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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"

20530 results found.

  1. EP250806a: Global MASTER-Net observations report
  2. EP250806a: refined analysis of the EP-WXT and EP-FXT observations
  3. EP250806a: Earlier Detection of the VT Candidate by COLIBRÍ and LS
  4. GRB 250806A: J-band upper limit from WINTER
  5. GRB 250806A: KAIT optical upper limit
  6. GRB 250806A: Kilonova-Catcher optical upper limits
  7. GRB 250806A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  8. GRB 250805A: ESO/VLT observations
  9. GRB 250804B: Swift-XRT observations
  10. GRB 250805A: TRT optical upper limits
  11. GRB 250805A: Swift-XRT observations
  12. Swift GRB250805.26: Global MASTER-Net observations report
  13. GRB 250804B: Tiled Swift observations
  14. Fermi trigger No 776041355: Global MASTER-Net observations report
  15. EP250802a: Global MASTER-Net observations report
  16. EP250802a: Einstein Probe detection of an X-ray transient
  17. LIGO/Virgo/KAGRA S250727dc: GRANDMA/OPD observations of AT2025smm
  18. GRB 250702B: SMA observations
  19. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS candidates
  20. LIGO/Virgo/KAGRA S250725j: GOTO pre-trigger detection of AT2025sib
  21. EP250711a: CrAO and Assy optical observations
  22. LIGO/Virgo/KAGRA S250727dc: DECam DESGW Epoch 1 Candidates
  23. EP250730a: Global MASTER-Net observations report
  24. EP250730a: Einstein Probe detection of an X-ray transient
  25. LIGO/Virgo/KAGRA S250725j: DECam DESGW Epoch 1-2 Candidates
  26. LIGO/Virgo/KAGRA S250726ak: Upper limits from Swift/BAT-GUANO
  27. LIGO/Virgo/KAGRA S250725l: Upper limits from Swift/BAT-GUANO
  28. LIGO/Virgo/KAGRA S250727dc: Upper limits from Swift/BAT-GUANO
  29. LIGO/Virgo/KAGRA S250727dc: Swift-XRT observations, 8 X-ray sources
  30. GRB 250725A: PRIME near-infrared observations
  31. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS upper limits of AT 2025smm
  32. LIGO/Virgo/KAGRA S250727dc: PRIME J-band upper limits of AT 2025smm
  33. GRB 250728A: Swift-XRT observations
  34. GRB 250727A: SVOM/ECLAIRs refined analysis
  35. EP-WXT trigger 01709195487: confirmation of a stellar flare by BOOTES-6 & BOOTES-7
  36. GRB 250728A: COLIBRÍ optical upper limit
  37. Fermi trigger No 775387550: Global MASTER-Net observations report
  38. GRB 250728A: Swift ToO observations
  39. GRB 250728A: Swift/BAT-GUANO arcminute localization of a short burst
  40. GRB 250727A: AST3-2 Upper limit
  41. GRB250727A: SVOM/VT optical upper limit
  42. GRB 250727A: Swift-XRT observations
  43. LIGO/Virgo/KAGRA S250725j: DECam GW-MMADS candidates
  44. LIGO/Virgo/KAGRA S250725j: NED Galaxies in the 3-Initial Localization Volume
  45. GRB 250725A: Global MASTER-Net: First Optical Synchronous Observatios of Short GRB.
  46. GRB 250725A: Swift/UVOT Upper Limits
  47. GRB 250725A: VLT/FORS2 spectroscopic redshift z = 5.26
  48. Fermi GRB 250725A: Global MASTER-Net observations report
  49. Swift GRB 250725A: Global MASTER-Net observations report
  50. EP250702a/GRB250702 B,E,D: MeerKAT radio observations at 3.06 GHz
  51. EP250702a/GRB250702 B,D,E: uGMRT Radio detection in 1.26 GHz
  52. SVOM J195836+32283/sb25072103: Second VT observation
  53. SVOM J195836+32283/sb25072103: Liverpool Telescope detection of an extended source
  54. SVOM J195836+32283/sb25072103: Swift XRT/UVOT upper limits
  55. SVOM J195836+32283/sb25072103: NIR observations with WINTER
  56. GRB 250721A: Swift-XRT observations
  57. GRB 250713A : SVOM/ECLAIRs refined analysis
  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. Fermi trigger No 774730635: Global MASTER-Net observations report
  61. EP250702a/GRB250702B,D,E: SVOM/VT optical upper limit
  62. LIGO/Virgo/KAGRA S250711q: Upper limits from Swift/BAT-GUANO
  63. GRB 250717B: Swift-XRT observations
  64. Swift GRB250718.01: Global MASTER-Net observations report
  65. GRB 250717B: Swift ToO observations
  66. GRB 270713A: Kitab and AbAO Optical Observations
  67. GRB 250717B: Swift/BAT-GUANO arcminute localization of a burst
  68. GRB 250716A: Swift-XRT afterglow detection
  69. GRB 250716A: Lesedi Detection of Fading Optical Transient GOTO25eyp
  70. GRB 250716A: Swift ToO observations
  71. GRB 250716A: GOTO tentative optical counterpart candidate
  72. Fermi GRB 250716A: Global MASTER-Net observations report
  73. Fermi GRB 250715A: Global MASTER-Net observations report
  74. EP250702a / GRB 250702B,D,E: Hubble Space Telescope Observations
  75. GRB 250702B,D,E / EP250702a: H.E.S.S. very-high-energy gamma-ray observations
  76. GRB 250713A: Mephisto optical upper limits
  77. Fermi GRB 250714A: Global MASTER-Net observations report
  78. GRB 250713A: NOT optical upper limits
  79. GRB 250713A: OHP/T193 upper limit
  80. GRB 250713A: SVOM/C-GFT upper limit
  81. GRB 250706B/C: 7DT Follow-up Observations
  82. GRB 250713A: Swift-XRT observations
  83. EP250711a: COLIBRÍ continuous optical observations
  84. GRB 250713A: JinShan optical upper limits
  85. EP250711a: Global MASTER-Net observations report
  86. GRB 250711A: DDOTI Optical Upper Limit
  87. EP250711a: COLIBRÍ refined photometry and optical confirmation of the candidate
  88. Fermi GRB 250711A: Global MASTER-Net observations report
  89. EP250702a: gamma-ray upper limits from joint observations by the LST-1 and MAGIC telescopes
  90. GRB 250704A: GRANDMA observations
  91. GRB 250704A: SVOM/ECLAIRs refined analysis
  92. GRB 250702B,D,E/EP250702A: JCMT sub-mm observations at 350 GHz
  93. GRB 250704B / EP250704a: 1.3 GHz MeerKAT Detection
  94. GRB 250702B,D,E / EP250702a: ALMA detection
  95. LIGO/Virgo/KAGRA S250629bs: Upper limits from Swift/BAT-GUANO
  96. LIGO/Virgo/KAGRA S250629ae: Upper limits from Swift/BAT-GUANO
  97. IceCube-250708A: No Candidates from WINTER
  98. IceCube-250708A: No Candidate Transients from the Zwicky Transient Facility
  99. GRB 250702B,D,E/EP250702A: MeerKAT radio observations at 1.28GHz
  100. GRB 250702B,D,E / EP250702a: 10 GHz detection with the VLA

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