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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"
  1. GRB 250216A: Fermi GBM Final Real-time Localization
  2. EP250212a: FTW optical and NIR upper limits
  3. GRB 250215A: Swift/UVOT Upper Limits
  4. GRB 250215A: COLIBRÍ/DDRAGO Optical Upper Limits on the Afterglow
  5. EP250215a / GRB 250215A : GTC redshift z = 4.61
  6. GRB 250215A: Fermi GBM Observation
  7. EP250215a / GRB 250215A : NOT optical observations
  8. GRB 250215A/EP250215a: 1.6m Mephisto optical observation report
  9. GRB 250215A / EP250215a: Gemini-South optical observation of a likely rebrightening
  10. LIGO/Virgo/KAGRA S250206dm: MASTER LC AT2025bbo
  11. GRB 250213A: COLIBRÍ/DDRAGO Optical Upper Limits on the Afterglow
  12. GRB 250215A: Swift-XRT refined Analysis
  13. GRB 250215A: SVOM/GRM observation
  14. EP250215a / GRB 250215A: AstroSat CZTI detection
  15. GRB 250215A / EP250215a: SVOM/VT optical candidate comfirmation
  16. EP250215a: Global MASTER-Net observations report
  17. EP250215A/GRB 250215A: INTEGRAL SPI-ACS detection
  18. EP250215a / GRB 250215A (potentially): NOT likely optical counterpart
  19. EP250215a: EP-WXT detection and FXT follow-up observation of an X-ray transient
  20. Fermi GRB 250215A: Global MASTER-Net observations report
  21. GRB 250215A: Fermi GBM Final Real-time Localization
  22. Fermi trigger No 761206993: Global MASTER-Net observations report
  23. GRB 250213A：SVOM/VT optical candidate
  24. Fermi Gamma-ray Burst Monitor trigger 761206993/250214266 is not a GRB
  25. EP250207b: Xinglong optical upper limit
  26. Fermi GRB 250214A: Global MASTER-Net observations report
  27. GRB 250213A: Swift ToO observations
  28. GRB 250214A: Fermi GBM Final Real-time Localization
  29. EP250212a: Xinglong optical upper limit
  30. LIGO/Virgo/KAGRA S250206dm: DECam GW-MMADS candidates
  31. GRB 250213A: SVOM detection of a burst
  32. EP250212a: Global MASTER-Net observations report
  33. GRB 250205A: VIRT Optical Upper Limit
  34. GRB 250205A: Leavitt Observatory optical upper limit
  35. GRB 250210A: GRBAlpha detection
  36. EP250207B: Chandra localization of the X-ray counterpart
  37. LIGO/Virgo/KAGRA S250206dm: FTW observations of counterpart candidates AT2025bbo and AT2025bcx, and of NED galaxies
  38. EP250207b: VLA radio upper limits
  39. EP250212a: Liverpool Telescope optical upper limits
  40. EP250212a: EP-WXT detection and FXT follow-up observation of a fast X-ray transient
  41. GRB250101A: Radio upper limits from GMRT observations
  42. EP trigger 10202399251 (possibly EP250212a): NOT J-band upper limit
  43. EP250207B: GTC z-band Observations
  44. Fermi GRB 250212A: Global MASTER-Net observations report
  45. LIGO/Virgo/KAGRA S250206dm: NEWFIRM NIR Follow-up of AT2025ber
  46. GRB 250205A: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  47. Fermi trigger No 760945500: Global MASTER-Net observations report
  48. EP250207b: NOT optical counterpart candidate
  49. GRB 250211A: SVOM trigger sb25021103 is not a GRB
  50. GRB 250211B: A long GRB detected by INTEGRAL
  51. LIGO/Virgo/KAGRA S250206dm: GECKO Continued Observaiton with 7DT
  52. GRB 250211A: Swift ToO observations
  53. Integral GRB250211.89: Global MASTER-Net observations report
