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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"

20558 results found.

  1. EP251118a: NOT candidate optical counterpart
  2. GRB 251118A: Swift ToO observations
  3. EP251118a: Einstein Probe detected of a fast X-ray transient
  4. Fermi GRB 251118B: Global MASTER-Net observations report
  5. LIGO/Virgo/KAGRA S251112cm: Upper limits from Glowbug gamma-ray observations
  6. GRB 251117A: FTW Observations of Swift candidate X-ray sources
  7. GRB 251116C: SVOM/ECLAIRs refined analysis
  8. GRB 251116B: SVOM/ECLAIRs refined analysis
  9. GRB 251013C: Koshka, SAO RAS, Mondy, and CrAO optical observations, possible SN detection
  10. GRB 251115A: Swift-XRT observations
  11. GRB 251117A: Swift/BAT-GUANO localization skymap of a short burst
  12. GRB 251117A: Tiled Swift observations
  13. LAT GRB251117.51: Global MASTER-Net observations report
  14. LIGO/Virgo/KAGRA S251112cm: J-GEM follow-up observations
  15. LIGO/Virgo/KAGRA S251112cm: Classification of reported candidates with SOAR/Goodman
  16. LIGO/Virgo/KAGRA S251112cm: WFST follow-up observations and preliminary results
  17. GRB 251116C: Swift-XRT observations
  18. EP251023a: Assy AZT-20 optical observations
  19. EP251023a: UAFO and AbAO optical observations
  20. LIGO/Virgo/KAGRA S251112cm: EP-FXT follow-up observations
  21. The EP-WXT trigger 01709247588: more evidence of flaring star from Mondy optical observations
  22. GRB 251025B: further Mondy optical observations
  23. LIGO/Virgo/KAGRA S251112cm: Observations with the NSF-DOE Vera C. Rubin Observatory
  24. SVOM GRB251116C: Global MASTER-Net observations report
  25. GRB 251116B: SVOM detection of a burst
  26. LIGO/Virgo/KAGRA S251112cm: GRANDMA observations of the skymap
  27. LIGO/Virgo/KAGRA S251112cm: AT2025adht follow-up at Maidanak observatory by GRANDMA
  28. GRB 251115A: Tiled Swift observations
  29. Fermi GRB 251115A: Global MASTER-Net observations report
  30. LIGO/Virgo/KAGRA S251112cm: NED Galaxies in the 4-Update Localization Volume
  31. LIGO/Virgo/KAGRA S251112cm: DECam GW-MMADS candidates
  32. Fermi trigger No 784717756: Global MASTER-Net observations report
  33. LIGO/Virgo/KAGRA S251112cm: ATLAS targeted observations of the skymap
  34. LIGO/Virgo/KAGRA S251112cm: Swift XRT observations, 20 X-ray sources
  35. Fermi GRB 251114A: Global MASTER-Net observations report
  36. LIGO/Virgo/KAGRA S251112cm: Candidates from the Zwicky Transient Facility
  37. LIGO/Virgo/KAGRA S251112cm: FTW observations of galaxies within localization region
  38. Fermi GRB 251113A: Global MASTER-Net observations report
  39. GRB 251111A: SVOM/ECLAIRs refined analysis
  40. GRB 251025B: SVOM/ECLAIRs refined analysis
  41. GRB 251112A: Swift/UVOT Upper Limits
  42. LIGO/Virgo/KAGRA S251112cm: ATLAS pre-detections of AT2025adgp and AT2025adgq
  43. LIGO/Virgo/KAGRA S251112cm: Detection of two young transients by BlackGEM/MeerLICHT: AT2025adgp and AT2025adgq
  44. LIGO/Virgo/KAGRA S251112cm: Coverage and upper limits from MAXI/GSC observations
  45. LIGO/Virgo/KAGRA S251112cm: Initial GOTO-South observations
  46. LIGO/Virgo/KAGRA S251112cm: Upper limits from Fermi-GBM Observations
