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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"

20968 results found.

  1. GRB 250805A: TRT optical upper limits
  2. GRB 250805A: Swift-XRT observations
  3. Swift GRB250805.26: Global MASTER-Net observations report
  4. GRB 250804B: Tiled Swift observations
  5. Fermi trigger No 776041355: Global MASTER-Net observations report
  6. EP250802a: Global MASTER-Net observations report
  7. EP250802a: Einstein Probe detection of an X-ray transient
  8. LIGO/Virgo/KAGRA S250727dc: GRANDMA/OPD observations of AT2025smm
  9. GRB 250702B: SMA observations
  10. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS candidates
  11. LIGO/Virgo/KAGRA S250725j: GOTO pre-trigger detection of AT2025sib
  12. EP250711a: CrAO and Assy optical observations
  13. LIGO/Virgo/KAGRA S250727dc: DECam DESGW Epoch 1 Candidates
  14. EP250730a: Global MASTER-Net observations report
  15. EP250730a: Einstein Probe detection of an X-ray transient
  16. LIGO/Virgo/KAGRA S250725j: DECam DESGW Epoch 1-2 Candidates
  17. LIGO/Virgo/KAGRA S250727dc: Swift-XRT observations, 8 X-ray sources
  18. GRB 250725A: PRIME near-infrared observations
  19. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS upper limits of AT 2025smm
  20. LIGO/Virgo/KAGRA S250727dc: PRIME J-band upper limits of AT 2025smm
  21. GRB 250728A: Swift-XRT observations
  22. GRB 250727A: SVOM/ECLAIRs refined analysis
  23. EP-WXT trigger 01709195487: confirmation of a stellar flare by BOOTES-6 & BOOTES-7
  24. GRB 250728A: COLIBRÍ optical upper limit
  25. Fermi trigger No 775387550: Global MASTER-Net observations report
  26. GRB 250728A: Swift ToO observations
  27. GRB 250728A: Swift/BAT-GUANO arcminute localization of a short burst
  28. GRB 250727A: AST3-2 Upper limit
  29. GRB250727A: SVOM/VT optical upper limit
  30. GRB 250727A: Swift-XRT observations
  31. LIGO/Virgo/KAGRA S250725j: DECam GW-MMADS candidates
  32. LIGO/Virgo/KAGRA S250725j: NED Galaxies in the 3-Initial Localization Volume
  33. GRB 250725A: Global MASTER-Net: First Optical Synchronous Observatios of Short GRB.
  34. GRB 250725A: Swift/UVOT Upper Limits
  35. Fermi GRB 250725A: Global MASTER-Net observations report
  36. Swift GRB 250725A: Global MASTER-Net observations report
  37. EP250702a/GRB250702 B,E,D: MeerKAT radio observations at 3.06 GHz
  38. EP250702a/GRB250702 B,D,E: uGMRT Radio detection in 1.26 GHz
  39. SVOM J195836+32283/sb25072103: Second VT observation
  40. SVOM J195836+32283/sb25072103: Liverpool Telescope detection of an extended source
  41. SVOM J195836+32283/sb25072103: Swift XRT/UVOT upper limits
  42. SVOM J195836+32283/sb25072103: NIR observations with WINTER
  43. GRB 250721A: Swift-XRT observations
  44. GRB 250713A : SVOM/ECLAIRs refined analysis
  45. The SVOM alert sb25072103 is not due to a GRB, but to a new galactic transient SVOM J195836+32283.
  46. GRB 250721A: Tiled Swift observations
  47. Fermi trigger No 774730635: Global MASTER-Net observations report
  48. EP250702a/GRB250702B,D,E: SVOM/VT optical upper limit
  49. GRB 250717B: Swift-XRT observations
  50. Swift GRB250718.01: Global MASTER-Net observations report
  51. GRB 250717B: Swift ToO observations
  52. GRB 270713A: Kitab and AbAO Optical Observations
  53. GRB 250717B: Swift/BAT-GUANO arcminute localization of a burst
  54. GRB 250716A: Swift-XRT afterglow detection
  55. GRB 250716A: Lesedi Detection of Fading Optical Transient GOTO25eyp
  56. GRB 250716A: Swift ToO observations
  57. GRB 250716A: GOTO tentative optical counterpart candidate
  58. Fermi GRB 250716A: Global MASTER-Net observations report
  59. Fermi GRB 250715A: Global MASTER-Net observations report
  60. EP250702a / GRB 250702B,D,E: Hubble Space Telescope Observations
  61. GRB 250702B,D,E / EP250702a: H.E.S.S. very-high-energy gamma-ray observations
  62. GRB 250713A: Mephisto optical upper limits
  63. Fermi GRB 250714A: Global MASTER-Net observations report
  64. GRB 250713A: NOT optical upper limits
  65. GRB 250713A: OHP/T193 upper limit
  66. GRB 250713A: SVOM/C-GFT upper limit
  67. GRB 250706B/C: 7DT Follow-up Observations
  68. GRB 250713A: Swift-XRT observations
  69. EP250711a: COLIBRÍ continuous optical observations
  70. GRB 250713A: JinShan optical upper limits
  71. EP250711a: Global MASTER-Net observations report
  72. GRB 250711A: DDOTI Optical Upper Limit
  73. EP250711a: COLIBRÍ refined photometry and optical confirmation of the candidate
  74. Fermi GRB 250711A: Global MASTER-Net observations report
  75. EP250702a: gamma-ray upper limits from joint observations by the LST-1 and MAGIC telescopes
  76. GRB 250704A: GRANDMA observations
  77. GRB 250704A: SVOM/ECLAIRs refined analysis
  78. GRB 250702B,D,E/EP250702A: JCMT sub-mm observations at 350 GHz
  79. GRB 250704B / EP250704a: 1.3 GHz MeerKAT Detection
  80. GRB 250702B,D,E / EP250702a: ALMA detection
  81. IceCube-250708A: No Candidates from WINTER
  82. IceCube-250708A: No Candidate Transients from the Zwicky Transient Facility
  83. GRB 250702B,D,E/EP250702A: MeerKAT radio observations at 1.28GHz
  84. GRB 250702B,D,E / EP250702a: 10 GHz detection with the VLA
  85. EP/WXT 01709181970: GOTO observations confirm stellar variability
  86. EP250704a/GRB 250704B: 10 GHz VLA detection
  87. GRB250702 B,D,E / EP250702a: MOSFIRE imaging of the afterglow
  88. LIGO/Virgo/KAGRA S250704ab: NED Galaxies in the 4-Update Localization Volume
  89. IceCube-250706A: No Candidates from WINTER
  90. IceCube-250706A: No Candidates from the Zwicky Transient Facility
  91. GRB 250704B / EP250704a: VLA radio detection
  92. Fermi GRB 250708A: Global MASTER-Net observations report
  93. IceCube-250708A: Global MASTER-Net observations report
  94. EP250704a/GRB250704B : HCT optical and NIR upper limits
  95. GRB 250706B: SVOM observations interpreted as the afterglow of GRB 250706C
  96. GRB 250704B: CALET Gamma-Ray Burst Monitor detection
  97. GRB 250704B / EP250704a: Mondy and AbAO optical observations
  98. GRB 250702F: radio detection with the VLA
  99. IceCube-250706A: EP-FXT follow-up observations
  100. Fermi-LAT Gamma-ray Observations of IceCube-250706A

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