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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"

20522 results found.

  1. GRB 250221A: VLA radio detection
  2. Fermi GRB 250223A: Global MASTER-Net observations report
  3. Fermi trigger No 762020305: Global MASTER-Net observations report
  4. GRB 250221A: continued Assy optical observations, brightening afterglow confirmation
  5. GRB 250221A: continued Mondy optical observations, brightening afterglow
  6. GRB 250221A: Optical counterpart detection by LCO.
  7. GRB 250221A: Mondy optical observations
  8. GRB 250221A: Assy optical observations
  9. EP250220a: FTW optical and NIR observations and upper limits
  10. EP250220a: EP-FXT follow-up observations
  11. GRB 250219A: NUTTelA-TAO / BSTI Optical Limits
  12. Fermi trigger No 761805304: Global MASTER-Net observations report
  13. GRB 250221A: NOT optical observations
  14. GRB 250221A: 1.6m Mephisto optical detection
  15. GRB 250221A: Swift/UVOT Detection
  16. EP250220a: Liverpool Telescope upper limits
  17. GRB 250219A: GRANDMA/Kilonova-Catcher upper limits
  18. GRB 250221A: REM optical/NIR afterglow detection
  19. IceCube-250207A: MASTER flaring blazar QSOJ0854+2006 with Zhirkov effect
  20. EP250220a: 1.6m Mephisto observations
  21. EP250220a: Optical upper limit with Kinder observations
  22. Swift GRB250221.15: Global MASTER-Net observations report
  23. EP250220a: Global MASTER-Net observations report
  24. GRB 250219A: Swift/UVOT Upper Limits
  25. GRB 250219A: OHP/T193 optical upper limit
  26. GRB 250219A: NOT optical observations
  27. GRB 250219A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
  28. GRB 250219A: 1.6m Mephisto optical upper limits
  29. GRB 250219A: SVOM/VT optical counterpart
  30. GRB 250219A: Swift-XRT observations
  31. LIGO/Virgo/KAGRA S250206dm: Upper limits from MSU cubesats observations
  32. GRB 250219A: Swift ToO observations
  33. GRB 250217C: Swift-XRT observations
  34. SVOM/sb25021804: QSO variability in Liverpool Telescope observations
  35. GRB 250217C: COLIBRÍ/DDRAGO Upper Limits on the Optical Counterpart
  36. GRB 250217C: DDOTI Upper Limits on the Optical Afterglow
  37. GRB 250217C: Tiled Swift observations
  38. GRB 250215A / EP250215A: Encouraging Follow-up Observations of a BdHN I with a Rest-Frame Duration 2.3 s at z=4.61
  39. GRB 250213A: Swift-XRT observations
  40. LIGO/Virgo/KAGRA S250206dm: AZT-33IK Target Optical Observations
  41. Fermi GRB 250217C: Global MASTER-Net observations report
  42. LIGO/Virgo/KAGRA S250206dm: observation in AbAO, optical transient near NED/GLADE+ galaxy WISEA J021210.14+514821.7
  43. Fermi GRB 250217A: Global MASTER-Net observations report
  44. GRANDMA/OPD observations of GRB250215A
  45. Fermi GRB 250216A: Global MASTER-Net observations report
  46. GRB 250215A / EP250215a: LCO detection of the afterglow
  47. EP250212a: FTW optical and NIR upper limits
  48. GRB 250215A: Swift/UVOT Upper Limits
  49. EP250215a / GRB 250215A : NOT optical observations
  50. GRB 250215A/EP250215a: 1.6m Mephisto optical observation report
  51. LIGO/Virgo/KAGRA S250206dm: MASTER LC AT2025bbo
  52. GRB 250213A: COLIBRÍ/DDRAGO Optical Upper Limits on the Afterglow
  53. GRB 250215A / EP250215a: SVOM/VT optical candidate comfirmation
  54. EP250215a: Global MASTER-Net observations report
  55. EP250215A/GRB 250215A: INTEGRAL SPI-ACS detection
  56. EP250215a / GRB 250215A (potentially): NOT likely optical counterpart
  57. Fermi GRB 250215A: Global MASTER-Net observations report
  58. Fermi trigger No 761206993: Global MASTER-Net observations report
  59. GRB 250213A：SVOM/VT optical candidate
  60. Fermi GRB 250214A: Global MASTER-Net observations report
  61. GRB 250213A: Swift ToO observations
  62. LIGO/Virgo/KAGRA S250206dm: DECam GW-MMADS candidates
  63. EP250212a: Global MASTER-Net observations report
  64. GRB 250205A: Leavitt Observatory optical upper limit
  65. EP250207B: Chandra localization of the X-ray counterpart
  66. LIGO/Virgo/KAGRA S250206dm: FTW observations of counterpart candidates AT2025bbo and AT2025bcx, and of NED galaxies
  67. EP250207b: VLA radio upper limits
  68. GRB250101A: Radio upper limits from GMRT observations
  69. EP trigger 10202399251 (possibly EP250212a): NOT J-band upper limit
  70. EP250207B: GTC z-band Observations
  71. Fermi GRB 250212A: Global MASTER-Net observations report
  72. LIGO/Virgo/KAGRA S250206dm: NEWFIRM NIR Follow-up of AT2025ber
  73. GRB 250205A: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  74. Fermi trigger No 760945500: Global MASTER-Net observations report
  75. EP250207b: NOT optical counterpart candidate
  76. LIGO/Virgo/KAGRA S250206dm: GECKO Continued Observaiton with 7DT
  77. GRB 250211A: Swift ToO observations
  78. Integral GRB250211.89: Global MASTER-Net observations report
  79. LIGO/Virgo/KAGRA S250206dm: AT 2025bbo observations with WFST
  80. GRB 250205A / EP250205A: radio detection with the VLA
  81. IceCube-250207A: One candidate from the Zwicky Transient Facility
  82. EP250207b: Tentative z-band brightening source
  83. LIGO/Virgo/KAGRA S250206dm: continued in SOAR galaxy targeted observations and identification of one possible transient
  84. LIGO/Virgo/KAGRA S250206dm: Kinder confirmation of a possible artefact in AT 2025bbo
  85. EP250207b: Liverpool Telescope possible optical counterpart
  86. EP250207b: Global MASTER-Net observations report
  87. Gemini-South spectroscopic redshift of EP250207b host galaxy candidate (z=0.082)
  88. GRB 250207A: Skynet optical afterglow observations
  89. LIGO/VIRGO/KAGRA S250206dm: AT 2025bbo spectroscopic observations with NIRES on Keck II
  90. LIGO/Virgo/KAGRA S250206dm: Gemini-North spectroscopic observation of AT2025bbo and its host galaxy
  91. EP250207b: Gemini GMOS-N z-band observations
  92. EP250207A: Upper limits from Fermi-GBM Observations
  93. GRB 250210A: INTEGRAL SPI-ACS detection
  94. EP250207b: a new X-ray transient detected by Einstein Probe
  95. Fermi GRB 250210A: Global MASTER-Net observations report
  96. LIGO/Virgo/KAGRA S250206dm: Upper limits from GECAM Observations
  97. LIGO/Virgo/KAGRA S250206dm: Global MASTER-Net observations report
  98. LIGO/Virgo/KAGRA S250206dm: COLIBRÍ/DDRAGO Observations of AT2025bbo and Galaxies in the Localization Volume
  99. IceCube Alert 250207.09: Global MASTER-Net observations report
  100. LIGO/Virgo/KAGRA S250206dm: Observations from WINTER

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