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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"

28036 results found.

  1. GRB 250807B: Enhanced Swift-XRT position
  2. GRB 250807A: Enhanced Swift-XRT position
  3. IceCube-Cascade 250804A: Upper limits from a search for additional neutrino events in IceCube
  4. GRB 250807B: Swift detection of a burst with an optical counterpart.
  5. GRB 250805A: Kilonova-Catcher optical upper limits
  6. GRB 250805A: Swift/UVOT Upper Limits
  7. GRB 250806A: Swift/UVOT U-band detection
  8. EP250806a: Liverpool telescope optical upper limit
  9. GRB 250807A: Swift detection of a burst with an optical counterpart
  10. EP250802a: EP-FXT follow-up observation
  11. EP250806a: refined analysis of the EP-WXT and EP-FXT observations
  12. EP250806a: SVOM /VT optical candidate
  13. GRB 250806A: J-band upper limit from WINTER
  14. GRB 250805A: Swift-BAT refined analysis
  15. GRB 250806A: KAIT optical upper limit
  16. GRB 250806A: Swift-XRT counterpart detection
  17. EP250806a: COLIBRÍ optical upper limit
  18. GRB 250806A: Kilonova-Catcher optical upper limits
  19. EP250806a: Einstein Probe detection of an X-ray transient
  20. GRB 250806A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  21. GRB 250806A: SVOM/VT optical upper limit
  22. GRB 250806A: SVOM detection of a soft burst
  23. GRB 250805A: SVOM/VT optical counterpart
  24. GRB 250805A: Swift-XRT refined Analysis
  25. GRB 250804B: Swift-XRT observations
  26. GRB 250805A: Enhanced Swift-XRT position
  27. GRB 250805A: TRT optical upper limits
  28. GRB 250805A: Swift-XRT observations
  29. GRB 250804B: SVOM/GRM observation of a short burst
  30. GRB 250804A: Fermi GBM Final Localization
  31. EP250802a: additional Liverpool Telescope upper limits
  32. EP250730a: SVOM/VT optical upper limit
  33. EP250802a: Liverpool Telescope optical upper limits
  34. EP250802a: Global MASTER-Net observations report
  35. EP250802a: GROWTH-India Telescope optical upper limit
  36. LIGO/Virgo/KAGRA S250802dn: Updated Sky localization
  37. LIGO/Virgo/KAGRA S250802dn: Identification of a GW compact binary merger candidate
  38. LIGO/Virgo/KAGRA S250727dc: GRANDMA/OPD observations of AT2025smm
  39. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS candidates
  40. LIGO/Virgo/KAGRA S250725j: GOTO pre-trigger detection of AT2025sib
  41. EP250711a: CrAO and Assy optical observations
  42. LIGO/Virgo/KAGRA S250727dc: DECam DESGW Epoch 1 Candidates
  43. EP250730a: COLIBRÍ optical upper limit
  44. GRB 250727A: Swift-XRT afterglow confirmation and refined analysis
  45. LIGO/Virgo/KAGRA S250725j: DECam DESGW Epoch 1-2 Candidates
  46. LIGO/Virgo/KAGRA S250726ak: Upper limits from Swift/BAT-GUANO
  47. LIGO/Virgo/KAGRA S250725l: Upper limits from Swift/BAT-GUANO
  48. LIGO/Virgo/KAGRA S250727dc: Upper limits from Swift/BAT-GUANO
  49. LIGO/Virgo/KAGRA S250727dc: Swift-XRT observations, 8 X-ray sources
  50. GRB 250727A: EP-FXT follow-up observation
  51. GRB 250725A: PRIME near-infrared observations
  52. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS upper limits of AT 2025smm
  53. LIGO/Virgo/KAGRA S250727dc: PRIME J-band upper limits of AT 2025smm
  54. GRB 250728A: Swift-XRT observations
  55. GRB 250728A: COLIBRÍ optical upper limit
  56. LIGO/Virgo/KAGRA S250727dc: Updated Sky localization
  57. GRB 250728A: Swift/BAT-GUANO arcminute localization of a short burst
  58. LIGO/Virgo/KAGRA S250727cl: Updated Sky localization
  59. GRB 250727A: EP-FXT counterpart detection
  60. GRB 250727A: Swift-XRT observations
  61. LIGO/Virgo/KAGRA S250727dc: Identification of a GW compact binary merger candidate
  62. LIGO/Virgo/KAGRA S250727cl: Identification of a GW compact binary merger candidate
  63. LIGO/Virgo/KAGRA S250725j: DECam GW-MMADS candidates
  64. LIGO/Virgo/KAGRA S250725l: Updated Sky localization
  65. LIGO/Virgo/KAGRA S250726ak: Updated Sky localization
  66. LIGO/Virgo/KAGRA S250726ak: Identification of a GW compact binary merger candidate
  67. GRB 250725A: Swift-XRT refined Analysis
  68. GRB 250725A: Fermi GBM Observation
  69. LIGO/Virgo/KAGRA S250725j: Updated Sky localization
  70. GRB 250725A: Swift-BAT refined analysis
  71. LIGO/Virgo/KAGRA S250725j: NED Galaxies in the 3-Initial Localization Volume
  72. GRB 250725A: SVOM/GRM observation
  73. GRB 250725A: Global MASTER-Net: First Optical Synchronous Observatios of Short GRB.
  74. GRB 250725A: Swift/UVOT Upper Limits
  75. GRB 250725A: Fermi-LAT detection
  76. GRB 250725A: BOOTES-7 early optical detection
  77. GRB 250725A: SVOM/VT optical candidate
  78. GRB 250725A: MASTER-OAFA optical detection of very fast afterglow
  79. LIGO/Virgo/KAGRA S250725l: Identification of a GW compact binary merger candidate
  80. LIGO/Virgo/KAGRA S250725j: Identification of a GW compact binary merger candidate
  81. GRB 250725A: Enhanced Swift-XRT position
  82. GRB 250725A: Swift detection of a burst
  83. Swift GRB 250725A: Global MASTER-Net OT detection
  84. EP250702a/GRB250702 B,E,D: MeerKAT radio observations at 3.06 GHz
  85. SVOM J195836+32283 is not a real source
  86. EP250702a/GRB250702 B,D,E: uGMRT Radio detection in 1.26 GHz
  87. SVOM J195836+32283/sb25072103: Liverpool Telescope detection of an extended source
  88. GRB 250721A: Fermi GBM Observation
  89. SVOM J195836+32283/sb25072103: NIR observations with WINTER
  90. GRB 250721A: Swift-XRT observations
  91. GRB 250717B: SVOM/GRM observation
  92. LIGO/Virgo/KAGRA S250711q: Updated Sky localization
  93. The SVOM alert sb25072103 is not due to a GRB, but to a new galactic transient SVOM J195836+32283.
  94. GRB 250721A: MAXI/GSC detection
  95. LIGO/Virgo/KAGRA S250720j: Retraction of GW compact binary merger candidate
  96. GRB 250717B: COLIBRÍ optical upper limit
  97. LIGO/Virgo/KAGRA S250711q: Upper limits from Swift/BAT-GUANO
  98. GRB 250717B: Swift-XRT observations
  99. Swift Trigger 1334535 / GRB 250718A: COLIBRÍ optical upper limits
  100. Swift GRB250718.01: Global MASTER-Net observations report

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