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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"

20212 results found.

  1. GRB 250812A: SVOM/COLIBRÍ (FM-GFT) optical observations
  2. EP250812a: Einstein Probe detection of an X-ray transient
  3. GRB 250812A: Swift-XRT afterglow detection
  4. GRB 250812A: TRT likely optical counterpart detection
  5. LIGO/Virgo/KAGRA S250810ck: Updated Sky localization and EM Bright Classification
  6. GRB 250809A: Swift/UVOT Detection
  7. LIGO/Virgo/KAGRA S250810ck: Identification of a GW compact binary merger candidate
  8. GRB 250809A: Swift-XRT refined Analysis
  9. GRB 250809A: LCOGT Optical Upper Limits
  10. GRB 250808A: VLT X-shooter candidate counterpart
  11. GRB 250809A: Swift detection of a gamma ray burst
  12. GRB 250808A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  13. GRB 250808A: SVOM detection of a long burst
  14. Konus-Wind detection of GRB 250807A
  15. GRB 250807B: Swift/UVOT Detection
  16. GRB 250807B: Kilonova-Catcher optical afterglow detection
  17. GRB 250807A: Swift/UVOT Detection
  18. GRB 250807A: Swift-XRT refined Analysis
  19. GRB 250806A: SVOM/MXT refined analysis
  20. EP250807a: NTT z-band optical upper limit
  21. GRB 250806A: Mondy optical observations, and nearby bright galaxy photometry
  22. GRB 250807A: SVOM/GRM observation
  23. GRB 250807A: AstroSat CZTI detection of bright long burst
  24. EP250807a: EP-WXT detection of a fast X-ray transient
  25. EP 250807.979: GOTO optical upper limit
  26. EP250807a: COLIBRÍ optical upper limit
  27. GRB 250807B: Enhanced Swift-XRT position
  28. GRB 250807A: Enhanced Swift-XRT position
  29. GRB 250807B: Swift detection of a burst with an optical counterpart.
  30. GRB 250805A: Kilonova-Catcher optical upper limits
  31. GRB 250805A: Swift/UVOT Upper Limits
  32. GRB 250806A: Swift/UVOT U-band detection
  33. EP250806a: Liverpool telescope optical upper limit
  34. GRB 250807A: Swift detection of a burst with an optical counterpart
  35. EP250806a: refined analysis of the EP-WXT and EP-FXT observations
  36. EP250806a: SVOM /VT optical candidate
  37. GRB 250806A: J-band upper limit from WINTER
  38. GRB 250806A: KAIT optical upper limit
  39. GRB 250806A: Swift-XRT counterpart detection
  40. EP250806a: COLIBRÍ optical upper limit
  41. GRB 250806A: Kilonova-Catcher optical upper limits
  42. EP250806a: Einstein Probe detection of an X-ray transient
  43. GRB 250806A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  44. GRB 250806A: SVOM/VT optical upper limit
  45. GRB 250806A: SVOM detection of a soft burst
  46. GRB 250805A: SVOM/VT optical counterpart
  47. GRB 250804B: Swift-XRT observations
  48. GRB 250805A: Enhanced Swift-XRT position
  49. GRB 250805A: TRT optical upper limits
  50. GRB 250805A: Swift-XRT observations
  51. GRB 250804B: SVOM/GRM observation of a short burst
  52. EP250802a: additional Liverpool Telescope upper limits
  53. EP250730a: SVOM/VT optical upper limit
  54. EP250802a: Liverpool Telescope optical upper limits
  55. EP250802a: GROWTH-India Telescope optical upper limit
  56. LIGO/Virgo/KAGRA S250802dn: Identification of a GW compact binary merger candidate
  57. LIGO/Virgo/KAGRA S250727dc: GRANDMA/OPD observations of AT2025smm
  58. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS candidates
  59. LIGO/Virgo/KAGRA S250725j: GOTO pre-trigger detection of AT2025sib
  60. EP250711a: CrAO and Assy optical observations
  61. LIGO/Virgo/KAGRA S250727dc: DECam DESGW Epoch 1 Candidates
  62. EP250730a: COLIBRÍ optical upper limit
  63. GRB 250727A: Swift-XRT afterglow confirmation and refined analysis
  64. LIGO/Virgo/KAGRA S250726ak: Upper limits from Swift/BAT-GUANO
  65. LIGO/Virgo/KAGRA S250725l: Upper limits from Swift/BAT-GUANO
  66. LIGO/Virgo/KAGRA S250727dc: Upper limits from Swift/BAT-GUANO
  67. LIGO/Virgo/KAGRA S250727dc: Swift-XRT observations, 8 X-ray sources
  68. GRB 250725A: PRIME near-infrared observations
  69. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS upper limits of AT 2025smm
  70. LIGO/Virgo/KAGRA S250727dc: PRIME J-band upper limits of AT 2025smm
  71. GRB 250727A: SVOM/ECLAIRs refined analysis
  72. GRB 250728A: COLIBRÍ optical upper limit
  73. LIGO/Virgo/KAGRA S250727dc: Identification of a GW compact binary merger candidate
  74. LIGO/Virgo/KAGRA S250727cl: Identification of a GW compact binary merger candidate
  75. LIGO/Virgo/KAGRA S250725j: DECam GW-MMADS candidates
  76. GRB 250727A: SVOM detection of a burst
  77. LIGO/Virgo/KAGRA S250726ak: Identification of a GW compact binary merger candidate
  78. Konus-Wind detection of GRB 250725A
  79. GRB 250725A: SVOM/GRM observation
  80. GRB 250725A: Global MASTER-Net: First Optical Synchronous Observatios of Short GRB.
  81. GRB 250725A: Swift/UVOT Upper Limits
  82. GRB 250725A: Fermi-LAT detection
  83. GRB 250725A: SVOM/VT optical candidate
  84. GRB 250725A: MASTER-OAFA optical detection of very fast afterglow
  85. LIGO/Virgo/KAGRA S250725l: Identification of a GW compact binary merger candidate
  86. LIGO/Virgo/KAGRA S250725j: Identification of a GW compact binary merger candidate
  87. GRB 250725A: Enhanced Swift-XRT position
  88. GRB 250725A: Swift detection of a burst
  89. Swift GRB 250725A: Global MASTER-Net OT detection
  90. EP250702a/GRB250702 B,E,D: MeerKAT radio observations at 3.06 GHz
  91. SVOM J195836+32283 is not a real source
  92. EP250702a/GRB250702 B,D,E: uGMRT Radio detection in 1.26 GHz
  93. SVOM J195836+32283/sb25072103: Liverpool Telescope detection of an extended source
  94. SVOM J195836+32283/sb25072103: NIR observations with WINTER
  95. GRB 250721A: Swift-XRT observations
  96. GRB 250717B: SVOM/GRM observation
  97. The SVOM alert sb25072103 is not due to a GRB, but to a new galactic transient SVOM J195836+32283.
  98. EP250702a/GRB250702B,D,E: SVOM/VT optical upper limit
  99. GRB 250717B: COLIBRÍ optical upper limit
  100. LIGO/Virgo/KAGRA S250711q: Upper limits from Swift/BAT-GUANO

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