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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 251117A: Tiled Swift observations
  2. LAT GRB251117.51: Global MASTER-Net observations report
  3. LIGO/Virgo/KAGRA S251112cm: J-GEM follow-up observations
  4. LIGO/Virgo/KAGRA S251112cm: Classification of reported candidates with SOAR/Goodman
  5. LIGO/Virgo/KAGRA S251112cm: WFST follow-up observations and preliminary results
  6. GRB 251116C: Swift-XRT observations
  7. EP251023a: Assy AZT-20 optical observations
  8. EP251023a: UAFO and AbAO optical observations
  9. LIGO/Virgo/KAGRA S251112cm: EP-FXT follow-up observations
  10. The EP-WXT trigger 01709247588: more evidence of flaring star from Mondy optical observations
  11. GRB 251025B: further Mondy optical observations
  12. LIGO/Virgo/KAGRA S251112cm: Observations with the NSF-DOE Vera C. Rubin Observatory
  13. SVOM GRB251116C: Global MASTER-Net observations report
  14. GRB 251116B: SVOM detection of a burst
  15. LIGO/Virgo/KAGRA S251112cm: GRANDMA observations of the skymap
  16. LIGO/Virgo/KAGRA S251112cm: AT2025adht follow-up at Maidanak observatory by GRANDMA
  17. GRB 251115A: Tiled Swift observations
  18. Fermi GRB 251115A: Global MASTER-Net observations report
  19. LIGO/Virgo/KAGRA S251112cm: NED Galaxies in the 4-Update Localization Volume
  20. LIGO/Virgo/KAGRA S251112cm: DECam GW-MMADS candidates
  21. Fermi trigger No 784717756: Global MASTER-Net observations report
  22. LIGO/Virgo/KAGRA S251112cm: ATLAS targeted observations of the skymap
  23. LIGO/Virgo/KAGRA S251112cm: Swift XRT observations, 20 X-ray sources
  24. Fermi GRB 251114A: Global MASTER-Net observations report
  25. LIGO/Virgo/KAGRA S251112cm: Candidates from the Zwicky Transient Facility
  26. LIGO/Virgo/KAGRA S251112cm: FTW observations of galaxies within localization region
  27. Fermi GRB 251113A: Global MASTER-Net observations report
  28. GRB 251111A: SVOM/ECLAIRs refined analysis
  29. GRB 251025B: SVOM/ECLAIRs refined analysis
  30. GRB 251112A: Swift/UVOT Upper Limits
  31. LIGO/Virgo/KAGRA S251112cm: ATLAS pre-detections of AT2025adgp and AT2025adgq
  32. LIGO/Virgo/KAGRA S251112cm: Detection of two young transients by BlackGEM/MeerLICHT: AT2025adgp and AT2025adgq
  33. LIGO/Virgo/KAGRA S251112cm: Coverage and upper limits from MAXI/GSC observations
  34. LIGO/Virgo/KAGRA S251112cm: Initial GOTO-South observations
  35. LIGO/Virgo/KAGRA S251112cm: Upper limits from Fermi-GBM Observations
  36. Fermi trigger No 784621743: Global MASTER-Net observations report
  37. LIGO/Virgo/KAGRA S251112cm: NED Galaxies in the 3-Initial Localization Volume
  38. GRB251111A: 1.3m DFOT optical upper limit
  39. GRB 251111A: Swift-XRT afterglow detection
  40. GRB 251111A: SVOM/VT optical observations with X-band data
  41. SVOM GRB251111.42: Global MASTER-Net observations report
  42. GRB 251111A: Swift-XRT observations
  43. SVOM GRB251111.22: Global MASTER-Net observations report
  44. GRB 251013C: Chandra X-ray observations and jet break detection
  45. GRB 251111A: SVOM/VT optical observations with VHF data
  46. GRB 251111A: KAIT optical upper limit
  47. GRB 251111A: SVOM/COLIBRÍ (FM-GFT) optical counterpart detection
  48. GRB 251106A: Swift/UVOT Upper Limits
  49. LIGO/Virgo/KAGRA S251108fi: DDOTI Optical Candidate
  50. Fermi trigger No 784329591: Global MASTER-Net observations report
  51. Fermi trigger No 784279167: Global MASTER-Net observations report
  52. SVOM GRB251108.54: Global MASTER-Net observations report
  53. SVOM GRB251106.83: Global MASTER-Net observations report
  54. GRB 251106A: Swift-XRT afterglow detection
  55. GRB 251106A: Kilonova-Catcher optical upper limit
  56. GRB 251106A: SVOM/COLIBRÍ (FM-GFT) detection of a likely optical counterpart
  57. GRB 251106A: MASTER optical observations
  58. Fermi trigger No 784034269: Global MASTER-Net observations report
  59. EP251102a: Xinglong 2.16-m clear-band observations of the optical counterpart
  60. LIGO/Virgo/KAGRA S251031dw: Candidates from the Zwicky Transient Facility
  61. GRB 251103B: Swift/UVOT Upper Limits
  62. Fermi GRB 251105A: Global MASTER-Net observations report
  63. EP251102a: FTW optical and NIR observations
  64. GRB 251103A: WFST optical observations
  65. EP251102a: OHP/T193 optical observations
  66. GRB 251103A: OHP/T193 optical observations
  67. GRB 251103A: KAIT optical observations
  68. GRB 251103B: Nanshan/HMT optical upper limit
  69. GRB 251013C: 7DT detection and Medium-band SED of Afterglow
  70. Fermi GRB 251103A: Global MASTER-Net observations report
  71. EP251102a: NIR observations with WINTER
  72. GRB 251103A: J-band detection with WINTER
  73. Swift GRB 251103B: Global MASTER-Net observations report
  74. GRB 251103A: Kilonova-Catcher optical afterglow detection
  75. GRB 251103A: Swift/UVOT Detection
  76. GRB 251103A: Swift-XRT afterglow detection
  77. GRB 251103A: SVOM/COLIBRÍ (FM-GFT) optical observations
  78. GRB 251025B: OHP/T193 optical upper limit
  79. EP251102a (WXT 11900459650): LCO observations confirm COLIBRÍ candidate
  80. GRB 251103A: LCO optical observation
  81. EP251102.890: COLIBRÍ optical counterpart candidate
  82. GRB 251103A: GOTO optical afterglow detection
  83. GRB 251103A: NOT optical afterglow candidate
  84. Fermi GRB 251102A: Global MASTER-Net observations report
  85. IceCube-251025A: Two Transient Candidates from the Zwicky Transient Facility
  86. GRB 251026B: SOAR Classification of GOTO25jgl/SN2025absf as a Type Ia supernova
  87. GRB 251022A: Swift-XRT confirmation of fading
  88. GRB 251026B: LBT near-infrared observations
  89. GRB 251026A/EP251026a: EP-FXT follow-up observation
  90. Fermi GRB 251028B: Global MASTER-Net observations report
  91. GRB 251025B: GROWTH-India Telescope continued multiband optical observations and rebrightening
  92. GRB251026B: PRIME H-band upper limit
  93. GRB251025B: 3.6m DOT Optical Observations
  94. GRB 251013C : 3.4-m telescope of Iranian National Observatory (INO340) optical observations
  95. GRB 251026B: Swift-XRT observations of GOTO25jgl/AT2025absf
  96. Fermi-LAT Gamma-ray Observations of IceCube-251025A
  97. GRB 251023B: Swift-UVOT Upper Limits
  98. GRB 251027A: Swift-XRT observations
  99. GRB 251026B: Swift ToO observations
  100. GRB 251026A/EP251026a: Einstein Probe detection of a fast X-ray transient

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