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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. LIGO/Virgo/KAGRA S250727dc: Updated Sky localization
  2. LIGO/Virgo/KAGRA S250727dc: Swift-UVOT detection of a new source, AT 2025smm
  3. GRB 250728A: Swift ToO observations
  4. GRB 250728A: Swift/BAT-GUANO arcminute localization of a short burst
  5. GRB 250727A: AST3-2 Upper limit
  6. LIGO/Virgo/KAGRA S250727cl: Updated Sky localization
  7. GRB 250727A: EP-FXT counterpart detection
  8. GRB250727A: SVOM/VT optical upper limit
  9. GRB 250727A: Swift-XRT observations
  10. LIGO/Virgo/KAGRA S250727dc: Identification of a GW compact binary merger candidate
  11. LIGO/Virgo/KAGRA S250727cl: Identification of a GW compact binary merger candidate
  12. LIGO/Virgo/KAGRA S250725j: DECam GW-MMADS candidates
  13. GRB 250727A: SVOM detection of a burst
  14. LIGO/Virgo/KAGRA S250725l: Updated Sky localization
  15. LIGO/Virgo/KAGRA S250726ak: Updated Sky localization
  16. The EP-WXT trigger 01709195487 is likely a flaring star
  17. Swift detection of the Soft Gamma Repeater PSR J1647-4552
  18. LIGO/Virgo/KAGRA S250726ak: Identification of a GW compact binary merger candidate
  19. GRB 250725A: Swift-XRT refined Analysis
  20. GRB 250725A: Fermi GBM Observation
  21. LIGO/Virgo/KAGRA S250725j: Updated Sky localization
  22. GRB 250725A: Swift-BAT refined analysis
  23. Konus-Wind detection of GRB 250725A
  24. LIGO/Virgo/KAGRA S250725j: NED Galaxies in the 3-Initial Localization Volume
  25. GRB 250725A: SVOM/GRM observation
  26. GRB 250725A: Global MASTER-Net: First Optical Synchronous Observatios of Short GRB.
  27. GRB 250725A: Swift/UVOT Upper Limits
  28. GRB 250725A: Fermi-LAT detection
  29. GRB 250725A: VLT/FORS2 spectroscopic redshift z = 5.26
  30. GRB 250725A: BOOTES-7 early optical detection
  31. GRB 250725A: SVOM/VT optical candidate
  32. GRB 250725A: MASTER-OAFA optical detection of very fast afterglow
  33. LIGO/Virgo/KAGRA S250725l: Identification of a GW compact binary merger candidate (duplicate submission)
  34. LIGO/Virgo/KAGRA S250725l: Identification of a GW compact binary merger candidate
  35. LIGO/Virgo/KAGRA S250725j: Identification of a GW compact binary merger candidate
  36. GRB 250725A: Enhanced Swift-XRT position
  37. GRB 250725A: Swift detection of a burst
  38. Swift GRB 250725A: Global MASTER-Net OT detection
  39. GRB 250725A: Fermi GBM Final Real-time Localization
  40. Fermi GRB 250725A: Global MASTER-Net observations report
  41. Swift GRB 250725A: Global MASTER-Net observations report
  42. EP250702a/GRB250702 B,E,D: MeerKAT radio observations at 3.06 GHz
  43. SVOM J195836+32283 is not a real source
  44. EP250702a/GRB250702 B,D,E: uGMRT Radio detection in 1.26 GHz
  45. SVOM J195836+32283/sb25072103: Second VT observation
  46. SVOM J195836+32283/sb25072103: Liverpool Telescope detection of an extended source
  47. GRB 250723B: Fermi GBM Final Real-time Localization
  48. GRB 250721A: Fermi GBM Observation
  49. GRB 250723A: Fermi GBM Final Real-time Localization
  50. SVOM J195836+32283/sb25072103: Swift XRT/UVOT upper limits
  51. SVOM J195836+32283/sb25072103: NIR observations with WINTER
  52. Swift-BAT trigger 1334535 is not a GRB
  53. GRB 250721A: Swift-XRT observations
  54. GRB 250722A: Fermi GBM Final Real-time Localization
  55. GRB 250713A : SVOM/ECLAIRs refined analysis
  56. GRB 250717B: SVOM/GRM observation
  57. LIGO/Virgo/KAGRA S250711q: Updated Sky localization
  58. The SVOM alert sb25072103 is not due to a GRB, but to a new galactic transient SVOM J195836+32283.
  59. GRB 250721A: Tiled Swift observations
  60. GRB 250721A: MAXI/GSC detection
  61. GRB 250721A: Fermi GBM Final Localization
  62. GRB 250720B: Fermi GBM Final Localization Correction
  63. GRB 250720A: Fermi GBM Final Localization
  64. Fermi trigger No 774730635: Global MASTER-Net observations report
  65. LIGO/Virgo/KAGRA S250720j: Retraction of GW compact binary merger candidate
  66. Fermi Gamma-ray Burst Monitor trigger 774670514/250720094 is not a GRB
  67. EP250702a/GRB250702B,D,E: SVOM/VT optical upper limit
  68. GRB 250717B: COLIBRÍ optical upper limit
  69. LIGO/Virgo/KAGRA S250711q: Upper limits from Swift/BAT-GUANO
  70. GRB 250717B: Swift-XRT observations
  71. GRB 250718B: Fermi GBM Final Localization Correction
  72. GRB 250718B: Fermi GBM Final Real-time Localization
  73. Swift Trigger 1334535 / GRB 250718A: COLIBRÍ optical upper limits
  74. Swift Trigger 1334535: a possible GRB 250718A
  75. Swift GRB250718.01: Global MASTER-Net observations report
  76. GRB 250717B: Swift ToO observations
  77. GRB 270713A: Kitab and AbAO Optical Observations
  78. GRB 250717B: Fermi GBM Observation
  79. GRB 250717B: Swift/BAT-GUANO arcminute localization of a burst
  80. Konus-Wind detection of GRB 250716A
  81. GRB 250716A: Swift-XRT afterglow detection
  82. GRB 250717B: Fermi GBM Final Real-time Localization
  83. GRB 250716A: Lesedi Detection of Fading Optical Transient GOTO25eyp
  84. GRB 250717A: Fermi GBM Final Real-time Localization
  85. GRB 250716A: Swift ToO observations
  86. GRB 250716A: GOTO tentative optical counterpart candidate
  87. GRB 250716A: Fermi GBM Observation
  88. GRB 250714A: SVOM/GRM observation
  89. Fermi GRB 250716A: Global MASTER-Net observations report
  90. GRB 250716A: Fermi GBM Final Real-time Localization
  91. Fermi GRB 250715A: Global MASTER-Net observations report
  92. GRB 250715A: Fermi GBM Final Real-time Localization
  93. EP250702a / GRB 250702B,D,E: Hubble Space Telescope Observations
  94. GRB 250702B,D,E / EP250702a: H.E.S.S. very-high-energy gamma-ray observations
  95. GRB 250713A: Mephisto optical upper limits
  96. Fermi GRB 250714A: Global MASTER-Net observations report
  97. GRB 250713A: SVOM/VT optical upper limit
  98. GRB 250713A: NOT optical upper limits
  99. GRB 250713A: OHP/T193 upper limit
  100. GRB 250713A: SVOM/C-GFT upper limit

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