250717B: Swift/BAT-GUANO arcminute localization of a burst
  84. Konus-Wind detection of GRB 250716A
  85. GRB 250716A: Swift-XRT afterglow detection
  86. GRB 250717B: Fermi GBM Final Real-time Localization
  87. GRB 250716A: Lesedi Detection of Fading Optical Transient GOTO25eyp
  88. GRB 250717A: Fermi GBM Final Real-time Localization
  89. GRB 250716A: Swift ToO observations
  90. GRB 250716A: GOTO tentative optical counterpart candidate
  91. GRB 250716A: Fermi GBM Observation
  92. GRB 250714A: SVOM/GRM observation
  93. Fermi GRB 250716A: Global MASTER-Net observations report
  94. GRB 250716A: Fermi GBM Final Real-time Localization
  95. Fermi GRB 250715A: Global MASTER-Net observations report
  96. GRB 250715A: Fermi GBM Final Real-time Localization
  97. EP250702a / GRB 250702B,D,E: Hubble Space Telescope Observations
  98. GRB 250702B,D,E / EP250702a: H.E.S.S. very-high-energy gamma-ray observations
  99. GRB 250713A: Mephisto optical upper limits
  100. Fermi GRB 250714A: Global MASTER-Net observations report

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