  47. Fermi trigger No 784621743: Global MASTER-Net observations report
  48. LIGO/Virgo/KAGRA S251112cm: NED Galaxies in the 3-Initial Localization Volume
  49. GRB251111A: 1.3m DFOT optical upper limit
  50. GRB 251111A: Swift-XRT afterglow detection
  51. GRB 251111A: SVOM/VT optical observations with X-band data
  52. SVOM GRB251111.42: Global MASTER-Net observations report
  53. GRB 251111A: Swift-XRT observations
  54. SVOM GRB251111.22: Global MASTER-Net observations report
  55. GRB 251013C: Chandra X-ray observations and jet break detection
  56. GRB 251111A: SVOM/VT optical observations with VHF data
  57. GRB 251111A: KAIT optical upper limit
  58. GRB 251111A: SVOM/COLIBRÍ (FM-GFT) optical counterpart detection
  59. GRB 251106A: Swift/UVOT Upper Limits
  60. LIGO/Virgo/KAGRA S251108fi: DDOTI Optical Candidate
  61. Fermi trigger No 784329591: Global MASTER-Net observations report
  62. Fermi trigger No 784279167: Global MASTER-Net observations report
  63. SVOM GRB251108.54: Global MASTER-Net observations report
  64. SVOM GRB251106.83: Global MASTER-Net observations report
  65. GRB 251106A: SVOM/COLIBRÍ (FM-GFT) fading of the optical counterpart
  66. GRB 251106A: Swift-XRT afterglow detection
  67. GRB 251106A: Kilonova-Catcher optical upper limit
  68. Fermi GBM Sub-Threshold Detection of GRB 251106A
  69. GRB 251106A: SVOM/COLIBRÍ (FM-GFT) detection of a likely optical counterpart
  70. GRB 251106A: MASTER optical observations
  71. Fermi trigger No 784034269: Global MASTER-Net observations report
  72. EP251102a: Xinglong 2.16-m clear-band observations of the optical counterpart
  73. LIGO/Virgo/KAGRA S251031dw: Candidates from the Zwicky Transient Facility
  74. GRB 251105A: Swift/BAT-GUANO localization skymap of a burst
  75. GRB 251023A: SVOM/ECLAIRs detection of a burst through targeted search
  76. Fermi GBM Sub-Threshold Detection of GRB 251105B
  77. GRB 251103B: Swift/UVOT Upper Limits
  78. Fermi GRB 251105A: Global MASTER-Net observations report
  79. EP251102a: FTW optical and NIR observations
  80. GRB 251103A: WFST optical observations
  81. EP251102a: OHP/T193 optical observations
  82. GRB 251103A: OHP/T193 optical observations
  83. GRB 251103A: KAIT optical observations
  84. GRB 251103B: Nanshan/HMT optical upper limit
  85. GRB 251013C: 7DT detection and Medium-band SED of Afterglow
  86. GRB 251103A: Swift/BAT-GUANO arcminute localization of a burst
  87. Fermi GRB 251103A: Global MASTER-Net observations report
  88. EP251102a: NIR observations with WINTER
  89. GRB 251103A: J-band detection with WINTER
  90. Swift GRB 251103B: Global MASTER-Net observations report
  91. GRB 251103A: Kilonova-Catcher optical afterglow detection
  92. GRB 251103A: Swift/UVOT Detection
  93. GRB 251103A: Swift-XRT afterglow detection
  94. GRB 251103A: SVOM/COLIBRÍ (FM-GFT) optical observations
  95. GRB 251025B: OHP/T193 optical upper limit
  96. EP251102a (WXT 11900459650): LCO observations confirm COLIBRÍ candidate
  97. GRB 251103A: LCO optical observation
  98. EP251102.890: COLIBRÍ optical counterpart candidate
  99. GRB 251103A: GOTO optical afterglow detection
  100. GRB 251103A: NOT optical afterglow candidate

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