  54. GRB 250212A: Fermi GBM Final Real-time Localization
  55. LIGO/Virgo/KAGRA S250206dm: AT 2025bbo observations with WFST
  56. LIGO/Virgo/KAGRA S250211be: Updated Sky localization
  57. GRB 250207A: Fermi GBM Observation
  58. GRB 250206A: Fermi GBM Observation
  59. GRB 250205A / EP250205A: radio detection with the VLA
  60. IceCube-250207A: One candidate from the Zwicky Transient Facility
  61. EP250207b: Tentative z-band brightening source
  62. LIGO/Virgo/KAGRA S250206dm: continued in SOAR galaxy targeted observations and identification of one possible transient
  63. LIGO/Virgo/KAGRA S250206dm: Kinder confirmation of a possible artefact in AT 2025bbo
  64. Konus-Wind detection of GRB 250207A
  65. Konus-Wind detection of GRB 250206A
  66. GRB 250210A: SVOM/GRM observation of a long burst
  67. EP250207b: Liverpool Telescope possible optical counterpart
  68. EP250207b: Global MASTER-Net observations report
  69. Fermi Gamma-ray Burst Monitor trigger 760945500/250211240 is not a GRB
  70. Gemini-South spectroscopic redshift of EP250207b host galaxy candidate (z=0.082)
  71. LIGO/Virgo/KAGRA S250211be: Identification of a GW compact binary merger candidate
  72. LIGO/Virgo/KAGRA S250211aa: Updated Sky localization and EM Bright Classification
  73. LIGO/Virgo/KAGRA S250211aa: Identification of a GW compact binary merger candidate
  74. GRB 250207A: Skynet optical afterglow observations
  75. LIGO/VIRGO/KAGRA S250206dm: AT 2025bbo spectroscopic observations with NIRES on Keck II
  76. LIGO/Virgo/KAGRA S250206dm: Gemini-North spectroscopic observation of AT2025bbo and its host galaxy
  77. GRB 241128A: VIRT Optical Upper Limit
  78. EP250207b: Gemini GMOS-N z-band observations
  79. EP250207A: Upper limits from Fermi-GBM Observations
  80. GRB 250210A: INTEGRAL SPI-ACS detection
  81. GRB 250210A: AstroSat CZTI detection
  82. EP250207b: a new X-ray transient detected by Einstein Probe
  83. LIGO/Virgo/KAGRA S250206dm: MASTER detection AT2025bbo
  84. GRB 250209A: MAXI/GSC detection (possible detection of an X-ray flare from 1RXS J145110.3+310648)
  85. Fermi GRB 250210A: Global MASTER-Net observations report
  86. GRB 250210A: Fermi GBM Final Real-time Localization
  87. LIGO/Virgo/KAGRA S250206dm: Upper limits from GECAM Observations
  88. IceCube-250207A: Upper limits from a search for additional neutrino events in IceCube
  89. LIGO/Virgo/KAGRA S250206dm: Global MASTER-Net observations report
  90. LIGO/Virgo/KAGRA S250206dm: COLIBRÍ/DDRAGO Observations of AT2025bbo and Galaxies in the Localization Volume
  91. IceCube Alert 250207.09: Global MASTER-Net observations report
  92. LIGO/Virgo/KAGRA S250206dm: Observations from WINTER
  93. GRB 250204B: GRBAlpha detection
  94. GRB 250204A: GRBAlpha detection
  95. LIGO/Virgo/KAGRA S250206dm & FRB 20250206A: MASTER observations and possible mother galaxy
  96. LIGO/Virgo/KAGRA S250206dm: Optical observations of candidate AT 2025bbo with Kinder
  97. Fermi-LAT Gamma-ray Observations of IceCube-250207A
  98. GRB 250207A: 1.3m DFOT Optical observations
  99. LIGO/Virgo/KAGRA S250206dm: WFST follow-up observations
  100. GRB 250206A: Swift-XRT observations

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