TITLE:   GCN CIRCULAR
NUMBER:  37015
SUBJECT: EP240801a: GRANDMA and Kilonova-Catcher optical observations
DATE:    24/08/02 14:53:29 GMT
FROM:    Damien Turpin at CEA-Saclay <dturpin-astro@hotmail.com>

D. Turpin (CEA-Saclay/Irfu), S. Aghayeva (Shamakhy Obs.), Z. Vidadi (Shamakhy Obs.), N. Kochiashvili (Abastumani Obs.), S. Antier (OCA), S. Karpov (FZU), M. Coughlin (UMN), C. Andrade (UMN), I. Tosta e Melo (UniCT-DFA), P. Hello, N. Leroy (IJCLAB), P-A Duverne (APC), T. Pradier (Unistra/IPHC), N. Guessoum (AUS), V.Aivazyan (AbAO), R. Inasaridze (AbAO), M. Masek (FZU), M. Prouza (FZU), M. Freeberg (KNC), S. Leonini (KNC, Montarrenti Obs.), Y. Rajabov (UBAI), M. Serrau (KNC) on behalf of the GRANDMA and Kilonova-Catcher collaborations:

We performed observations with GRANDMA and its citizen science project Kilonova-catcher (KNC) on the X-ray transient EP240801a detected by Einstein Probe (EP) WXT on T0 = 2024-08-01T09:06:03 (Zhou et al., GCN 36997). Our observations were made from 2024-08-01T20:32:01 to 2024-08-02T08:49:33 UTC, starting 11.4 hours after the EP trigger. 

In most of our images, we did not detect the optical counterpart identified by several other follow-up observations (Fu et al., GCN 36998; Li et al. GCN 36999; Zheng et al. 36999; Aryan et al., GCN 37002; An et al., GCN 37004; Pérez-Fournon et al. GCN 37007; Malesani et al., GCN 37008, Zhu et al. GCN 37010, Moskvitin et al. GCN 37012, Quirola-Vásquez et al. GCN 37013; Moretti et al., GCN 37014). Our 5 sigma upper limits are consistent with the reported detections. In addition, we note a marginal detection in one of our stacked frame taken at a midtime ~15.7h after the EP/WXT trigger time with the following magnitude G = 22.1 +/- 0.5.

All our observations and upper limits (5 sigma C.L.) can be found here:
+--------------+------------+-------+-----------+---------------------+
|      MJD     | T-T0 (hrs) |Filter | Mag (AB)  |      Instrument     |
+==============+============+===================+=====================+
| 60523.855567 | 11.43      |  R    |20.7 (U.L) | AbAO-T70            |
+--------------+------------+-------+-----------+---------------------+
| 60523.951979 | 13.74      |  R    |20.2 (U.L.)| UBAI-NT60           |
+--------------+------------+-------+-----------+---------------------+
| 60523.953785 | 13.79      |  R    |19.3 (U.L.)| KNC-Montarrenti Obs.|
+--------------+------------+-------+-----------+---------------------+
| 60523.997921 | 14.85      |  R    |18.4 (U.L.)| FRAM-CTA-N          |
+--------------+------------+-------+-----------+---------------------+
| 60524.032112 | 15.67      | Gaia G|22.1+/-0.5 | KNC-Dauban Meade 12"|
+--------------+------------+-------+-----------+---------------------+
| 60524.055914 | 16.24      | sdssr |21.0 (U.L.)| KNC-CDK17           |
+--------------+------------+-------+-----------+---------------------+
| 60524.279711 | 21.61      | sdssr |21.2 (U.L.)| KNC-T160FL          |
+--------------+------------+-------+-----------+---------------------+

Images obtained in Johnson Cousin filters were calibrated using the Gaia DR3 Synphot catalog, images taken with Sloan filters were calibrated using the Pan-STARRS DR1 Catalog while images taken with Gaia G filters were calibrated using the Gaia eDR3 catalog.

All the data have been reduced by a single data processing pipeline STDPIPE (Karpov et al., 2022). We use the Skyportal application (skyportal.io) to monitor our observational campaign.

GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/).