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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"

19551 results found.

  1. EP250807a: COLIBRÍ optical upper limit
  2. GRB 250807B: Enhanced Swift-XRT position
  3. GRB 250807A: Enhanced Swift-XRT position
  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. EP250806a: refined analysis of the EP-WXT and EP-FXT observations
  11. EP250806a: Earlier Detection of the VT Candidate by COLIBRÍ and LS
  12. EP250806a: SVOM /VT optical candidate
  13. GRB 250806A: J-band upper limit from WINTER
  14. GRB 250806A: KAIT optical upper limit
  15. EP250806a: COLIBRÍ optical upper limit
  16. GRB 250806A: Kilonova-Catcher optical upper limits
  17. EP250806a: Einstein Probe detection of an X-ray transient
  18. GRB 250806A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  19. GRB 250806A: SVOM/VT optical upper limit
  20. GRB 250806A: SVOM detection of a soft burst
  21. GRB 250805A: SVOM/VT optical counterpart
  22. GRB 250805A: Enhanced Swift-XRT position
  23. GRB 250804C: AstroSat CZTI detection of a long burst
  24. GRB 250805A: TRT optical upper limits
  25. GRB 250805A: Swift-XRT observations
  26. GRB 250804B: Tiled Swift observations
  27. GRB 250804B: SVOM/GRM observation of a short burst
  28. EP250802a: additional Liverpool Telescope upper limits
  29. EP250730a: SVOM/VT optical upper limit
  30. EP250802a: Liverpool Telescope optical upper limits
  31. EP250802a: GROWTH-India Telescope optical upper limit
  32. LIGO/Virgo/KAGRA S250727dc: GRANDMA/OPD observations of AT2025smm
  33. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS candidates
  34. LIGO/Virgo/KAGRA S250725j: GOTO pre-trigger detection of AT2025sib
  35. EP250711a: CrAO and Assy optical observations
  36. EP250730a: COLIBRÍ optical upper limit
  37. GRB 250727A: Swift-XRT afterglow confirmation and refined analysis
  38. LIGO/Virgo/KAGRA S250726ak: Upper limits from Swift/BAT-GUANO
  39. LIGO/Virgo/KAGRA S250725l: Upper limits from Swift/BAT-GUANO
  40. LIGO/Virgo/KAGRA S250727dc: Upper limits from Swift/BAT-GUANO
  41. LIGO/Virgo/KAGRA S250727dc: Swift-XRT observations, 8 X-ray sources
  42. GRB 250725A: PRIME near-infrared observations
  43. LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS upper limits of AT 2025smm
  44. LIGO/Virgo/KAGRA S250727dc: PRIME J-band upper limits of AT 2025smm
  45. GRB 250728A: COLIBRÍ optical upper limit
  46. GRB 250728A: Swift ToO observations
  47. LIGO/Virgo/KAGRA S250727cl: Identification of a GW compact binary merger candidate
  48. LIGO/Virgo/KAGRA S250725j: DECam GW-MMADS candidates
  49. GRB 250727A: SVOM detection of a burst
  50. LIGO/Virgo/KAGRA S250726ak: Identification of a GW compact binary merger candidate
  51. GRB 250725A: SVOM/GRM observation
  52. GRB 250725A: Global MASTER-Net: First Optical Synchronous Observatios of Short GRB.
  53. GRB 250725A: Swift/UVOT Upper Limits
  54. GRB 250725A: SVOM/VT optical candidate
  55. GRB 250725A: Enhanced Swift-XRT position
  56. GRB 250725A: Swift detection of a burst
  57. EP250702a/GRB250702 B,E,D: MeerKAT radio observations at 3.06 GHz
  58. SVOM J195836+32283 is not a real source
  59. EP250702a/GRB250702 B,D,E: uGMRT Radio detection in 1.26 GHz
  60. SVOM J195836+32283/sb25072103: Liverpool Telescope detection of an extended source
  61. SVOM J195836+32283/sb25072103: NIR observations with WINTER
  62. GRB 250721A: Swift-XRT observations
  63. GRB 250713A : SVOM/ECLAIRs refined analysis
  64. GRB 250717B: SVOM/GRM observation
  65. The SVOM alert sb25072103 is not due to a GRB, but to a new galactic transient SVOM J195836+32283.
  66. GRB 250721A: Tiled Swift observations
  67. GRB 250717B: COLIBRÍ optical upper limit
  68. LIGO/Virgo/KAGRA S250711q: Upper limits from Swift/BAT-GUANO
  69. Swift Trigger 1334535 / GRB 250718A: COLIBRÍ optical upper limits
  70. GRB 250717B: Swift ToO observations
  71. GRB 270713A: Kitab and AbAO Optical Observations
  72. GRB 250716A: Swift-XRT afterglow detection
  73. GRB 250716A: Swift ToO observations
  74. GRB 250714A: SVOM/GRM observation
  75. EP250702a / GRB 250702B,D,E: Hubble Space Telescope Observations
  76. GRB 250713A: Mephisto optical upper limits
  77. GRB 250713A: SVOM/VT optical upper limit
  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. EP250711a: COLIBRÍ continuous optical observations
  83. GRB 250713A: JinShan optical upper limits
  84. GRB 250713A: SVOM detection of a long burst
  85. GRB 250711A: DDOTI Optical Upper Limit
  86. EP250711a: COLIBRÍ refined photometry and optical confirmation of the candidate
  87. GRB 250711A: SVOM/GRM observation
  88. EP250711a: NOT optical counterpart candidate
  89. EP250711a: EP-WXT detection and FXT follow-up observation of a fast X-ray transient
  90. EP candidate (ID=08500000365): COLIBRÍ optical Upper limit
  91. EP250702a: gamma-ray upper limits from joint observations by the LST-1 and MAGIC telescopes
  92. GRB 250704A: GRANDMA observations
  93. GRB 250704A: SVOM/ECLAIRs refined analysis
  94. LIGO/Virgo/KAGRA S250629bs: Upper limits from Swift/BAT-GUANO
  95. LIGO/Virgo/KAGRA S250629ae: Upper limits from Swift/BAT-GUANO
  96. IceCube-250708A: No Candidates from WINTER
  97. IceCube-250708A: No Candidate Transients from the Zwicky Transient Facility
  98. EP250704a/GRB 250704B: 10 GHz VLA detection
  99. IceCube-250706A: No Candidates from WINTER
  100. IceCube-250706A: No Candidates from the Zwicky Transient Facility

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