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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"

19548 results found.

  1. GRB 250807B: Swift detection of a burst with an optical counterpart.
  2. GRB 250805A: Kilonova-Catcher optical upper limits
  3. GRB 250805A: Swift/UVOT Upper Limits
  4. GRB 250806A: Swift/UVOT U-band detection
  5. EP250806a: Liverpool telescope optical upper limit
  6. GRB 250807A: Swift detection of a burst with an optical counterpart
  7. EP250806a: refined analysis of the EP-WXT and EP-FXT observations
  8. EP250806a: Earlier Detection of the VT Candidate by COLIBRÍ and LS
  9. EP250806a: SVOM /VT optical candidate
  10. GRB 250806A: J-band upper limit from WINTER
  11. GRB 250806A: KAIT optical upper limit
  12. EP250806a: COLIBRÍ optical upper limit
  13. GRB 250806A: Kilonova-Catcher optical upper limits
  14. EP250806a: Einstein Probe detection of an X-ray transient
  15. GRB 250806A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  16. GRB 250806A: SVOM/VT optical upper limit
  17. GRB 250806A: SVOM detection of a soft burst
  18. GRB 250805A: SVOM/VT optical counterpart
  19. GRB 250805A: Enhanced Swift-XRT position
  20. GRB 250804C: AstroSat CZTI detection of a long burst
  21. GRB 250805A: TRT optical upper limits
  22. GRB 250805A: Swift-XRT observations
  23. GRB 250804B: Tiled Swift observations
  24. GRB 250804B: SVOM/GRM observation of a short burst
  25. EP250802a: additional Liverpool Telescope upper limits
  26. EP250730a: SVOM/VT optical upper limit
  27. EP250802a: Liverpool Telescope optical upper limits
  28. EP250802a: GROWTH-India Telescope optical upper limit
  29. LIGO/Virgo/KAGRA S250727dc: GRANDMA/OPD observations of AT2025smm
  30. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS candidates
  31. LIGO/Virgo/KAGRA S250725j: GOTO pre-trigger detection of AT2025sib
  32. EP250711a: CrAO and Assy optical observations
  33. EP250730a: COLIBRÍ optical upper limit
  34. GRB 250727A: Swift-XRT afterglow confirmation and refined analysis
  35. LIGO/Virgo/KAGRA S250726ak: Upper limits from Swift/BAT-GUANO
  36. LIGO/Virgo/KAGRA S250725l: Upper limits from Swift/BAT-GUANO
  37. LIGO/Virgo/KAGRA S250727dc: Upper limits from Swift/BAT-GUANO
  38. LIGO/Virgo/KAGRA S250727dc: Swift-XRT observations, 8 X-ray sources
  39. GRB 250725A: PRIME near-infrared observations
  40. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS upper limits of AT 2025smm
  41. LIGO/Virgo/KAGRA S250727dc: PRIME J-band upper limits of AT 2025smm
  42. GRB 250728A: COLIBRÍ optical upper limit
  43. GRB 250728A: Swift ToO observations
  44. LIGO/Virgo/KAGRA S250727cl: Identification of a GW compact binary merger candidate
  45. LIGO/Virgo/KAGRA S250725j: DECam GW-MMADS candidates
  46. GRB 250727A: SVOM detection of a burst
  47. LIGO/Virgo/KAGRA S250726ak: Identification of a GW compact binary merger candidate
  48. GRB 250725A: SVOM/GRM observation
  49. GRB 250725A: Global MASTER-Net: First Optical Synchronous Observatios of Short GRB.
  50. GRB 250725A: Swift/UVOT Upper Limits
  51. GRB 250725A: SVOM/VT optical candidate
  52. GRB 250725A: Enhanced Swift-XRT position
  53. GRB 250725A: Swift detection of a burst
  54. EP250702a/GRB250702 B,E,D: MeerKAT radio observations at 3.06 GHz
  55. SVOM J195836+32283 is not a real source
  56. EP250702a/GRB250702 B,D,E: uGMRT Radio detection in 1.26 GHz
  57. SVOM J195836+32283/sb25072103: Liverpool Telescope detection of an extended source
  58. SVOM J195836+32283/sb25072103: NIR observations with WINTER
  59. GRB 250721A: Swift-XRT observations
  60. GRB 250713A : SVOM/ECLAIRs refined analysis
  61. GRB 250717B: SVOM/GRM observation
  62. The SVOM alert sb25072103 is not due to a GRB, but to a new galactic transient SVOM J195836+32283.
  63. GRB 250721A: Tiled Swift observations
  64. GRB 250717B: COLIBRÍ optical upper limit
  65. LIGO/Virgo/KAGRA S250711q: Upper limits from Swift/BAT-GUANO
  66. Swift Trigger 1334535 / GRB 250718A: COLIBRÍ optical upper limits
  67. GRB 250717B: Swift ToO observations
  68. GRB 270713A: Kitab and AbAO Optical Observations
  69. GRB 250716A: Swift-XRT afterglow detection
  70. GRB 250716A: Swift ToO observations
  71. GRB 250714A: SVOM/GRM observation
  72. EP250702a / GRB 250702B,D,E: Hubble Space Telescope Observations
  73. GRB 250713A: Mephisto optical upper limits
  74. GRB 250713A: SVOM/VT optical upper limit
  75. GRB 250713A: NOT optical upper limits
  76. GRB 250713A: OHP/T193 upper limit
  77. GRB 250713A: SVOM/C-GFT upper limit
  78. GRB 250706B/C: 7DT Follow-up Observations
  79. EP250711a: COLIBRÍ continuous optical observations
  80. GRB 250713A: JinShan optical upper limits
  81. GRB 250713A: SVOM detection of a long burst
  82. GRB 250711A: DDOTI Optical Upper Limit
  83. EP250711a: COLIBRÍ refined photometry and optical confirmation of the candidate
  84. GRB 250711A: SVOM/GRM observation
  85. EP250711a: NOT optical counterpart candidate
  86. EP250711a: EP-WXT detection and FXT follow-up observation of a fast X-ray transient
  87. EP candidate (ID=08500000365): COLIBRÍ optical Upper limit
  88. EP250702a: gamma-ray upper limits from joint observations by the LST-1 and MAGIC telescopes
  89. GRB 250704A: GRANDMA observations
  90. GRB 250704A: SVOM/ECLAIRs refined analysis
  91. LIGO/Virgo/KAGRA S250629bs: Upper limits from Swift/BAT-GUANO
  92. LIGO/Virgo/KAGRA S250629ae: Upper limits from Swift/BAT-GUANO
  93. IceCube-250708A: No Candidates from WINTER
  94. IceCube-250708A: No Candidate Transients from the Zwicky Transient Facility
  95. EP250704a/GRB 250704B: 10 GHz VLA detection
  96. IceCube-250706A: No Candidates from WINTER
  97. IceCube-250706A: No Candidates from the Zwicky Transient Facility
  98. GRB 250704B / EP250704a: VLA radio detection
  99. EP250704a/GRB250704B : HCT optical and NIR upper limits
  100. GRB 250708A: Fermi GBM Final Real-time Localization

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